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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Krylov A. S., Sofronova S. N., Kolesnikova E. M., Vtyurin A. N., Isaenko L. I.
Заглавие : Lattice dynamics of oxyfluoride Rb2KMoO3F3
Коллективы : International Symposium on Ferroic Domains and Micro- to Nanoscopic Structures, Russia/CIS/Baltic/Japan Symposium on Ferroelectricity
Место публикации : Ferroelectrics: Taylor & Francis LTD, 2012. - Vol. 441. - P.52-60. - ISSN 0015-0193, DOI 10.1080/00150193.2012.743791
Примечания : Cited References: 23
Предметные рубрики: PHASE-TRANSITIONS
RAMAN-SCATTERING
ELPASOLITE
CRYSTALS
DISORDER
SPECTRA
CS
Ключевые слова (''Своб.индексиров.''): oxyfluorides--lattice dynamics--ramam measurements
Аннотация: The complete Raman spectra of oxyfluoride Rb2KMoO 3F3 were obtained. At T ≈ 185 K phase transitions were found. Lattice dynamics of disordered structures of the investigated compound was simulated, and "soft" vibrational modes were found in the calculated spectrum. Copyright © Taylor & Francis Group, LLC.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Krylov A. S., Goryainov S. V., Laptash N. M., Vtyurin A. N., Mel'nikova S. V., Krylova S. N.
Заглавие : Influence of the molecular groups ordering on structural phase transitions in (NH4)2WO2F4 crystal
Место публикации : Cryst. Growth Des.: American Chemical Society, 2014. - Vol. 14, Is. 1. - P.374-380. - ISSN 1528-7483, DOI 10.1021/cg400899m. - ISSN 1528-7505
Примечания : Cited References: 27. - This work was partly supported by the Russian Foundation for the Basic Research project no. 12-02-00056, no. 13-02-00825, and integration project SB RAS no. 28, SS-4828.2012.2.Published as part of the Crystal Growth & Design virtual special issue Anion-controlled New Inorganic Materials.
Предметные рубрики: RAMAN-SCATTERING
NEUTRON-SCATTERING
SOLID-STATE
OXYFLUORIDES
DISORDER
POLAR
ANION
Аннотация: Phase transitions of the (NH4)2WO2F 4 crystal were studied by Raman spectroscopy in the range from 10 to 350 K. The mechanism of two phase transitions at T1 = 201 and T 2 = 160 K was proposed. The significant spectra changes occur in the range corresponding to the W-O vibrations. The first temperature phase transition is due to the ordering of the quasi-octahedral groups [WO 2F4]2- and partial ordering of ammonium groups. Experimental data allow for attributing the first (T1 = 201 K) phase transition to the first order close to the tricritical point. The noticeable changes of the Raman spectrum have been found in the range corresponding to the ammonium vibrations below the temperature T2. The second phase transition is associated with the further ordering of ammonium groups. Room temperature (296 K) experiments have been carried out under high hydrostatic pressure up to 10 GPa. Above 2 GPa, new spectral features appear, allowing for the assumption of the existence of a new high-pressure phase of (NH 4)2WO2F4, which is mainly connected with ordering of the [WO2F4]2- quasi-octahedral groups.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Krylov A. S., Sofronova S. N., Kolesnikova E. M., Ivanov Y. N., Sukhovsky A. A., Goryainov S. V., Ivanenko A. A., Shestakov N. P., Kocharova A. G., Vtyurin A. N.
Заглавие : Experimental and theoretical methods to study structural phase transition mechanisms in K3WO3F3 oxyfluoride
Коллективы : Russian Foundation for Basic Research [4828.2012.2, 12-02-31205]; Federal Special Program "Scientific and scientific-pedagogical staff of innovative Russia" [8379]
Место публикации : J. Solid State Chem. - 2014. - Vol. 218. - P.32-37. - ISSN 0022-4596, DOI 10.1016/j.jssc.2014.05.028. - ISSN 1095-726X
Примечания : Cited References: 21. - The Authors are grateful to Prof. Zinenko V.I. for constructive discussion of the results. The work has been done with financial support of the Russian Foundation for Basic Research projects nos. 4828.2012.2, 12-02-31205; Federal Special Program "Scientific and scientific-pedagogical staff of innovative Russia" project no. 8379.
