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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Рогинский Е. М., Крылов, Александр Сергеевич, Марков Ю. Ф.
Заглавие : Неэмпирические подходы при изучении фазовых переходов и барическое поведение фононов в молекулярных кристаллах
Место публикации : Наноматер. и нанострукт. - XXI век: Радиотехника, 2015. - Т. 6, № 2. - С. 21-27. - ISSN 2225-0999
Примечания : Библиогр.: 12
Ключевые слова (''Своб.индексиров.''): ab initio--фононы--сегнетоэластики--фазовые переходы--раман-спектроскопия--динамика решетки--phonon--ferroelastics--phase transition--raman spectra--lattice dynamics
Аннотация: При изучении барического поведения фононного спектра кристаллов Hg2Cl2 были предсказаны теоретически и обнаружены экспериментально в низкосимметричной, ромбической фазе мягкие моды из различных высокосимметричных точек зоны Бриллюэна (ЗБ), частоты которых уменьшается при повышении давления. В раман спектрах наблюдается мягкий фонон, который смягчается вплоть до критического давления c = 9,2 ГПа, выше которого полностью исчезает, что свидетельствует в пользу второго структурного фазового перехода, обнаруженного в настоящей работе, в кристаллах Hg2Cl2. Показано, что в случае молекулярных или квазимолекулярных кристаллов для корректного описания электронной структуры важно учитывать дисперсионные дальнодействующие поправки функционала зарядовой плотности.Under the study of phonon spectra pressure behaviour of Hg2Cl2 crystals the soft modes at the set of high-symmetry Brillouin zone(BZ) points was predicted theoretically and observed experimentally. The frequency of soft modes reduces under pressure. In the raman spectra soft mode at the center of BZ was observed and studied. The frequency of soft mode decrease at the hydrostatic pressure up to P c = 9.2 GPa and disappears at higher pressure in spectra. Such changes in spectra points to the existence of the second phase transition observed in the present work. It was shown that in the case of molecular crystals the long-range dispersion corrections of the electron density functional is required for a proper electronic structure description.
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Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Zinenko V. I., Sofronova S. N.
Заглавие : The nonempirical calculation of the cation ordering and lattice dynamics in the solid solutions of PbSc1/2Nb1/2O3 and PbSc1/2Ta1/2O3
Место публикации : 11th International Conference on Phonon Scattering in Condensed Matter (PHONONS 2004) (JUL 25-30, 2004, St Petersburg, RUSSIA): WILEY-V C H VERLAG GMBH, 2004. - P3047-3051. - ISBN 3-527-40588-7, DOI 10.1002/pssc.200405286
Примечания : Cited References: 10
Аннотация: An effective Hamiltonian for the study of Sc-Nb(Ta) cation ordering in PbSc1/2Nb(Ta)(1/2)O-3 solid solutions is written out. To determine the parameters of the effective Hamiltonian, a nonempirical calculation is performed within an ionic-crystal model taking into account the deformation, dipole and quadrupole polarizabilities of ions. The phase transition temperatures are calculated by mean field, cluster approximations and Monte-Carlo method. Within the same ionic-crystal model, we calculated the high-frequency permittivity, Born dynamic charges, and the phonon spectrum for a completely disordered and ordered phases. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zinenko V. I., Pavlovskii M. S.
