An Investigation of Successive Phase Transitions in KCdF₃ by EPR Probe of Gd³⁺–V_cd Centre

Abstract

The structural phase transition in KCdF₃ is investigated by analysing EPR spectra of Gd³⁺ centres with Cd²⁺ vacancies on nearest neighbour lattice sites. Temperature and field-direction dependence of the spectra shows occurrence of successive phase transitions at around 485 and 471 K. In the second phase 471 K<T<485 K, the field-direction dependence obtained in this experiment is not consistent with that expected from the condensation of the M₃^z phonon mode which was previously reported. The experimental results are interpreted by a model that these phase transitions are due to the condensation of the alternate rotations around two cubic axes at 485 K and around another axis at 471 K.