Предметные рубрики: LATTICE-DYNAMICS
RAMAN-SCATTERING
ELPASOLITE
(NH4)3WO3F3
SPECTROSCOPY
CRYSTALS
Ключевые слова (''Своб.индексиров.''): raman spectroscopy--ir spectroscopy--nmr spectroscopy--high hydrostatic pressure--oxyfluorides--lattice dynamics calculations
Аннотация: The results of structural phase transitions mechanisms study in K3WO3F3oxyfluoride are represented by different experimental and theoretical methods. The structural phase transition anomalies at T1=452 K and T2=414 K of Raman and IR spectra have been analyzed. Using vibrational spectroscopy methods, the NMR-experiment has been done to clarify the nature of found phase transitions: displacive types or order-disorder types. The model of “disordered” crystal was proposed, and the results of lattice dynamics calculation in frameworks of the generalized Gordon–Kim method of ordered (R3) and “disordered” crystals were compared. The high pressure phases were studied by the Raman technique too.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aleksandrov K. S., Bartolome J.
Заглавие : Structural distortions in families of perovskite-like crystals
Место публикации : Phase Transit.: TAYLOR & FRANCIS LTD, 2001. - Vol. 74, Is. 3. - P.255-335. - ISSN 0141-1594, DOI 10.1080/01411590108228754
Примечания : Cited References: 262
Предметные рубрики: LOW-TEMPERATURE PHASE
INELASTIC-NEUTRON-SCATTERING
POWDER PROFILE REFINEMENT
MII = CO
X-RAY
RAMAN-SCATTERING
ORDERED PEROVSKITE
RHOMBOHEDRAL PEROVSKITES
RB2KMIIIF6 ELPASOLITES
MAGNETIC-PROPERTIES
Ключевые слова (''Своб.индексиров.''): structural phase transitions--perovskites--perovskite-like crystals--group theoretical classification
Аннотация: The crystallographic and group theoretical analysis of the structural phase transitions in perovskite and perovskite-like crystals is reviewed. We include ABX(3) perovskites and their relative crystals of ReO3 type (G(0) = O-h(1)), elpasolites, cryolites and their relatives (G(0) = O-h(5)) layered crystals of TIAIF(4) series (G(0) = D-4h(1)), Aurivillius and Ruddlesden-Popper series (G(0) = D-4h(17)). The structures in their initial phase G(0) often contain n layers (n = 1, 2,3) of vertex linked octahedra. The distorted phases produced by one kind of tilt and by superposition of tilts in the slabs are enumerated. Most of the tilts correspond to symmetry changes, which can be associated to definite librational lattice modes irreducible representations of the G(0) group. The softening of modes associated to the PT has been found experimentally in many perovskites, elpasolites and layered crystals with n = 1. In contrast, no such soft modes have been found yet for even-layered (n = 2) crystals. Examples of successive phase transitions due to the superposition of tilts in these types of crystals have been collected.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Flerov I. N., Aleksandrov K. S., Tressaud A., Grannec J., Couzi M.
