На главную              К списку выставок

Полиморфные и химические превращения в твердых телах

Журнальные статьи

1.U15909
Akita, Chikayo; Kawaguchi, Tatsuya; Kaneko, Fumitoshi; Quasi-elastic neutron scattering study on polymorphism of tristearin: relationship between dynamical properties and subcell structures //JOURNAL OF CRYSTAL GROWTH Volume: 275 Issue: 1-2 Pages: E2187-E2193 Published: FEB 15 2005

Dynamical properties of the three polymorphic phases alpha, beta' and beta of tristearin [C3H5(OCOC17H35)(3)] have been studied by incoherent quasi-elastic neutron scatteringand X-ray diffraction. At 293 K the difference in the lateral packing density of hydrocarbon chains significantly affected the mean square displacement < U-2 >. As compared with beta, an increase by 4% in the cross-sectional area for beta' resulted in a twofold increase in < U-2 >. In case of alpha, an increase by 7% led to a threefold increase in < U-2 >. The molecular motion in the alpha phase was analyzed usingthe model of the uniaxial rotational diffusion in a onefold cosine potential. It has been clarified that the rotational fluctuation about the chain axis in the alpha phase is rather restricted compared with that in the rotator phase of n-alkanes. The < U-2 > in the alpha phase decreased significantly with the temperature, and reached the level of the < U-2 > in the beta phase at 193 K.

2.U53243
Armstrong, A. Robert; Lyness, Christopher; Menetrier, Michel; Structural Polymorphism in Li2CoSiO4 Intercalation Electrodes: A Combined Diffraction and NMR Study //CHEMISTRY OF MATERIALS Volume: 22 Issue: 5 Pages: 1892-1900 Published: MAR 9 2010

Li2CoSiO4 was prepared in three polymorphic forms. The beta(II) (Pmn2(1)) polymorph was obtained by hydrothermal synthesis (150 degrees C), and subsequent heat treatments yielded the beta(1) (Pbn2(1)) form (700 degrees C) and the gamma(0) (P-2,/n) form (1100 degrees then quenching from 850 degrees C). Rietveld refinement of X-ray and neutron powder diffraction patterns reveal considerable Li/Co mixing for beta(II), very moderate mixing for beta(I), and no mixing for gamma(0) Li-7 MAS NMR spectra have been recorded for the three forms. The mechanism of the Fermi contact interaction that leads to negatively shifted signals is as yet unexplained, but the nature and the number of signals were analyzed in relation to the site occupancies for each compound. The agreement is good for beta(II), although the extent of disorder leads to very poorly defined NMR signals, it is reasonable (although not fully quantitative) for beta(I), where well-defined NMR signals can be assigned to definite environments, finally, the gamma(0) sample surprisingly leads to a single rather broad NMR signal, whereas two well-defined and rather different environments are present in the structure deduced from diffraction.

3.U17285
Baraldi, C.; Gamberini, M. C.; Tinti, A.; Vibrational study of acetazolamide polymorphism //JOURNAL OF MOLECULAR STRUCTURE Volume: 918 Issue: 1-3 Pages: 88-96 Published: JAN 29 2009

In this paper, an acetazolamide vibrational study has been conducted to identify its two known polymorphic forms (A and B). Other techniques, such as Hot-stage and X-ray powder diffraction, have been also reported. Moreover, the thermodynamic and spectroscopic behaviour of ground form A has been investigated. In this study, acetazolamide form A was ground at different times (1, 5,10,15, 20 min) and FT-IR/ATR and DSC measurements have been carried out. The grinding process, decreasing the particle sizes, has been induced a polymorphic transformation of A to B form. To determine the B in A percentages, calibration curves have been performed by FT-Raman measurements.

4.U60213
Bashkirava, Anastasiya; Andrews, Philip C.; Junk, Peter C.; Conformational polymorphism in N-(4 '-methoxyphenyl)-3-bromothiobenzamide //CHEMISTRY-AN ASIAN JOURNAL Volume: 2 Issue: 4 Pages: 530-538 Published: 2007

Three conformational polymorphs of N-(4'-methoxyphenyl)-3-bromothiobenzamide, yellow a, orange beta, and yellow gamma, have been identified by single-crystal X-ray diffraction. The properties and structure of the polymorphs were examined with FT Raman, FTIR (ATR), and UV/Vis spectroscopy, as well as differential scanning calorimetry. Computational data on rotational barriers in the isolated gas-phase molecule indicate that the molecular conformation found in the a form is energetically preferred, but only by around 2 kJ mol(-1) over the gamma conformation. The planar molecular structure found in the beta form is destabilized by 10-14 kJ mol(-1), depending on the calculation method. However, experimental evidence suggests that the beta polymorph is the most stable crystalline phase at room temperature. This is attributed to the relative planarity of this structure, which allows more and stronger intermolecular interactions, that is, more energetically effective packing. Calculated electronic-absorption maxima were in agreement with experimental spectra.

5.U22813
Becker, P; Bohaty, L; Frohlich, R; Non-centrosymmetric molybdates CsLiMoO(4) and CsLiMoO(4)center dot(1)(3)H(2)O: crystal growth, polymorphism, efficient Stokes and anti-Stokes generation and cascaded self-frequency [chi((3))(SRS) ->chi((2)) (SFM)] conversion effects .//PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE Volume: 202 Issue: 13 Pages: 2543-2564 Published: OCT 2005

New nonlinear-laser properties of the non-centrosymmetric cubic crystals CsLiMoO(4) and CsLiMoO(4) (.) 1/3H(2)O were studied by stimulated Raman scattering spectroscopy (SRS). Multiple Stokes and anti-Stokes generation sidebands in the visible and near-IR under picosecond laser pumping have been observed for the first time. All recorded Raman induced lasing components were identified and attribute to two of the SRS-promoting A(1)(v(1))-stretching approximate to 925 cm(-1)) and E(v(2))-bending (omega(SRS2) approximate to 310 cm(-1)) vibration modes of the MoO(4)(2-) units of the crystals. The estimation measurement of the steady-state Raman gain coefficients in the near-IR region for both first Stokes generations in the CsLiMoO(4) (.) 1/3H(2)O Crystal showed that they are not less than 3.1 cm (.) GW(-1). Besides of high-order Stokes and anti-Stokes lasing in this hydrated molybdate cascaded chi((3)) -> chi((2)) sum-frequency mixing interaction was observed under one-micron pumping. Large single crystals of optical quality of both compounds were grown and characterized with respect to their structure and structural stability. Ferroic phase transitions, that occur in CsLiMoO(4) are suppressed in the novel compound CsLiMoO(4) (.) 1/3H(2)O. We classify these molybdates as attractive SRS-active crystalline materials.

6.J01240
Belenkov E.A., Agalyamova E.N., Greshnyakov V.A. МОДЕЛИРОВАНИЕ SIC ФАЗ НА ОСНОВЕ НАНОСТРУКТУР// Наносистемы: физика, химия, математика = Nanosystems: physics, chemistry, mathematics. 2011. Т. 2. № 3. С. 79-92

Предложена классификационная схема и модельный метод формирования фаз карбида кремния на основе наноструктур. Методами молекулярной механики и полуэмпирическими квантовомеханическими методами выполнен расчет геометрически оптимизированной структуры кластеров полиморфных разновидностей карбида кремния, определены их структурные параметры и некоторые свойства - плотности, энергии сублимации. Установлено, что возможно существование двадцати одной SiC-фазы, атомы в которых находятся в кристаллографически эквивалентных состояниях. Структура 17 из этих карбидкремниевых фаз описана и исследована для карбида кремния впервые.

7.U57757
Bond, Andrew D.; Boese, Roland; Desiraju, Gautam R On the polymorphism of aspirin //ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Volume: 46 Issue: 4 Pages: 615-617 Published: 2007

8.U58533
Carria, E.; Mio, A. M.; Gibilisco, S.; Polymorphism of Amorphous Ge2Sb2Te5 Probed by EXAFS and Raman Spectroscopy //ELECTROCHEMICAL AND SOLID STATE LETTERS Volume: 14 Issue: 12 Pages: H480-H482 Published: 2011

The local order of amorphous Ge2Sb2Te5 films (50 nm) prepared by sputtering (AD), melt quenching (MQ), or ion irradiation (II) has been probed by EXAFS and Raman spectroscopy. The Ge K edge of the AD sample shows a stronger contribution from homopolar Ge-Ge bonds with respect to irradiated films. Raman spectroscopy measurements indicate a greater abundance of homopolar Te-Te bonds in AD film with respect to MQ and II. Irradiation of deposited amorphous GST films results in a reduction of "wrong" homopolar bonds. This variation is probably the origin of the faster crystallization speed of MQ and II amorphous samples.

9.U53243
Colon, C; Alonso-Medina, A; Fernandez, F; Correlation between polymorphism and optical bandwidths in AgNd(WO4)(2) //CHEMISTRY OF MATERIALS Volume: 17 Issue: 26 Pages: 6635-6643 Published: DEC 27 2005

The preparation and characterization of two polymorphic phases of AgNd(WO4)(2) are described. The high-temperature phase of AgNd(WO4)(2) is prepared as it polycrystalline powder and as a single crystal. X-ray diffraction analysis indicates that the crystal has at 300 K the tetragonal symmetry of the space group (SG) l4 (No. 82), with two independent crystal sites, 2b and 2d, for Nd3+ cations and structural disorder around them. The 5 K ground state optical absorption of this tetragonal crystal clearly differs from that corresponding to the monoclinic SG C2/m (No. 12) ordered phase found in polycrystalline samples prepared below 800 degrees C. Four times larger bandwidths and a weaker crystal field (CF), that is, lesser CF splitting for all Nd3+ L-2S+1(j) manifolds, are observed for the tetragonal phase. Well-defined S-4 polarization rules have been determined in the tetragonal phase, and then the observed 99 Nd3+ energy levels were labeled with the appropriate Gamma(7,8) or Gamma(5,6) irreducible representations. A detailed Hamiltonian of 26 free ion and CF parameters have been used in the simulation of the phenomenological energy levels and associated wave functions of the 4f(3) configuration of Nd3+ in the tetragonal AgNd(WO4)(2) single crystal, with final sigma = 12.6 cm(-1). The validity of the above set of CF parameters and wave functions has been established through the good reproduction of the thermal variation of the measured anisotropic paramagnetic susceptibility X. As a result of this simulation it is shown that the larger bandwidths of the tetragonal phase contain nonresolved contributions from the two Nd3+ sites. A method to control overheating events is proposed on the basis of the nonreversibility of the tetragonal phase into the monoclinic one.

10.U17641
Coppede, Nicola; Toccoli, Tullio; Pallaoro, Alessia; Polymorphism and phase control in titanyl phthalocyanine thin films grown by supersonic molecular beam deposition .//JOURNAL OF PHYSICAL CHEMISTRY A Volume: 111 Issue: 49 Pages: 12550-12558 Published: DEC 13 2007

Phonons in the alpha-quaterthiophene (4T) and alpha-sexithiophene (6T) polymorph phases are investigated using the direct method combined with density functional theory (DFT)-based total energy calculations. The simulation of inelastic neutron scattering spectra (INS) on the LT and HT polymorph phases of 4T and 6T enable the corresponding spectral signatures of these materials to be identified. In particular, there are two fingerprints: (i) the low-frequency vibrational modes (frequencies lower than 200 cm(-1)) and (ii) the vibrational modes in the 600-900 cm(-1) frequency range. The good agreement with the INS experimental data allows us to assign unambiguously the origin of all features (first-order and high-order processes) of these spectra and to predict that the LT phase is the phase measured experimentally both on the 4T and 6T materials. Moreover, the broad background in the 600-1400 cm(-1) frequency range and the well-defined features which appear around 940 cm(-1) in the calculated INS spectra of 4T/HT and 6T/HT are assigned to multiphonon contributions. This multiphonon contribution at 940 cm(-1), which is absent in the 4T/LT and 6T/LT INS spectra, also constitutes a fingerprint of the HT phases. Finally, the calculated dispersion curves of the two polymorph phases of 4T and 6T are given.

