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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Rasch JCE, Boehm M., Ritter C., Mutka H., Schefer J., Keller L., Abramova G. M., Cervellino A., Loffler J. F.
Заглавие : Magnetoelastic coupling in the triangular lattice antiferromagnet CuCrS2
Коллективы : Russian Academy of Science (RAS), Siberian Branch [06-1000013-9002]
Место публикации : Phys. Rev. B. - 2009. - Vol. 80, Is. 10. - Ст.104431. - ISSN 1098-0121, DOI 10.1103/PhysRevB.80.104431
Примечания : Cited References: 30. - We are grateful for support and allocated beam time at the Institut Laue-Langevin (D1A, IN3),Grenoble, France, the spallation neutron source SINQ (TriCS, DMC) and the SLS-MS beamline, both Paul Scherrer Insitut, Villigen, Switzerland. This work was supported by INTAS Grant No. 06-1000013-9002 of the Russian Academy of Science (RAS), Siberian Branch.
Предметные рубрики: NEUTRON POWDER DIFFRACTION
MAGNETIC-STRUCTURE
STRUCTURAL-PROPERTIES
PHASE-TRANSITION
SOLID OXYGEN
ALPHA-PHASES
BETA-PHASES
SELENIDES
SULFIDES
Аннотация: CuCrS2 is a triangular lattice Heisenberg antiferromagnet with a rhombohedral crystal structure. We report on neutron and synchrotron powder diffraction results which reveal a monoclinic lattice distortion at the magnetic transition and verify a magnetoelastic coupling. CuCrS2 is therefore an interesting material to study the influence of magnetism on the relief of geometrical frustration.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Lyubutin I. S., Ovchinnikov S. G., Gavriliuk A. G., Struzhkin V. V.
Заглавие : Spin-crossover-induced Mott transition and the other scenarios of metallization in 3d(n) metal compounds
Разночтения заглавия :авие SCOPUS: Spin-crossover-induced Mott transition and the other scenarios of metallization in 3 dn metal compounds
Место публикации : Phys. Rev. B: AMER PHYSICAL SOC, 2009. - Vol. 79, Is. 8. - Ст.85125. - ISSN 1098-0121, DOI 10.1103/PhysRevB.79.085125
Примечания : Cited References: 41
Предметные рубрики: RARE-EARTH ORTHOFERRITES
NARROW ENERGY BANDS
HIGH-PRESSURE
MAGNETIC COLLAPSE
ELECTRON CORRELATIONS
PHASE-TRANSITION
STATE
Y3FE5O12
OXIDES
EQUATION
Ключевые слова (''Своб.индексиров.''): bismuth compounds--hubbard model--localised states--metal-insulator transition--metallisation--spin systems
Аннотация: A different "Hubbard energy control" mechanism of the insulator-metal transition (IMT) in Mott-Hubbard insulators is discussed. This mechanism can be initiated by the lattice compression and it is driven by a spin crossover of 3d(5) ions from the high-spin state to the low-spin state. The spin crossover suppresses the effective Hubbard parameter U-eff down to the value enabling the insulator-metal transition according to the Mott mechanism U-eff/W approximate to 1. The classification of possible scenarios of metallization in the other 3d(n) metal compounds is also performed.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Averyanov E. M.
Заглавие : Orientation ordering and critical behavior of discoid nematics
Место публикации : Zhurnal Eksperimentalnoi Teor. Fiz.: MEZHDUNARODNAYA KNIGA, 1996. - Vol. 110, Is. 5. - P1820-1840. - ISSN 0044-4510
Примечания : Cited References: 55
Предметные рубрики: LIQUID-CRYSTALS
PHASE-TRANSITION
ISOTROPIC-PHASE
LOCAL FIELD
SMECTIC-A
MOLECULES
SUSCEPTIBILITY
CONFORMATION
PARAMETER
DYNAMICS
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kazak N. V., Gavriliuk A. G., Ovchinnikov S. G., Lyubutin I. S., Edel'man I. S., Rudenko V. V.