Заглавие : Phase transitions in elpasolites (ordered perovskites)
Место публикации : Materials Science and Engineering R: Reports. - 1998. - Vol. 24, Is. 3. - P.81-151. - ISSN 0927-796X
Примечания : Cited References: 174
Предметные рубрики: ELASTIC NEUTRON-DIFFRACTION
MII = CO
RAMAN-SCATTERING
THERMODYNAMIC PROPERTIES
CRYSTAL-STRUCTURE
SINGLE-CRYSTALS
RB2KMIIIF6 ELPASOLITES
CUBIC PEROVSKITES
TEMPERATURE FORM
HIGH-RESOLUTION
Ключевые слова (''Своб.индексиров.''): crystal atomic structure--crystal growth--crystal lattices--crystallization--crystallography--ferroelectricity--hydrostatic pressure--order disorder transitions--single crystals--thermodynamics--elpasolites--landau theory--perovskite
Аннотация: Many compounds with general chemical formula A2BB?X6 and with tolerance factor value t < 1 crystallize in the elpasolite (ordered perovskite) structure. Different preparative methods have been considered. For example, the Bridgman technique is the most suitable method of growing single crystals of halogenated elpasolites with monoatomic cations. Group-theory and symmetry analyses have allowed us to build a scheme of possible structural distortions connected with octahedral rotations and displacements of ions. Experimental observations have proven that ferroelastic phase transitions occurring most frequently in elpasolites are due to small octahedra tilts. Quantitative analysis allows the possibility of describing these transitions in the framework of the thermodynamic Landau theory. Hydrostatic pressure and the substitution of atoms in different crystallographic sites allow to change significantly the succession and the temperature of phase transitions. The hypothesis of bond stresses is able to predict the possible occurrence of a phase transition for a particular elpasolite and/or the role of the octahedra rotations in the transformation. The mechanism of phase transitions in elpasolites and related compounds has also been considered. One can assume that a displacive mechanism associated with a strong anharmonicity plays a large role in phase transitions occurring in compounds with monoatomic cations. On the other hand, for instance, in cryolites with ammonium cations, the transitions originate from an order-disorder phenomenon. В© 1998 Elsevier Science S.A. All rights reserved.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kurnosov V. S., Tsapenko V. V., Bezmaternykh L. N., Gudim, I. A.
Заглавие : IR spectroscopy of the low-frequency phonon spectrum of the TbFe3(BO3)(4) single-crystal
Место публикации : Low Temp. Phys.: American Institute of Physics, 2014. - Vol. 40, Is. 12. - P.1087-1096. - ISSN 1063, DOI 10.1063/1.4904002. - ISSN 10906517(eISSN)
Примечания : Cited References:27
Предметные рубрики: EARTH FERROBORATES RFe3(BO3)4
RAMAN-SCATTERING
TERBIUM FERROBORATE
Аннотация: A study of the IR reflectance spectra of the TbFe3(BO3)4 crystal. We determined the frequencies of the polar lattice phonons in the high-temperature R32, and low- temperature P3121, phases. All 8A 2 ⊕ 11E-modes were found in the high-temperature phase, with nine of them corresponding to lines of the absorption spectrum. In the low-temperature phase, of the 20A 2 ⊕ 35E-modes allowed by the symmetry of the crystal lattice, 20A 2 ⊕ 25E-modes were found.
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Вид документа : Однотомное издание
Шифр издания :
Автор(ы) : Flerov I. N., Gorev M. V., Molokeev M. S., Laptash N. M.
Заглавие : Ferroelastic and ferroelectric phase transitions in fluoro- and oxyfluorometallates
Место публикации : Photonic and electronic properties of fluoride materials: Elsevier, 2016. - Chapter 16. - P.355-381. - (Progress in fluorine science series). - , DOI 10.1016/B978-0-12-801639-8.00016-7
Примечания : Cited References: 92. - The reported study was partially supported by RFBR, research project No. 15-02-02009 a
Предметные рубрики: ELASTIC NEUTRON-DIFFRACTION
ORIENTATIONAL DISORDER
CRYSTAL-STRUCTURES
THERMODYNAMIC PROPERTIES
NONCRITICAL PARAMETERS
CUBIC PEROVSKITES
RAMAN-SCATTERING
SINGLE-CRYSTALS
A2BX4 STRUCTURE
HIGH-RESOLUTION
Аннотация: Different degree of structural disorder is one of the main features of many fluoro- and oxyfluorometallates crystallizing in high symmetry structures. The comprehensive study of these compounds (perovskites, elpasolites, pyrochlores, etc.) enabled to determine a great effect of the size and shape as well as crystallographic sites of cationic and anionic species on the mechanism of structural ordering. Ferroelastic and ferroelectric phase transitions of different order, type, and succession can be realized as a result of chemical and hydrostatic pressure change. It was found that the substitution of monoatomic cations for tetrahedral ammonium group was accompanied by rather significant change of electron density distribution, entropy, and phase diagrams. Some compounds studied were considered to be promising solid-state refrigerants owing to the pronounced barocaloric effect resulting from large entropy and baric coefficient of phase transitions.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zinenko V. I., Zamkova N. G.