11.U57757
Crawford, Stephen; Kirchner, Michael T.; Blaeser, Dieter; Isotopic Polymorphism in Pyridine //ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Volume: 48 Issue: 4 Pages: 755-757 Published: 2009

12.U16899
Cuevas, F; Latroche, M; Percheron-Guegan, A. Relationship between polymorphism and hydrogenation properties in Ti0.64Zr0.36Ni alloyBy: Conference: 9th International Symposium on Metal-Hydrogen Systems, Fundamentals and Applications Location: AGH Univ Sci & Technol, Fac Phys & Comp Sci, Cracow, POLAND Date: SEP 05-10, 2004 Sponsor(s): Polish Minist Sci & Informat Soc Technologies; LOT, Polish Airlines; TALES; SURPHARE; Hydrogen & Energy Sci Sci Instruments // JOURNAL OF ALLOYS AND COMPOUNDS Volume: 404 Pages: 545-549 Published: DEC 8 2005

The influence of the parent crystal structure on the hydrogenation of Ti0.64Zr0.36M alloy has been investigated. Austenitic Ti0.64Zr0.36M alloy with cubic CsCl-type structure preserves its metal sublattice structure after hydrogenation. It forms Ti0.64Zr0.36NiH1.6 hydride (P-H2 = 1 MPa and T = 373 K) through a cell-volume expansion of 10.4%. On the contrary, the monoclinic TiNi-type structure of martensitic Ti0.64Zr0.36M alloy is modified after hydrogen absorption. At P-H2 = 0.06 MPa and T = 373 K, two hydrides coexist with orthorhombic CrB-type structure and compositions Ti0.64Zr0.36NiH and Ti0.64Zr0.36NiH2.2, which induces a cell-volume expansion of 5.36 and 18.3%, respectively. The stability of these crystal structures is discussed by comparison with other AB intermetallic compounds (A = Ti, Zr, Hf) and B = (Fe, Co, Ni).

13.U53243
Di Profio, Gianluca; Tucci, Selene; Curcio, Efrem; Controlling polymorphism with membrane-based crystallizers: Application to form I and II of paracetamol //CHEMISTRY OF MATERIALS Volume: 19 Issue: 10 Pages: 2386-2388 Published: MAY 15 2007

14.U00034
Duan, Xinrui; Liu, Libing; Feng, Fude Cationic Conjugated Polymers for Optical Detection of DNA Methylation, Lesions, and Single Nucleotide Polymorphisms.//ACCOUNTS OF CHEMICAL RESEARCH Volume: 43 Issue: 2 Pages: 260-270 Published: FEB 2010

Simple, rapid, and sensitive technologies to detect nucleic acid modifications have important applications in genetic analysis, clinical diagnosis, and molecular biology. Because genetic modifications such as single nucleotide polymorphisms (SNP), DNA methylation, and other lesions can serve as hallmarks of human disease, interest in such methods has increased in recent years. This Account describes a new strategy for the optical detection of these DNA targets using cationic conjugated polymers (CCPs). Because of their unique signal amplification properties, researchers have extensively investigated conjugated polymers as optical transducers in highly sensitive biosensors. Recently, we have shown that cationic polyfluorene can detect SNPs within the DNA of clinical samples. When we incorporated deoxyguanosine triphosphate (dGTP-FI) into the DNA chain at an SNP site where the target/probe pair is complementary, we observed higher fluorescence resonance energy transfer (FRET) efficiency between cationic polyfluorene and fluorescein label on the dGTP. By monitoring the change in emission intensity of cationic polyfluorene or fluorescein, we identified the homozygous or heterozygous SNP. The high sensitivity of this assay results from the 10-fold enhancement of fluorescein emission intensity by the FRET from polyfluorene. This method can detect allele frequencies (the proportion of all copies of a gene that is made up of a particular gene variant) as low as 2%. Using this novel method, we clearly discriminated among the SNP genotypes of 76 individuals of Chinese ancestry. Improving on this initial system, we designed a method for multicolor and one-tube SNP genotyping assays based on cationic polyfluorene using fluorescein-labeled deoxyuridine triphosphate (dUTP-FI) and Cy3-labeled deoxycytidine triphosphate (dCTF-Cy3) in extension reactions. We also developed a one-step method for direct detection of SNP genotypes from genomic DNA by combining allele-specific PCR with CCPs. In 2008, we developed a new method for DNA methylation detection based on single base extension reaction and CCPs. Treatment of DNA with bisulfite followed by PCR amplification converts unmethylated DNA into a C/T polymorphism, which allows us to characterize the methylation status of the target DNA. Furthermore, we used CCPs to detect DNA lesions caused by ultraviolet light irradiation for the first time. By monitoring the color change of cationic polythiophene before and after DNA cleavage, we also detected oxidative damage to DNA by hydroxyl radical. These CCP-based new assays avoid primer labeling, cumbersome workups, and sophisticated instruments, leading to simpler procedures and improved sensitivity. We expect that these features could lead to major advances in human disease diagnostics and genomic study in the near future.

15.U57757
Filinchuk, Yaroslav; Chernyshov, Dmitry; Nevidomskyy, Andriy; et al. High-pressure polymorphism as a step towards destabilization of LiBH4 //ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Volume: 47 Issue: 3 Pages: 529-532 Published: 2008

16.U16899
Frommen, Christoph; Aliouane, Nadir; Deledda, Stefano; Crystal structure, polymorphism, and thermal properties of yttrium borohydride Y(BH4)(3) //JOURNAL OF ALLOYS AND COMPOUNDS Volume: 496 Issue: 1-2 Pages: 710-716 Published: APR 30 2010

Y(BH4)(3) was synthesized by cryo-milling mixtures of LiBH4 and YCl3 and characterized by powder X-ray and neutron diffraction (PXD, PND), differential scanning calorimetry (DSC), and temperature programmed desorption (TPD). The crystal structure was refined in the space group Pa-3 (no. 205) with lattice constant a = 10.8522(7)angstrom from B-11 and D (H-2) substituted samples using PND. It was found to contain Y3+ cations in a highly distorted octahedral environment formed by six [BD4](-) complex anions. Heat treatment under 10 MPa of deuterium at 475 K led to a phase transformation from the primitive cubic room-temperature phase to a face-centered cubic high-temperature phase with space group Fm-3c (no. 226) and lattice constant a = 11.0086(1) angstrom. This high-temperature phase shows an ideal and undistorted octahedral coordination around the central Y3+ cation. In situ synchrotron radiation powder X-ray diffraction experiments (SR-PXD) show the presence of an intermediate phase during the thermal decomposition of Y(BH4)(3) with presumably orthorhombic symmetry, and lattice constants a = 12.170(14) angstrom, b = 7.670(5) angstrom, and c = 7.478 (6) angstrom, in a narrow temperature region between 473 K and 520 K.

17.U53243
Gaillard, Cedric; Novales, Bruno; Jerome, Francois; Broad polymorphism of fatty acids with amino organosilane counterions, towards novel templates //CHEMISTRY OF MATERIALS Volume: 20 Issue: 4 Pages: 1206-1208 Published: FEB 26 2008

18.U31371
Gavezzotti, Angelo; Demartin, Francesco; Castellano, Carlo; Polymorphism of As4S3 (tris-(mu(2)-sulfido)-tetra-arsenic): accurate structure refinement on natural alpha- and beta-dimorphites and inferred room temperature thermodynamic properties //PHYSICS AND CHEMISTRY OF MINERALS Volume: 40 Issue: 2 Pages: 175-182 Published: FEB 2013

An accurate structure refinement, using single-crystal X-ray diffraction data, on natural alpha- and beta-dimorphites collected at Solfatara di Pozzuoli, in the Phlegraean Fields, near Naples and at Vesuvius (Italy) is reported. Theoretical calculations at various levels of sophistication have been used to calculate molecular vibrational frequencies and gas-phase specific heats, to analyze the crystal packing, and to estimate lattice energies of both phases. All computational methods contribute to demonstrate that the beta-phase is the thermodynamically stable one at room temperature.

19.U16899
Gbabode, Gabin; Negrier, Philippe; Mondieig, Denise; Fatty acids polymorphism and solid-state miscibility Pentadecanoic acid-hexadecanoic acid binary system .//JOURNAL OF ALLOYS AND COMPOUNDS Volume: 469 Issue: 1-2 Pages: 539-551 Published: FEB 5 2009

The pentadecanoic acid-hexadecanoic acid (C(15)H(29)OOH-C(16)H(31)OOH) binary system is dealt with in this article. The polymorphism of 20 mixed materials has been investigated combining calorimetric measurements, isothermal and versus temperature X-ray powder diffraction and also FTIR spectroscopy. In particular, the cell parameters of the stable forms, temperatures and heats of phase changes for the two constituents and a proposal of phase diagram are given in this article. Three solid forms are created by mixing in addition with the four solid forms of the pure components. All these solid forms are stabilized on narrow domains of composition, implying a reduced solid-state miscibility of the pentadecanoic and hexadecanoic acids.

20.U06083
Hino, Kazuyuki; Nakajima, Kiyohiko; Kawahara, Miyoko; Polymorphism of 4 '-Dimethylamino-3-hydroxyflavone //BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN Volume: 84 Issue: 11 Pages: 1234-1236 Published: NOV 15 2011

Structures of two polymorphic crystals 1a and 1b of 4'-dimethylamino-3-hydroxyflavone (1) have been determined. Each crystal has intermolecular hydrogen-bonded dimers with the adjacent molecule. The dimeric structure in crystal la is nearly planar, whereas that in crystal 1b is slightly bent with respect to the chromane moieties. In both crystals there is a stacking structure of the dimers linked by pi-pi interactions.

21.U06083
Hino, Kazuyuki; Nakajima, Kiyohiko; Kawahara, Miyoko; Polymorphism of 4 '-Diethylamino-3-hydroxyflavone //BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN Volume: 86 Issue: 6 Pages: 721-723 Published: JUN 15 2013

Crystallization of 4'-diethylamino-3-hydroxyflavone (1) yields two polymorphic crystals. One is monoclinic, space group P2(1)/n (1a), and the other triclinic, P (1) over bar (1b). In both crystals, the two adjacent molecules form a dimeric unit by two intermolecular O-H center dot center dot center dot O hydrogen bonds. The hydrogen-bonded dimer in crystal 1a is nearly planar, whereas that in crystal 1b is centrically twisted, having cis-like and trans-like conformations for the terminal carbon atoms at the diethylamino group.

22.U53243
Im, WB; Kim, YI; Jeon, Thermal stability study of BaAl2Si2O8 : Eu2+ phosphor using its polymorphism for plasma display panel application //CHEMISTRY OF MATERIALS Volume: 18 Issue: 5 Pages: 1190-1195 Published: MAR 7 2006

We have evaluated the thermal stability of BaAl2Si2O8:Eu2+ (BAS:Eu2+) phosphor using its polymorph property and hexagonal and monoclinic crystal structure, depending upon firing temperature for plasma display panel application. When BAS:Eu2+ samples having each characteristic crystal structure were baked at 500 degrees C in air for 30 min, the baked monoclinic BAS:Eu2+ showed the same photoluminescence (PL) intensity as the fresh one, whereas the baked hexagonal one lost its PL intensity significantly, corresponding to about 34%. From analyses of electron spin resonance on Eu2+ and Rietveld refinement, the difference of thermal stability between hexagonal and monoclinic BAS:Eu2+ could be ascribed to both the crystal structure of host materials and the average interatomic distances between the Eu2+ ion and oxygen which plays the key role of shield for Eu2+ ions against an oxidation atmosphere

23.U53243
Jung, KT; Kim, WB; Rhee, CH; Effects of transition metal addition on the solid-state transformation of molybdenum trioxide to molybdenum carbides //CHEMISTRY OF MATERIALS Volume: 16 Issue: 2 Pages: 307-314 Published: JAN 27 2004

Direct conversion Of MoO3 to molybdenum carbides by temperature-programmed reaction (TPR) with a reacting gas mixture of CH4/4H(2) has been studied in the presence of a transition metal selected from Pt, Pd, Ni, Co, Cu, and pre-synthesized Mo2C loaded on MoO3. Loading of the metals reduced the temperatures of MoO3 reduction and increased the specific surface area of produced carbides. However, the obtained phase of molybdenum carbides differed depending on the employed transition metal; Pt, Pd, or Ni produced cubic alpha-MoC1-x, while Co, Cu, or pre-synthesized Mo2C formed hexagonal beta-Mo2C, which was the same phase as that produced from the direct transformation Of MoO3 itself without any metal loading. The nature of transition metals loaded on MoO3 also led to different TPR patterns for the transformation to molybdenum carbide, suggesting that different reaction routes were involved. Thus, MoO3 loaded with Co, Cu, or Mo2C showed TPR patterns similar to that of MoO3 itself, except for slightly lower temperatures for the initiation of the reduction. With these metals, the transformation Of MoO3 to carbides followed a nontopotactic route involving the MoO2 intermediate phase. By contrast, loading of Pt, Pd, or Ni to MoO3 drove MoO3 reduction into a topotactic transformation through a MoOxCy intermediate phase. However, unlike the well-established topotactic MoO3 --> Mo2N --> alpha-MoC1-x transformation, the pseudomorphism was only partly maintained in this metal-promoted, direct MoO3 --> alpha-MoC1-x transformation.