Заглавие : Evolution of the optical absorption spectra and electronic structure of the VBO3 crystal under high pressures
Коллективы : Russian Foundation for Basic Research [07-02-00490a, 08-02-00897a, 08-02-90708 mob_st, 09-02-00171a, 07-02-00226]; Federal Agency for Science and Innovation [MK-4278.2008.2, 01.164.12.HB11]; Russian Academy of Sciences
Место публикации : J. Exp. Theor. Phys. - 2009. - Vol. 109, Is. 3. - P.455-465. - ISSN 1063-7761, DOI 10.1134/S1063776109090118
Примечания : Cited References: 27. - We would like to thank A. D. Vasil'ev for performing the X-ray diffraction investigations.This study was supported by the Russian Foundation for Basic Research (project nos. 07-02-00490a, 08-02-00897a, 08-02-90708 mob_st, 09-02-00171a, and 07-02-00226), the Federal Agency for Science and Innovation (Rosnauka) (project no. MK-4278.2008.2, contract no. 01.164.12.HB11), and the Branch of Physical Sciences of the Russian Academy of Sciences within the framework of the program "Strongly Correlated Electrons."
Предметные рубрики: BAND-STRUCTURE
PHASE-TRANSITION
FEBO3
FE1-XVXBO3
STATE
MODEL
Ключевые слова (''Своб.индексиров.''): charge-transfer excitations--d-d transitions--ferromagnetic semiconductor--fundamental absorption edge--high pressure--optical absorption spectrum--absorption--boron--boron compounds--electronic properties--electronic structure--optical materials--oxygen--vanadium--light absorption
Аннотация: The evolution of optical absorption spectra of the ferromagnetic semiconductor VBO3 under high pressures up to 70 GPa has been investigated. It has been revealed that, below the fundamental absorption edge (E (g1) = 3.02 eV), the spectra exhibit a series of bands V1 (2.87 eV), V2 (2.45 eV), V3 (1.72 eV), and V4(1.21 eV) due to the d-d transitions in the V3+ ion and charge-transfer excitations. A model of the electronic structure of the VBO3 semiconductor has been constructed. This model combines the one-electron description of the s and p states of boron and oxygen and the many-electron description of the vanadium d states.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aleksandrova I. P., Ivanov Y. N., Sukhovskii A. A., Vakhrushev S. B.
Заглавие : Na-23 NMR in the relaxor ferroelectric Na1/2Bi1/2TiO3
Разночтения заглавия :авие SCOPUS: 23Na NMR in the relaxor ferroelectric Na1/2Bi 1/2TiO3
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2006. - Vol. 48: 17th All-Russia Conference on the Physics of Ferroelectrics (VKS-XVII) (JUN 26-JUL 01, 2005, Penza, RUSSIA), Is. 6. - P1120-1123. - ISSN 1063-7834, DOI 10.1134/S106378340606031X
Примечания : Cited References: 8
Предметные рубрики: NEUTRON-SCATTERING
PHASE-TRANSITION
NA0.5BI0.5TIO3
Аннотация: The Na-23 NMR spectra of a Na1/2Bi1/2TiO3 crystal are studied at frequencies of 79.4 and 15.7 MHz in the temperature range 150-720 K. It is revealed that, at all temperatures, the crystal contains regions with a nearly cubic matrix and polar clusters. The temperature dependence of the local distortion of the Na environment in the clusters is determined. The dynamics of the reorientation of the local cluster polarization in the tetragonal and trigonal NBT phases is analyzed.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Bondarenko I. N., Gekht R. S., Ponomarev V. I.
Заглавие : Magnetic transitions in layered triangular antiferromagnets
Место публикации : Phys. Lett. A: ELSEVIER SCIENCE BV, 1996. - Vol. 222, Is. 4. - P269-274. - ISSN 0375-9601, DOI 10.1016/0375-9601(96)00635-4
Примечания : Cited References: 22
Предметные рубрики: HEISENBERG-ANTIFERROMAGNET
PHASE-TRANSITION
VBR2
SYSTEMS
FIELD
VCL2
Ключевые слова (''Своб.индексиров.''): triangular antiferromagnets--quantum and thermal fluctuations--successive phase transitions--quantum and thermal fluctuations--successive phase transitions--triangular antiferromagnets
Аннотация: Magnetic states and phase transitions of the layered triangular antiferromagnets in an applied field are studied. It is shown that in compounds like VBr2 and VCl2 quantum effects change the ground state structure and cause successive phase transitions as the magnetic field increases. Coplanar structures of different spin configuration are realized far from the saturation field and a noncoplanar structure of umbrella-type configuration is realized near this field. The ground-state phase diagram is constructed, and a finite region of fields where the collinear phase is also possible is indicated.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Myagkov V. G., Mikhlin Y. N., Bykova L. E., Mal'tsev V. K., Bondarenko G. N.