Заглавие : Lattice dynamics and the phase transition from the cubic phase to the tetragonal phase in the LaMnO3 crystal within the polarizable-ion model
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2007. - Vol. 49, Is. 9. - P1749-1758. - ISSN 1063-7834, DOI 10.1134/S1063783407090235
Примечания : Cited References: 23
Предметные рубрики: NEUTRON-DIFFRACTION
PEROVSKITES
MANGANITES
PHONONS
Аннотация: The paper reports on the results of ab initio calculations of the static and dynamic properties of the LaMnO3 crystal with a perovskite structure in the cubic, rhombohedral, and orthorhombic phases. The calculations are performed within the ionic crystal model, which takes into account the deformability and polarizability of the ions. It is revealed that the spectrum of lattice vibrations in the cubic phase contains unstable vibrational modes, which occupy the phase space in the entire Brillouin zone. The eigenvectors of the softest mode at the boundary point R of the Brillouin zone are associated with the displacements of the oxygen ions and correspond to the "rotation" of the MnO6 octahedron. The condensation of one, two, and three components of this mode leads to the tetragonal, orthorhombic, and rhombohedral distortions of the structure. The structural phase transition is described in terms of the local mode approximation with the use of the double perovskite unit cell, in which the MnO6 octahedron is explicitly separated. The parameters of the model Hamiltonian are determined. The static properties are investigated by the Monte Carlo method. The calculated temperature of the phase transition from the cubic phase (9800 K) is considerably higher than the melting temperature of the crystal under investigation. The calculated frequencies of long-wavelength lattice vibrations in the experimentally observed orthorhombic and rhombohedral phases are in reasonable agreement with experimental data.
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Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Zamkova N. G., Zinenko V. I.
Заглавие : Lattice dynamics and ferroelectric phase transitions in solid solutions PbSc(1/2)Nb(1/2)O(3) and PbSc(1/2)Ta(1/2)O(3)
Разночтения заглавия :авие SCOPUS: Lattice dynamics and ferroelectric phase transitions in solid solutions PbSc1/2Nb1/2O3 and PbSc1/2Ta 1/2O3
Место публикации : 12TH INTERNATIONAL CONFERENCE ON PHONON SCATTERING IN CONDENSED MATTER (PHONONS 2007). Ser. Journal of Physics Conference Series: IOP PUBLISHING LTD, 2007. - Vol. 92: 12th International Conference on Phonon Scattering in Condensed Matter (PHONONS 2004) (JUL 15-20, 2007, Paris, FRANCE). - Ст.12162. - ISBN 1742-6588, DOI 10.1088/1742-6596/92/1/012162
Примечания : Cited References: 14
Предметные рубрики: PEROVSKITES
BATIO3
Аннотация: The calculation of the lattice dynamics and ferroelectric phase transitions for disordered and ordered solid solution PbSc(1/2)Nb(1/2)O(3) and PbSC(1/2)Ta(1/2)O(3) in the framework of the Gordon-Kim model are performed. The unstable ferroelectric modes were found in all cases. The model Hamiltonian for the study finite temperature behavior during for the ferroelectric phase transition is used. The transition temperatures, phase sequences and spontaneous polarizations are calculated by Monte-Carlo method.
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Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Popov A. K., Shalaev M. I., Myslivets S. A., Slabko, V. V.
Заглавие : Unidirectional Amplification and Shaping of Optical Pulses by Three-Wave Mixing with Negative Phonons
Коллективы : International Conference on Metamaterials, Photonic Crystals and Plasmonics
Место публикации : The 4th International Conference on Metamaterials, Photonic Crystals and Plasmonics (META’13): Proceedings. - 2013. - P.35-40
Примечания : Библиогр.: 30 назв.
Аннотация: A possibility to greatly enhance frequency-conversion efficiency of stimulated Raman scattering is shown by making use of extraordinary properties of three-wave mixing of ordinary and backward waves. Such processes are commonly attributed to negative-index plasmonic metamaterials. This work demonstrates the possibility to replace such metamaterials that are very challenging to engineer by readily available crystals which support elastic waves with contradirected phase and group velocities. The main goal of this work is to investigate specific properties of indicated nonlinear optical process in short pulse regime and to show that it enables elimination of fundamental detrimental effect of fast damping of optical phonons on the process concerned. Among the applications is the possibility of creation of a family of unique photonic devices such as unidirectional Raman amplifiers and femtosecond pulse shapers with greatly improved operational properties.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Popov A. K., Shalaev M. I., Myslivets S. A., Slabko V. V.
