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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ignatchenko V. A., Maradudin A. A., Poszdnyakov A. V.
Заглавие : Waves in a superlattice with anisotropic inhomogeneities
Место публикации : JETP Letters. - 2003. - Vol. 78, Is. 9. - P.592-596. - ISSN 0021-3640, DOI 10.1134/1.1641491
Примечания : Cited References: 28
Предметные рубрики: PERIODIC MULTILAYERS
SPIN-WAVES
SPECTRUM
LOCALIZATION
SYSTEMS
MEDIA
DISORDER
AVERAGE
Аннотация: Dependences of the dispersion laws and damping of waves in an initially sinusoidal superlattice on inhomogeneities with anisotropic correlation properties are studied for the first time. The period of the superlattice is modulated by the random function described by the anisotropic correlation function K-phi(r) that has different correlation radii, k(parallel toparallel to)(-1) and k(perpendicular to)(-1), along the axis of the superlattice z and in the plane xy, respectively. The anisotropy of the correlation is characterized by the parameter lambda = 1 - k(perpendicular to)/k(parallel toparallel to) that can change from lambda = 0 to lambda = 1 when the correlation wave number k(perpendicular to) changes from k(perpendicular to) = k(parallel toparallel to) (isotropic 3D inhomogeneities) to k(perpendicular to) = 0 (1D inhomogeneities). The correlation function of the superlattice K(r) is developed. Its decreasing part goes to the asymptote L that divides the correlation volume into two parts, characterized by finite and infinite correlation radii. The dependences of the width of the gap in the spectrum at the boundary of the Brillouin zone Deltanu and the damping of waves xi on the value of lambda are studied. It is shown that decreasing L leads to the decrease of Deltanu, and increase of xi, with the increase of lambda. (C) 2003 MAIK "Nauka / Interperiodica".
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Fokina V. D., Flerov I. N., Gorev M. V., Bogdanov E. V., Bovina A. F., Laptash N. M.
Заглавие : Thermophysical studies of the phase transitions in (NH4)(3)NbOF6 crystals
Разночтения заглавия :авие SCOPUS: Thermophysical studies of the phase transitions in (NH4) 3NbOF6 crystals
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2007. - Vol. 49, Is. 8. - P1548-1553. - ISSN 1063-7834, DOI 10.1134/S1063783407080240
Примечания : This work was supported by the Russian Foundation for Basic Research (project no. 06-02-16102), Krasnoyarsk Regional Science Foundation (project no.16G098), and the Council on Grants from President of the Russian Federation for the Support of Leading Scientific Schools of the Russian Federation (project NSh-4137.2006.2). - Cited References: 17
Предметные рубрики: OXYFLUORIDES
DISORDER
RB
CS
Аннотация: The thermophysical properties of oxyfluoride (NH4)(3)NbOF6 were studied in detail over wide ranges of temperatures and pressures. At atmospheric pressure, a sequence of four structural phase transitions was established with the following changes in entropy: Delta S (1) = Rln 2.7, delta S (2) = Rln38.3, Delta S (3) = 0.08R, and Delta S (4) = 0.17R. An external hydrostatic pressure was found to narrow the region of existence of the initial cubic phase. A triple point was detected in the p-T diagram; at a pressure above 0.07 GPa, the transition between the tetragonal and monoclinic phases occurs through a distorted high-pressure phase.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Pogorel'tsev E. I., Bogdanov E. V., Molokeev M. S., Voronov V. N., Isaenko L. I., Zhurkov S. A., Laptash N. M., Gorev M. V., Flerov I. N.
Заглавие : Thermodynamic Properties and Structure of Oxyfluorides Rb(2)KMoO(3)F(3) and K(2)NaMoO(3)F(3)
Разночтения заглавия :авие SCOPUS: Thermodynamic properties and structure of oxyfluorides Rb2KMoO3F3 and K2NaMoO3F3
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2011. - Vol. 53, Is. 6. - P1202-1211. - ISSN 1063-7834, DOI 10.1134/S1063783411060266
Примечания : Cited References: 24. - This study was supported by the Siberian Branch of the Russian Academy of Sciences within the framework of the Interdisciplinary Integration project no. 34 SO RAN and the Council on Grants from the President of the Russian Federation for Support of Leading Scientific Schools of the Russian Federation (project no. NSh-4645-2010.2).
