The temperature dependence of the structures of RbCaF3, and the determination of the low temperature phases

Abstract

The temperature dependence of the structural parameters (ions coordinates and ions temperature factors) in the vicinity of the cubic to tetragonal structural phase transition of RbCaF3 at 193 K is reported together with the structure of this compound below 50 K. The neutron powder profile refinement method has been used to carry out this study. The same space group (Pnma-D162h) has been found at 20 K and 4.5 K. Equality of the CaF6 tilt angles about each of the three < 100 ) cubic axes in the low temperature phase and the behaviour of the temperature factors in the cubic and tetragonal phases indicate an order-disorder character of the 193 K and 50 K phase transitions