Заглавие : Unidirectional amplification and shaping of optical pulses by three-wave mixing with negative phonons
Коллективы : US Air Force Office of Scientific Research [FA950-12-1-298]; US National Science Foundation [ECCS-1028353]; Presidium of the Russian Academy of Sciences [24-31]; Russian Federal Program on Science, Education and Innovation [14.A18.21.1942]
Место публикации : Appl. Phys. A: Springer, 2013. - Vol. 115, Is. 2. - P.523-529. - ISSN 0947-8396, DOI 10.1007/s00339-013-8078-4. - ISSN 1432-0630
Примечания : Cited References: 32. - This work was supported in parts by the US Air Force Office of Scientific Research under Grant No. FA950-12-1-298, by the US National Science Foundation under Grant No. ECCS-1028353, by the Presidium of the Russian Academy of Sciences under Grant No. 24-31 and by the Russian Federal Program on Science, Education and Innovation under Grant No. 14.A18.21.1942.
Предметные рубрики: LEFT-HANDED METAMATERIALS
2ND-HARMONIC GENERATION
INDEX METAMATERIALS
NONLINEAR OPTICS
PARAMETRIC AMPLIFICATION
COMPENSATING LOSSES
BACKWARD WAVES
OSCILLATOR
CRYSTALS
Аннотация: A possibility to greatly enhance frequency-conversion efficiency of stimulated Raman scattering is shown by making use of extraordinary properties of three-wave mixing of ordinary and backward waves. Such processes are commonly attributed to negative-index plasmonic metamaterials. This work demonstrates the possibility to replace such metamaterials that are very challenging to engineer by readily available crystals which support elastic waves with contra-directed phase and group velocities. The main goal of this work was to investigate specific properties of indicated nonlinear optical process in short-pulse regime and to show that it enables elimination of fundamental detrimental effect of fast damping of optical phonons on the process concerned. Among the applications is the possibility of creation of a family of unique photonic devices such as unidirectional Raman amplifiers and femtosecond pulse shapers with greatly improved operational properties.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Hoffman A. E.J., Senkovska I., Wieme J., Krylov A. S., Kaskel S., Van Speybroeck V.
Заглавие : Unfolding the terahertz spectrum of soft porous crystals: rigid unit modes and their impact on phase transitions
Место публикации : J. Mater. Chem. A. - 2022. - Vol. 10, Is. 33. - P.17254-17266. - ISSN 20507488 (ISSN), DOI 10.1039/d2ta01678h
Примечания : Cited References: 80. - This work was financially supported by the Fund for Scientific Research Flanders (FWO), the Research Board of the Ghent University (BOF), the Deutsche Forschungsgemeinschaft (DFG, project number 448809307), and the Russian Foundation for Basic Research (RFBR, project number 21-52-12018). The authors thank Kerstin Zechel for sample synthesis. The computational resources and services used in this work were provided by the Flemish Supercomputer Center (VSC), funded by FWO and the Flemish Government
Аннотация: Phase transitions in flexible metal-organic frameworks or soft porous crystals are mediated by low-frequency phonons or rigid-unit modes. The alteration of specific building blocks may change the lattice dynamics of these frameworks, which can influence the phase transition mechanism. In this work, the impact of building block substitution on the rigid-unit modes in flexible MIL-53 analogs with a winerack topology will be investigated via ab initio lattice dynamics calculations. First, the accuracy of the theoretical simulations is verified via experimental Raman measurements, which provide unique fingerprint vibrations in the terahertz range to characterize the phase transition. Following analysis of the low-frequency vibrations shows that there exists a set of universal rigid-unit modes inducing translations and/or rotations of the building blocks. The theoretical results demonstrate that linker substitutions have a large effect on the rigid-unit mode frequencies, whereas this is less so for inorganic chain substitutions. These findings may help to rationally tune the phonon frequencies in soft porous crystals.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Podoprigora V. G., Remizov I. A., Shabanov V. F., Botvich A. N.