Заглавие : Long-Range Chemical Interaction in Solid-State Synthesis: The Formation of a CuAu Alloy in Au/beta-Co(001)/Cu(001) Epitaxial Film Structures
Коллективы : Russian Foundation for Basic Research [07-03-00190]; Ministry of Education and Science of the Russian Federation
Разночтения заглавия :авие SCOPUS: Long-range chemical interaction in solid-state synthesis: The formation of a CuAu alloy in Au/β-Co(001)/Cu(001) epitaxial film structures
Место публикации : JETP Letters. - 2009. - Vol. 90, Is. 2. - P.111-115. - ISSN 0021-3640, DOI 10.1134/S0021364009140069
Примечания : Cited References: 25. - This work was supported by Russian Foundation for Basic Research ( project no. 07-03-00190) and the Ministry of Education and Science of the Russian Federation ( program "Development of the Scientific Potential of Higher Education").
Предметные рубрики: THIN-FILMS
PHASE-TRANSITION
DIFFUSION
MICROSTRUCTURE
INTERLAYER
INTERFACE
COSI2
AU
Аннотация: The effect of an inert Co layer (0, 210, 480 nm) on the chemical interaction between Cu and Au in Au/beta-Co(001)/Cu(001) epitaxial films has been investigated by X-ray diffraction, nuclear magnetic resonance, photoelectron spectroscopy, and magnetic structure measurements. Mixing at interfaces in Cu/beta-Co(001) and Au/beta-Co(001) bilayer films has not been revealed up to a temperature of 600 C. The solid-state synthesis of ordered CuAu| and CuAu|| phases occurs through the Co inert buffer layer in Au/beta-Co(001)/Cu(001) trilayer film systems with an increase in the annealing temperature. The initiation temperatures of the CuAu| and CuAu|| phases increase only slightly with the thickness of the Co buffer layer. The assumption of the long range of the chemical interaction between Cu and Au through the chemically inert Co layer is justified using the performed investigations.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Dudnikov V. A., Kazak N. V., Orlov Yu. S., Vereshchagin S. N., Gavrilkin, S. Yu., Tsvetkov, A. Yu., Gorev M. V., Veligzhanin A. A., Trigub A. L., Troyanchuk I. O., Ovchinnikov S. G.
Заглавие : Structural, Magnetic, and Thermodynamic Properties of Ordered and Disordered Cobaltite Gd0.1Sr0.9CoO3 – δ
Коллективы : Russian Foundation for Basic Research [17-02-00826, 16-02-00507, 18-52-00017 Bel_a]; Russian Federation [SP-1844.2016.1]; Ministry of Education and Science of the Russian Federation [RFMEFI61917X0007]
Место публикации : J. Exp. Theor. Phys. - 2019. - Vol. 128, Is. 4. - P.630-640. - ISSN 1063-7761, DOI 10.1134/S1063776119020171. - ISSN 1090-6509(eISSN)
Примечания : Cited References: 27. - This work was supported by the Russian Foundation for Basic Research (grant nos. 17-02-00826, 16-02-00507, and 18-52-00017 Bel_a) and by the Council on Grants of the President of the Russian Federation (SP-1844.2016.1). X-ray spectra were recorded using the equipment of a unique scientific facility Kurchatov Synchrotron Radiation Source financed by the Ministry of Education and Science of the Russian Federation (project ID RFMEFI61917X0007).
Предметные рубрики: PROFILE REFINEMENT
PHASE-TRANSITION
OXYGEN SORPTION
PEROVSKITE
Аннотация: The effect of cationic and anionic orderings on the crystal structure and magnetic properties of substituted rare-earth cobaltites Gd0.1Sr0.9CoO3 – δ was studied using X-ray diffraction, measurement of XANES spectra, and magnetic and thermodynamic characteristics. The effects of ordering cause a decrease in symmetry to tetragonal and a distortion of the coordination octahedra of CoO6. Anomalous magnetic and thermodynamic quantities are observed at 260 and 360 K, respectively, for disordered and ordered samples. The XANES spectra measured at the CoK edge did not reveal a noticeable shift in the absorption edge compared with the spectrum of original GdCoO3. This suggests that the charge compensation process is associated not only with a change in the electronic state of cobalt ions, but also with the emergence of holes in the 2p states of oxygen.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Wang, Naizheng, Jiang, Xingxing, Molokeev M. S., Song, Gaomin, Guo, Shibin, Huang, Rongjin, Li, Laifeng, Wu, Yicheng, Lin, Zheshuai
Заглавие : Linear Zero Thermal Expansion in a Deep-Ultraviolet Transparent Crystal of BPO4 with Cristobalite-like Structure
Коллективы : National Scientific Foundations of China [51872297, 51702330, 51802321, 51890864]; Fujian Institute of Innovation [FJCXY18010201]; Youth Innovation Promotion Association in CAS [2017035]
Место публикации : Cryst. Growth Des. - 2019. - Vol. 19, Is. 6. - P.3109-3112. - ISSN 1528-7483, DOI 10.1021/acs.cgd.9b00361. - ISSN 1528-7505(eISSN)
Примечания : Cited References: 32. - This work was supported by the National Scientific Foundations of China (Grants 51872297, 51702330, 51802321 and 51890864) and Fujian Institute of Innovation (FJCXY18010201) in CAS, and the Youth Innovation Promotion Association in CAS (outstanding member for Z.L. and Grant 2017035 for X.J.).
