Phase transitions in Rb2KLuF6 crystal

The Raman spectra of Rb₂KLuF₆ elpasolite crystal have been studied in a wide temperature range, including two phase transitions: from the cubic phase to the tetragonal phase and then to the monoclinic phase. The results of an analysis of the temperature dependences of the parameters of spectral lines are in good agreement with the thermodynamic data on the phase transitions. The analysis of Raman spectra shows that the transition from cubic to tetragonal phase is a second-order transition and the transition from the tetragonal to the monoclinic phase is a weak first-order transition.