Заглавие : Surface phonons in molecular-crystals
Место публикации : Phys. Status Solidi B. - 1987. - Vol. 139, Is. 1. - P.109-115. - ISSN 0370-1972, DOI 10.1002/pssb.2221390108
Примечания : Cited References: 9
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Davydov V. Yu., Klochikhin A. A., Smirnov A. N., Strashkova I. Y., Krylov A. S., Lu H., Schaff W. J., Lee H. M., Hong Y. L., Gwo S.
Заглавие : Selective excitation of E-1(LO) and A(1)(LO) phonons with large wave vectors in the Raman spectra of hexagonal InN
Коллективы : RFBR [09-02-01280]; NSC-RFBR [08-02-92003-HHC]
Разночтения заглавия :авие SCOPUS: Selective excitation of E1 (LO) and A1 (LO) phonons with large wave vectors in the Raman spectra of hexagonal InN
Место публикации : Phys. Rev. B. - 2009. - Vol. 80, Is. 8. - Ст.81204. - ISSN 1098-0121, DOI 10.1103/PhysRevB.80.081204
Примечания : Cited References: 15. - We are thankful to B. N. Mavrin and A. N. Vtyurin for the arrangement NIR measurements and S. A. Permogorov for the critical reading of the manuscript. This work was supported by RFBR (Grant No. 09-02-01280), NSC-RFBR (Grant No. 08-02-92003-HHC), and the Program of RAS "New materials and structures."
Предметные рубрики: SCATTERING
RESONANCE
Ключевые слова (''Своб.индексиров.''): iii-v semiconductors--indium compounds--phonon dispersion relations--raman spectra--wide band gap semiconductors
Аннотация: It is shown that dispersions of E-1(LO) and A(1)(LO) modes of InN can be restored in a wide interval of wave vectors by studying impurity-induced first-order Raman scattering as a function of exciting light energy. It is also shown that due to the resonance character of scattering the observed phonon energies correspond to the wave vectors strictly defined by exciting photon energies. The frequencies of E-1(LO) and A(1)(LO) phonons at the Gamma point obtained by extrapolation to zero wave vectors were found to be 604 and 592 cm(-1), respectively.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Roginskii E. M., Krylov A. S., Markov Y. F.
Заглавие : Lattice Dynamics and Baric Behavior of Phonons in the Hg2Br2 Model Ferroelastics
Место публикации : Phys. Solid State. - 2019. - Vol. 61, Is. 2. - P.187-191. - ISSN 10637834 (ISSN), DOI 10.1134/S1063783419020227
Примечания : Cited References: 13. - This study was supported by the Presidium of the Russian Academy of Sciences, Programs no. 1.4 “Urgent Problems of Low-Temperature Physics” and no. 1.7 “Physics of Condensed Matter and New-Generation Materials.” The authors are grateful to Yu.E. Kitaev for fruitful discussions.
Аннотация: Raman spectra of Hg2Br2 model improper ferroelastic crystals have been investigated in a wide range of high hydrostatic pressures. Baric dependences of the phonon frequencies have been obtained; of greatest interest are the observed soft mode originating from the slowest TA1 acoustic branch at the Brillouin zone boundary (X point) of the tetragonal phase and the anomalous behavior of this mode. In the ferroelastic phase spectra, the ignition of the second acoustic TA2 from the same point has also been detected and its baric behavior has been studied. Under sufficiently high pressures, splitting of doubly degenerate phonons with the Eg symmetry has been observed and explained. The parameters of the Grüneisen constants have been determined from the baric dependences of the phonon frequencies and discussed.
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11.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Davydov V. Yu., Klochikhin A. A., Smirnov A. N., Strashkova I. Y., Krylov A. S., Lu H., Schaff W. J., Lee H. M., Hong Y. L., Gwo S.