Предметные рубрики: PHASE-TRANSITION
DIFFRACTION
QUARTZ
Аннотация: We report the discovery of the zero thermal expansion (ZTE) effect in BPO4, a famous deep-ultraviolet (DUV) optical material with cristobalite-like structure. It is revealed that BPO4 has a linear ZTE coefficient of -0.16(5) MK-1 along the c-axis as temperature increases from 13 to 300 K, which originates from the subtle counterbalance between the rotation-induced expansion and contraction effects among BO4 and PO4 groups. BPO4 is a unique DUV cristobalite-like material exhibiting the linear ZTE behavior.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ji, Haipeng, Hou, Xinghui, Molokeev M. S., Ueda, Jumpei, Tanabe, Setsuhisa, Brik M. G., Zhang, Zongtao, Wang, Y.u., Chen, Deliang
Заглавие : Ultrabroadband red luminescence of Mn4+ in MgAl2O4 peaking at 651 nm
Место публикации : Dalton Trans. - 2020. - Vol. 49, Is. 17. - P.5711-5721. - ISSN 1477-9226, DOI 10.1039/d0dt00931h. - ISSN 1477-9234(eISSN)
Примечания : Cited References: 54. - This study was partly supported by the National Natural Science Foundation of China (Grant No. 51902291 and 51574205), the China Postdoctoral Science Foundation (2019M662524, 2019M652574), the Postdoctoral Research Sponsorship in Henan Province (19030025, 001802045), the Natural Science Foundation of Guangdong Province (2018B030311022), the Guangdong Innovation Research Team for Higher Education (2017KCXTD030), and the High-level Talents Project of Dongguan University of Technology (KCYKYQD2017017). J. U. and S. T. were also supported by the JSPS KAKENHI (16H06441, 19H02798) and M. M. was also supported by the RFBR (19-52-80003).
Предметные рубрики: EMITTING PHOSPHOR
PHOTOLUMINESCENCE PROPERTIES
PHASE-TRANSITION
Аннотация: Blue light pumped red luminescence with broadband and high photon-energy emission is highly desired for phosphor-converted white light-emitting diodes (pc-wLEDs), to achieve a high color rendering index and high luminous efficacy. Mn4+-doped red-emitting phosphors generally exhibit sharp vibronic emissions associated with the parity- and spin-forbidden 2Eg → 4A2g transitions. In this paper, two abnormal luminescence behaviors were observed for Mn4+ in the MgAl2O4:Mn4+ spinel phosphor with a short wavelength emission band peaking at 651 nm. Firstly, the Mn4+ 2Eg → 4A2g transition exhibits ultrabroadband luminescence in MgAl2O4 and the large full-width at half-maximum (FWHM) is dependent both on the calcination temperature and on the partial substitution of Al3+ with Ga3+. Secondly, the thermal quenching behavior of the Mn4+ 2Eg → 4A2g luminescence in MgAl2O4 shows a dependence on its thermal treatment and preparation method. The Rietveld refinement and Raman results demonstrate that the variation in the FWHM of the luminescence spectra is a sum effect of structural ordering (i.e., isotropic displacement decrease of constituent atoms) and the Mg ↔ Al anti-site disorder. A model for the observed varying thermal quenching of luminescence was tentatively proposed. The intrinsic thermal quenching temperature of Mn4+ luminescence in MgAl2O4 was found to be 390–400 K using the samples prepared by the co-precipitation and molten salt methods. The present work gives a novel perspective to understand the luminescence spectra of Mn4+ 2Eg → 4A2g transition.
