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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aleksandrova I. P., Sukhovsky A. A., Ivanov Y. N., Raevsky I. P.
Заглавие : Local structure of disordered PbSc1/2Nb1/2O3 in the region of the diffuse tetragonal phase-rhombohedral phase transition
Место публикации : Phys. Solid State: MAIK Nauka-Interperiodica / Springer, 2012. - Vol. 54, Is. 2. - P.316-323. - ISSN 1063-7834, DOI 10.1134/S1063783412020047
Примечания : Cited References: 16. - This study was supported by the Council on Grants from the President of the Russian Federation for Support of the Leading Scientific Schools of the Russian Federation (grant no. NSh-4645.2010.2).
Предметные рубрики: Neutron-diffraction
Order
BaTiO3
PbNiO3
NMR
Аннотация: The local structure of the ferroelectric-relaxor PbSc1/2Nb1/2O3 in the temperature range from 550 to 220 K has been investigated using 45Sc nuclear magnetic resonance. It has been found that, in the paraelectric phase at temperatures below 550 K, the crystal consists of regions of an ordered elpasolite structure and inclusions of the disordered tetragonal perovskite phase with displacements along directions of the [001] type. The relative weight of the tetragonal structure in the region of the paraelectric phase is approximately equal to 0.28. Below the temperature of the phase transition from the disordered modification to the polar phase, the relative weight of the tetragonal phase decreases with decreasing temperature. The tetragonal structure is replaced by the trigonal polar structure. In a wide temperature range (∼50 K), there exists a heterophase structure that is characteristic of relaxors. Note that the correlation length of displacements in the tetragonal phase should be very small to explain the absence of indications of the existence of this phase in the diffraction data.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Drokina T. V., Petrakovskii G. A., Velikanov D. A., Molokeev M. S.
Заглавие : Specific features of magnetic ordering in the SmFeGe2O7 compound
Место публикации : Phys. Solid State: MAIK Nauka-Interperiodica / Springer, 2014. - Vol. 56, Is. 6. - P.1131-1136. - ISSN 1063-7834, DOI 10.1134/S1063783414060122. - ISSN 1090-6460
Примечания : Cited References: 10
Предметные рубрики: NEUTRON-DIFFRACTION
PR
FERGE2O7
R=LA
Аннотация: The results of the experimental investigation of the magnetic properties of the SmFeGe2O7 compound have been presented. It has been found that the temperature dependence of the susceptibility exhibits two features that coincide with the anomalies in the temperature dependence of the specific heat and indicate magnetic phase transitions in SmFeGe2O7. The external magnetic field induces a magnetic transition, the critical field of which depends on the temperature.
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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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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Flerov I. N., Gorev M. V., Aleksandrov K. S., Tressaud A., Fokina V. D.
Заглавие : Ferroelastic phase transitions in fluorides with cryolite and elpasolite structures
Место публикации : Crystallogr. Rep. - 2004. - Vol. 49, Is. 1. - P.100-107. - ISSN 1063-7745, DOI 10.1134/1.1643969
Примечания : Cited References: 43
Предметные рубрики: NUCLEAR MAGNETIC-RESONANCE
THERMODYNAMIC PROPERTIES
RB2KMIIIF6 ELPASOLITES
NEUTRON-DIFFRACTION
CRYSTALS
PEROVSKITES
DIAGRAM
SC
RB2KGAXSC1-XF6
SCATTERING
Аннотация: The ferroelastic phase transitions are investigated in several series of fluoride crystals belonging to the elpasolite and cryolite families (space group Fm (3) over barm) with the general formula A(2)BB'F-6. The influence of the size and shape of cations and anions on the entropy and the mechanism of structural distortions is discussed. (C) 2004 MAIK "Nauka/Interperiodica".
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Makarova I. P., Verin I. A., Aleksandrov K. S.
Заглавие : Structure and twinning of RbLiCrO4 crystals
Место публикации : Acta Crystallogr. B. - 1993. - Vol. 49. - P.19-28. - ISSN 0108-7681, DOI 10.1107/S0108768192006141
Примечания : Cited References: 14
Предметные рубрики: LITHIUM POTASSIUM-SULFATE
NEUTRON-DIFFRACTION
THERMAL VIBRATIONS
KLISO4
PROGRAM
LIKSO4
Аннотация: The crystal structures of the G3 (space group P31c) and G2 (space group P6(3)) phases of RbLiCrO4 have been determined from X-ray diffraction data (Mo Kalpha radiation) at 293, 428, 493 and 523 K (G3 phase) and 553 and 583 K (G2 phase). The RbLiCrO4 crystals exhibit twinning by merohedry with twin laws in the G3 phase: 2 parallel-to [001], m perpendicular-to [001], 1BAR; in the G2 phase: m parallel-to [001], 2 perpendicular-to [001], 1BAR. The analysis of diffraction intensities and influence of anomalous scattering on them provided the unambiguous determination of the twin laws for all the specimens investigated. The structure has been refined using the approximation of the anharmonic thermal vibrations of atoms.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Atuchin V. V., Aleksandrovsky A. S., Chimitova O. D., Diao C. P., Gavrilova T. A., Kesler V. G., Molokeev M. S., Krylov A. S., Bazarov B. G., Bazarova J. G., Lin Z. S.