24.U06083
Konno, Yosuke; Matsushita, Nobuyuki Crystalline polymorphism of bis[o-semibenzoquinonediimine(1-)]platinum(II) //BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN Volume: 79 Issue: 8 Pages: 1237-1239 Published: AUG 15 2006

A platinum complex with a non-innocent ligand, [Pt-II(L)(2)] (1), where L is o-semibenzoquinonediimine mono-anion, has two polymorphs. In one polymorph, molecules related by translation are arranged in the same orientation along the c axis, while in the other, molecules related by a c-glide plane are aligned alternately in different orientation.

25.U16899
Kozlenko, D. P.; Dang, N. T.; Jabarov, S. H.; Structural polymorphism in multiferroic BiMnO3 at high pressures and temperatures //JOURNAL OF ALLOYS AND COMPOUNDS Volume: 585 Pages: 741-747 Published: FEB 5 2014

Structural phase transitions in BiMnO3 were studied by means of energy-dispersive X-ray diffraction in the pressure 0-4 GPa and temperature 300-900 K ranges, and also by means of angle-dispersive X-ray diffraction and Raman spectroscopy at high pressures up to 50 GPa and ambient temperature. The P-T phase diagram of BiMnO3 was constructed. A suppression of the transition temperatures between monoclinic C2/c and orthorhombic Pnma phases was observed under pressure. The temperature and pressure dependencies of lattice parameters were obtained. A new orthorhombic Imma phase was observed at P > 20 GPa. The lattice dynamics calculations were performed for the analysis of the Raman spectra of BiMnO3.

26.U53243
Lange, Stefan; Bawohl, Melanie; Wilmer, Dirk; Polymorphism, structural frustration, and electrical properties of the mixed conductor Ag10Te4Br3 //CHEMISTRY OF MATERIALS Volume: 19 Issue: 6 Pages: 1401-1410 Published: MAR 20 2007

Ag10Te4Br3 is polymorphic with four polymorphs in the temperature range from 3 to 450 K. It represents the first member of a formerly unseen class of materials featuring covalently and ionically bonded tellurium substructures. Thermal analyses (DSC and C-p) prove the reversibility of the alpha-beta, beta-gamma, and gamma-delta phase transitions at 355, 317, and 290 K, respectively. The existence of the low-temperature delta-phase is substantiated by C-p measurements down to 3 K. Temperature-dependent single-crystal structure analysis and nonharmonic refinements of the silver distribution for all polymorphs reveal a high silver mobility over the whole temperature range. A significant change in the dimensionality of the silver distribution, from an exclusively 2D (delta, gamma) to a 3D (beta, alpha) arrangement, can be observed for Ag10Te4Br3 with the increase in temperature. The enhanced silver mobility causes a structural frustration and disorder phenomena of the predominantly covalently bonded tellurium substructure for the high-temperature alpha- and beta-polymorphs. The increase in disorder comes along with the occurrence of diffuse scattering in form of Kagome nets, indicating a structural frustration in a rod packing arrangement. An ionic conductivity, approaching the values of most of the known silver super ion conductors and only 1 order of magnitude lower than that in RbAg4I5, are a remarkable feature of air-, photo-, and moisture-stable Ag10Te4Br3.

27.U53243
Laukhina, E; Tkacheva, V; Chekhlov, A; Polymorphism of a new bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) based molecular conductor; Novel transformations in metallic BEDT-TTF layers // CHEMISTRY OF MATERIALS Volume: 16 Issue: 12 Pages: 2471-2479 Published: JUN 15 2004

The synthesis, structure, anion composition, and physical properties of a new organic conductor (BEDT-TTF)(2)[(IBr2)(0.2)(BrICl)(0.1)(ICl2)(0.7)], where BEDT-TTF = bis(ethylenedithio)-tetrathiafulvalene, are described in detail. This molecular conductor exists as two polymorphs displaying semiconducting (beta'-phase) and metallic (beta"-phase) transport properties. Complete beta" to beta and partial beta" to beta' transformation have been discovered for the first time in conducting BEDT-TTF-based salts and studied by using ESR spectroscopy. Both transformations are irreversible, the beta" --> beta one resulting from high-temperature solid-state reactions. The beta"- and beta-phases are variable in composition.

28.U15909
Lercher, Christoph; Resel, Roland; Balandier, Jean-Yves; Effects of temperature on the polymorphism of alpha,omega-dioctylterthiophene in thin films //JOURNAL OF CRYSTAL GROWTH Volume: 386 Pages: 128-134 Published: JAN 15 2014

Polymorphism of alpha,omega-dioctylterthiophene (DOTT) thin films (less than 100 nm-thick) deposited onto standard silicon substrates is investigated by combining specular and in-plane grazing incidence X-ray diffraction measurements. Two crystal phases are revealed: the bulk phase (b) and the surface-induced phase (s). Previous results showed that s-phase was the most favored close to the substrate surface while b-phase is predominant at the DOTT-air interface. We show here that the relative proportion of these polymorphs is related to sample preparation. Indeed, the preferential crystallization of one phase or the other can be tuned as a function of substrate temperature during film deposition, s-phase being mainly present at high substrate temperature while b-phase is most observed at low substrate temperature. Particularly noteworthy is that thin films exhibiting only b-phase or only s-phase can be obtained according to sample preparation. Furthermore, when samples are annealed above the melting temperature (smectic G phase), the polymorph observed after cooling back to room temperature depends upon the cooling rate, s-phase being predominant at high cooling rate while it is rather b-phase for slow cooling. This behavior is independent of the crystalline phase that was present at room temperature before annealing

29.U42107
Majeed, Bivragh; Jones, Ben; Tezcan, Deniz S.; Silicon Based System for Single-Nucleotide-Polymorphism Detection: Chip Fabrication and Thermal Characterization of Polymerase Chain Reaction Microchamber // JAPANESE JOURNAL OF APPLIED PHYSICS Volume: 51 Issue: 4 Special Issue: SI Article Number: 04DL01 Part: 2 Published: APR 2012

A single nucleotide polymorphism (SNP) is a difference in the DNA sequence of one nucleotide only. We recently proposed a lab-on-a-chip (LoC) system which has the potentiality of fast, sensitive and highly specific SNP detection. Most of the chip components are silicon based and fabricated within a single process. In this paper, the newly developed fabrication method for the silicon chip is presented. The robust and reliable process allows etching structures on the same chip with very different aspect ratios. The characterization of a crucial component to the LoC SNP detector, the microreactor where DNA amplification is performed, is also detailed. Thanks to innovative design and fabrication methodologies, the microreactor has an excellent thermal isolation from the surrounding silicon substrate. This allows for highly localized temperature control. Furthermore, the microreactor is demonstrated to have rapid heating and cooling rates, allowing for rapid amplification of the target DNA fragments. Successful DNA amplification in the microreactor is demonstrated

30.U08233
Marme, Nicole; Friedrich, Achim; Denapaite, Dalia; Single nucleotide polymorphism analysis using different colored dye dimer probes //CHEMICAL PHYSICS LETTERS Volume: 428 Issue: 4-6 Pages: 440-445 Published: SEP 20 2006

Fluorescence quenching by dye dimer formation has been utilized to develop hairpin-structured DNA probes for the detection of a single nucleotide polymorphism (SNP) in the penicillin target gene pbp2x, which is implicated in the penicillin resistance of Streptococcus pneumoniae. We designed two specific DNA probes for the identification of the pbp2x genes from a penicillin susceptible strain R6 and a resistant strain Streptococcus mitis 661 using green-fluorescent tetramethylrhodamine (TMR) and red-fluorescent DY-636, respectively. Hybridization of each of the probes to its respective target DNA sequence opened the DNA hairpin probes, consequently breaking the nonfluorescent dye dimers into fluorescent species. This hybridization of the target with the hairpin probe achieved single nucleotide specific detection at nanomolar concentrations via increased fluorescence.

31.U08229
Medvedev, S. A.; Eremets, M. I.; Evers, J.; Pressure induced polymorphism in ammonium azide (NH4N3) //CHEMICAL PHYSICS Volume: 386 Issue: 1-3 Pages: 41-44 Published: JUL 28 2011

Pressure-dependent Raman spectroscopy studies reveal polymorph phase transition in simple molecular ionic crystal NH4N3 at pressure approximate to 3 GPa unobserved by recent ab initio evolutionary structure searches. Hydrogen bonding is spectroscopically evident in both low-and high-pressure phases. The strength of hydrogen bond appears to be modified at the phase transition: in the low-pressure phase NH4N3 behaves as system with very strong hydrogen bonding whereas changes of spectra with pressure in the high-pressure phase are indicative of weak or medium-strength hydrogen bonds. The high pressure phase is most likely thermodynamically stable at least up to pressure approximate to 55 GPa contradicting the ab initio studies predicting transformation of NH4N3 to nonmolecular hydronitrogen solid at 36 GPa.

32.U58317
Mereau, Raphael; Desmedt, Arnaud; Harris, Kenneth D. M. Mechanistic aspects of the solid-state transformation of ammonium cyanate to urea at high pressure //JOURNAL OF PHYSICAL CHEMISTRY B Volume: 111 Issue: 15 Pages: 3960-3968 Published: APR 19 2007

The chemical transformation of ammonium cyanate into urea has been of interest to many generations of scientists since its discovery by Friedrich Wohler in 1828. Although widely studied both experimentally and theoretically, several mechanistic aspects of this reaction remain to be understood. In this paper, we apply computational methods to investigate the behavior of ammonium cyanate in the solid state under high pressure, employing a theoretical approach based on the self-consistent-charges density-functional tight-binding method (SCC-DFTB). The ammonium cyanate crystal structure was relaxed under external pressure ranging from 0 to 700 GPa, leading to the identification of five structural phases. Significantly, the phase at highest pressure (above 535 GPa) corresponds to the formation of urea molecules. At ca. 25 GPa, there is a phase transition of ammonium cyanate (from tetragonal P4/nmm to monoclinic P2(1)/m) involving a rearrangement of the ammonium cyanate molecules. This transformation is critical for the subsequent transformation to urea. The crystalline phase of urea obtained above 535 GPa also has P2(1)/m symmetry (Z = 2). This polymorph of urea has never been reported previously. Comparisons to the known (tetragonal) polymorph of urea found experimentally at ambient pressure suggests that the new polymorph is more stable above ca. 8 GPa. Our computational studies show that the transformation of ammonium cyanate into urea is strongly exothermic (enthalpy change -170 kJ mol(-1) per formula unit between 530 and 535 GPa). The proposed mechanism for this transformation involves the transfer of two hydrogen atoms of the ammonium cation toward nitrogen atoms of neighboring cyanate anions, and the remaining NH2 group creates a C-NH2 bond with the cyanate unit.

33.U15909
Minamisono, Takuma; Takiyama, Hiroshi. Control of polymorphism in the anti-solvent crystallization with a particular temperature profile //Conference: 5th Asia Conference on Crystal Growth and Crystal Technologies (CGCT) Location: SINGAPORE Date: 2011 JOURNAL OF CRYSTAL GROWTH Volume: 362 Pages: 135-139 Published: JAN 1 2013

Anti-solvent crystallization is widely used in the pharmaceutical industry for high yield production. However, addition methods to control polymorph in anti-solvent crystallization have not been discussed enough. In this study, indomethacin (IMC), which has three polymorphs (alpha-form, alpha'-form and gamma-form) was used. The purpose of this study is to establish a production method of the required polymorph (gamma-form). Acetone was used as the original solvent and heptane was used as the anti-solvent. In order to prevent the alpha- or alpha'-form deposition, the solution compositions must not exceed the solubility of the alpha- or alpha'-form, respectively. A simulation was performed to determine the anti-solvent addition rate, which satisfies these solution conditions based on the ternary phase diagram. Experiments were carried out using four different kinds of addition methods. Method A, B and C were performed under isothermal condition but they have different anti-solvent addition methods. Method D was continuous addition at the constant rate with a particular temperature profile. In order to determine both the anti-solvent addition rate and a temperature profile, the temperature dependent ternary phase diagram was determined. Using this phase diagram and the simulation, the required polymorph was successfully obtained in the anti-solvent crystallization with a certain level of yield.

34.U4688X
Miyachi, H; Ikebukuro, K; Yano, K; Single nucleotide polymorphism typing on DNA array with hydrophobic surface fabricated by plasma-polymerization technique //BIOSENSORS & BIOELECTRONICS Volume: 20 Issue: 2 Pages: 184-189 Published: SEP 15 2004

A DNA array has been fabricated on glass substrates, which enables high-throughput analysis of single-base mismatches. In this work, microfabrication-compatible plasma-polymerization (PP) method was used for immobilizing probe DNAs to study the hybridization behavior by changing surface properties. The immobilization matrix consisting of 35 Angstrom of PP layer, applied additionally on the streptavidin absorbed hexamethyldisiloxane (HMDS)-PP layer, was constructed on the substrates to anchor biotinylated DNA probes onto the surface. The hydrophobic immobilization matrix was considered to enhance hybridization accuracy and efficiency, compared with its hydrophilic acetonitrile-PP layers. The oligonucleotide arrays fabricated on HMDS-PP surface were shown to be effective in detection of single nucleotide polymorphisms (SNPs) of ApoE gene.