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11.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zaytseva I. V., Pugachev A. M., Okotrub K. A., Surovtsev N. V., Mikerin S. L., Krylov A. S.
Заглавие : Residual mechanical stresses in pressure treated BaTiO3 powder
Коллективы : RFBR [17-32-5009, 18-02-00399, AAAA-A17-117052410033-9]
Место публикации : Ceram. Int. - 2019. - Vol. 45, Is. 9. - P.12455-12460. - ISSN 0272-8842, DOI 10.1016/j.ceramint.2019.03.179. - ISSN 1873-3956(eISSN)
Примечания : Cited References: 33. - The reported study was funded by RFBR according to the research projects No. 17-32-5009, 18-02-00399 and State assignment No AAAA-A17-117052410033-9. The experiments were performed in the multiple-access center "High-Resolution Spectroscopy of Gases and Condensed Matter" in IA&E SBRAS (Novosibirsk, Russia) and Center for Common Use of the Krasnoyarsk Scientific Center, SBRAS (Krasnoyarsk, Russia).
Предметные рубрики: DIELECTRIC-PROPERTIES
PHASE-TRANSITION
DIAMOND ANVILS
RAMAN
Ключевые слова (''Своб.индексиров.''): residual mechanical stress--raman spectroscopy--high non-hydrostatic pressure--temperature treatment--residual pressure--batio3 ceramics
Аннотация: Here we present Raman spectroscopy approach to monitor the spatial distribution and the magnitude of the residual mechanical stresses in ceramic after non-hydrostatic pressure treatments. The residual pressure can be found from the E-phonon line shift (∼307 cm−1) in the Raman spectra. The relationship between the non-hydrostatic pressure (up to 11 GPa) and the shift of this line has been established. It is demonstrated that the change in the Raman line position (1332 cm−1) of the diamond anvil can be used for monitoring of applied non-hydrostatic pressures. A linear dependence of residual mechanical stresses on the applied pressures is found. Micro-Raman spectroscopy shows that the residual mechanical stresses are distributed fairly uniformly in the studied BaTiO3 samples at the micron scale. In the future, the proposed Raman technique can be used for monitoring the quality of produced BaTiO3 ceramics.
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12.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Drokina T. V., Petrakovskii G. A., Molokeev M. S., Bondarev V. S., Velikanov D. A.
Заглавие : Synthesis and study of structural, thermodynamic, and magnetic properties of NaxLi1–xFeGe2O6 (x = 0.1–0.9) compounds
Место публикации : Phys. Solid State: MAIK Nauka-Interperiodica / Springer, 2016. - Vol. 58, Is. 7. - P.1361-1370. - ISSN 10637834 (ISSN), DOI 10.1134/S1063783416070143
Примечания : Cited References: 20
Предметные рубрики: CLINOPYROXENE-TYPE LiFeGe2O6
PHASE-TRANSITION
PYROXENES
TEMPERATURE
LiFeSi2O6
CRYSTAL
Аннотация: The properties of NaxLi1–xFeGe2O6 (x = 0.1–0.9) solid solutions obtained via a solid-phase synthesis have been measured by X-ray diffraction, calorimetry, and magnetic method. The order–disorder transformations in low-dimensional NaxLi1–xFeGe2O6 (x = 0.1–0.9) spin systems with predominately antiferromagnetic exchange interaction have been revealed in the low-temperature susceptibility dependences. The study of thermal and physical properties has confirmed that substituting the sodium ions with the lithium ones induces the first-order structural phase transitions of the displacement type which are characterized by a symmetry change in monoclinic crystals from high-temperature C2/c space group to low-temperature P21/c space group. © 2016, Pleiades Publishing, Ltd.
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13.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Верещагин С. Н., Дудников, Вячеслав Анатольевич, Соловьев, Леонид Александрович
Заглавие : Изучение фазового перехода порядок-беспорядок в нестехиометрическом Sr-Gd-кобальтате методами ДСК, ТГ и РСА
Место публикации : Журн. СФУ. Сер. "Химия". - 2016. - Т. 9, № 3. - С. 326-336. - ISSN 1998-2836, DOI 10.17516/1998-2836-2016-9-3-326-336; J. Sib. Fed. Univ. Chem. - ISSN 2313-6049(eISSN)
Примечания : Библиогр.: 26. - Исследование выполнено при финансовой поддержке Российского фонда фундаментальных исследований, Правительства Красноярского края, Красноярского краевого фонда поддержки научной и научно-технической деятельности в рамках научного проекта 16-43-240505 «р_а».
