Phase transitions and thermodynamic properties of (NH4)(3)VO2F4 cryolite

作者：Fokina Valentina D^*; Gorev Mikhail V; Kocharova Alla G; Pogoreltsev Evgenii I; Flerov Igor N

来源：Solid State Sciences, 2009, 11(4): 836-840.

DOI：10.1016/j.solidstatesciences.2008.11.004

• Oxyfluorides
• Phase transition
• Calorimetry
• Phase diagram
• Ferroelectricity

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.

• 出版日期2009-4