Заглавие : Electronic structure of β-RbSm(MoO4)2 and chemical bonding in molybdates
Коллективы : Ministry of Education and Science of the Russian Federation; National Natural Science Foundation of China [11174297, 11474292]; National Basic Research Project of China [2011CB922204]; Foundation of the Director of Technical Institute of Physics and Chemistry, CAS; RAS [24-29]; RFBR [13-02-00825]
Разночтения заглавия :. в WoS: Electronic structure of beta-RbSm(MoO4)2 and chemical bonding in molybdates
Место публикации : Dalton Trans.: Royal Society of Chemistry, 2015. - Vol. 44, Is. 4. - P.1805-1815. - ISSN 1477-9226, DOI 10.1039/c4dt03203a. - ISSN 1477-9234
Примечания : Cited References: 121. - VVA and ASA gratefully acknowledge the Ministry of Education and Science of the Russian Federation for financial support. ZL acknowledges the support by National Natural Science Foundation of China (11174297 and 11474292), the National Basic Research Project of China (2011CB922204), and Foundation of the Director of Technical Institute of Physics and Chemistry, CAS. The work was partially supported by RAS Project 24-29 and RFBR Grant 13-02-00825.
Предметные рубрики: RAY PHOTOELECTRON-SPECTROSCOPY
CRYSTAL-STRUCTURE
X-RAY
NEUTRON-DIFFRACTION
MAGNETIC-PROPERTIES
PHASE-FORMATION
CORE LEVELS
2ND-HARMONIC GENERATION
LUMINESCENCE PROPERTIES
VIBRATIONAL PROPERTIES
Аннотация: Microcrystals of orthorhombic rubidium samarium molybdate, beta-RbSm(MoO4)(2), have been fabricated by solid state synthesis at T = 450 degrees C, 70 h, and at T = 600 degrees C, 150 h. The crystal structure has been refined by the Rietveld method in space group Pbcn with cell parameters a = 5.0984(2), b = 18.9742(6) and c = 8.0449(3) angstrom (R-B = 1.72%). Thermal properties of beta-RbSm(MoO4)(2) were traced by DSC over the temperature range of T = 20-965 degrees C, and the earlier reported β ↔ α phase transition at T similar to 860-910 degrees C was not verified. The electronic structure of beta-RbSm(MoO4) 2 was studied by employing theoretical calculations and X-ray photoelectron spectroscopy. It has been established that the O 2p-like states contribute mainly to the upper part of the valence band and occupy the valence band maximum, whereas the Mo 4d-like states contribute mainly to the lower part of the valence band. Chemical bonding effects have been analysed from the element core level binding energy data. In addition, it was found that the luminescence spectrum of beta-RbSm(MoO4)(2) is rather peculiar among the Sm3+ containing materials. The optical refractive index dispersion in beta-RbSm(MoO4)(2) was also predicted by the first-principles calculations.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Janoschek M., Fischer P., Schefer J., Roessli B., Pomjakushin V., Meven M., Petricek V., Petrakovskii G. A., Bezmaternykh L. N.