Предметные рубрики: T PHASE-DIAGRAM
HEAT-CAPACITY
TRANSITIONS
(NH4)(3)MOO3F3
(NH4)(3)TIOF5
(NH4)(3)WO3F3
RB2KTIOF5
CRYSTALS
CRYOLITE
DISORDER
Аннотация: According to the results of calorimetric and structural studies, the Fm (3) over barm phase in K(2)NaMoO(3)F(3) remains stable at least to 100 K. No ferroelectric transformation assumed earlier has been revealed in a series of Rb(2)KMoO(3)F(3) samples prepared using various technologies. Only a phase transition of nonferroelectric origin has been observed near 195 K, and its thermodynamic characteristics have been determined. An analysis of the stability of the cubic structure of molybdenum fluorine-oxygen elpasolites-cryolites has been performed in the framework of the hypothesis on strengths of interatomic bonds. The barocaloric effect in Rb(2)KMoO(3)F(3) has been estimated.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Pogorel'tsev E. I., Mel'nikova S. V., Kartashev A. V., Gorev M. V., Flerov I. N., Laptash N. M.
Заглавие : Thermal, optical, and dielectric properties of Fluoride Rb2TaF7
Коллективы : Russian Foundation for Basic Research, Government of Krasnoyarsk Territory, Krasnoyarsk Region Science and Technology Support Fund [16-42-243001]
Место публикации : Phys. Solid State: MAIK Nauka-Interperiodica / Springer, 2017. - Vol. 59, Is. 5. - P.986-991. - ISSN 1063-7834, DOI 10.1134/S1063783417050250. - ISSN 1090-6460(eISSN)
Примечания : Cited References:21. - The reported study was funded by the Russian Foundation for Basic Research, Government of Krasnoyarsk Territory, Krasnoyarsk Region Science and Technology Support Fund to the research project no. 16-42-243001.
Предметные рубрики: PHASE-TRANSITIONS
X-RAY
DISORDER
NMR
DIFFRACTION
OXYFLUORIDE
Аннотация: The thermal, optical, and dielectric properties of fluoride Rb2TaF7 were investigated. It was observed that the variation in chemical pressure in fluorides A2+TaF7 caused by the cation substitution of rubidium for ammonium does not affect the ferroelastic nature of structural distortions, but leads to stabilization of the high- and low-temperature phases and enhancement of birefringence. The entropy of the phase transition P4/nmm ↔ Cmma is typical of the shift transformations, which is consistent with a model of the initial and distorted phase structures. The anisotropy of chemical pressure causes the change of signs of the anomalous strain and baric coefficient dT/dp of Rb2TaF7 as compared with the values for its ammonium analog.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Melnikova S. V., Vasilev A. D., Kocharova A. G.
Заглавие : The role of structural and nonstructural water in oxyfluoride K2WO2F4 center dot H2O
Разночтения заглавия :авие SCOPUS: The role of structural and nonstructural water in oxyfluoride K2WO2F4 В· H2O
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2011. - Vol. 53, Is. 12. - P2435-2440. - ISSN 1063-7834, DOI 10.1134/S1063783411120146
Примечания : Cited References: 16. - This work was supported by the Presidential Grant of the Russian Federation NSh-4645.2010.2, by the Russian Foundation for Basic Research, project no. 09-02-00062, and by the Integration Project of the Siberian Branch of the Russian Academy of Sciences no. 101.