35.U53243
Montanari, E; Calestani, G; Migliori, A; High-temperature polymorphism in metastable BiMnO3 //CHEMISTRY OF MATERIALS Volume: 17 Issue: 25 Pages: 6457-6467 Published: DEC 13 2005

The multiferroic perovskite BiMnO3, synthesized under high-pressure conditions, decomposes if heated at room-pressure in the temperature range of 500-650 degrees C. Comparative studies by high-temperature X-ray diffraction, electron diffraction, thermal analysis, and magnetic investigation revealed the existence of a complex pathway to decomposition, depending on the heating rate, pressure, and atmosphere that involves different metastable phases. In particular the as-prepared monoclinic phase (I) transforms to a second monoclinic form (II) at 210 degrees C and then to an orthorhombic phase (III) at 490 degrees C. These phase transitions, fast and reversible, occur on heating with a drop in volume and are moved at higher temperatures when pressure is decreased. The transition from II to III, typically observed in inert atmosphere, can be detected also in air when the heating rate is kept sufficiently high. When III is heated in an oxygen-containing atmosphere a slow irreversible transition to variants IV and then V takes place with kinetics depending on temperature, heating rate, and oxygen partial pressure. Both IV and V are oxidized ferromagnetic phases containing Mn4+ characterized by a modulated structure based on fundamental triclinic perovskite cells. Their magnetic behavior shows a strong analogy with thin films of BiMnO3, suggesting for the latter an oxidized nature and for the former a possible multiferroic behavior.

36.U53243
Montanari, E; Righi, L; Calestani, G; Room temperature polymorphism in metastable BiMnO3 prepared by high-pressure synthesis .//CHEMISTRY OF MATERIALS Volume: 17 Issue: 7 Pages: 1765-1773 Published: APR 5 2005

The BiMnO3 perovskite is a very interesting multiferroic material that, once synthesized at high pressure and high temperature, survives as a metastable phase at ambient conditions. We investigated ceramic samples prepared in different conditions (temperature, pressure, and composition), and the existence of polymorphism at room temperature was clearly evidenced by electron diffraction and high-resolution electron microscopy in all the samples. A new polymorph, characterized by a different distortion of the perovskite basic cell, was found to coexist as a minor phase with the well-known C2 monoclinic form. The new polymorph, which can be described by a triclinic (pseudorhombohedral) superstructure with a = 13.62 angstrom, b = 13.66 angstrom, c = 13.66 angstrom, alpha = 110.0 degrees, beta = 108.8 degrees, and gamma = 108.8 degrees, is mostly segregated at the grain surface. Magnetic characterizations revealed for this second form a critical temperature of 107 K, a few degrees above the ferromagnetic transition of the monoclinic C2 form measured at 99 K. The new phase disappears by reheating the samples at ambient pressure, suggesting the idea of a higher energy polymorph, which kinetically converts in the usual phase once a sufficient temperature has been achieved.

37.U57757
Nagarathinam, Mangayarkarasi; Vittal, Jagadese J.Anisotropic movements of coordination polymers upon desolvation: Solid-state transformation of a linear 1D coordination polymer to a ladderlike structure // ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Volume: 45 Issue: 26 Pages: 4337-4341 Published: 2006

38.U00034
Nangia, Ashwini Conformational polymorphism in organic crystals //ACCOUNTS OF CHEMICAL RESEARCH Volume: 41 Issue: 5 Pages: 595-604 Published: MAY 2008

Polymorphs are different crystalline modifications of the same chemical substance. When different conformers of the same molecule occur in different crystal forms, the phenomenon is termed conformational polymorphism. Occasionally, more than one conformer is present in the same crystal structure. The influence of molecular conformation changes on the formation and stability of polymorphs is the focus of this Account. X-ray crystal structures of conformational polymorphs were analyzed to understand the interplay of intramolecular (conformer) and intermolecular (lattice) energy in the crystallization and stability of polymorphs. Polymorphic structures stabilized by strong O-H center dot center dot center dot O/N-H center dot center dot center dot O hydrogen bonds, weak C-H center dot center dot center dot O interactions, and dose packing were considered. 4,4-Diphenyl-2,5-cyclohexadienone (1) and bis(p-tolyl) ketone p-tosylhydrazone (3) are prototypes of C-H center dot center dot center dot O and N-H center dot center dot center dot O hydrogen-bonded structures. Distance-angle scatter plots of O-H center dot center dot center dot O and C-H center dot center dot center dot O hydrogen bonds extracted from,the Cambridge Structural Database indicate that polymorphs with a larger number of symmetry-independent molecules (high Z) generally have better interactions when compared with the polymorphs with lower Z values, with the implication that these symmetry-independent molecules have different conformations. Since molecular conformer (E-cont) and crystal lattice (U-latt) energy differences are of the same magnitude in organic crystals (typically <5 kcal mol(-1)), situations wherein these two factors compensate or cancel one another are illustrative. Calculation of conformer and lattice energies using Gaussian 03 and Cerius(2) in 23 recently published polymorph sets shows that a strained conformer (higher E-conf) is stabilized by stronger interactions or better Crystal packing (lower U-latt) in two-thirds of the cases, whereas there is no energy balance in the remaining structures. Organic molecules with flexible torsions and low-energy conformers have a greater likelihood of exhibiting polymorphism because (1) different conformations lead to new hydrogen -bonding and close-packing modes and (2) the tradeoff reduces the total energy difference between alternative crystal structures. As a test case, polymorph promiscuity in fuchsones (6) is related to the conformational diversity at the exo-methylene phenyl rings and the small energy difference computed for dimethyl fuchsone polymorphs. These ideas find application in the design of putative pharmaceutical polymorphs and crystal structure prediction.

39.U53243
Panin, RV; Shpanchenko, RV; Mironov, AV; Crystal structure, polymorphism, and properties of the new vanadyl phosphate Na4VO(PO4)(2) //CHEMISTRY OF MATERIALS Volume: 16 Issue: 6 Pages: 1048-1055 Published: MAR 23 2004

The new vanadyl phosphate Na4VO(PO4)(2) was synthesized and investigated by X-ray powder and single-crystal diffraction, high-temperature X-ray diffraction, electron diffraction, high-resolution electron microscopy, thermal analysis, magnetic susceptibility, and conductivity measurements. The compound undergoes a reversible phase transition at about 200 degreesC. The crystal structure of low-temperature beta-Na4VO(PO4)(2) was solved using X-ray single-crystal data. This phase has an orthorhombic unit cell with lattice parameters a = 16.0068(12) Angstrom, b = 14.5129(8) Angstrom, c = 7.0231(5) Angstrom, S.G. Pbca, and Z = 8. The crystal structure of beta-Na4-VO(PO4)(2) is built by isolated chains formed by corner-shared V4+O6 octahedra linked additionally via corners by two PO4 tetrahedra. All chains in the structure are equivalent. Na cations are located between the chains in an ordered manner. High-temperature alpha-Na4VO(PO4)(2) also has.an orthorhombic cell with lattice parameters a = 15.595(l) Angstrom, b = 14.651(2) Angstrom, c = 7.0262(6) Angstrom, S.G. Ibam, and Z = 8. Electron diffraction study revealed an existence of various structural transformations occurring in situ in the transmission electron microscope. In both alpha- and beta-modifications, the susceptibility follows a Curie-Weiss law with a very small Curie-Weiss temperature, indicating a very weak magnetic exchange among the V4+ ions.

40.U53243
Parat, B; Pardo, LC; Barrio, M; Polymorphism of CBrCl3 //CHEMISTRY OF MATERIALS Volume: 17 Issue: 13 Pages: 3359-3365 Published: JUN 28 2005

The polymorphism of bromotrichloromethane (CBrCl3) has been investigated by X-ray powder diffraction and high-pressure density experiments. Phase transitions as a function of temperature and pressure between the different phases have been characterized at normal pressure as well as at high pressures (up to 300 MPa). From the p-v-T diagram (and the derived p-T diagram) the volume variations at the transition points have been calculated and compared with those obtained by means of X-ray powder diffraction characterization. Special attention is given to the lattice symmetry of the orientational disordered phase II, characterized as rhombohedral (a = 14.639(8) angstrom, alpha = 89.44(1)degrees at 240.2 K). The existence of a glass transition from the monoclinic low-temperature stable ordered phase (III) to its nonergodic state (associated with the freezing of exchange positions between Cl and Br atoms) is analyzed in terms of the asymmetry of the intermolecular interactions, and a new "fingerprint" for the glass transition is proposed on the basis of the aspherism index. Lattice parameters as a function of temperature were determined in order to build up the thermal expansion tensor.

41.U08233
Pedone, Alfonso; Presti, Davide; Menziani, Maria Cristina On the ability of periodic dispersion-corrected DFT calculations to predict molecular crystal polymorphism in para-diiodobenzene //CHEMICAL PHYSICS LETTERS Volume: 541 Pages: 12-15 Published: JUL 10 2012

Periodic DFT calculations employing the PBE, PBE0 and B3LYP functionals coupled with different dispersion correction schemes have been applied to para-diiodobenzene molecular crystal in order to determine how they perform in reproducing the energetic and crystal geometry of its two well known polymorphs. Our results demonstrate that, provided that the dispersion correction scheme proposed by Tkatchenko and Scheffler [Phys. Rev. Lett. 102 (2009) 073005] is used, DFT can be successfully employed to predict the geometric structure and energy ordering of the alpha and beta forms of para-diiodobenzene molecular crystal, with an accuracy comparable to that yielded by diffusion Monte Carlo calculations.

42.U03117
Pravica, MG; Shen, YR; Nicol, MF. High pressure Raman spectroscopic study of structural polymorphism in cyclohexane //APPLIED PHYSICS LETTERS Volume: 84 Issue: 26 Pages: 5452-5454 Published: JUN 28 2004

We have performed a Raman spectroscopic study of cyclohexane at high pressures up to 40 GPa at ambient temperature and present evidence for one or two new phases of cyclohexane which appear around 10 and between 25 and 37 GPa. The R-1 and R-2 lines of a ruby in the cyclohexane sample were well-resolved to our highest pressure, and the sample was highly transparent. Because cyclohexane is nonpolar, relatively inert, and a liquid at room temperature, it is an excellent and easy-to-use pressure medium, especially for reactive materials. At 40 GPa, we heated the sample to 200 degreesC for several hours and then performed Raman measurements while decreasing pressure at ambient temperature. The material remained in its original liquid form demonstrating that the molecule is remarkably resilient.

43.U00034
Price, Sarah (Sally) L Computed Crystal Energy Landscapes for Understanding and Predicting Organic Crystal Structures and Polymorphism .//ACCOUNTS OF CHEMICAL RESEARCH Volume: 42 Issue: 1 Pages: 117-126 Published: JAN 2009

The phenomenon of polymorphism, the ability of a molecule to adopt more than one crystal structure, is a well-established property of crystalline solids. The possible variations in physical properties between polymorphs make the reliable reproduction of a crystalline form essential for all research using organic materials, as well as quality control in manufacture. Thus, the last two decades have seen both an increase in interest in polymorphism and the availability of the computer power needed to make the computational prediction of organic crystal structures a practical possibility. In the past decade, researchers have made considerable improvements in the theoretical basis for calculating the sets of structures that are within the energy range of possible polymorphism, called crystal energy landscapes. It is common to find that a molecule has a wide variety of ways of packing with lattice energy within a few kilojoules per mole of the most stable structure. However, as we develop methods to search for and characterize "all" solid forms, it is also now usual for polymorphs and solvates to be found. Thus, the computed crystal energy landscape reflects and to an increasing extent "predicts" the emerging complexity of the solid state observed for many organic molecules. This Account will discuss the ways in which the calculation of the crystal energy landscape of a molecule can be used as a complementary technique to solid form screening for polymorphs. Current methods can predict the known crystal structure, even under "blind test" conditions, but such successes are generally restricted to those structures that are the most stable over a wide range of thermodynamic conditions. The other low-energy structures can be alternative polymorphs, which have sometimes been found in later experimental studies. Examining the computed structures reveals the various compromises between close packing, hydrogen bonding, and pi-pi stacking that can result in energetically feasible structures. Indeed, we have observed that systems with many almost equi-energetic structures that contain a common interchangeable motif correlate with a tendency to disorder and problems with control of the crystallization product. Thus, contrasting the computed crystal energy landscape with the known crystal structures of a given molecule provides a valuable complement to solid form screening, and the examination of the low-energy structures often leads to a rationalization of the forms found.