Заглавие : Resonant Raman Scattering and Dispersion of Polar Optical and Acoustic Phonons in Hexagonal InN
Коллективы :
Разночтения заглавия :авие SCOPUS: Resonant raman scattering and dispersion of polar optical and acoustic phonons in hexagonal inn
Место публикации : Semiconductors: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2010. - Vol. 44, Is. 2. - P161-170. - ISSN 1063-7826, DOI 10.1134/S1063782610020065
Примечания : Cited References: 19. - This study was supported by the Russian Foundation for Basic Research (project nos. 09-02-01280 and 08-02-92003-NNS) and by the program of the Russian Academy of Sciences "New Materials and Structures."
Аннотация: It is shown that a study of the dependence of impurity-related resonant first-order Raman scattering on the frequency of excitation light makes it possible to observe the dispersion of polar optical and acoustic branches of vibrational spectrum in hexagonal InN within a wide range of wave vectors. It is established that the wave vectors of excited phonons are uniquely related to the energy of excitation photon. Frequencies of longitudinal optical phonons E(1)(LO) and A(1)(LO) in hexagonal InN were measured in the range of excitation-photon energies from 2.81 to 1.17 eV and the frequencies of longitudinal acoustic phonons were measured in the range 2.81-1.83 eV of excitation-photon energies. The obtained dependences made it possible to extrapolate the dispersion of phonons A(1)(LO) and E(1)(LO) to as far as the point Gamma in the Brillouin zone and estimate the center-band energies of these phonons (these energies have not been uniquely determined so far).
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12.

Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Vtyurin A. N., Goryainov S. V., Krylov A. S., Krylova S. N., Shefer A. D., Zamkova N. G., Zinenko V. I.
Заглавие : Raman spectra and pressure-induced lattice instabilities in RbMnCl3 crystal
Разночтения заглавия :авие SCOPUS: Raman spectra and pressure-induced lattice instabilities in RbMnCl 3 crystal
Место публикации : 11th International Conference on Phonon Scattering in Condensed Matter (PHONONS 2004) (JUL 25-30, 2004, St Petersburg, RUSSIA): WILEY-V C H VERLAG GMBH, 2004. - 11th International Conference on Phonon Scattering in Condensed Matter (PHONONS 2004) (JUL 25-30, 2004, St Petersburg, RUSSIA). - P3097-3100. - ISBN 3-527-40588-7, DOI 10.1002/pssc.200405332
Примечания : Cited References: 14
Предметные рубрики: PHASE-TRANSITION
SPECTROSCOPY
Ключевые слова (''Своб.индексиров.''): frequencies--hydrostatic pressure--mathematical models--parameter estimation--raman scattering--spectrometers--stability--ambient conditions--anomalies--lattice instabilities--structural units--rubidium compounds
Аннотация: Raman scattering spectra of the RbMnCl3 crystal have been studied under ambient conditions and under high hydrostatic pressure. The results produced have been interpreted with the ab initio model. The experimental data agree well with the estimated values in the low frequency range and show a slightly worse agreement at higher frequencies. A phase transition from the hexagonal phase to the perovskite phase predicted earlier within the same model was observed under high pressure (above 0.7 GPa) and new transitions to lower symmetry phases were found at higher pressures (1.1 GPa and 5 GPa). (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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13.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Krylov A. S., Vtyurin A. N., Bulou A., Voronov V. N.
Заглавие : Raman spectra and phase transitions in the Rb2KScF6 elpasolite
Коллективы : Russian-CIS-Baltic-Japanese symposium on ferroelectricity
Место публикации : Ferroelectrics: Taylor & Francis LTD, 2003. - Vol. 284. - P221-238. - ISSN 0015-0193, DOI 10.1080/00150190390204709
Примечания : Cited References: 13
Предметные рубрики: LIGHT-SCATTERING
OPTICAL PHONONS
MODE
Ключевые слова (''Своб.индексиров.''): rb2kscf6--phase transitions--raman scattering--soft modes
Аннотация: Raman spectra of Rb2KScF6 elpasolite crystal have been studied in a wide temperature range, including two transition points: from cubic to tetragonal, and then-to the monoclinic phase. For the first time both for this crystal and for fluoride elpasolites in general soft modes restoration has been found below transition points; in agreement with selection rules a splitting of degenerate modes has been observed as well both for lattice vibrations and internal modes of ScF6 octahedrons. Parameters of Raman lines have been quantitatively analyzed and found in good agreement with known thermodynamic characteristics of these transitions; in particular, lines widths are shown to be determined by tree-phonons anharmonic interactions. A wide region of pretransitional fluctuations was found above the upper transition point.