Предметные рубрики: PHASE-TRANSITIONS
OXOPEROXOFLUORO COMPLEXES
MO V
CRYSTAL STRUCTURE
OXOFLUORO
(NH4)(2)NBOF5
(NH4)(2)WO2F4
MONOHYDRATE
DISORDER
Аннотация: X-ray structural and polarization optical investigations have been performed, and birefringence and rotation angles of the optical indicatrix phi (b) and phi (c) of the K2WO2F4 center dot H2O crystal have been measured in the temperature range of 100-600 K. The structure and symmetry of compounds at room temperature have been refined. It has been established that the layered crystal K2WO2F4 center dot H2O can exist in two states (A and B) depending on the atmospheric humidity and undergoes the sequence of reversible and irreversible phase transformations G (3)↔ G (2)↣ G (1)↣ G (0). The sequences of changes in the phase symmetry P (1) over bar↔C2/m↣ {4/nmm for samples A and m↔ C2/m↣P4/nmm for samples B havve been found. The second older proper ferroelastic phase transition (P(1) over bar↔ C2/m) at T-03 = 2700-290 K (G (3)↔ G (2)) is accompanied by twinning and appearance of the shift deformation x (6). The crystal system of the substance for the B crystals remains invariable after the second-order phase transition G (3) a dagger" G (2). The irreversible first-order phase transition G (2)↣ G (1) occurs in a temperature range T (02) a parts per thousand 350-380 K; it is accompanied by the loss of the crystallization water, which then is reduced easily from the atmosphere for a day. The substance decomposes at T (01) approximate to 510 K (G (1)↣ G (0)). The distinction between the A and B crystals has been explained by the presence or absence of free water in interlayer spacings.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Molokeev M. S., Misyul' S. V.
Заглавие : Structural transformations and the critical and noncritical parameters during the phase transition in the (NH4)(2)KWO3F3 oxyfluoride
Разночтения заглавия :авие SCOPUS: Structural transformations and the critical and noncritical parameters during the phase transition in the (NH4)2KWO3F3 oxyfluoride
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2011. - Vol. 53, Is. 8. - P1672-1679. - ISSN 1063-7834, DOI 10.1134/S1063783411080208
Примечания : Cited References: 18. - This study was supported by the Council on Grants from the President of the Russian Federation for Support of Leading Scientific Schools of the Russian Federation (grant no. NSh-4645.2010.2).
Предметные рубрики: MOLECULAR CRYSTALS
DISORDER
(NH4)(3)WO3F3
Аннотация: The structures of two phases of the (NH4)(2)KWO3F3 crystal have been determined from X-ray diffraction data obtained for a powder sample. The profile and structural parameters have been refined according to the procedure implemented in the DDM program. The results obtained have been discussed with invoking the group-theoretical analysis of the complete order parameter condensate, which takes into account the critical and noncritical atomic orderings and allows one to interpret the experimental data. It has been found that the symmetry transformation in the crystal can be schematically represented in the form Fm (3) over barm (10-10((X) over bar5)) - ((eta, 0, 0, 0, 0, 0)) Pmmn.This transformation is accompanied by the ordering of WO3F3 polyhedra and the displacement of NH4 and K ions.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zinenko V. I., Sofronova S. N.
Заглавие : Statistical mechanics of cation ordering in PbSc1/2Ta1/2O3 and PbSc1/2Nb1/2O3 solid solutions
Разночтения заглавия :авие SCOPUS: Statistical mechanics of cation ordering in PbSc1/2Ta 1/2O3 and PbSc1/2Nb1/2O3 solid solutions
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2005. - Vol. 47, Is. 12. - P2309-2314. - ISSN 1063-7834, DOI 10.1134/1.2142896
Примечания : Cited References: 17
Предметные рубрики: PHASE-TRANSITION
PEROVSKITE
DISORDER
FERROELECTRICS
CRYSTALS
MODEL
Аннотация: A model Hamiltonian for B cation ordering (Sc-Nb(Ta)) in PbSc1/2Nb1/2O3 and PbSc1/2Ta1/2O3 solid solutions is constructed. The parameters of the model Hamiltonian are determined from the ab initio calculation within the ionic crystal model with allowance made for the deformability and the dipole and quadrupole polarizabilities of the ions. The temperatures of the phase transition due to the ordering of the B cations are calculated by the Monte Carlo method in the mean-field and cluster approximations. The phase transition temperatures calculated by the Monte Carlo method (1920 K for PbSc1/2Ta1/2O3 and 1810 K for PbSc1/2Nb1/2O3) are consistent with the experimental data (1770 and 1450 K, respectively). The thermodynamic properties of the cation ordering are investigated using the Monte Carlo method. (c) 2005 Pleiades Publishing, Inc.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Fokina V. D., Bovina A. F., Bogdanov E. V., Pogorel'tsev E. I., Laptash N. M., Gorev M. V., Flerov I. N.
