Structures and phase transition in Rb 2NaHoF 6

Abstract

The phase transition at T c=172(2) K and high as well as the low temperature structures at 205 K and 17 K were studied with a low temperature Guinier diffractometer and camera. A second order phase transition (Γ-condensation of the T 1g mode) lowers the symmetry from Fm3m at T>;T c to I4/m at T<T c. In the low temperature phase the octahedra are tilted (5.2 degrees at 17 K) and slightly stretched. The increase of the tilt angle and the linear increase of the tetragonal distortion suggests a mean field power law. This classical behaviour would agree with the assumption of a Jahn Teller splitting of the Ho 3+ electronic state.