Предметные рубрики: PEROVSKITE-TYPE OXIDES
PHASE-TRANSITION
OXYGEN SORPTION
PERFORMANCE
Ключевые слова (''Своб.индексиров.''): perovskite--order-disorder--phase transition--dsc--перовскит--порядок-беспорядок--фазовый переход--дск
Аннотация: Методами термического и рентгеноструктурного анализа в интервале температур 11001473 К изучен процесс взаимопревращения тетрагонального перовскита Sr ( 0.8 ) Gd ( 0.2 ) CoO ( 3-d ) с упорядоченным расположением катионов Sr/Gd и анионных вакансий в кубическую разупорядоченную модификацию. Показано, что фазовое превращение протекает как размытый фазовый переход первого рода. Процесс разупорядочения не зависит от скорости нагрева и контролируется термодинамическими характеристиками процессов в кристалле, тогда как процесс образования упорядоченной тетрагональной структуры контролируется кинетическими факторами. Проведен количественный анализ температурной зависимости теплоемкости на основе размытых фазовых переходов.Process of interconversion of tetragonal Sr(0.8) Gd(0.2) CoO(3-d) (with ordered Sr/Gd cations and anion vacancies) to cubic one (with disordered structure) was studied by X-ray structural and thermal analysis at 1100-1473 K. It was shown that the transformation is a first order diffuse phase transition. The ramp rate does not affect cation and anion vacancies disordering which is controlled by thermodynamic parameters of the processes in the solid whereas cubic to tetragonal transition is kinetically controlled. A theory of diffuse phase transition was applied to quantitatively analyze heat capacity temperature dependence.
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14.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Аверьянов, Евгений Михайлович
Заглавие : Температурные зависимости показателей преломления одноосных каламитных жидких кристаллов с высоким двупреломлением
Место публикации : Жидк. кристаллы и их практич. использ. - 2018. - Т. 18, № 2. - С. 53-63. - ISSN 1991-3966, DOI 10.18083/LCAppl.2018.2.53; Liq. Cryst. Appl.
Примечания : Библиогр.: 29
Предметные рубрики: PHASE-TRANSITION
ORIENTATIONAL ORDER
ISOTROPIC LIQUID
MOLECULES
Ключевые слова (''Своб.индексиров.''): жидкие кристаллы--температурные зависимости показателей преломления--liquid crystals--temperature dependences of the refractive indices
Аннотация: Температурные зависимости показателей преломления nj(t) и величин n(t) = (n|| + 2n⊥)/3, n(t) =ε-1/2, ε= (ε|| + 2ε⊥)/3, εj = nj2 для световых волн с поляризацией вдоль (j = ||) и нормально директору (j = ⊥) в одноосных каламитных жидких кристаллах (ЖК) исследованы в рамках микроскопического подхода с учетом анизотропии тензора локального поля fj(t) =1 + Lj(t)[εj(t)–1] и тензора Лорентца Lj(t). Показано, что известные отрицательные производные n(t)' = dn(t)/dt, n' и точка to минимума на зависимости n⊥(t) в каламитных ЖК отвечают малым и средним значениям двупреломления Δn = n|| – n⊥. Для ЖК с высокими величинами Δn и компонентами L⊥, превышающими пороговое значение L⊥e(nj), предсказаны два новых эффекта: положительные значения n', и наличие точки te максимума на зависимости n||(t). Для ряда нематиков с высокими значениями Δn определены компоненты Lj(t), подтверждено наличие предсказанных эффектов и условий их проявления, получены значения te и прослежена их связь с величиной Δn. Выяснены особенности перехода от ЖК с точкой to к ЖК с точкой te по мере роста Δn.The temperature dependences of the refractive indices nj(t) and the values n(t) = (n|| + 2n⊥)/3, n(t) =ε-1/2, ε= (ε|| + 2ε⊥)/3, εj = nj2 for the light waves polarized along (j = ||) and across (j = ⊥) the director in uniaxial calamitic liquid crystals (LCs) were studied within the microscopic approach with taking into account the anisotropy of the local-field tensor fj(t) =1 + Lj(t)[εj(t)–1] and the Lorentz tensor Lj(t). The known negative derivatives n(t)' = dn(t)/dt, n' and the point to of minimum at the dependence n⊥(t) for calamite LCs were shown to correspond to small and medium values of the birefringence Δn = n|| – n⊥. For LCs with high values of δn and components L⊥ exceeding the threshold value L⊥e two new effects were predicted: positive derivatives n', and the presence of the point te of maximum at the dependence n||(t). For a number of nematics with high values of Δn the components Lj(t) were determined, the presence of the predicted effects and the conditions for their manifestation were confirmed, the values te were obtained and their connection with the magnitude Δn were established. The features of the transition from LCs with point to to LCs with point c under gradual increase in Δn were cleared up.