Заглавие : Specific heat, cell parameters, phase T-p diagram, and permittivity of cryolite (NH4)(3)Nb(O-2)(2)F-4
Разночтения заглавия :авие SCOPUS: Specific heat, cell parameters, phase T-p diagram, and permittivity of cryolite (NH4)3Nb(O2)2F4
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2011. - Vol. 53, Is. 10. - P2147-2153. - ISSN 1063-7834, DOI 10.1134/S1063783411100131
Примечания : Cited References: 19. - This study was performed within the Interdisciplinary integration project of the Siberian Branch of the Russian Academy of Science no. 34 and supported by the grant of the President of the Russian Federation for Leading Scientific Schools of the Russian Federation (NSh-4645.2010.2).
Предметные рубрики: CRYSTAL-STRUCTURES
TRANSITIONS
(NH4)(3)TIOF5
OXYFLUORIDE
COMPLEXES
CAPACITY
DISORDER
Аннотация: The temperature dependences of the specific heat, unit cell parameters, susceptibility to hydrostatic pressure, and permittivity of cryolite (NH4)(3)Nb(O-2)(2)F-4 have been studied. Phase transitions of nonferroelectric nature have been detected. Entropy parameters point to the relation of structure distortions to ordering processes.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Molokeev M. S., Misjul S. V., Flerov I. N., Laptash N. M.
Заглавие : Reconstructive phase transition in (NH4)3TiF7 accompanied by the ordering of TiF6 octahedra
Место публикации : Acta Crystallogr. B: Wiley-Blackwell, 2014. - Vol. 70. - P.924-931. - ISSN 0108-7681, DOI 10.1107/S2052520614021192. - ISSN 1600-5740
Примечания : This study was supported by Russian Fund of Basic Research, project No. 12-02-00056 a
Предметные рубрики: CRYSTAL-STRUCTURE
NEUTRON-DIFFRACTION
POWDER DIFFRACTION
FLUORIDES
DISORDER
MECHANISM
PATHWAYS
COMPLEX
LI3THF7
ALPHA
Ключевые слова (''Своб.индексиров.''): reconstructive phase transition--ammonium heptafluorotitanate--order-disorder transition
Аннотация: An unusual phase transition P4/mnc →Pa3 has been detected after cooling the (NH4)3TiF7 compound. Some TiF6 octahedra, which are disordered in the room-temperature tetragonal structure, become ordered in the low-temperature cubic phase due to the disappearance of the fourfold axis. Other TiF6 octahedra undergo large rotations resulting in huge displacements of the F atoms by 1.5-1.8 Å that implies a reconstructive phase transition. It was supposed that phases P4/mbm and Pm3m could be a high-temperature phase and a parent phase, respectively, in (NH4)3TiF7. Therefore, the sequence of phase transitions can be written as Pm3m → P4/bm → P4/mnc → Pa3. The interrelation between (NH4)3TiF7, (NH4)3GeF7 and (NH4)3PbF7 is found, which allows us to suppose phase transitions in relative compounds.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Krylov A. S., Merkushova E. M., Vtyurin A. N., Isaenko L. I.
Заглавие : Raman spectroscopic study of the lattice dynamics in the Rb2KMoO3F3 oxyfluoride
Место публикации : Phys. Solid State: MAIK Nauka-Interperiodica / Springer, 2012. - Vol. 54, Is. 6. - P.1275-1280. - ISSN 1063-7834, DOI 10.1134/S1063783412060170
Примечания : Cited References: 24. - This study was supported by the Russian Foundation for Basic Research (project nos. 11-02-98002-r_sibir', 09-02-00062, and NSh-4645.2010.2).