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14.

Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Vtyurin A. N., Isaenko L. I., Krylova S. N., Yelisseyev A., Shebanin A. P., Turchin P. P., Zamkova N. G., Zinenko V. I.
Заглавие : Raman spectra and elastic properties of KPb2Cl5 crystals
Место публикации : 11th International Conference on Phonon Scattering in Condensed Matter (PHONONS 2004) (JUL 25-30, 2004, St Petersburg, RUSSIA): WILEY-V C H VERLAG GMBH, 2004. - P3142-3145. - ISBN 3-527-40588-7, DOI 10.1002/pssc.200405401
Примечания : Cited References: 10
Предметные рубрики: LATTICE-DYNAMICS
Ключевые слова (''Своб.индексиров.''): computer simulation--crystal structure--eigenvalues and eigenfunctions--halogen compounds--nonlinear optics--phonons--potassium compounds--vectors--elastic constants--heavy cations--ionic electron envelopes--ionic interactions--raman scattering
Аннотация: Raman scattering spectra and elastic constants of KPb2Cl5 crystals have been studied. The results obtained are interpreted in terms of the ab initio lattice dynamics model taking into account multipole moments of ionic electron envelopes. The experimental results have been found to be in good agreement with numerical simulation; the narrow phonon spectra are shown to be due to a considerable contribution of heavy cations into the eigenvectors of the higher frequency lattice modes.
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15.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Krylov A. S., Krylova S. N., Vtyurin A. N., Voronov V. N., Oreshonkov A. S.
Заглавие : Raman Scattering Study Temperature Phase Transitions of Rb2KInF6 Crystal
Место публикации : Ferroelectrics: TAYLOR & FRANCIS LTD, 2011. - Vol. 416. - P95-100. - ISSN 0015-0193, DOI 10.1080/00150193.2011.577713
Примечания : Cited References: 9. - Authors wish to thank prof. K. S. Aleksandrov and prof. I. N. Flerov for their valuable support and useful discussions. This work has been financially supported by grants RFFBR 08-02-00066, 09-02-00062, SS-1011.2008.2.
Предметные рубрики: LIGHT-SCATTERING
LATTICE-DYNAMICS
OPTICAL PHONONS
ELPASOLITE
RB2KSCF6
Ключевые слова (''Своб.индексиров.''): rb2kinf6--temperature phase transitions--raman scattering--lattice dynamics
Аннотация: Raman scattering spectra of Rb2KInF6 crystal have been studied in a wide temperature range, including two phase transitions: from cubic to tetragonal, and then - to the monoclinic phase. Hardening of soft phonon modes was observed that attributes them to the transitions of displacive type. Parameters of Raman lines have been quantitatively analyzed and found in good agreement with known thermodynamic characteristics of these transitions. No evidences of order - disorder processes were observed in the Raman spectra of the high-symmetry phase.
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16.

Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Vtyurin A. N., Krylov A. S., Gerasimova J. V., Fokina V. D., Kocharova A. G., Laptash N. M., Voyt E. I., Surovtsev N. V.