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15.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gekht R. S., Bondarenko I. N.
Заглавие : A quantum spin liquid in a two-layer triangular antiferromagnet
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2005. - Vol. 101, Is. 5. - P868-880. - ISSN 1063-7761, DOI 10.1134/1.2149066
Примечания : Cited References: 43
Предметные рубрики: ONE-DIMENSIONAL ANTIFERROMAGNETS
DIMER GROUND-STATE
MEAN-FIELD THEORY
HEISENBERG-ANTIFERROMAGNET
SYSTEM SRCU2(BO3)(2)
PHASE-TRANSITION
GAP
FLUCTUATIONS
EXCITATIONS
LATTICE
Ключевые слова (''Своб.индексиров.''): antiferromagnetic materials--magnetic fields--magnetization--phase diagrams--spectrum analysis--thermodynamics--analogous systems--square lattices--thermodynamic quantities--two-layer triangular antiferromagnets--quantum theory
Аннотация: The possibility of implementing a quantum-spin-liquid-type state in a two-layer triangular spin-1/2 antiferromagnet at T = 0 is investigated. The ratio of intra- to interlayer exchange constants (j) is found under which a transition from the classical state with 120 degrees triangular order to a quantum state with zero magnetization per site occurs; in this case, the spins of adjacent layers form singlets that are separated from triplet excitations by an energy gap. Compared with an analogous system with the square lattice, the range of j in which the classical ordered state is realized turns out to be an order of magnitude smaller due to the effects of frustration; in this case, the behavior of thermodynamic quantities is analogous, on the whole, to that in two-layer square lattices; a difference manifests itself in the behavior of the gap in the spectrum of quasiparticles in an external magnetic field h. For small fields h, a j-h phase diagram is constructed that determines the domains in which the 120 degrees and the singlet phases exist. It is established that, in the neighborhood of the second-order phase transition, the contribution, to the thermodynamic quantities, of longitudinal spin fluctuations, which are disregarded in the spin-wave description, is comparable to the contribution of transverse fluctuations. (c) 2005 Pleiades Publishing, Inc.
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16.

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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17.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Zabluda V. N.
Заглавие : The energy band structure and optical spectra of FeBO3 calculated with allowance for strong electron correlations
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2004. - Vol. 98, Is. 1. - P135-143. - ISSN 1063-7761, DOI 10.1134/1.1648107
Примечания : Cited References: 32. - This study was supported by the Russian Foundation for Basic Research (project no. 03-02-16286) and by the “Strongly Correlated Electrons” Program of the Department of Physical Sciences of the Russian Academy of Sciences
Предметные рубрики: PHASE-TRANSITION
HIGH-PRESSURE
FERROMAGNETISM
MODEL
Ключевые слова (''Своб.индексиров.''): atomic physics--band structure--charge transfer--excitons--green's function--light absorption--dielectric gap--energy band structure--lehmann spectral representation--optical spectra--iron compounds
Аннотация: A model of the energy band structure of iron borate (FeBO3) is proposed that combines a one-electron description of the sp states of boron and oxygen with a many-electron description of the d states of iron. The Green functions of d electrons are calculated using the exact Lehmann spectral representation. The energies of the d-type quasiparticles are calculated using terms of the d(4) , d(5) , and d(6) electron configurations. The optical absorption spectrum of FeBO3 is determined by local excitons and by the electron excitations with charge transfer. The latter excitations control the nature of the dielectric gap in FeBO3 crystals. The model parameters are determined from a comparison to the exciton energies. The density of single-particle states in FeBO3 is calculated. The main bands in the calculated optical absorption spectrum agree well with experimental data for energies up to 3 eV. (C) 2004 MAIK "Nauka/Interperiodica".
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18.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Abramova G. M., Volkov N. V., Petrakovskii G. A., Mita Y., Bayukov O. A., Velikanov D. A., Vorotynov A. A., Sokolov V. V., Bovina A. F.