44.U14075
Ramaswamy, Padmini; Prabhu, Ramanath; Natarajan, Srinivasan. Synthesis, Structure, and Solid-State Transformation Studies of Phosphonoacetate Based Hybrid Compounds of Uranium and Thorium //INORGANIC CHEMISTRY Volume: 49 Issue: 17 Pages: 7927-7934 Published: SEP 6 2010

Three new phosphonoacetate hybrid frameworks based on the actinide elements uranium and thorium have been synthesized. The compounds [C(4)N(2)H(14)][(UO(2))(2)(O(3)PCH(2)COO)(2)]center dot H(2)O, I, [C(4)N(2)H(14)][(UO(2))(2)(C(2)O(4))(O(3)PCH(2)COOH)(2)], II, and Th(H(2)O)(2)(O(3)PCH(2)COO)(C(2)O(4))(0.5). H(2)O, III, are built up from the connectivity between the metal polyhedra and the phosphonoacetate/oxalate units. Compound II has been prepared using a solvent-free approach, by a solid state reaction at 150 degrees C. It has been shown that II can also be prepared through a room temperature mechanochemical (grinding) route. The layer arrangement in III closely resembles to that observed in I. The compounds have been characterized by powder X-ray diffraction, IR spectroscopy, thermogravimetric analysis, and fluorescence studies.

45.U08500
Saito, Hironori; Suzuki, Mitsuaki; Miyamae, Hiroshi; Solid-state Transformation of Achiral Crystals to a Chiral Crystal by Guest Release from Host-Guest Inclusion Crystals of Achiral Host Compound //CHEMISTRY LETTERS Volume: 38 Issue: 11 Pages: 1080-1081 Published: NOV 5 2009

Solid-state transformation of achiral crystals into a chiral crystal was induced by thermal guest release from the host-guest inclusion complexes of 2,5-bis(hydroxydiphenylmethyl)thieno[3,2-b]thiophene as a host component. The chilarity of the resulting guest-free crystals, also obtained by recrystallization from dichloromethane, is attributed to conformational freezing of the achiral molecule into a chiral molecular structure in the solid state.

46.U4688X
Schwonbeck, S; Krause-Griep, A; Gajovic-Eichelmann, N; Cohort analysis of a single nucleotide polymorphism on DNA chips //BIOSENSORS & BIOELECTRONICS Volume: 20 Issue: 5 Pages: 956-966 Published: NOV 15 2004

A method has been developed to determine SNPs on DNA chips by applying a flow-through bioscanner. As a practical application we demonstrated the fast and simple SNP analysis of 24 genotypes in an array of 96 spots with a single hybridisation and dissociation experiment. The main advantage of this methodical concept is the parallel and fast analysis without any need of enzymatic digestion. Additionally, the DNA chip format used is appropriate for parallel analysis up to 400 spots. The polymorphism in the gene of the human phenol sulfotransferase SULTlAl was studied as a model SNP. Biotinylated PCR products containing the SNP (The SNP summary web site: http://www.ncbi.nlm.nih.gov/SNP/snp-summary.cgi) (mutant) and those containing no mutation (wild-type) were brought onto the chips coated with NeutrAvidin using non-contact spotting. This was followed by an analysis which was carried out in a flow-through biochip scanner while constantly rinsing with buffer. After removing the non-biotinylated strand a fluorescent probe was hybridised, which is complementary to the wild-type sequence. If this probe binds to a mutant sequence, then one single base is not fully matching. Thereby, the mismatched hybrid (mutant) is less stable than the full-matched hybrid (wild-type). The final step after hybridisation on the chip involves rinsing with a buffer to start dissociation of the fluorescent probe from the immobilised DNA strand. The online measurement of the fluorescence intensity by the biochip scanner provides the possibility to follow the kinetics of the hybridisation and dissociation processes. According to the different stability of the full-match and the mismatch, either visual discrimination or kinetic analysis is possible to distinguish SNP-containing sequence from the wild-type sequence.

47.U17641
Seliger, J.; Zagar, V. N-14 NQR Study of Polymorphism and Hydrogen Bonding in Molecular Complex Isonicotinamide-Oxalic Acid (2:1) //JOURNAL OF PHYSICAL CHEMISTRY A Volume: 114 Issue: 45 Pages: 12083-12087 Published: NOV 18 2010

The complete N-14 nuclear quadrupole resonance (NQR) spectra have been measured in the two polymorphic crystalline phases of the molecular complex isonicotinamide-oxalic acid (2:1) by nuclear quadrupole double resonance. The observed NQR frequencies, quadrupole coupling constants, and asymmetry parameters (eta) have been assigned to the two nitrogen positions (ring and amide) in a molecule on the basis of the intensity and multiplicity of the double resonance signals. The NQR data for the ring nitrogen in both polymorphic phases deviate from the correlation relations observed in substituted pyridines. This deviation is analyzed in a model, where it is assumed that an additional electric charge on the nitrogen atom changes the NQR parameters. The model suggests that this additional electric charge is negative so that the N center dot center dot center dot H-O hydrogen bond seem to be partially ionic, of the type N-center dot center dot center dot H-O.

48.U15256
Shandalov, Michael; McIntyre, Paul C. Size-dependent polymorphism in HfO2 nanotubes and nanoscale thin films //JOURNAL OF APPLIED PHYSICS Volume: 106 Issue: 8 Article Number: 084322 Published: OCT 15 2009

Many metal oxides exhibit size-dependent phase transitions among multiple polymorphs. In this work, the microstructure and crystallinity of ultrathin HfO2 films and utrathin-wall nanotubes were investigated by high-resolution electron microscopy and electron diffraction after high-temperature annealing. Nanotubes were formed by atomic layer deposition of HfO2 on epitaxial Ge < 111 > nanowire arrays on Si (111) substrates followed by selective etching of the Ge wires. A size-dependent phase transition sequence from amorphous (a-HfO2) to tetragonal (t-HfO2) and from tetragonal to monoclinic (m-HfO2) phase was observed with increasing film and nanotube wall thickness. These results are analyzed in light of recent predictions of surface energy-driven phase transitions in nanoscale fluorite-structure oxides.

49.U15256
Shanthi, S; Hashimoto, M; Zhou, YK; Polymorphism in the ferromagnetic GaCrN-diluted magnetic semiconductor: Luminescence and structural investigations //JOURNAL OF APPLIED PHYSICS Volume: 98 Issue: 1 Article Number: 013526 Published: JUL 1 2005

Luminescence properties of the transition-metal chromium-doped gallium nitride (GaCrN) epitaxial layers on sapphire substrates have been extensively studied by varying the doping level, excitation intensity, and temperature of study. Photoluminescence spectra of the doped films were found to be dominated by an excitonic peak around 3.25-3.29 eV in accordance with the doping level, due to the transition of neutral-donor bound excitions of GaCrN cubic modification. It is attributed that Cr, which is an acceptor in GaN matrix, acts as a surfactant and modifies the growth kinetics to induce phase modification from wurtzite to zinc blende of GaN. Moreover, Cr doping induced a blue band centered around 2.9 eV, which is a donor-acceptor pair, and also two bound excitonic lines at 3.36 and 3.31 eV at some locations of the sample: the expected origin of these is due to the transitions of excitons bound at the stacking faults which are formed due to the co-existence of hexagon and cubic modifications of GaN. The Raman-scattering spectra have also showed both the wurtzite GaN characteristic phonon signal E-2 (high) at 568 cm(-1) and cubic GaN (TO)-phonon signal at 553 cm(-1), and confirmed the existence of polymorphism in the doped films. High-resolution transmission electron microscopy and selected area electron-diffraction patterns give a visual comparison and authenticate the doping-induced polymorphism in the GaCrN films.

50.U08500
Shiozaki, H; Inoue, Y; Sakurai, Y. Polymorphism, photoluminescence, and electroluminescence of diaminodicyanopyrazine //CHEMISTRY LETTERS Volume: 34 Issue: 3 Pages: 304-305 Published: MAR 2005

A diaminodicyanopyrazine derivative, having bulky substituents, was designed and synthesized. The synthesized dye exhibited an intense photoluminescence in the solid state. An electroluminescent device was prepared by using the dye. The dye exhibited polymorphism. Red and yellow single crystals of the dye were prepared by using a gas-phase sublimation growth procedure. The spectral shift due to the polymorphism is also discussed, and a candidate dye for red colored electroluminescent devices is proposed.

51.U53243
Tenga, A; Garcia-Garcia, FJ; Mikhaylushkin, AS; Sphalerite-chalcopyrite polymorphism in semimetallic ZnSnSb2 //CHEMISTRY OF MATERIALS Volume: 17 Issue: 24 Pages: 6080-6085 Published: NOV 29 2005

We have investigated the system ZnSnSb2 in the course of our attempts to modify thermoelectric Zn-Sb frameworks. ZnSnSb2 is only accessible when employing Sn as reactive flux in the synthesis. The material shows an order-disorder transition in the temperature interval between 225 and 240 degrees C and decomposes peritectically at about 360 degrees C. The high-temperature form of ZnSnSb2 adopts the Zn/Sn disordered cubic sphalerite-type structure. Electron microscopy investigations reveal that samples quenched from 350 degrees C already contain domains of the low-temperature form, which has the Zn/Sn ordered tetragonal chalcopyrite structure. The c/a ratio of the tetragonal structure is, within experimental errors, identical to the ideal value 2. This gives rise to intricate microtwinning in the low-temperature chalcopyrite form of ZnSnSb2 as obtained in samples quenched from 250 degrees C. First principles electronic structure calculations demonstrate that the tetragonal low-temperature form of ZnSnSb2 has a narrow band gap of about 0.2 eV. This is in agreement with the semimetallic behavior of the material found from resistivity measurement. The shape of the electronic density of states for ZnSnSb2 is similar to thermoelectric binary Zn-Sb frameworks. However, the thermopower of ZnSnSb2 is rather low with room-temperature values ranging from 10 to 30,mu V/K.

52.U57757
Thun, Juergen; Seyfarth, Lena; Senker, Juergen; Polymorphism in benzamide: Solving a 175-year-old riddle //. ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Volume: 46 Issue: 35 Pages: 6729-6731 Published: 2007

53.U58321
Tian, Yun-Qi; Yao, Shi-Yan; Gu, Dong;Cadmium Imidazolate Frameworks with Polymorphism, High Thermal Stability, and a Large Surface Area //CHEMISTRY-A EUROPEAN JOURNAL Volume: 16 Issue: 4 Pages: 1137-1141 Published: 2010

54.U57757
Ting, Valeska P.; Schmidtmann, Marc; Wilson, Chick C.; et al. Cisplatin: Polymorphism and Structural Insights into an Important Chemotherapeutic Drug //ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Volume: 49 Issue: 49 Pages: 9408-9411 Published: 2010

55.U16899
Tobash, Paul H.; Bobev, Svilen; Thompson, Joe D.; Polymorphism in binary rare-earth metal germanides. Synthesis, structure and properties of the new hexagonal forms of Tb3Ge5 and Dy3Ge5 .// JOURNAL OF ALLOYS AND COMPOUNDS Volume: 488 Issue: 2 Pages: 533-537 Published: DEC 4 2009

Reported are the synthesis, crystal structure determination and magnetic properties of new polymorphic forms of the rare-earth metal germanides Tb3Ge5 and Dy3Ge5. Both compounds are isostructural and crystallize with the hexagonal space group P (6) over bar 2c (No. 190, Z = 2) with unit-cell parameters a = 6.861(2) angstrom; c = 8.339(6) angstrom for Tb3Ge5 and a = 6.8387(10) angstrom; c = 8.293(2) angstrom for Dy3Ge5, respectively. The structures are derivatives of the ubiquitous AlB2 type and can be regarded as its 6-fold superstructure (a' = a x 3(1/2) and c' = c x 2), arising from the long range ordering of Ge vacancies. They are therefore best described as flat Ge-layers, stacked in a hexagonal close-packed manner along the crystallographic c-axis, which are separated by layers of rare-earth metal atoms. Magnetic susceptibility measurements reveal that both Tb3Ge5 and Dy3Ge5 exhibit anti ferro magnetic order at temperatures below 23 K and 9 K, respectively

56.U57757
Verel, Rene; Tomka, Ivan T.; Bertozzi, Carlo; Polymorphism in an amyloid-like fibril-forming model peptide //ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Volume: 47 Issue: 31 Pages: 5842-5845 Published: 2008

57.U53243
Vila, E; Rojo, JM; Iglesias, JE; Polymorphism and electrical properties in the new oxide Bi6Mo2O15 //CHEMISTRY OF MATERIALS Volume: 16 Issue: 9 Pages: 1732-1739 Published: MAY 4 2004

A new oxide of composition Bi6Mo2O15 has been isolated in the binary system Bi2O3- MoO3. A wet-chemistry procedure, different from coprecipitation, has been used to prepare a nanosized, very reactive precursor. Annealing at different temperatures and for different time lengths leads to isolated polycrystalline polymorphs. X-ray powder diffraction studies on the hitherto unknown low-temperature form, L-Bi6Mo2O15, show that it crystallizes in the monoclinic system, with unit-cell parameters a = 29.0674(5) Angstrom, b = 5.64795(7) A, c 8.6620(1) Angstrom, beta = 97.979(1)degrees, and V = 1408.3 Angstrom(3). The high-temperature polymorph, H-Bi6Mo2O15, belongs to the well-known [Bi12O14] columnar structural type. The relationship between the unit-cell parameters of both phases points at the connection of their structural frameworks. Impedance spectroscopy measurements show that the transition L-H-Bi6Mo2O15 is partially reversible, as well as the existence of a second high-temperature phase H', similar to H. In contrast, the transition H-->H'-Bi6Mo2O15 is not reversible. These materials turn out to be good ionic conductors, with conductivities in the order L < H < H' for all temperatures tested.

