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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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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ignatchenko V. A., Mankov Y. I., Maradudin A. A.
Заглавие : Effects of one- and three-dimensional inhomogeneities on the wave spectrum of multilayers with finite interface thicknesses
Место публикации : Phys. Rev. B: AMERICAN PHYSICAL SOC, 2002. - Vol. 65, Is. 2. - Ст.24207. - ISSN 1098-0121, DOI 10.1103/PhysRevB.65.024207
Примечания : Cited References: 24
Предметные рубрики: PERIODIC MULTILAYERS
SPIN-WAVES
LOCALIZATION
SUPERLATTICES
SYSTEMS
DISORDER
AVERAGE
MEDIA
Аннотация: To describe a partially randomized multilayer structure with arbitrary thicknesses of the interfaces between layers, we introduce a model in which the dependence of a material parameter along the axis of such a Superlattice is described by a Jacobian elliptic sine function with a random spatial modulation of its period. Both one- and three-dimensional inhomogeneities of the period are considered. We develop the correlation function for this model, and investigate the dispersion law and damping of averaged waves in this superlattice. The dependencies of the widths of the gaps in the spectrum and the damping at the boundaries of all odd Brillouin zones, on the thicknesses of the interfaces, and on the dimensionality, intensity, and correlation wave number of the inhomogeneities are found. It is shown that experimental investigations of the widths of the gaps and damping for several Brillouin zones could permit, in principle, determining all parameters of the superlattice as well as the parameters of the inhomogeneities from these spectral characteristics.
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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) : Ignatchenko V. A., Mankov Y. I., Maradudin A. A.
Заглавие : Effects of the dimensionality of inhomogeneities on the wave spectrum of superlattices
Место публикации : Phys. Rev. B: AMERICAN PHYSICAL SOC, 2003. - Vol. 68, Is. 2. - Ст.24209. - ISSN 1098-0121, DOI 10.1103/PhysRevB.68.024209
Примечания : Cited References: 26
Предметные рубрики: ELASTIC MEDIUM THEORY
PERIODIC MULTILAYERS
SPIN-WAVES
LOCALIZATION
SYSTEMS
MEDIA
DISORDER
Аннотация: Dependences of the dispersion laws and damping of waves in an initially sinusoidal superlattice on the dimensionality of inhomogeneities modulating the period of the superlattice are studied. The cases of one- and three-dimensional modulations, as well as modulation by a mixture of inhomogeneities of both of these dimensionalities, are considered. The correlation function of the superlattice K(r) has the form of a product of the same periodic function and a decreasing function that is significantly different for these different cases. For r -- infinity the decreasing function goes to zero for the one-dimensional inhomogeneities and to a nonzero asymptote for the three-dimensional ones. Consequently, the transition from the disordered to ordered states is accompanied in the three-dimensional case not only by an increase of the correlation radius as in the one-dimensional case, but also by a change in the relationship between the volumes of the superlattices with finite and infinite correlation radii. The decreasing part of the correlation function for the mixture of inhomogeneities of different dimensionalities has the form of a product of the decreasing parts of the correlation functions of the components of the mixture. This leads to the nonadditivity of the contributions of the components of different dimensionalities to the resulting modification of the parameters of the wave spectrum that are due to the inhomogeneities (the damping of waves for the mixture of these components is smaller than the sum of the dampings of the components, the maximum gap in the spectrum corresponds to the simultaneous presence of both components, and so on).
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ignatchenko V. A., Mankov Y. I., Maradudin A. A.
Заглавие : Effects of the mixture of one- and three-dimensional inhomogeneities on the wave spectrum of superlattices
Место публикации : JETP Letters. - 2003. - Vol. 77, Is. 6. - P.285-290. - ISSN 0021-3640, DOI 10.1134/1.1577758
Примечания : Cited References: 24
Предметные рубрики: PERIODIC MULTILAYERS
SPIN-WAVES
LOCALIZATION
SYSTEMS
THICKNESSES
DISORDER
AVERAGE
MEDIA
