This article is cited in 7 papers

Phase transitions

Ferroelastic phase transitions in (NH$_4$)$_2$TaF$_7$

E. I. Pogoreltsev^a, S. V. Melnikova^a, A. V. Kartashev^a, M. S. Molokeev^a, M. V. Gorev^a, I. N. Flerov^a, N. M. Laptash<sup>b

a</sup> L. V. Kirensky Institute of Physics, Siberian Branch of the Russian Academy of Sciences, Krasnoyarsk
^b Institute of Chemistry, Far East Branch of the Russian Academy of Sciences, Vladivostok

Abstract: The heat capacity, unit cell parameters, permittivity, optical properties, and thermal expansion of the (NH$_4$)$_2$TaF$_7$ compound with a seven-coordinated anion polyhedron have been measured. It has been found that the compound undergoes two successive phase transitions with the symmetry change: tetragonal $\to$ ($T_1$ = 174 K) orthorhombic $\to$ ($T_2$ = 156 K) tetragonal. The ferroelastic nature of structural transformations has been established, and their entropy and susceptibility to hydrostatic pressure have been determined.

Received: 22.08.2012

 English version: Physics of the Solid State, 2013, 55:3, 611–618

Bibliographic databases:

•