GOREV, Mikhail V.; FLEROV, Igor N.; TRESSAUD, Alain; DURAND, Etienne

doi:10.1088/0953-8984/14/25/312

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GOREV, Mikhail V.
L.V. Kirensky Institute of Physics

FLEROV, Igor N.
L.V. Kirensky Institute of Physics

TRESSAUD, Alain
Institut de Chimie de la Matière Condensée de Bordeaux [ICMCB]

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Journal of Physics: Condensed Matter. 2002, vol. 14, n° 25, p. 6447-6453

IOP Publishing

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The heat capacity and the effect of hydrostatic pressure on structural phase transitions in ammonium hexafluoroaluminate, (NH4)3AlF6, 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 ΔS1 = 15.3 ± 0.5 J mol-1 K-1 and ΔS2 = 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 (ptp = 0.12 GPa, Ttp = 221 K) and high-pressure phase. The mechanism of transformations and generalized p-T phase diagram for compounds of the (NH4)3MIIIF6 family are discussed within the framework of the rotational order-disorder model.< Leer menos

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Ammonium hexafluoroaluminate

Phase diagrams

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The p-T phase diagram of ammonium hexafluoroaluminate

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