58.U16899
Voronkova, V. I.; Kharitonova, E. P.; Rudnitskaya, O. G Refinement of Bi2WO6 and Bi2MoO6 polymorphism //JOURNAL OF ALLOYS AND COMPOUNDS Volume: 487 Issue: 1-2 Pages: 274-279 Published: NOV 13 2009

Bi2WO6 (BW) and Bi2MoO6 (BM) single-layer Aurivillius phases have been prepared by crystal growth and solid-state reactions, and their thermal and electrical properties have been studied with the aim of gaining detailed insight into their polymorphism. The results demonstrate that both compounds exist in four polymorphs: low-temperature polar orthorhombic (gamma), polar orthorhombic (gamma'''), nonpolar orthorhombic (gamma '') and high-temperature monoclinic nonpolar (gamma'). Accordingly, they undergo three phase transitions: gamma -> gamma''' (ferroelectric-ferroelectric phase transition between two polar phases), gamma''' -> gamma '' (ferroelectric-paraelectric transition from polar to nonpolar phase) and gamma ''-> gamma' (reconstructive transition between two nonpolar phases). BW has been shown experimentally for the first time to have an intermediate orthorhombic phase (gamma '') in a temperature range as narrow as 30 degrees C between its ferroelectric-paraelectric and reconstructive structure phase transitions. The ferroelectric-paraelectric transition of BW can be detected by dielectric measurements, and its reconstructive transition, by calorimetry, which has enabled their temperatures to be determined: 930 and 960 degrees C, respectively. Calorimetry data confirm that the gamma -> gamma''' phase transition occurs at 310 degrees C in BM and at 640-660 degrees C in BW. BW single crystals exhibit a weak lambda-type dielectric anomaly at 640 degrees C, suggesting that the gamma -> gamma''' phase transition is ferroelectric-ferroelectric. The ferroelectric transition in the n=1 materials BW and BM involves a change from polar orthorhombic to nonpolar orthorhombic symmetry, rather than to tetragonal (4/mmm).

59.U53243
Walsh, Aron; Watson, Graerne W.Polymorphism in bismuth stannate: A first-principles study // CHEMISTRY OF MATERIALS Volume: 19 Issue: 21 Pages: 5158-5164 Published: OCT 16 2007

From the wide range of Sn-IV-based pyrochlores, Bi2Sn2O7 stands out as a material that deviates from the standard cubic-lattice symmetry. At low temperatures, Bi2Sn2O7 adopts a distorted monoclinic root 2 x root 2 x 2 expansion of the pyrochlore structure (cc-phase) and only favors the cubic lattice (gamma-phase) above 900 K. In this study, we calculate and examine the electronic structure of both the alpha- and gamma-phases of Bi2Sn2O7 and compare them to the results of two regular pyrochlore materials, La2Sn2O7 and Y2Sn2O7. Our analysis highlights the importance of covalent interactions between the electronic states of the metal with O 2p in Bi2Sn2O7, which are not present in the other oxides. The formation of an asymmetric electron density on Bi is observed as the driving force behind the distorted geometry favored by Bi2Sn2O7.

60.U08500
Wang, Jinping; Ito, Kenya; Nakanishi, Takuya; Tb3+-enhanced Potentiometric Detection of Single Nucleotide Polymorphism by Field Effect Transistors .//CHEMISTRY LETTERS Volume: 38 Issue: 4 Pages: 376-377 Published: APR 5 2009

The use of Tb3+ as a center ion and media to introduce more exogenously negative charges onto double-stranded DNA (dsDNA), can greatly enhance potentiometric signals produced by the shift of gate voltage of field effect transisitor (FET). Furthermore, different affinities of Tb3+ to normal and mismatched dsDNAs amplified the signal difference between their detections, which can improve the discrimination of single nucleotide polymorphism.

61.U58321
Wishkerman, Sara; Bernstein, Joel Polymorphism and structural mechanism of the phase transformation of phenyl carbamate (PC) //CHEMISTRY-A EUROPEAN JOURNAL Volume: 14 Issue: 1 Pages: 197-203 Published: 2008

Crystallization experiments with phenyl carbamate as a hydrogen-bond donor with crown ethers have led to the discovery of three unknown polymorphs of phenyl carbamate. In this contribution, we characterize the phenyl carbamate polymorphs by a variety of methods including variable temperature powder X-ray diffraction (PXRD), vibrational spectroscopy (infrared and Raman), calorimetry (DSC) and optical microscopy (HSM). The phase transformation from form I to form II is rapid by both solution-mediated and solid state transformation processes. Through comparison of the two structures of form I and form II it is possible to propose a mechanism for the transformation.

62.U57757
Xiao, Yi; Plakos, Kory J. I.; Lou, Xinhui; et al Fluorescence Detection of Single-Nucleotide Polymorphisms with a Single, Self-Complementary, Triple-Stem DNA Probe //ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Volume: 48 Issue: 24 Pages: 4354-4358 Published: 2009

63.U15909
Xu, Jinjiang; Tian, Yong; Liu, Yu; Polymorphism in hexanitrohexaazaisowurtzitane crystallized from solution .//JOURNAL OF CRYSTAL GROWTH Volume: 354 Issue: 1 Pages: 13-19 Published: SEP 1 2012

An investigation has been performed on the effect of the properties of solvent and anti-solvent, addition method of anti-solvent and crystallization temperature on the polymorphic transformation of HNIW precipitated from solution. The crystallization behavior of HNIW polymorphs were confirmed by powder X-ray diffraction (PXRD) and the polymorphic content was evaluated by Rietveld analysis. It was observed that the dipole moment of anti-solvent and the supersaturation were related to the variations in polymorphic form. The metastable form beta always was precipitated initially in high polarity anti-solvent or in high supersaturation case, and then transformed to the stable form epsilon by solution mediated process, which obeyed the Ostwald's rule of stages. A new acetone solvate was isolated in acetone solution, which was so unstable that it quickly desolated to obtain form beta. The stability of the hydrate form alpha depends on the degree of hydration and hence the low hydration degree of form alpha precipitated from solution can transform to form epsilon. Forms gamma and epsilon are enantiotropic relationship and the transformation temperature Tc is associated with the solvent system. The investigation of the polymorphic transformation of HNIW contributes to the understanding of the crystallization mechanism and the preparing of the four pure forms of HNIW

64.U4688X
Xu, Qinghua; Chang, Kai; Lu, Weiping; Detection of single-nucleotide polymorphisms with novel leaky surface acoustic wave biosensors, DNA ligation and enzymatic signal amplification //BIOSENSORS & BIOELECTRONICS Volume: 33 Issue: 1 Pages: 274-278 Published: MAR 15 2012

This manuscript describes a new technique for detecting single-nucleotide polymorphisms (SNPs) by integrating a leaky surface acoustic wave (LSAW) biosensor, enzymatic DNA ligation and enzymatic signal amplification. In this technique, the DNA target is hybridized with a capture probe immobilized on the surface of a LSAW biosensor. Then, the hybridized sequence is ligated to biotinylated allele-specific detection probe using Taq DNA ligase. The ligation does not take place if there is a single-nucleotide mismatch between the target and the capture probe. The ligated detection probe is transformed into a streptavidin-horseradish peroxidase (SA-HRP) terminal group via a biotin-streptavidin complex. Then, the SA-HRP group catalyzes the polymerization of 3,3-diaminobenzidine (DAB) to form a surface precipitate, thus effectively increasing the sensitivity of detecting surface mass changes and allowing detection of SNPs. Optimal detection conditions were found to be: 0.3 mol/L sodium ion concentration in PBS, pH 7.6, capture probe concentration 0.5 mu mol/L and target sequence concentration 1.0 mu mol/L. The detection limit was found to be 1 x 10(-12) mol/L. Using this technique, we were able to detect a single-point mutation at nucleotide A2293G in Japanese encephalitis virus.

65.U00034
Yu, Lian Polymorphism in Molecular Solids: An Extraordinary System of Red, Orange, and Yellow Crystals //ACCOUNTS OF CHEMICAL RESEARCH Volume: 43 Issue: 9 Pages: 1257-1266 Published: SEP 2010

Diamond and graphite are polymorphs of each other: they have the same composition but different structures and properties. Many other substances exhibit polymorphism: inorganic and organic, natural and manmade. Polymorphs are encountered in studies of crystallization, phase transition, materials synthesis, and biomineralization and in the manufacture of specialty chemicals. Polymorphs can provide valuable insights into crystal packing and structure property relationships. 5-Methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile, known as ROY for its red, orange, and yellow crystals, has seven polymorphs with solved structures, the largest number in the Cambridge Structural Database.

66.U5508X
Zhu Min; Meng Lingpeng; Zheng Shijun; et al Theoretical Studies on the Hydrogen-bonding and p-Stacking Interactions in the m-Nisoldipine Polymorphism Dimers .//CHINESE JOURNAL OF CHEMISTRY Volume: 30 Issue: 2 Pages: 233-240 Published: FEB 2012

The intermolecular interactions in the dimers of m-nisoldipine polymorphism were studied by B3LYP calculations and quantum theory of "atoms in molecules" (QTAIM) studies. Four geometries of dimers were obtained: dimer I (a-dimer, O...H-N), dimer II (b-dimer, O...H-N), dimer III (b-dimer, pi-stacking-c), and dimer IV (b-dimer, pi-stacking-p). The interaction energies of the four dimers are along the sequence of II > I > III > IV. The intermolecular distance of the interactions follows the order: I (O...H-N)< II (O...H-N), and III (p-stacking)< IV (pi-stacking). Both the O...H-N hydrogen-bonding and p-stacking interactions belong to weak non-covalent interactions. The O...H-N hydrogen-bonding interactions with more electrostatic characters are stronger than the pi-stacking interactions. The strength of the weak interactions decreases in the order: I > II > III > IV, and the electrostatic character decreases along the sequence: I > II > III > IV.

67.006774
Бондарев В.Н., Тарасевич Д.В. ГРАНИЦЫ ТЕРМОДИНАМИЧЕСКОЙ УСТОЙЧИВОСТИ КЛАССИЧЕСКИХ КРИСТАЛЛОВ БЛАГОРОДНЫХ ГАЗОВ И ПРОБЛЕМА ПОЛИМОРФИЗМА//Физика низких температур. 2011. Т. 37. № 7. С. 752-763.

Уравнения статистической теории кристаллов с парным межатомным взаимодействием по Леннард-Джонсу применены к расчету области термодинамической устойчивости обсуждавшейся в литературе гипотетической ОЦК фазы кристаллов типа Ar. Показано, что эта область целиком расположена внутри рассчитанной авторами ранее аналогичной области для реальной ГЦК фазы таких кристаллов. Этот результат делает маловероятной возможность реализации ОЦК модификации, предсказанную группой авторов в компьютерных «экспериментах» на ксеноне при высоких температурах и давлениях и вызвавшую критическую дискуссию в литературе. Проведен также учет квантовых поправок к термодинамическим функциям «классических» кристаллов благородных газов и рассчитано отклонение линии спинодали неона от «универсальной». Обнаружено хорошее количественное согласие полученных результатов с данными численных «экспериментов» на модельных (с взаимодействием по Леннард-Джонсу) «кристаллах» Ar, Kr, Xe, а также Ne в «экзотической» области отрицательных давлений. Хотя в настоящее время экспериментально не зафиксированы признаки полиморфного превращения неона в модификацию, отличную от ГЦК, обнаружение этого явления в предсказываемой области температур Т < 70 К и давлений р > 0,3 ГПa представляло бы принципиальный интерес.

68.001751
Васильев А.Д., Лапташ Н.М. ПОЛИМОРФИЗМ КРИСТАЛЛОВ KNANBOF5//Журнал структурной химии. 2012. Т. 52. № 5. С. 922-926.