Аннотация: Dependences of the dispersion laws and damping of waves in an initially sinusoidal superlattice on the dimensionality of inhomogeneities modulating the period of the superlattice are studied. The cases of one- and three-dimensional modulations, as well as modulation by a mixture of inhomogeneities of both of these dimensionalities, are considered. The correlation function of the superlattice K(r) has the form of a product of the same periodic function and a decreasing function that is significantly different for these different cases. The decreasing part of the correlation function for the mixture of inhomogeneities of different dimensionalities has the form of a product of the decreasing parts of the correlation functions of the components of the mixture. This leads to the nonadditivity of the contributions of the components of different dimensionalities to the resulting modification of the parameters of the wave spectrum that are due to the inhomogeneities (the damping of waves for the mixture of these components is smaller than the sum of the dampings of the components, the maximum gap in the spectrum corresponds to the simultaneous presence of both components of the mixture, not only of the three-dimensional inhomogeneities). (C) 2003 MAIK "Nauka / Interperiodica".
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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) : Ignatchenko V. A., Mankov Y. I.
Заглавие : Effect of the correlation properties of one- and three-dimensional inhomogeneities on the high-frequency magnetic susceptibility of sinusoidal superlattices
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2005. - Vol. 47, Is. 3. - P587-594. - ISSN 1063-7834, DOI 10.1134/1.1884725
Примечания : Cited References: 29
Предметные рубрики: PERIODIC MULTILAYERS
WAVE SPECTRUM
SPIN-WAVES
LOCALIZATION
SYSTEMS
DISORDER
Аннотация: The effect of one-(1D) and three-dimensional (3D) inhomogeneities on the high-frequency magnetic susceptibility at the boundary of the first Brillouin zone of a ferromagnetic superlattice is studied. The study is performed with an earlier developed method of random spatial modulation (RSM) of the superlattice period. In this method, structural inhomogeneities are described in terms of the random-phase model, in which the phase depends on three coordinates in the general case. The frequency spacing Delta v(m) between two peaks in the imaginary part of the averaged Green's function, which characterizes the gap width in the frequency spectrum at the boundary of the Brillouin zone, is calculated as a function of both the root-mean-square fluctuations gamma(i) and the correlation wavenumbers eta(i) of phase inhomogeneities (i = 1 and 3 for 1D and 3D inhomogeneities, respectively). The function Delta v(m)(gamma(1), eta(1)) for 1D inhomogeneities is shown to be symmetric with respect to inter- changing the variables gamma(1)(2) and eta(1), whereas the function Delta v(m)(gamma(3), eta(3)) for 3D inhomogeneities is strongly asym- metric with respect to interchanging gamma(3)(2) eta(3). This effect is associated with the difference in form between the correlation functions of 1D and 3D inhomogeneities and can be used to determine the dimensionality of inhomogeneities from the results of spectral studies of such superlattices. (c) 2005 Pleiades Publishing, Inc.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ignatchenko V. A., Mankov Y. I.
Заглавие : Effects of cross correlations between 1D and 3D inhomogeneities on the high-frequency susceptibility of superlattices
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2006. - Vol. 102, Is. 4. - P625-635. - ISSN 1063-7761, DOI 10.1134/S106377610604011X
Примечания : Cited References: 29
Предметные рубрики: ELASTIC MEDIUM THEORY
3-DIMENSIONAL INHOMOGENEITIES
PERIODIC MULTILAYERS
SPIN-WAVES
LOCALIZATION
SPECTRUM
SYSTEMS
MEDIA
DISORDER
Ключевые слова (''Своб.индексиров.''): correlation methods--damping--function evaluation--wave equations--brillouin zone--distribution function--random variables--superlattices
Аннотация: Cross Correlations between components of a mixture of one-dimensional (I D) and three-diniensional (3D) inhomogenetics are described by introducing a distribution function taking into account correlations between absolute values of two random variables in the absence of correlations between the variables themselves. This distribution function is used for derivation and analysis of the superlattice correlation function containing a mixture of cross-correlated 1D and 3D in homogeneitics. The effect of such inhomogeneities on the high-frequency susceptibility at the edge of the first Brillouin zone of the superlattice is investigated. It is shown that positive cross correlations partly suppress the effect of a mixture of 1D and 3D inhomogeneities on the wave spectrum: the gap at the boundary of the Brillouin zone increases, and wave damping decreases as compared to the effect produced by a mixture of 1D and 3D inhomogeneities in the absence of cross correlations. Negative cross correlations lead to the opposite effect: the gap decreases and wave damping increases. Cross correlations also lead to the emergence of new resonance effects: a narrow dip or a narrow peak at the center of the band gap (depending on the sign of the correlation factor).
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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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10.

