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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Vtyurin A. N., Krylov A. S., Goryainov S. V., Krylova S. N., Oreshonkov A. S., Voronov V. N.
Заглавие : A raman study of hydrostatic pressure induced phase transitions in Rb2KInF6 crystals
Место публикации : Phys. Solid State: MAIK Nauka-Interperiodica / Springer, 2012. - Vol. 54, Is. 5. - P.934-936. - ISSN 1063-7834, DOI 10.1134/S1063783412050472
Примечания : Cited References: 16. - This study was supported by the Russian Foundation for Basic Research (project nos. 11-02-98002-r_sibir' and 09-02-00062), the Siberian Branch of the Russian Academy of Sciences (integration project no. 101), and the Council on Grants from the President of the Russian Federation (grant no. HSh-4645.2010.2).
Предметные рубрики: LATTICE-DYNAMICS
ELPASOLITES
SPECTRA
Аннотация: The Raman spectra of the elpasolite (Rb2KInF6) crystal have been studied in the pressure range from 0 to 5.3 GPa at a temperature of 295 K. A phase transition at a pressure of approximately 0.9 GPa has been found. An analysis of the variations in the spectral parameters has led to the conclusion that the phase transition to a distorted phase is accompanied by the doubling of the volume of the primitive cell of the initial cubic phase. Numerical calculations of the lattice dynamics in the Rb2KInF6 crystal have been performed. The numerical simulation has established that the phase transition at a pressure of 0.9 GPa is associated with condensation of the F (lg) mode. A probable high-pressure phase is the phase with space group C2/m.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aleksandrov K. S., Vtyurin A. N., Gerasimova J. V., Krylov A. S., Laptash N. M., Voyt E. I., Kocharova A. G., Surovtsev S. V.
Заглавие : Raman spectra and ordering processes in alcaline-tungsten oxyfluorides
Коллективы : Russian-CIS-Baltic-Japanese symposium on ferroelectricity
Место публикации : Ferroelectrics: Taylor & Francis LTD, 2007. - Vol. 347. - P.79-85. - ISSN 0015-0193, DOI 10.1080/00150190601187070
Примечания : Cited References: 8
Предметные рубрики: PHASE-TRANSITIONS
ELPASOLITES
Аннотация: Raman spectra of perovskite-like (NH4)(3)WO3F3 (assigned below as A3), (NH4)(2)KWO3F3 (A2K), Cs-2(NH4)WO3F3 (C2A) oxyfluorides are obtained in a wide temperature range including transition points for A3 and A2 K crystals. Transition anomalies are found and analyzed. Transformation in A3 crystal is shown to be bound with octahedron groups ordering and 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 A2 K crystal, but without lattice ordering. C2A lattice stays disordered down to 15 K.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zinenko V. I., Zamkova N. G.
Заглавие : Lattice dynamics and statistical mechanics of the Fm3m - I4/m structural phase transition in Rb2KInF6
Разночтения заглавия :авие SCOPUS: Lattice dynamics and statistical mechanics of the Fm3m I4/m structural phase transition in Rb2KInF6
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2001. - Vol. 43, Is. 12. - P2290-2300. - ISSN 1063-7834, DOI 10.1134/1.1427959
Примечания : Cited References: 18
Предметные рубрики: FIRST-PRINCIPLES THEORY
RB2KSCF6 CRYSTAL
ELPASOLITES
PEROVSKITES
Аннотация: The static and dynamic properties of cubic Rb2KInF6 crystals with elpasolite structure are calculated using a nonempirical method. Calculations are performed within a microscopic ionic-crystal model taking into account the deformation and polarization of ions. The deformation parameters of ions are determined by minimizing the total energy of the crystal. The calculated equilibrium lattice parameters agree satisfactorily with the experimental data. It is found that in the cubic phase there are vibrational modes that are unstable everywhere in the Brillouin zone. The eigenvectors of the unstablest mode at the center of the Brillouin zone of the cubic phase are associated with the displacements of F ions and correspond to rotations of InF6 octahedra. Condensation of this mode leads to a tetragonal distortion of the structure. In order to describe the Fm3m -- I4/m phase transition, an effective Hamiltonian is constructed under the assumption that the soft mode whose eigenvector corresponds to octahedron rotation is local and coupled with homogeneous elastic strains. The parameters of the effective Hamiltonian are determined using the calculated crystal energy for the distorted structures due to soft-mode condensation. The thermodynamic properties of the system with this model Hamiltonian are investigated using the Monte Carlo method. The phase transition temperature is calculated to be 550 K, which is twice its experimental value (283 K). The tetragonal phase remains stable down to T = 0 K; the effective Hamiltonian used in this paper thus fails to describe the second phase transition (to the monoclinic phase). Thus, the transition to the tetragonal phase occurs for the most part through octahedron rotations; however, additional degrees of freedom, first of all, the displacements of Rb ions, should be included into the effective Hamiltonian in order to describe the transition to the monoclinic phase. (C) 2001 MAIK "Nauka/ Interperiodica".