Методом рентгеноструктурного анализа исследован ?конкомитантный? полиморфизм кристаллов KNaNbOF5. Впервые обнаружена вторая ?-модификация соединения, кристаллизующаяся в тетрагональной сингонии: пр. гр. P4/nmm, a = 5,9352(2), с =8,5487(5) A, V = 301,14(2) A3, Z = 2, R1 = 0,0095. Уточнены параметры ромбической нецентросимметричной структуры ?-фазы, описанной ранее Поппельмейером и др. (Poeppelmeier et al. // J. Amer. Chem. Soc. - 2007. - 129. - P. 13963 - 13969) и проведен сравнительный анализ обеих структур. Структуры характеризуются полным упорядочением в расположении атомов кислорода и фтора, при этом расстояние Nb-O в ?-фазе (1,738(1) A) заметно больше такового в ?-фазе (1,709(2) A). Чередующиеся октаэдры NbOF5 и NaOF5 в ?-KNaNbOF5 объединяются через общие вершины, в то время как в ?-KNaNbOF5 они связаны как общими вершинами, так и ребрами. Существование неполярной центросимметричной ?-модификации KNaNbOF5 отменяет предположение о существенном вкладе катионов калия в создание полярной структуры ?-KNaNbOF5.

69.003899
Воронкова B.И., Яновский В.К., Харитонова Е.П. КИСЛОРОДПРОВОДЯЩИЕ КРИСТАЛЛЫ LA2MO2O9: ВЫРАЩИВАНИЕ И ОСНОВНЫЕ СВОЙСТВА//Кристаллография. 2005. Т. 50. № 5. С. 940-943.

С помощью кристаллизации из нестехиометрического расплава получены монокристаллы анионного проводника La2Mo2O9 и изучены их полиморфизм, доменная структура и температурные зависимости электропроводности и диэлектрической проницаемости. Проводимость этих кристаллов в области 750-600°С достигает 10-1-10-2 Ом-1 см-1.

70.002260
Зырянов В.В., Костровский В.Г. ПОЛИМОРФИЗМ НАНОПОРОШКОВ ZRO2 И МЕХАНОХИМИЧЕСКИЙ СИНТЕЗ ZR0.88SC0.1CE0.01Y0.01O1.955// Неорганические материалы. 2008. Т. 44. № 12. С. 1464-1470.

Приведены результаты структурных исследований методами РФА и Рамановской спектроскопии порошков ZrO2, полученных дегидратацией гидроксида циркония, а также измельчением, в т.ч. с введением помольных добавок NaF, CaF2, алмаза и Cu. Образцы с наименьшим размером кристаллитов получены с добавкой меди. Получены механохимическим синтезом из нанопрекурсоров и охарактеризованы керамические порошки Zr0.88Sc0.1Ce0.01Y0.01O1.955 для использования в качестве твердых электролитов для топливных элементов. Наблюдаемое в дифракционных картинах “повышение” симметрии в наноразмерных сильно агрегированных порошках метастабильного диоксида циркония связано с двойникованием, которому способствует высокая концентрация вакансий.

71.001681
Карелин A.И., Никитина З.К. ИК-СПЕКТРОСКОПИЯ ПОЛЯРИЗОВАННЫХ СОСТОЯНИЙ ИОНА [D2O...D-OD2]+ В КРИСТАЛЛИЧЕСКОМ ПЕРХЛОРАТЕ ДЕЙТЕРОДИОКСОНИЯ// Журнал неорганической химии. 2006. Т. 51. № 11. С. 1916-1922.

Методом ИК-спектроскопии поглощения исследован полиморфизм кристаллического DC1O4 2D2O с 99 ат. %D. Найдена ранее неизвестная фаза, которая легко определяется по совокупности признаков: наблюдаются широкая интенсивная полоса при 2125 см-1 колебаний vs, as(D3O) дейтерооксони-евой группы и довольно узкая интенсивная полоса при 2506 см-1 колебания vas(D2O) нейтральной молекулярной группы. Характерная для симметричной внутрикатионной водородной связи D5O+2C1O4 континуальная полоса vas(O...D...O) в этом случае отсутствует. Указанные признаки свидетельствуют о значительной поляризации катиона дейтерооксония: [D2O...D-OD2]+. Низкая симметрия объясняется значительным смещением мостикового атома D из центра прочной водородной связи к одной из двух имеющихся молекул D2O под влиянием несимметричных взаимодействий в кристаллическом поле. Фиксированные водородными связями диоксония ионы С104 также занимают низкосимметричные позиции. При кристаллизации DC1O4 2D2O с ? 10 ат. % Н обнаружен полиморфный изотопный эффект: зависимость кристаллической структуры от изотопного Н-D-разбавления в условиях одинаково продолжительной термической обработки всех образцов.

72.005767
Князев А.В., Черноруков Н.Г., Жижин М.Г., Сажина Ю.С., Ершова А.В. ТЕРМОХИМИЯ И ТЕРМИЧЕСКИЕ СВОЙСТВА СОЕДИНЕНИЙ ВА2М UOG (M = MG, CA, SR, BA)//Радиохимия. 2006. Т. 48. № 6. С. 510-512.

Методом твердофазного синтеза получен ряд соединений урана с общей формулой Ba2MIIUO6 (M = Mg, Ca, Sr, Ba). Методом высокотемпературной рентгеновской дифрактометрии изучен полиморфизм для Ba2SrU06 и определены коэффициенты теплового расширения. Методом реакционной калориметрии определены стандартные энтальпии образования кристаллических Ва2МIIUO6 при 298.15 К.

73.003899
Колесникова Д.С., Харитонова Е.П., Воронкова В.И. СИНТЕЗ И ФАЗОВЫЕ ПЕРЕХОДЫ КИСЛОРОДПРОВОДЯЩЕГО СОЕДИНЕНИЯ LA2MO2O9, ЛЕГИРОВАННОГО ЩЕЛОЧНЫМИ ЭЛЕМЕНТАМИ//Кристаллография. 2011. Т. 56. № 2. С. 342-347.

Исследованы особенности синтеза, полиморфизм и электропроводность кислородпроводящих соединений La2 - xMexMo2O9 - y, где Ме = Na, K, Rb, Cs. Керамические образцы были получены методом твердофазного синтеза в области температур 960–1100С. Была отмечена зависимость областей существования твердых растворов от температуры обжига образца. Фазовый переход из моноклинной ( ) в кубическую ( ) фазу по калориметрическим и электрофизическим исследованиям в образцах, легированных калием и рубидием, исчезал при х = 0.02 и 0.04 соответственно. В этих случаях наблюдался единственный переход в области 450С из кубической фазы ms в высокотемпературную кубическую фазу . При легировании натрием и цезием фазовый переход не подавлялся.

74.008036
Кузьмин A.В., Горелов В.П., Ваганов Е.Г., Корзун И.В., Казанцев B.А., Аксенова Т.И., Хромушин И.В. ФАЗОВЫЕ ПЕРЕХОДЫ, ТЕРМОДЕСОРБЦИЯ ГАЗОВ И ЭЛЕКТРОПРОВОДНОСТЬ ВАСЕО3 -БАЗОВОГО СОЕДИНЕНИЯ ДЛЯ ВЫСОКОТЕМПЕРАТУРНЫХ ПРОТОННЫХ ПРОВОДНИКОВ//Электрохимия. 2005. Т. 41. № 5. С. 620-626.

Проведены исследования фазовых переходов в чистом ВаСеОз методами дилатометрии, дифференциальной сканирующей калориметрии (ДСК), изучена термодесорбция газов и температурные зависимости электропроводности в сухом и влажном воздухе. Установлено, что церат бария обладает сложным полиморфизмом, претерпевая целый ряд структурных изменений в интервале 300-1300 К. Пики на спектрах термодесорбции СО2 и Н2О коррелируют с изменениями кристаллической решетки. Структурные изменения в церате бария оказывают влияние на процессы переноса: изменяются энергии активации транспорта носителей и доли парциальных проводимостей.

75.003899
Кулешова Л.Н., Аверкиев Б.Б., Гусев Д.В., Супоницкий К.Ю., Антипин М.Ю. КОНФОРМАЦИОННЫЙ ПОЛИМОРФИЗМ N(4-БУТОКСИФЕНИЛ)-4-(4'-НИТРОФЕНИЛ)-2-ТИАЗОЛАМИНА//Кристаллография. 2004. Т. 49. № 5. С. 886-894.

Методом рентгеноструктурного анализа изучено молекулярное и кристаллическое строение трех сопутствующих полиморфных модификаций N-(4-бутоксифенил)-4-(4'-нитрофенил)-2-тиазоламина, образующихся одновременно при перекристаллизации из толуола. Установлено, что разная окраска полиморфов обусловлена различной конформацией молекулы в кристаллах. Оценена относительная энергетическая выгодность конформеров и энергия кристаллических упаковок. Обсуждается возможность структурного фазового перехода между полиморфами.

76.000710
Михалев О.В., Федянин И.В., Тарасевич Б.Н., Ильина И.Г., Бутин ПОЛИМОРФИЗМ 2,4,6-ТРИНИТРО-4'-ЙОДОДИФЕНИЛАМИНА К.П.//Вестник Московского университета. Серия 2: Химия. 2007. Т. 48. № 2. С. 118-124.

Найдены экспериментальные условия выделения четырех различноокрашенных полиморфных модификаций для автокомплекса пикрильного ряда - 2,4,6-тринитро-4'-йододифениламина. ИК-спектральным и рентгеноструктурным методами изучены закономерности внутри- и межмолекулярных взаимодействий в полученных полиморфных модификациях, одна из которых нецентросимметрична.

77.001751
Окманов Р.Я., Тожибоев А.Г.У., Тургунов К.К., Ташходжаев Б., Мукаррамов Н.И., Шахидоятов Х.М. НОВАЯ ПОЛИМОРФНАЯ МОДИФИКАЦИЯ КРИСТАЛЛИЧЕСКОЙ СТРУКТУРЫ БРОМПЕГАНОЛА//Журнал структурной химии. 2009. Т. 49. № 2. С. 396-398.

Обнаружена и рентгеноструктурным анализом установлена кристаллическая структура 6-бромпеганола в новой полиморфной модификации. Для кристаллической структуры нового полиморфа также характерно образование центросимметричного замкнутого димера (ассоциата), состоящего из двух молекул бромпеганола, связанных ?встречными? центросимметричными водородными связями O-H…N(1). Данный полиморф отличается от известной модификации взаимным расположением и взаимодействием этих ассоциатов.

78.039301
Пестов C.М., Молочко В.А., Климова Э.В.ПОЛИМОРФИЗМ МЕЗОГЕНОВ И ЕГО ПРОЯВЛЕНИЕ В СИСТЕМАХ//Жидкие кристаллы и их практическое использование. 2005. № 3-4. С. 100-110.

79.001681
Притужалов В.А., Ардашникова Е.И., Долгих В.А., Абакумов А.М. ПОЛИМОРФИЗМ, АНИОННАЯ ПРОВОДИМОСТЬ//Журнал неорганической химии. 2011. Т. 56. № 3. С. 355-366.

Тисонитоподобные твердые растворы Bi1-x BaxOyF3-x-2y в системе BiF3 BiOF BaF2 были получены твердофазным синтезом в герметичных медных ампулах в атмосфере аргона при 873 К с последующим закаливанием. Твердые растворы были исследованы методами рентгенографии, электронной дифракции и импедансной спектроскопии. По результатам рентгенофазового анализа определены области их гомогенности и предложена схема расположения твердых растворов в системе BiF3 BiOF BaF2 при 873 К. Использование гетеровалентного замещения одновременно в катионной и анионной подрешетках Ba2+ Bi3+ и O2 F- позволило варьировать концентрацию анионных вакансий. Установлено, что при высокой концентрации анионных дефектов при 873 К устойчивой является гексагональная модификация тисонита c пр. гр. P 63/mmc. C уменьшением концентрации дефектов устойчивой становится тригональная модификация тисонита c пр. гр. Р с1. Выявлена упорядоченная моноклинная тисонитоподобная модификация BiOyF3 - 2y (0.13 < y < 0.23). Для областей гомогенности всех тисонитоподобных фаз приведены зависимости параметров элементарных ячеек и проводимости от состава вдоль разрезов с постоянным содержанием бария или кислорода. В работе обсуждается наиболее вероятное расположение ионов кислорода и анионных вакансий в тисонитной структуре изученных фаз.