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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11.

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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12.

13.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ignatchenko V. A., Mankov Y. I., Tsikalov D. S.
Заглавие : High-Frequency Susceptibility of a Superlattice with 2D Inhomogeneities
Коллективы :
Разночтения заглавия :авие SCOPUS: High-frequency susceptibility of a superlattice with 2D inhomogeneities
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2008. - Vol. 107, Is. 4. - P603-611. - ISSN 1063-7761, DOI 10.1134/S1063776108100075
Примечания : Cited References: 26. - This work was supported in part by grant no. 3818.2008.3 from the President of Russia in accordance with the program supporting leading scientific schools.
Предметные рубрики: SPIN-WAVE SUSCEPTIBILITY
PERIODIC MULTILAYERS
LOCALIZATION
SYSTEMS
SPECTRUM
DISORDER
MEDIA
Ключевые слова (''Своб.индексиров.''): energy conservation--energy gap--energy management--frequency bands--gallium alloys--green's function--probability density function--three dimensional--band gaps--energy conservation laws--green functions--high frequencies--imaginary parts--magnon crystals--scattered waves--superlattice layers--wave spectrums--phase interfaces
Аннотация: We investigate the high-frequency susceptibility (Green function) of an initially sinusoidal 1D superlattice with 2D phase inhomogeneities that model the deformations of the interfaces between the superlattice layers. For waves propagating along the superlattice axis ( the geometry of a photon or magnon crystal), we have found a peculiar behavior of the imaginary part of the Green function that consists in a significant difference between the peaks corresponding to the edges of the band gap in the wave spectrum. The peak corresponding to the lower-frequency band edge remains essentially unchanged as the root-mean-square fluctuation of the 2D inhomogeneities. 2 increases, while the peak corresponding to the higher-frequency band edge broaden and decreases sharply in height until its complete disappearance with increasing gamma(2). This behavior of the peaks corresponds to a band gap closure mechanism that differs from the traditional one characteristic of 1D and 3D inhomogeneities. These effects can be explained by a peculiarity of the energy conservation laws for the incident and scattered waves for 2D inhomogeneities in a 1D superlattice.
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14.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Misyul S. V., Mel'nikova S. V., Bovina A. F., Laptash N. M.
Заглавие : Optical and X-ray Diffraction Studies of the Symmetry of Distorted Phases of the (NH4)(3)ZrF7 Crystal
Коллективы :
Разночтения заглавия :авие SCOPUS: Optical and x-ray diffraction studies of the symmetry of distorted phases of the (NH4)3ZrF7crystal
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2008. - Vol. 50, Is. 10. - P1951-1956. - ISSN 1063-7834, DOI 10.1134/S1063783408100272
Примечания : Cited References: 12. - This work was supported by the Council on Grants from the President of the Russian Federation (project NSh-4137.2006.2).
Предметные рубрики: AMMONIUM HEPTAFLUOROZIRCONATE
DISORDER
TRANSITION
K3ZRF7
Аннотация: (NH4)(3)ZrF7 single crystals were grown, and polarization-optical and x-ray diffraction studies were performed on powders and crystalline plates of various cuts over a wide temperature range. Phase transitions are revealed at temperatures T-1 up arrow = 280 K, T-2 up arrow = 279.6 K, T-3 up arrow = 260-265 K, and T-4 up arrow = 238 K on heating and at T-1 down arrow = 280 K, T-2 down arrow = 269-270 K, T-3 down arrow = 246 K, and T-4 down arrow = 235 K on cooling. The sequence of changes in symmetry is established to be as follows: O-h(5) (Z = 4)↔ D-2h(25) (Z = 2) ↔ C-2h(3) (Z = 2)↔ C-i(1) (Z = 108)↔ monoclinic(2) (Z = 216).
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15.

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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16.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zhandun V. S., Zamkova N. G., Zinenko V. I.
Заглавие : Lattice dynamics and the ferroelectric phase transition in ordered Pb-2 B'BaEuro(3)O(6) (B' = Ga, In, Lu; BaEuro(3) = Nb, Ta) solid solutions
Коллективы :
Разночтения заглавия :авие SCOPUS: Lattice dynamics and the ferroelectric phase transition in ordered Pb2 B′ B″O6 (B′ = Ga, In, Lu; B″ = Nb, Ta) solid solutions
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2010. - Vol. 52, Is. 2. - P357-363. - ISSN 1063-7834, DOI 10.1134/S1063783410020228
Примечания : Cited References: 19. - This study is supported by the Russian Foundation for Basic Research (project no. 09-02-00067) and the Council on Grants from the President of the Russian Federation for Support of the Leading Scientific Schools (grant no. NSh-4137.2006.2).
Предметные рубрики: PEROVSKITES
CRYSTALS
DISORDER
RELAXOR
BATIO3
PBTIO3
Аннотация: The lattice vibration spectrum, rf permittivity, and dynamic Born charges have been calculated for ordered Pb-2 B'BaEuro(3)O(3) (B'=Ga, In, Lu; BaEuro(3)=Nb, Ta) solid solutions in terms of the generalized Gordon-Kim model. It has been shown that all compounds exhibit a ferroelectric instability and that the frequencies of "soft" ferroelectric modes are close in magnitude. The ferroelectric phase-transition temperatures and the spontaneous polarization in the ferroelectric phase of the solid solutions under consideration have been calculated by the Monte Carlo method using the model Hamiltonian in the local mode approximation. The transition temperature is found to increase with increasing atomic number of the B' ion.
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17.

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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18.

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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19.

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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20.

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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