Заглавие : Metal-insulator transition in FexMn1-xS crystals
Разночтения заглавия :авие SCOPUS: Metal-insulator transition in Fe x Mn1-x S crystals
Место публикации : JETP Letters. - 2007. - Vol. 86, Is. 6. - P.371-374. - ISSN 0021-3640, DOI 10.1134/S0021364007180051
Примечания : Cited References: 15
Предметные рубрики: ALPHA-MNS
PHASE-TRANSITION
SULFIDES
Аннотация: Results of an experimental study of MnS, FeS, and FexMn1-xS single crystals are presented. The phase composition, the lattice parameters, and the state of paramagnetic ions in FexMn1-xS have been determined by x-ray diffraction analysis and Mossbauer spectroscopy. A sequence of transitions have been found in iron manganese sulfide with x = 0.29 at temperatures T-1 approximate to 25-50 K, T-2 approximate to 125 K, and T-3 approximate to 190 K with a change in kinetic properties and the formation of a metallic state at low temperatures T approximate to 2 K. The possibility of a Mott-Hubbard transition in FexMn1-xS sulfides with variation of the composition and the temperature is discussed.
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19.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aplesnin S. S., Romanova O. B., Har'kov A. M., Balaev D. A., Gorev M. V., Vorotynov A. M., Sokolov V. V., Pichugin A.
Заглавие : Metal–semiconductor transition in SmxMn1−xS solid solutions
Место публикации : Phys. Status Solidi B. - 2012. - Vol. 249, Is. 4. - P.812-817. - ISSN 0370-1972, DOI 10.1002/pssb.201147327
Примечания : Cited References: 27. - This study was supported by the Russian Foundation for Basic Research project No 09-02-00554_a; No 09-02-92001-NNS_a; No 11-02-98018 r_sibir_a; ADTP "Development of scientific potential of the higher school" No. 2.1.1/11763.
Предметные рубрики: Magnetic-properties
Phase-transition
SmS
Valence
Pressure
Crystal
Lattice
CeRhSb
Ключевые слова (''Своб.индексиров.''): kondo effect--metal-semiconductor transition--semiconductors--variable-valence elements
Аннотация: The electrical resistivity of the SmxMn1−xS (0.15 ≤ x ≤ 0.25) solid solutions in the temperature range of 80–300 K was measured. Minimum and maximum in the temperature dependence of the resistivity were found, respectively, at T = 220 K for x = 0.15 and at T = 100 K for x = 0.2 compounds. This behavior is explained from the result of the mobility-edge movement, the disorder being due to elastic deformation and spin density fluctuations with short-range order. Metal–semiconductor phase transition versus concentration at xc = 0.25 is observed. Resistivity is described by scattering electrons with acoustic phonon mode and with localized manganese spin. From the thermal expansion coefficient the compression of the lattice below the Néel temperature for Sm0.2Mn0.8S is found.
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20.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Ovchinnikova T. M., Plotkin V. V., Dyad'kov P. G.
Заглавие : Spin crossover and Mott-Hubbard transition under high pressure and high temperature in the low mantle of the Earth
Коллективы : International conference on interaction of intense energy fluxes , International Conference on Interaction of Intense Energy Fluxes with Matter (XXX; 1–6 March 2015; Elbrus, Kabardino-Balkaria, Russia)
Место публикации : J. Phys.: Conf. Ser./ International conference on interaction of intense energy fluxes (30 ; 2015 ; March ; 01-06): IOP Publishing, 2015. - Vol. 653. - Ст.012095. - ISSN 1742-6588, DOI 10.1088/1742-6596/653/1/012095
Примечания : Cited References:22
Предметные рубрики: PHASE-TRANSITION
GEOMAGNETIC DATA
MAGNESIOWUSTITE
IRON
METALLIZATION
LAYER
Аннотация: Effect of high pressure induced spin crossover on the magnetic, electronic and structural properties of the minerals forming the Earth's low mantle is discussed. The low temperature P, T phase diagram of ferropericlase has the quantum phase transition point P = 56 GPa at T = 0 confirmed recently by the synchrotron Mossbauer spectroscopy. The LDA+GTB calculated phase diagram describes the experimental data. Its extension to the high temperature resulted earlier in prediction of the metallic properties of the Earth's mantle at the depth 1400 km h 1800 km. Estimation of the electrical conductivity based on the percolation theory is given. We discuss also the thermodynamic properties and structural anomalies resulting from the spin crossover and metal insulator transition and compare them with the experimental seismic and geomagnetic field data.
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