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/ M. V. Gorev [et al.] // J. Phys.: Condens. Matter. - 2002. - Vol. 14, Is. 25. - P. 6447-6453, DOI 10.1088/0953-8984/14/25/312. - Cited References: 17 . - ISSN 0953-8984РУБ Physics, Condensed Matter

Аннотация: The heat capacity and the effect of hydrostatic pressure on structural phase transitions in ammonium hexafluoroaluminate, (NH4)(3)AlF6, have been studied. Two heat capacity anomalies have been found with maxima at T-1 = 218.5 +/- 0.5 K and T-2 = 179 +/- 2 K. Respective entropy changes of phase transitions are DeltaS(1) = 15.3 +/- 0.5 J mol(-1) K-1 and DeltaS(2) = 2.5 +/- 0.5 J mol(-1) K-1. It is shown that the p-T phase diagram of this compound is rather complex and contains a triple point (p(tp) = 0.12 GPa, T-tp = 221 K) and high-pressure phase. The mechanism of transformations and generalized p-T phase diagram for compounds of the (NH4)(3)(MF6)-F-III family are discussed within the framework of the rotational order-disorder model.

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Держатели документа:
LV Kirenskii Inst Phys, Krasnoyarsk 660036, Russia
Inst Chim Mat Condensee Bordeaux, F-33608 Pessac, France
ИФ СО РАН
L. V. Kirensky Institute of Physics, 660036 Krasnoyarsk, Russian Federation
Institut de Chimie de la Matiere Condensee de Bordeaux, 33608 Pessac, France

Доп.точки доступа:
Gorev, M. V.; Горев, Михаил Васильевич; Flerov, I. N.; Флёров, Игорь Николаевич; Tressaud, A.; Durand, E.

/ I. N. Flerov [et al.] // Phys. Solid State. - 2001. - Vol. 43, Is. 12. - P. 2301-2306, DOI 10.1134/1.1427960. - Cited References: 19 . - ISSN 1063-7834РУБ Physics, Condensed Matter

Аннотация: The heat capacity of (NH4)(2)KGaF6 elpasolite is measured in the temperature range from 80 to 350 K. A sequence of three phase transitions at T-1 = 288.5 K, T-2 = 250 K, and T-3 = 244.5 K is revealed, and the thermodynamic characteristics of these transitions are determined. The influence of hydrostatic pressure on the phase transition temperature is investigated. The results obtained are discussed within the model of orientational ordering of NH4+ and GaF63- ionic groups. (C) 2001 MAIK "Nauka/Interperiodica".

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

Доп.точки доступа:
Flerov, I. N.; Флёров, Игорь Николаевич; Gorev, M. V.; Горев, Михаил Васильевич; Afanas'ev, M. L.; Ushakova, T. V.