Предметные рубрики: PHASE-TRANSITIONS
SCATTERING
(NH4)3WO3F3
CRYSTALS
DISORDER
Cs
Аннотация: The lattice dynamics of the Rb2KMoO3F3 oxyfluoride has been studied by Raman spectroscopy in the temperature range 7–400 K. A phase transition has been revealed at T ≈ 185 K with decreasing temperature. Anomalies of the frequencies and Raman line half-widths have been analyzed. No condensation of soft lattice modes has been found. The character of changes in the Raman spectra of the Rb2KMoO3F3 oxyfluoride shows that the phase transition is related to variations in the [MoO3F3]3− molecular octahedron.
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11.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Krylov A. S., Krylova S. N., Laptash N. M., Vtyurin A. N.
Заглавие : Raman scattering study of temperature induced phase transitions in crystalline ammonium heptafluorozirconate, (NH4)3ZrF7
Место публикации : Vib. Spectrosc.: Elsevier Science BV, 2012. - Vol. 62. - P.258-263. - ISSN 0924-2031, DOI 10.1016/j.vibspec.2012.07.003
Примечания : Cited References: 31. - This work was partly supported by integration project SB RAS No 28, Russian Foundation for Basic Research project No 11-02-98002-r_siberia, No 12-02-00056, SS-4828.2012.2. The authors are grateful to Dr. I.N. Flerov for helpful discussions. The assistance of Dr. S. Skokov is sincerely appreciated.
Предметные рубрики: VIBRATIONAL-SPECTRA
X-RAY
DISORDER
DIFFRACTION
ELPASOLITE
SYMMETRY
RB2KSCF6
IF7
Ключевые слова (''Своб.индексиров.''): raman spectroscopy--phase transition--ammonium heptafluorozirconate--low temperature
Аннотация: This paper reports on a Raman spectroscopy investigation of phase transitions in (NH4)3ZrF7 crystal. Raman spectra were obtained and analyzed in a wavenumber range from 3800 to 15 cm−1 and in the temperature range from 7 to 360 K. The anomalies caused by a series of subsequent structural phase transitions have been analyzed. A soft phonon mode restoring in the distorted phase was found. The spectral changes observed in the current study are similar to those typically found in phase transitions near a tricritical point. The spectral changes in the middle wavenumber range, 700–150 cm−1, indicate that the phase transitions are due to structural ordering of pentagonal ZrF73− bipyramids. Spectral data also show that a phase transition near 225 K is accompanied by an increase of the unit cell volume. In addition, spectral changes in the range of internal vibrations of ammonium ions indicate that the ion's motion slows down with decrease of temperature.
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12.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Molokeev M. S., Misyul' S. V.
Заглавие : Processes of ordering of structural elements, critical and noncritical parameters of phase transitions in the (NH4)3WO3F3 crystal
Место публикации : Phys. Solid State: MAIK Nauka-Interperiodica / Springer, 2012. - Vol. 54, Is. 1. - P.155-165. - ISSN 1063-7834, DOI 10.1134/S1063783412010222. - ISSN 1090-6460
Примечания : Cited References: 18. - This study was supported by the Russian Foundation for Basic Research (project no. 09-02-00062) and the Council on Grants from the President of the Russian Federation for Support of Leading Scientific Schools of the Russian Federation (grant no. NSh-4645.2010.2).
Предметные рубрики: OXYFLUORIDE
TRANSFORMATIONS
(NH4)3TiOF5
DISORDER
Аннотация: The structure of the low-temperature triclinic phase of the (NH4)3WO3F3 crystal has been determined and the structure of the cubic phase of this crystal has been refined from data of an X-ray diffraction experiment performed for a powder sample. The profile and structural parameters have been refined according to the procedure implemented in the DDM program. The results obtained have been discussed with invoking the group-theoretical analysis of the complete order parameter condensate, which takes into account the critical and noncritical atomic orderings and allows one to interpret the obtained experimental data. It has been found that the symmetry transformation in the crystal can be schematically represented in the following form: Fm3¯m(Z=4)→P1¯(Z=1)→P1¯(Z=6)Fm\bar 3m(Z = 4) \to P\bar 1(Z = 1) \to P\bar 1(Z = 6) . This transformation is accompanied by the complete ordering of WO3F3 polyhedra and the displacement of NH4 ions.
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13.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aleksandrov K. S.
