Raman scattering and phase transition in orthorhombic crystals of K₃Mn(CN)₆ and K₃Cr(CN)₆

Abstract

In the polarized Raman spectra of K,Mn(CN), and K,Cr(CN),, soft modes are observed in both the roomtemperature and the low-temperature phases. The frequencies of these modes decrease as the transition temperatures I205 K for K,Mn(CN), and 215 K for K,Cr(CN),] are approached from both sides. Unambiguous spectroscopic evidence for the second-order displacive phase transition was obtained on the basis of the soft mode behaviour in both crystals. High-pressure Raman spectra of K,Cr(CN), were measured up to 35 kbar using a diamond anvil cell. A pressure-induced phase transition occurs at ca 10 kbar.