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1.


   
    Phase transitions in elpasolites (ordered perovskites) / I. N. Flerov [et al.] // Materials Science and Engineering R: Reports. - 1998. - Vol. 24, Is. 3. - P. 81-151. - Cited References: 174 . - ISSN 0927-796X
РУБ Materials Science, Multidisciplinary + Physics, Applied
Рубрики:
ELASTIC NEUTRON-DIFFRACTION
   MII = CO

   RAMAN-SCATTERING

   THERMODYNAMIC PROPERTIES

   CRYSTAL-STRUCTURE

   SINGLE-CRYSTALS

   RB2KMIIIF6 ELPASOLITES

   CUBIC PEROVSKITES

   TEMPERATURE FORM

   HIGH-RESOLUTION

Кл.слова (ненормированные):
Crystal atomic structure -- Crystal growth -- Crystal lattices -- Crystallization -- Crystallography -- Ferroelectricity -- Hydrostatic pressure -- Order disorder transitions -- Single crystals -- Thermodynamics -- Elpasolites -- Landau theory -- Perovskite
Аннотация: Many compounds with general chemical formula A2BB?X6 and with tolerance factor value t < 1 crystallize in the elpasolite (ordered perovskite) structure. Different preparative methods have been considered. For example, the Bridgman technique is the most suitable method of growing single crystals of halogenated elpasolites with monoatomic cations. Group-theory and symmetry analyses have allowed us to build a scheme of possible structural distortions connected with octahedral rotations and displacements of ions. Experimental observations have proven that ferroelastic phase transitions occurring most frequently in elpasolites are due to small octahedra tilts. Quantitative analysis allows the possibility of describing these transitions in the framework of the thermodynamic Landau theory. Hydrostatic pressure and the substitution of atoms in different crystallographic sites allow to change significantly the succession and the temperature of phase transitions. The hypothesis of bond stresses is able to predict the possible occurrence of a phase transition for a particular elpasolite and/or the role of the octahedra rotations in the transformation. The mechanism of phase transitions in elpasolites and related compounds has also been considered. One can assume that a displacive mechanism associated with a strong anharmonicity plays a large role in phase transitions occurring in compounds with monoatomic cations. On the other hand, for instance, in cryolites with ammonium cations, the transitions originate from an order-disorder phenomenon. В© 1998 Elsevier Science S.A. All rights reserved.

Scopus
Держатели документа:
L.V. Kirensky Institute of Physics, Krasnoyarsk 660036, Russian Federation
Inst. Chim. Matiere Cond. B., Universite Bordeaux I, 33608, Pessac Cedex, France
Lab. de Phys.-Chim. Molec., Universite Bordeaux I, 33405, Talence Cedex, France

Доп.точки доступа:
Flerov, I. N.; Флёров, Игорь Николаевич; Aleksandrov, K. S.; Александров, Кирилл Сергеевич; Tressaud, A.; Grannec, J.; Couzi, M.
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2.


   
    Ferroelastic and ferroelectric phase transitions in fluoro- and oxyfluorometallates / I. N. Flerov [и др.] // Photonic and electronic properties of fluoride materials : Elsevier, 2016. - Chapter 16. - P. 355-381. - (Progress in fluorine science series), DOI 10.1016/B978-0-12-801639-8.00016-7. - Cited References: 92. - The reported study was partially supported by RFBR, research project No. 15-02-02009 a
   Перевод заглавия: Сегнетоэластические и сегнетоэлектрические фазовые переходы во фтор- и оксифторидметаллатах
РУБ Chemistry, Organic + Chemistry, Physical
Рубрики:
ELASTIC NEUTRON-DIFFRACTION
   ORIENTATIONAL DISORDER

   CRYSTAL-STRUCTURES

   THERMODYNAMIC PROPERTIES

   NONCRITICAL PARAMETERS

   CUBIC PEROVSKITES

   RAMAN-SCATTERING

   SINGLE-CRYSTALS

   A2BX4 STRUCTURE

   HIGH-RESOLUTION

Аннотация: Different degree of structural disorder is one of the main features of many fluoro- and oxyfluorometallates crystallizing in high symmetry structures. The comprehensive study of these compounds (perovskites, elpasolites, pyrochlores, etc.) enabled to determine a great effect of the size and shape as well as crystallographic sites of cationic and anionic species on the mechanism of structural ordering. Ferroelastic and ferroelectric phase transitions of different order, type, and succession can be realized as a result of chemical and hydrostatic pressure change. It was found that the substitution of monoatomic cations for tetrahedral ammonium group was accompanied by rather significant change of electron density distribution, entropy, and phase diagrams. Some compounds studied were considered to be promising solid-state refrigerants owing to the pronounced barocaloric effect resulting from large entropy and baric coefficient of phase transitions.

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Доп.точки доступа:
Flerov, I. N.; Флёров, Игорь Николаевич; Gorev, M. V.; Горев, Михаил Васильевич; Molokeev, M. S.; Молокеев, Максим Сергеевич; Laptash, N. M.
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3.


    Flerov, I. N.
    Entropy and the mechanism of phase transitions in elpasolites / I. N. Flerov, M. V. Gorev // Phys. Solid State. - 2001. - Vol. 43, Is. 1. - P. 127-136, DOI 10.1134/1.1340198. - Cited References: 33 . - ISSN 1063-7834
РУБ Physics, Condensed Matter
Рубрики:
ORDERED PEROVSKITE PB2MGTEO6
   ELASTIC NEUTRON-DIFFRACTION

   THERMODYNAMIC PROPERTIES

   CUBIC PEROVSKITES

   CRYSTAL-STRUCTURE

   HIGH-RESOLUTION

   PB2MGWO6

   CSPBCL3

Аннотация: The phase transitions in series of crystals with the general formulas A(2)BB'X-6 (X = F, Cl, Br, or CN) and Pb2BB'O-6 that belong to the elpasolite family (space group Fm(3) over bar m) are analyzed. The influence of the size and the shape of cations and anions on the entropy and the mechanism of structural distortions is discussed. (C) 2001 MAIK "Nauka/Interperiodica".

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Держатели документа:
Russian Acad Sci, Siberian Div, Kirenskii Inst Phys, Krasnoyarsk 660036, Russia
ИФ СО РАН
Kirenskii Inst. of Physics, Siberian Division, Russian Academy of Sciences, Akademgorodok, Krasnoyarsk, 660036, Russian Federation

Доп.точки доступа:
Gorev, M. V.; Горев, Михаил Васильевич; Флёров, Игорь Николаевич
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