Заглавие : Single magnetic chirality in the magnetoelectric NdFe3((BO3)-B-11)(4)
Разночтения заглавия :авие SCOPUS: Single magnetic chirality in the magnetoelectric NdFe3( 11BO3 )4
Место публикации : Phys. Rev. B: AMER PHYSICAL SOC, 2010. - Vol. 81, Is. 9. - Ст.94429. - ISSN 1098-0121, DOI 10.1103/PhysRevB.81.094429
Примечания : Cited References: 55
Предметные рубрики: NEUTRON-DIFFRACTION
PHASE-TRANSITIONS
SLOW-NEUTRONS
CRYSTAL
NDFE3(BO3)(4)
EXTINCTION
NUCLEAR
ORDER
MNSI
ANTIFERROMAGNETS
Аннотация: We have performed an extensive study of single crystals of the magnetoelectric NdFe3 ((BO3)-B-11)(4) by means of a combination of single-crystal neutron diffraction and spherical neutron polarimetry. Our investigation did not detect significant deviations at low temperatures from space group R32 concerning the chemical structure. With respect to magnetic ordering our combined results demonstrate that in the commensurate magnetic phase below T-N approximate to 30 K all three magnetic Fe moments and the magnetic Nd moment are aligned ferromagnetically in the basal hexagonal plane but align antiferromagnetically between adjacent planes. The phase transition to the low-temperature incommensurate (IC) magnetic structure observed at T-IC approximate to 13.5 K appears to be continuous. By means of polarized neutron studies it could be shown that in the incommensurate magnetic phase the magnetic structure of NdFe3((BO3)-B-11)(4) is transformed into a long-period antiferromagnetic helix with single chirality. Close to the commensurate-incommensurate phase transition third-order harmonics were observed, which in addition indicate the formation of magnetic solitons.
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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 журнала
Шифр издания :
Автор(ы) : Aplesnin S. S.
Заглавие : Effect of bond fluctuations on the transport properties of manganites and nickelates
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2007. - Vol. 104, Is. 5. - P766-774. - ISSN 1063-7761, DOI 10.1134/S1063776107050111
Примечания : Cited References: 26
Предметные рубрики: NEUTRON-DIFFRACTION
CHARGE DISPROPORTIONATION
ELECTRONIC-STRUCTURE
MAGNETIC ORDER
TRANSITIONS
PEROVSKITES
PRNIO3
GAP
Ключевые слова (''Своб.индексиров.''): crystal structure--manganites--optimization--thermal conductivity--thermal effects--bond fluctuations--nickelates--orthorhombic crystal structure--nickel compounds
Аннотация: For the manganites RMnO(3) (R = La, Pr, Nd), a mechanism is proposed to explain the anomalous temperature dependences of the kinetic coefficients, resistivity, and thermoelectric power during the transition from the pseudocubic O to the orthorhombic O' crystal structure. The contributions of the bending and stretching modes of the octahedron to the formation of thermal-conductivity maxima and to the deviation from the linear dependence of ln(rho/T) on 1/T at low temperatures have been estimated. In nickelates, the metal-insulator transition is caused by lattice-polaron pinning by the stretching mode of the octahedron, and the low-temperature anomaly of the thermal conductivity is related to electron scattering by the bending mode of the octahedron.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Oreshonkov A. S., Roginskii E. M., Krylov A. S., Ershov A. A., Voronov V. N.
Заглавие : Structural, electronic and vibrational properties of LaF3 according to density functional theory and Raman spectroscopy
Коллективы : RFBR [17-52-53031, 16-02-00102]; Ministry of Education and Science of the Russian Federation; Krasnoyarsky regional fund of scientific support and scientific-technical activity
Место публикации : J. Phys.: Condens. Matter. - 2018. - Vol. 30, Is. 25. - Ст.255901. - ISSN 0953-8984, DOI 10.1088/1361-648X/aac452. - ISSN 1361-648X(eISSN)
Примечания : Cited References: 39. - The reported study was funded by RFBR according to the research project No. 17-52-53031 and 16-02-00102. It was partially supported by the Ministry of Education and Science of the Russian Federation and the 'Krasnoyarsky regional fund of scientific support and scientific-technical activity'. The computations were performed using facilities of the Computational Centre of the Research Park of St. Petersburg State University.
Предметные рубрики: CRYSTAL-STRUCTURE
NEUTRON-DIFFRACTION
NANOPARTICLES
CONDUCTIVITY
Ключевые слова (''Своб.индексиров.''): laf3--tysonite structure--dft--electronic structure--lattice vibrations--raman spectroscopy
Аннотация: Crystal structure of LaF3 single crystal is refined in tysonite-type trigonal unit cell P c1 using density functional theory calculations and Raman spectroscopy. It is shown that trigonal structure with P c1 space group is more energy-efficient than hexagonal structure with space group P63 cm. Simulated Raman spectra obtained using LDA approximation is in much better agreement with experimental data than that obtained with PBE and PBEsol functionals of GGA. The calculated frequency value of silent mode B 2 in case of hexagonal structure P63 cm was found to be imaginary (unstable mode), thus the energy surface obtains negative curvature with respect to the corresponding normal coordinates of the mode which leads to instability of the hexagonal structure in harmonic approximation. The A 1g line at 214 cm−1 in Raman spectra of LaF3 related to the translation of F2 ions along c axis can be connected with F2 ionic conductivity.
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