Заглавие : Phase-transitions and distortions of the structure in the family of crystals related to alpha-k2so
Место публикации : Kristallografiya. - 1993. - Vol. 38, Is. 1. - P.128-139. - ISSN 0023-4761; Crystallogr. Rep.
Примечания : Cited References: 38
Предметные рубрики: X-RAY
EXPECTED STRUCTURES
A2BX4 COMPOUNDS
TEMPERATURE
(NH4)2BEF4
CHEMISTRY
DISORDER
SYMMETRY
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14.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Mel'nikova S. V., Laptash N. M., Zhogal' A. L.
Заглавие : Phase transitions in the oxyfluoride (NH4)(3)NbOF6
Разночтения заглавия :авие SCOPUS: Phase transitions in the oxyfluoride (NH4)3NbOF 6
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2007. - Vol. 49, Is. 5. - P958-962. - ISSN 1063-7834, DOI 10.1134/S1063783407050253
Примечания : Cited References: 11
Предметные рубрики: RAY-DIFFRACTION INVESTIGATIONS
DISTORTED PHASES
SYMMETRY
DISORDER
CRYSTAL
Аннотация: (NH4)(3)NbOF6 single crystals were grown, polarization-optical studies were performed, and birefringence was measured over the temperature range 90-500 K. A sequence of first-order structural phase transitions was found at temperatures T (1 down arrow) = 259.7 K and T (2 down arrow) = 257.7 K with temperature hysteresis delta T-1 = 0.9 K and delta T-2 = 1.9 K. The transitions are accompanied by twinning and the following change in the crystal symmetry: cubic paired left right arrows tetragonal paired left right arrows monoclinic. Optical second harmonic generation is found to occur at room temperature, which indicates that the cubic phase is not centrosymmetric. It is assumed that the phase transitions are ferroelastic and ferroelectric in nature.
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15.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Fokina V. D., Bogdanov E. V., Gorev M. V., Molokeev M. S., Pogorel'tsev E. I., Flerov I. N., Laptash N. M.
Заглавие : Phase transitions in the (NH4)(2)NbOF5 oxyfluoride
Коллективы :
Разночтения заглавия :авие SCOPUS: Phase transitions in the (NH4)2NbOF5 oxyfluoride
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2010. - Vol. 52, Is. 4. - P781-788. - ISSN 1063-7834, DOI 10.1134/S1063783410040189
Примечания : Cited References: 13. - We would like to thank A. A. Udovenko (Institute of Chemistry, Far Eastern Branch, Russian Academy of Sciences, Vladivostok, Russia) for kindly supplied detailed data on the atomic coordinates in the structure of the (NHINF4/INF)INF2/INFNbOFINF5/INF oxyfluoride.This study was supported by the Russian Foundation for Basic Research (project no. 09-02-00062) and the Council on Grants from the President of the Russian Federation for Support of Leading Scientific Schools of the Russian Federation (grant no. NSh-1011.2008.2).
Предметные рубрики: CRYSTAL-STRUCTURE
(NH4)(2)WO2F4
MECHANISM
DISORDER
Аннотация: The thermal and dielectric properties of the (NH4)(2)NbOF5 oxyfluoride have been investigated. It has been established that the structural phase transitions Cmc2(1) - C2 - Ia observed at the temperatures T (1) = 258.0 K and T (2) = 218.9 K exhibit a nonferroelectric nature. The hydrostatic pressure, which stabilizes the initial phase and destabilizes the low-temperature phase, hardly affects the temperature range of stability of the intermediate phase. The model of sequential ordering of the structural elements due to phase transitions has been analyzed using experimental data on the entropies of the phase transitions.
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16.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Krylov A. S., Laptash N. M., Vtyurin A. N., Krylova S. N.