Заглавие : Raman scattering study of ordering processes and phase transitions in A(2)BWO(3)F(3) oxyfluorides crystals
Разночтения заглавия :авие SCOPUS: Raman scattering study of ordering processes and phase transitions in A2BWO3F3oxyfluorides crystals
Место публикации : 12TH INTERNATIONAL CONFERENCE ON PHONON SCATTERING IN CONDENSED MATTER (PHONONS 2007). Ser. Journal of Physics Conference Series: IOP PUBLISHING LTD, 2007. - Vol. 92: 12th International Conference on Phonon Scattering in Condensed Matter (PHONONS 2004) (JUL 15-20, 2007, Paris, FRANCE). - Ст.12158. - ISBN 1742-6588, DOI 10.1088/1742-6596/92/1/012158
Примечания : Cited References: 6
Предметные рубрики: (NH4)(3)WO3F3
Аннотация: Raman spectra of perovskite-like (NH(4))(3)WO(3)F(3), (NH(4))(2)KWO(3)F(3) and Cs(2)(NH(4))WO(3)F(3) oxyfluorides are obtained in a wide temperature range including transition points. Transition anomalies are found and analyzed. Transformation in (NH(4))(3)WO(3)F(3) is shown to be bound with octahedron groups ordering and strong distortion of ammonium ions due to H-bond formation, that is accompanied by cell volume multiplication, hardening and formation of complex discrete low frequency lattice spectrum. Same cell doubling was found in (NH(4))(2)KWO(3)F(3), but without lattice ordering Cs(2)(NH(4))WO(3)F(3) lattice stays disordered down to 15 K.
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17.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Fausti D., Nugroho A. A., van Loosdrecht PHM, Klimin S. A., Popova M. N., Bezmaternykh L. N.
Заглавие : Raman scattering from phonons and magnons in RFe3(BO3)(4)
Разночтения заглавия :авие SCOPUS: Raman scattering from phonons and magnons in RFe3 (BO3) 4
Место публикации : Phys. Rev. B: AMER PHYSICAL SOC, 2006. - Vol. 74, Is. 2. - Ст.24403. - ISSN 1098-0121, DOI 10.1103/PhysRevB.74.024403
Примечания : Cited References: 26
Предметные рубрики: IRON BORATE GDFE3(BO3)(4)
LIGHT-SCATTERING
CRYSTALS
ND
CRYSTALLIZATION
TRANSITIONS
GENERATION
LASER
Аннотация: Inelastic light scattering spectra of several members of the RFe3(BO3)(4) family reveal a cascade of phase transitions as a function of temperature, starting with a structural, weakly first-order, phase transition followed by two magnetic phase transitions. Those consist of the ordering of the Fe-spin sublattice, revealed by all the compounds, and a subsequent spin-reorientational transition for GdFe3(BO3)(4). The Raman data evidence a strong coupling between the lattice and magnetic degrees of freedom in these borates. The Fe-sublattice ordering leads to a strong suppression of the low-energy magnetic scattering, and a multiple peaked two-magnon scattering continuum is observed. Evidence for short-range correlations is found in the "paramagnetic" phase by the observation of a broad magnetic continuum in the Raman data, which persists up to surprisingly high temperatures.
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18.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Prokert F., Aleksandrov K. S.
Заглавие : Neutron scattering studies on phase transition and phonon dispersion in Cs//2NaBiCl//6
Место публикации : Phys Status Solidi B. - 1984. - Vol. 124, Is. 2. - P.503-513. - ISSN 0370-1972, DOI 10.1002/pssb.2221240208
Примечания : Cited References: 24
Ключевые слова (''Своб.индексиров.''): neutrons - scattering--phonons--phase transition--phonon dispersion--cesium compounds
Аннотация: The structural phase transition (PT) of elpasolite-type crystal Cs//2NaBiCl//6 is investigated by neutron scattering. At first the acoustic phonon dispersion is measured at room temperature for the high-symmetric directions DELTA , SIGMA , and LAMBDA of the Brillouin zone. The transverse rotary mode is studied for phonon wave vectors q parallel as well as perpendicular to DELTA and the dispersion shows a quasi-two-dimensional behavior of the Cl-octahedra rotation. At cooling down to the PT, this branch shows a softening along DELTA , reaching the lowest energies at the zone center. The PT, which is found to be of weakly first order, seems to be driven and triggered by the ferrorotative octahedra mode.