Заглавие : Lattice dynamics of MF3 crystals (M = Al, Ga, and In)
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2000. - Vol. 42, Is. 7. - P1348-1353. - ISSN 1063-7834, DOI 10.1134/1.1131391
Примечания : Cited References: 11
Предметные рубрики: RAMAN-SCATTERING
FERROELECTRICITY
BATIO3
PBTIO3
Аннотация: The phonon spectra, Born effective charges, and dielectric constants epsilon(infinity) for the square AlF3, square GaF3, and square InF3 crystals (where is a vacancy) have been calculated in terms of the generalized Gordon-Kim method. The calculated spectra of lattice vibrations contain no imaginary vibrational frequencies. This suggests the stability of the cubic phase of these compounds but contradicts the observable structural transition from cubic to rhombohedral phase. It is assumed that such a transition in the square AlF3, square GaF3, and square InF3 crystals is brought about by structural defects. The calculated spectrum of lattice vibrations of the "completely defective" crystal M square F-3 (M = Al, Ga, and In) indicates a strong instability of the cubic phase. Within the mean crystal approximation, the cubic phase of M-x M1 - xF3 crystals appears to be unstable at small x less than or equal to 0.05. (C) 2000 MAIK "Nauka/Interperiodica".
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Shalaev V. M., Poliakov E. Y., Markel V. A.
Заглавие : Small-particle composites .2. Nonlinear optical properties
Место публикации : Phys. Rev. B: AMERICAN PHYSICAL SOC, 1996. - Vol. 53, Is. 5. - P2437-2449. - ISSN 0163-1829, DOI 10.1103/PhysRevB.53.2437
Примечания : Cited References: 45
Предметные рубрики: FRACTAL CLUSTERS
RAMAN-SCATTERING
SUSCEPTIBILITY
CONDUCTIVITY
EXCITATIONS
COLLOIDS
LIGHT
Аннотация: Strong fluctuations of local fields may result in very large optical nonlinearities in small-particle composites. Enhancement associated with particle clustering is found for a number of optical processes, including four-wave mixing (FWM), third-harmonic generation (THG), Raman scattering, and nonlinear refraction and absorption in Kerr media. Field fluctuations and optical nonlinear susceptibilities are especially large in fractal clusters. The enhancement of optical processes is expressed in terms of the resonant linear absorption by collective dipolar eigenmodes in a cluster, and quality factors, q, of the modes (q much greater than 1). It is shown that the susceptibility of a composite material consisting of random small-particle clusters is proportional to q(3) for Raman scattering and the Kerr optical nonlinearity, and to q(4) and q(6) for THG and FWM, respectively. For all of these processes, a spectral dependence of the effective susceptibility is found. Broad-scale numerical simulations of the optical response in small-particle composites are performed to complement the theory. The simulations are in reasonable agreement with available experimental data.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Mel'nikova S. V., Krylov A. S., Zhogal' A. L., Laptash N. M.
Заглавие : Optical studies of phase transitions in the (NH4)(3)Ti(O-2)F-5 crystal
Коллективы : Russian Federation [NSh-1011.2008.2]; Russian Foundation for Basic Research [06-02-16102]; RFBR Enisei [07-02-096800]
Разночтения заглавия :авие SCOPUS: Optical studies of phase transitions in the (NH4) 3Ti(O2)F5 crystal
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2009. - Vol. 51, Is. 4. - P817-822. - ISSN 1063-7834, DOI 10.1134/S1063783409040301
Примечания : Cited References: 13. - This work was supported by the Council on Grants from the President of the Russian Federation (project no. NSh-1011.2008.2), the Russian Foundation for Basic Research (project no. 06-02-16102), and RFBR Enisei (project no. 07-02-096800).