80. 006793
Седых В.Д., Зверькова И.И., Шехтман В.Ш., Дубовицкий А.В., Кулаков В.И. МЕССБАУЭРОВСКИЕ И РЕНТГЕНОВСКИЕ ИССЛЕДОВАНИЯ СТРУКТУРНЫХ ФАЗОВЫХ ПРЕВРАЩЕНИЙ И ПОДАВЛЕНИЯ ПОЛИМОРФИЗМА В LA1-XSRXMN0.98FE0.02O3+DELTA (X=0.05-0.30)//Физика твердого тела. 2010. Т. 52. № 3. С. 545-551.

Методами мессбауэровской спектроскопии и рентгеновской дифрактометрии проведено систематическое исследование особенностей структурых превращений в La1-xSrxMn0.98Fe0.02O3+delta (x=0.05-0.30) в зависимости от содержания Sr. Показано, что при концентрации Sr менее 10% формируются три фазы: PnmaII, PnmaI и R-3c. В интервале концентрации Sr от 10 до 20% образуются фазы PnmaI и R-3c. При 20% Sr формируется ромбоэдрическая фаза, при 30% Sr кроме ромбоэдрической фазы формируется предположительно моноклинная (искаженный куб). Проведено сравнение особенностей формирования и подавления фаз в базовом соединении LaMn0.98Fe0.02O3+delta и в соединении, легированном стронцием La1-xSrxMn0.98Fe0.02O3+delta, выявлены как общие закономерности структурных превращений, так и существенные различия между ними. Работа выполнена при поддержке РФФИ (грант N 09-02-00767-a) и Программы РАН "Квантовая физика конденсированных сред".

81.006793
Седых В.Д., Шехтман В.Ш., Дубовицкий А.В., Зверькова И.И., Кулаков В.И. МЕССБАУЭРОВСКИЕ И РЕНТГЕНОВСКИЕ ИССЛЕДОВАНИЯ ДИНАМИКИ ФАЗОВЫХ ПРЕВРАЩЕНИЙ И ПОДАВЛЕНИЯ ПОЛИМОРФИЗМА В СОЕДИНЕНИИ LAMN1-XFEXO3+DELTA (X=0.015-0.5)//Физика твердого тела. 2009. Т. 51. № 2. С. 351-358.

Методами рентгеновской дифракции и мессбауэровской спектроскопии исследовано влияние примеси железа на структурные превращения и подавление полиморфизма в соединении LaMn1-xFexO3+delta (x=0.015-0.5). Показано, что примесь железа активно влияет на полиморфные превращения манганита. При малом содержании примеси Fe (до 10 at.%) в пределах фазы PnmaII происходит локальное формирование фазы PnmaI. Обсуждаются механизмы подавления полиморфизма. Работа выполнена при поддержке РФФИ (проект N 06-02-16535) и программы РАН "Свойства конденсированных сред". PACS: 06.05.cp, 06.05.Qr, 61.50.Ks, 61.72.sd

82.003899
Сережкин В.Н., Сережкина Л.Б. НОВЫЙ КРИТЕРИЙ КОНФОРМАЦИОННОГО ПОЛИМОРФИЗМА//Кристаллография. 2012. Т. 57. № 1. С. 39.

С помощью молекулярных полиэдров Вороного–Дирихле проведен анализ невалентных взаимодействий в 29 структурах кристаллов соединений состава СaHbNcOd (салицилальдоксим, глицин и 2,4,6,8,10,12-гексаазаизовюрцитан), обладающих полиморфизмом. Установлено, что каждому конформационному полиморфу отвечает уникальное сочетание типов реализующихся внутри- и межмолекулярных невалентных контактов. Показано, что для выявления конформационных полиморфов может быть использован критерий, учитывающий общее число внутримолекулярных невалентных контактов и их распределение в зависимости от природы соседних атомов и ранга граней молекулярных полиэдров Вороного–Дирихле.

83.001770
Сережкин В.Н., Сережкина Л.Б., Пушкин Д.В. АНАЛИЗ НЕВАЛЕНТНЫХ ВЗАИМОДЕЙСТВИЙ В КРИСТАЛЛАХ КОНФОРМАЦИОННЫХ ПОЛИМОРФОВ СОСТАВА СAHBNCODSE ПРИ ПОМОЩИ МОЛЕКУЛЯРНЫХ ПОЛИЭДРОВ ВОРОНОГО–ДИРИХЛЕ//Журнал физической химии. 2011. Т. 85. № 5. С. 914-922.

С помощью молекулярных полиэдров Вороного–Дирихле проведен анализ невалентных взаимодействий в кристаллах соединений состава СaHbNcOdSe, обладающих конформационным полиморфизмом и имеющих не менее четырех структурно охарактеризованных модификаций. Установлено, что каждому конформационному полиморфу отвечает уникальное сочетание типов реализующихся внутри- и межмолекулярных невалентных контактов. Обнаружено, что чаще всего в структурах кристаллов реализуются невалентные взаимодействия с участием атомов водорода, а наиболее редко – с участием атомов S, N и О.

84.002237
Сирота Н.Н., Коноплин Н.А., Сошнина Т.М. ПОЛИМОРФИЗМ ЖЕЛЕЗА В ДВОЙНЫХ СИСТЕМАХ//Металлы. 2006. № 1. С. 102-107.

Разработан метод определения равновесных границ ?- и ?-модификаций железа в двойных системах с ограниченной и расширенной ?-областью. Линии равновесия определены по откло- нению разности свободных энергий полиморфных модификаций относительно соответствующих значений для чистого железа. Получено количественное выражение границ переходов ?-? и ?-? в зависимости от состава и температуры.

85.001573
Сирота Н.Н., Морозов А.В., Сирота И.М., Сошнина Т.М. ВЫСОКОТЕМПЕРАТУРНЫЙ ПОЛИМОРФИЗМ РЕДКОЗЕМЕЛЬНЫХ F-ЭЛЕМЕНТОВ//Доклады Академии наук. 2005. Т. 405. № 2. С. 188-192.

86.J01929
Теслева Е.П. ОРИЕНТАЦИОННЫЙ ПОРЯДОК-БЕСПОРЯДОК В ИОННО-МОЛЕКУЛЯРНЫХ КРИСТАЛЛАХ: ОТКЛИК В АКУСТИКЕ И ТЕПЛОФИЗИКЕ. АЗОТСОДЕРЖАЩИЕ КРИСТАЛЛЫ НАТРИЯ//Фундаментальные проблемы современного материаловедения. 2005. Т. 2. № 2. С. 24-26.

Экспериментально установлены особенности отклика явления полиморфизма в кристаллах азида (NaN3), нитрита (NaNO2), нитрата (NaNO3) нитрата натрия в их акустических, упругих и теплофизических свойствах.

87.034789
Титов В.В., Титов С.В., Резниченко Л.А. ВЛИЯНИЕ ПОЛИМОРФИЗМА NB2O5 НА МУЛЬТИФРАКТАЛЬНЫЕ ПАРАМЕТРЫ ЗЕРЕННОЙ СТРУКТУРЫ, СОВЕРШЕНСТВО КРИСТАЛЛИЧЕСКОЙ СТРУКТУРЫ И СВОЙСТВА НИОБАТНЫХ СЕГНЕТОКЕРАМИК//Физическая мезомеханика. 2004. Т. 7. № S1-1. С. 275-280.

Проведена мультифрактальная параметризация микроструктуры (зеренной структуры) сегнетопьезоэлектрических керамик, полученных из пентаоксида ниобия с различными соотношениями основных полиморфных модификаций. Обнаружено, что па-раметры спектров фрактальных размерностей границ зерен керамики являются чувствительным индикатором неоднородностей в получаемых материалах, приводящих к изменениям мезоскопических параметров структуры кристаллитов - микродеформации и областей когерентного рассеяния. Установлены оптимальные режимы термообработки исходного Nb2O5 для получения мате-риалов с существенно улучшенными целевыми характеристиками.

88.001751
Тожибоев А.Г., Тургунов К.К., Ташходжаев Б., Мусаева Г.В. КРИСТАЛЛИЧЕСКАЯ И МОЛЕКУЛЯРНАЯ СТРУКТУРА ДВУХ ПОЛИМОРФНЫХ МОДИФИКАЦИЙ БИС(2,3-ПЕНТАМЕТИЛЕН-3,4-ДИГИДРОXИНAЗОЛИНИЙ)-ТЕТРАХЛОР-ЦИНКАТА//Журнал структурной химии. 2005. Т. 46. № 5. С. 982-986.

Проведено рентгеноструктурное исследование двух полиморфных модификаций солевого комплекса 2,3-пентаметилен-3,4-дигидрохиназолин гидрохлорида с хлоридом цинка, выращенных в разных температурных условиях. Проанализирована геометрия молекулярного комплекса.

89.003899
Федоров П.П. ПАРАДОКС ТАММАНА И АМОРФИЗАЦИЯ ВЕЩЕСТВ ПОД ДАВЛЕНИЕМ//Кристаллография. 2008. Т. 53. № 1. С. 117-121.

Показано, что аморфизация веществ под давлением может быть связана с фундаментальным свойством поверхности изобарно изотермического потенциала как функции температуры и давления – ее выпуклостью. Аморфизация представляет собой холодное плавление. Максимумы на кривых зависимости температуры плавления от давления представляют собой не аномальные явления, а общий случай, реализация которого ограничивается полиморфизмом. Предложена модель аморфного состояния вблизи абсолютного нуля температуры, а именно – нанокерамика, образованная по механизму полисинтетического двойникования.

90.001732
Фетисов А.В., Петрова С.А., Захаров Р.Г., Гуляева Р.И. ВЛИЯНИЕ ПРОЦЕССА МЕХАНОАКТИВАЦИИ НА ФАЗОВЫЙ СОСТАВ, СТРУКТУРУ И ПОЛИМОРФИЗМ ОКСИДА YBA2CU3O6+?// Журнал прикладной спектроскопии. 2012. Т. 79. № 1. С. 95-103.

Проведен комплексный анализ механоактивированных порошков YBa2Cu3O6+? методами термического анализа, сканирующей электронной микроскопии, высокотемпературной рентгенографии и рентгеновской фотоэлектронной спектроскопии. Показано, что в результате напряженного помола существенно уменьшается размер областей когерентного рассеяния (с 83 до 17 нм), а материал переходит в наноструктурированное состояние. Отмечен рост реакционной способности материала, проявляющийся в усиленном накоплении в его структуре интеркалированной воды. При этом не наблюдалось заметного увеличения объема примесных фаз в порошке и влияния примесей на параметры кристаллической решетки. С помощью высокотемпературных рентгеновских исследований параметров кристаллической решетки YBa2Cu3O6+? -фазы установлено, что в случае механоактивированных порошков на зависимости c(T) имеют место скачкообразные рост (в интервале температур 430-630 °С) и падение (после 630 °С) величины параметра c. Обнаружена заметная редукция температуры перехода из орторомбической структурной модификации в тетрагональную. Указанные эффекты объяснены изменением в процессе механоактивации зарядовых состояний ионов кислорода, входящих в состав базовой плоскости оксида YBa2Cu3O6+? .

91.
Франк-Каменецкая О.В. КОМПОЗИТНЫЙ АНАЛИЗ КРИСТАЛЛИЧЕСКИХ СТРУКТУР ТВЕРДЫХ РАСТВОРОВ// Вестник Нижегородского университета им. Н.И. Лобачевского. Серия: Физика твердого тела. 2004. № 1. С. 103-110

Проведен композитный анализ кристаллических структур твердых растворов с многочисленными атомарными дефектами (точечными, объемными, плоскостными и линейными). Обсуждены симметрия, упорядоченность, способы описания, особенности диагностики по дифракционной картине. Полученные результаты позволяют утверждать, что реальным кристаллам присущ полиморфизм.

92.00676X
Шабашов В.А., Заматовский А.Е., Пилюгин В.П. АККОМОДАЦИОННЫЕ НАПРЯЖЕНИЯ И СТРУКТУРНО-ФАЗОВЫЕ ПЕРЕХОДЫ В FE–NI-СПЛАВАХ ПРИ СЖАТИИ В НАКОВАЛЬНЯХ БРИДЖМЕНА//Физика металлов и металловедение. 2009. Т. 108. № 5. С. 504-512.

Методом мессбауэровской спектроскопии in situ при квазигидростатическом сжатии до 25 ГПа в наковальнях Бриджмена исследованы полиморфные фазовые переходы в железе и сплавах Fe–Ni (Ni, ат. % = 15, 25, 32). Установлена связь вида полиморфизма и объема превращений со сверхтонкими параметрами, магнитной текстурой и напряжениями в структуре исходной и образующейся фаз. В железе и сплаве Fe–15Ni установлено бароупругое изменение направления магнитной текстуры -фазы, обусловленное возникновением ориентированных аккомодационных напряжений между - и -фазами. В области составов 15–25 ат. % Ni обнаружено появление сверхтонкой магнитной структуры спектров в фазе высокого давления.

На главную              К списку выставок