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zinenko V. I., Zamkova N. G.
Заглавие : Theory of an Fm3m - I4/m structural phase transition in an Rb2KScF6 crystal
Разночтения заглавия :us: Theory of an Fm3mI4/m Structural Phase Transition in an Rb2KScF6 Crystal
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2000. - Vol. 91, Is. 2. - P314-323. - ISSN 1063-7761, DOI 10.1134/1.1311990
Примечания : Cited References: 16
Предметные рубрики: FIRST-PRINCIPLES THEORY
LATTICE-DYNAMICS
PEROVSKITES
ELPASOLITES
Аннотация: An Rb2KScF6 crystal having an elpasolite structure undergoes a sequence of Fm3m -- I4/m -- P12(1)/n1 structural phase transitions where the transition to the tetragonal phase is associated with "rotation" of the ScF6 octahedron. An effective Hamiltonian is constructed to describe the Fm3m -- I4/m transition using the approximation of a local mode for which we selected a "soft mode" whose eigenvector corresponds to the rotation of the octahedron. The effective Hamiltonian also includes the relationship between the local mode and the homogeneous elastic strains. The parameters of the effective Hamiltonian were determined using the generalized Gordon-Kim model of an ionic crystal which allows for the deformability and polarizability of the ions. The thermodynamic properties of a system with this model Hamiltonian were investigated using the Monte Carlo method. The calculated phase transition temperature of 250 K is almost the same as the experimental value (252 K). The tetragonal phase remains stable as far as T = 0 K and a second transition (to the monoclinic phase) cannot be obtained using this effective Hamiltonian. This suggests that if the transition to the tetragonal phase is mainly associated with "rotations" of the octahedrons, in order to describe the phase transition to the monoclinic phase the effective Hamiltonian must allow for additional degrees of freedom mainly associated with the motion of rubidium ions. (C) 2000 MAIK "Nauka/Interperiodica".
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Flerov I. N., Gorev M. V., Ushakova T. V.
Заглавие : Calorimetric investigations of phase transitions in the cryolites (NH4)(3)Ga1-xScxF6 (x = 1.0, 0.1, 0)
Место публикации : Phys. Solid State: AMER INST PHYSICS, 1999. - Vol. 41, Is. 3. - P468-473. - ISSN 1063-7834, DOI 10.1134/1.1130805
Примечания : Cited References: 19
Предметные рубрики: FERROELASTICS
ELPASOLITES
CRYSTALS
PRESSURE
Аннотация: The specific heat of the cryolites (NH4)(3)Ga1-xScxF6 with x=1.0, 0.1, and 0 was measured. The thermodynamic parameters of the phase transitions were determined. A previously unknown phase transition was found in the scandium compound at T=243 K. (C) 1999 American Institute of Physics. [S1063-7834(99)03003-8].
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Flerov I. N., Gorev M. V., Voronov V. N., Bovina A. F.
Заглавие : Thermodynamic characteristics and phase transitions in Rb3B3+F6 (B3+=Ga, DY) cryolite fluoride crystals
Место публикации : Fiz. Tverd. Tela: MEZHDUNARODNAYA KNIGA, 1996. - Vol. 38, Is. 7. - P2203-2213. - ISSN 0367-3294
Примечания : Cited References: 26
Предметные рубрики: HYDROSTATIC-PRESSURE
ELPASOLITES
CS2RBDYF6
RB2KFEF6
DIAGRAMS
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Krylov A. S., Vtyurin A. N., Voronov V. N., Krylova S. N.
Заглавие : Manifestations of Structural Phase Transitions in a Rb2KLuF6 Crystal in Its Raman Spectra
Коллективы : Russian Foundation for Basic Research [16-02-00102, 18-02-00754]
Место публикации : Opt. Spectrosc. - 2019. - Vol. 126, Is. 4. - P.341-345. - ISSN 0030-400X, DOI 10.1134/S0030400X1904012X. - ISSN 1562-6911(eISSN)
Примечания : Cited References: 27. - This work was supported by the Russian Foundation for Basic Research, project nos. 16-02-00102, 18-02-00754.
Предметные рубрики: SCATTERING
ELPASOLITES
LUMINESCENCE
TRANSFORMATIONS
FLUORIDES
Аннотация: The Raman spectra of an Rb2KLuF6 crystal are studied in the temperature range from 8 to 375 K, which includes two phase transitions: one of which proceeds from a cubic to a tetragonal phase, while the other transition takes place from a tetragonal to a monoclinic phase. An analysis of the temperature dependences of parameters of spectral lines shows that the former transition is of the second kind, while the latter transition is of the first kind, close to the tricritical point. It is shown that the structural phase transitions in the Rb2KLuF6 double perovskite are not associated with disordering. The former transition is associated with rotations of LuF6 octahedra around the fourth-order axis, while the latter transition is related with rotations of octahedra and displacements of rubidium ions.
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