Предметные рубрики: (NH4)(3)WO3F3 OXYFLUORIDE
RAMAN-SCATTERING
DISORDER
Аннотация: Polarization-optical study of twinning and measurements of the Raman spectra and birefringence in oxyfluoride (NH4)(3)Ti(O-2)F-5 were carried out over the temperature range 90-350 K. Phase transitions were detected at temperatures T (01) = 266 K (second-order transition) and T (02) = 225 K (first order). It is assumed that the crystal symmetry is changed as follows: Fm3m a dagger" I4/mmm a dagger" I4/m. Anomalies of the spectral parameters are established in the frequency range of internal vibrations of ammonium ions and Ti(O-2)F-5 complexes. An analysis of the results shows that the transition at T (01) is likely due to small shifts of the tetrahedral groups from their position on the triad axis and that the transition at T (02) is due to fluorine-oxygen ordering of Ti(O-2)F-5 complexes.
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11.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Krylov A. S., Molokeev M. S., Misyul S. V., Krylova S. N., Oreshonkov A. S., Ivanenko A. A., Zykova V. A., Ivanov Y. N., Sukhovsky A. A., Voronov V. N., Safonov I. N., Vtyurin A. N.
Заглавие : Crystal structure and phase transitions of a layered perovskite-like CsScF4 crystal
Коллективы : Russian Foundation for Basic Research [16-02-00102]
Место публикации : CrystEngComm: Royal Society of Chemistry, 2016. - Vol. 18, Is. 43. - P.8472-8486. - ISSN 1466-8033, DOI 10.1039/c6ce01144f
Примечания : Cited References:47. - The authors are grateful to Prof. I. N. Flerov for valuable support and useful discussions. This work was partly supported by the Russian Foundation for Basic Research, Project 16-02-00102. The research is partially conducted within the framework of the state task of the Ministry of Education and Science of the Russian Federation for Siberian Federal University on R&D performance in 2014 (Task 3.2534.2014/K). X-ray data from powders, Raman NMR, and IR spectra were obtained with use the analytical equipment of Krasnoyarsk Center of collective use SB RAS.
Предметные рубрики: NEGATIVE THERMAL-EXPANSION
RAMAN-SCATTERING
LATTICE-DYNAMICS
Аннотация: This work is devoted to the complex research on temperature phase transitions in a CsScF4 crystal. The crystal structure was solved and refined at different temperatures by using the Rietveld method. Structural phase transitions were investigated by using the following spectroscopic methods, some of them for the first time: Brillouin spectroscopy, Raman spectroscopy, IR absorption spectroscopy and NMR. The symmetry analysis of the Brillouin zone center of all phases is presented. The vibrational spectra of the crystal in three phases have been calculated. The structural phase transition mechanism was determined. The transitions at T-1 = 475 K and T-2 = 317.5 K are of displacement type. The Raman soft modes have been associated with rotations of the ScF6 octahedral group.
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12.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Krylov A. S., Krylova S. N., Gudim I. A., Vtyurin A. N.
Заглавие : Soft modes in HoFe2.5Ga0.5(BO3)4 solid solution
Коллективы : European Meeting on Ferroelectricity , Russian Foundation for Basic Research GrantRussian Foundation for Basic Research (RFBR) [1802-00754]
Место публикации : Ferroelectrics. - 2020. - Vol. 556, Is. 1. - P.16-22. - ISSN 0015-0193, DOI 10.1080/00150193.2020.1713334. - ISSN 1563-5112(eISSN)
Примечания : Cited References: 14. - This work was supported by the Russian Foundation for Basic Research Grant No 1802-00754.
Предметные рубрики: RAMAN-SCATTERING
SPECTRA
HO1-XNDXFE3(BO3)(4)
Аннотация: The condensation of two soft modes has been found when studying the Raman spectra of the solid solution HoFe2.5Ga0.5(BO3)4 in the temperature range from 7 to 350 K. The first high-temperature soft mode is associated with the structural phase transition from the R32 phase to the P3121 phase. The second soft mode is related to the reveal of the phonon-magnon interaction during magnetic ordering in the crystal. The temperatures of the structural phase transition T1 = 266 K and the magnetic phase transition T2 = 28 K are established. Experimentally interaction between the structural phase transition order parameter fluctuations and the magnetic order parameter fluctuations was found.
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