Заглавие : Phase transitions in (NH4)2MoO2F4 crystal
Коллективы : International Symposium on Two-Dimensional Correlation Spectroscopy
Место публикации : J. Mol. Struct.: Elsevier Science, 2016. - Vol. 1124, Special Issue: Novel developments and applications of two-dimensional correlation spectroscopy — A festschrift in honor of professor Isao Noda. - P.125-130. - ISSN 0022-2860, DOI 10.1016/j.molstruc.2016.03.009. - ISSN 1872-8014(eISSN)
Примечания : Cited References:17
Предметные рубрики: OXYFLUORIDE
(NH4)2WO2F4
DISORDER
DIAGRAMS
Ключевые слова (''Своб.индексиров.''): phase transitions--raman high-pressure--two-dimensional correlations--oxyfluorides
Аннотация: The mechanisms of temperature and high pressure phase transitions have been studied by Raman spectroscopy. Room temperature (295 K) experiments under high hydrostatic pressure up to 3.6 GPa for (NH4)(2) MoO2 F-4 have been carried out. Experimental data indicates a phase transition into a new high-pressure phase for (NH4)(2) MoO2 F-4 at 1.2 GPa. This phase transition is related to the ordering anion octahedron groups [MoO2 F-4](2) and is not associated with ammonium group. Raman spectra of small non-oriented crystals ranging from 10 to 350 K have been observed. The experiment shows anion groups [MoO2 F-4](2-) and ammonium in high temperature phase are disordered. The phase transition at T-1 = 269.8 K is of the first-order, close to the tricritical point. The first temperature phase transition is related to the ordering anion octahedron groups [MoO2 F-4](2-). Second phase transitions T-2 = 180 K are associated with the ordering of ammonium. The data presented within this study demonstrate that 2D correlation analysis combined with traditional Raman spectroscopy are powerful tool to study phase transitions in the crystals. (C) 2016 Elsevier B.V. All rights reserved.
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17.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ignatchenko V. A., Mankov Y. I.
Заглавие : Partial restoration of the wave spectrum of a superlattice due to cross correlations between one- and three-dimensional inhomogeneities
Место публикации : Phys. Rev. B: AMERICAN PHYSICAL SOC, 2007. - Vol. 75, Is. 23. - Ст.235422. - ISSN 1098-0121, DOI 10.1103/PhysRevB.75.235422
Примечания : Cited References: 32
Предметные рубрики: ELASTIC MEDIUM THEORY
PERIODIC MULTILAYERS
SPIN-WAVES
LOCALIZATION
SYSTEMS
SUSCEPTIBILITY
DISORDER
MEDIA
Аннотация: Effects of cross correlations between one-dimensional (1D) and three-dimensional (3D) random inhomogeneities on the wave spectrum in sinusoidal superlattices are studied theoretically. The situation when the gap in the spectrum (the forbidden zone) at the first Brillouin zone boundary of the superlattice is closed under the action of the 1D inhomogeneities is considered. The phenomenon of the partial opening of this gap is found when the 3D inhomogeneities cross correlated with the 1D inhomogeneities add to the superlattice. The appearance of the logarithmic resonance in the center of the forbidden zone under the action of the cross correlations is shown. The physical nature of the effects in the wave spectrum of the superlattice that are caused by the cross correlations and the relation of these effects with the asymptotic properties of the correlation function of inhomogeneities are discussed.
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18.

19.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Mel'nikova S. V., Laptash N. M.
Заглавие : Optical studies of the (T-x) phase diagram of oxyfluoride (NH4)2MoO2F4-Rb2MoO2F4 solid solutions
Коллективы : Russian Federation [NSh-924.2014.2]
Место публикации : Phys. Solid State: MAIK Nauka-Interperiodica / Springer, 2015. - Vol. 57, Is. 6. - P.1201-1205. - ISSN 1063, DOI 10.1134/S1063783415060256. - ISSN 10906460(eISSN)
Примечания : Cited References:8. - This study was supported by the Council on Grants from the President of the Russian Federation for Supporting of Leading Scientific Schools of the Russian Federation (grant NSh-924.2014.2).
Предметные рубрики: TRANSITIONS
(NH4)2WO2F4
CRYSTALS
DISORDER
Аннотация: Single crystals of solid solutions (NH4)2 − x Rb x MoO2F4 (including individual complex Rb2MoO2F4) have been grown and studied using polarization-optical methods. The birefringence Δn(T) has been measured in the temperature range of 100–400 K. The complete (T-x) phase diagram has been constructed.
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20.

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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