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19.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Shneyder E. I., Nikolaev S. V., Zotova M. V., Kaldin R. A., Ovchinnikov S. G.
Заглавие : Polaron transformations in the realistic model of the strongly correlated electron system
Коллективы : Russian Foundation for Basic Research, Government of Krasnoyarsk Territory; Krasnoyarsk Regional Fund of Science [18-42-240017, 19-42240007]
Место публикации : Phys. Rev. B. - 2020. - Vol. 101, Is. 23. - Ст.235114. - ISSN 2469-9950, DOI 10.1103/PhysRevB.101.235114. - ISSN 2469-9969(eISSN)
Примечания : Cited References: 69. - We acknowledge the stimulating discussions with V. A. Gavrichkov, G. Seibold, and K. I. Kugel. The reported study was funded by Russian Foundation for Basic Research, Government of Krasnoyarsk Territory and Krasnoyarsk Regional Fund of Science according to the research project "Features of electron-phonon coupling in high-temperature superconductors with strong electronic correlations" No. 18-42-240017 and project "Electronic correlation effects and multiorbital physics in iron-based materials and cuprates" No. 19-42240007.
Предметные рубрики: ANOMALOUS-DISPERSION
PHONON INTERACTION
PHASE-TRANSITIONS
LO PHONONS
Аннотация: Electron-phonon coupling, diagonal in a real space formulation, leads to a polaron paradigm of smoothly varying properties. However, fundamental changes, namely the singular behavior of polarons, occur if off-diagonal pairing is involved into consideration. The study of polaron transformations and related properties of matter is of particular interest for realistic models, since competition between diagonal and off-diagonal electron-phonon contributions in the presence of other strong interactions can result in unconventional behavior of the system. Here we consider a two-dimensional multiband pd model of cuprate superconductors with electron-phonon interaction and analyze the features of the systems that are caused by the competition of diagonal and off-diagonal electron-phonon contributions in the limit of strong electron correlations. Using the polaronic version of the generalized tight-binding method, we describe the evolution of the band structure, Fermi surface, density of states at Fermi level, and phonon spectral function in the space of electron-phonon parameters ranging from weak to strong coupling strength of the adiabatic limit. On the phase diagram of polaron properties we reveal two quantum phase transitions and show how electron-phonon interaction gives rise to Fermi surface transformation (i) from hole pockets to true Fermi arcs and (ii) from hole to electron type of conductivity. We also demonstrate the emergence of new states in the phonon spectral function of the polaron and discuss their origin.
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20.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Bikbaev R. G., Vetrov S. Ya., Timofeev I. V., Shabanov V. F.
Заглавие : Photosensitivity and reflectivity of the active layer in a Tamm-plasmon-polariton-based organic solar cell
Место публикации : Appl. Opt. - 2021. - Vol. 60, Is. 12. - P.3338-3343. - ISSN 1559128X (ISSN), DOI 10.1364/AO.421374
Примечания : Cited References: 49. - The reported study was funded by the grant of the President of Russian Federation No. MK-46.2021.1.2 and by Russian Foundation for Basic Research, Government of Krasnoyarsk Territory, Krasnoyarsk Region Science and Technology Support Fund to the research project No. 19-42-240004
Аннотация: We report on a model of an organic solar cell in which a photosensitive layer doped with plasmon nanoparticles acts as not only an absorbing element but also a mirror involved in the formation of the Tamm plasmon polariton. It is shown that such solar cells can be fabricated without metal contacts, thus avoiding undesired losses in the system. Methods for an additional increase in the integral absorption by applying metal or dielectric mirrors to the lower boundary of the photonic crystal are proposed. It has been found that the integral absorption in the active layer can be increased by15%compared to classical optimized planar solar cells.
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