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/ S. V. Mel'nikova, A. G. Kocharova // Phys. Solid State. - 2009. - Vol. 51, Is. 3. - P. 597-600, DOI 10.1134/S1063783409030275. - Cited References: 7. - This work was supported by the Council on Grants from the President of the Russian Federation (grant NSh-1011.2008.2) and the Russian Foundation for Basic Research (project no. 06-02-16 102). . - ISSN 1063-7834РУБ Physics, Condensed Matter

Аннотация: (NH4)(3)VO2F4 crystals were grown, and polarization-optical studies and measurements of birefringence were conducted on crystal plates of various cuts over a wide temperature range. Phase transitions were detected at temperatures T-1 up arrow = 417 K, T-3 up arrow = 211 K, and T-4 up arrow = 205 K (on heating) and at T-1 down arrow = 413 K, T-3 down arrow = 210 K, and T-4 down arrow = 200 K (on cooling). The transitions are accompanied by anomalies of the birefringence and by twinning. The sequence of changes in the phase symmetry is assumed to be as follows: cubic Fm (3) over barm↔ orthorhombic Immm (I222(1)) monoclinic 112/m)↔ triclinic P (1) over bar. Near temperatures T-2 approximate to 240-250 K, an additional anomaly of the birefringence is observed, with the crystal retaining the orthorhombic symmetry.

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Держатели документа:
[Mel'nikova, S. V.
Kocharova, A. G.] Russian Acad Sci, Kirensky Inst Phys, Siberian Branch, Krasnoyarsk 660036, Russia
ИФ СО РАН
Kirensky Institute of Physics, Siberian Branch, Russian Academy of Sciences, Akademgorodok, Krasnoyarsk 660036, Russian Federation

Доп.точки доступа:
Kocharova, A. G.; Кочарова, Алла Георгиевна; Мельникова, Светлана Владимировна; Russian Federation [NSh-1011.2008.2]; Russian Foundation for Basic Research [06-02-16 102]

/ V. D. Fokina [et al.] // Solid State Sci. - 2009. - Vol. 11, Is. 4. - P. 836-840, DOI 10.1016/j.solidstatesciences.2008.11.004. - Cited Reference Count: 17. - Гранты: The authors are grateful to Dr. SM. Mel'nikova for the permission to use the unpublished results.; This work was supported by the Russian Foundation for Basic Research (project 06-02-16102). - Финансирующая организация: Russian Foundation for Basic Research [06-02-16102] . - ISSN 1293-2558
Аннотация: Calorimetric measurements performed in a wide temperature range on (NH4)(3)VO2F4 have shown the presence of four heat capacity anomalies at T-1 = 438 K, T-2 = 244 K, T-3 = 210.2 K, T-4 = 205.1 K associated with the first order phase transitions. In accordance with the permittivity behavior, the structural transformations are of nonferroelectric nature. Pressure dependence of the phase transition temperatures has been studied by DTA under pressure. The entropy of phase transitions is analyzed mainly in the framework of the orientational disordering of NH4+ and VO2F43- ions in a cubic phase. (C) 2008 Elsevier Masson SAS. All rights reserved.

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Держатели документа:
RAS, Siberian Branch, LV Kirensky Phys Inst, Krasnoyarsk 660036, Russia
Siberian Fed Univ, Krasnoyarsk 660074, Russia

Доп.точки доступа:
Fokina, V. D.; Фокина, Валентина Дмитриевна; Gorev, M. V.; Горев, Михаил Васильевич; Kocharova, A. G.; Кочарова, Алла Георгиевна; Flerov, I. N.; Флёров, Игорь Николаевич; Pogoreltsev, E.I.