Micro-Raman Mapping Study of the Phase Transition in K 2 Mn 2 (SO 4 ) 3

Micro-probed Raman scattering spectra of the langbeinite-type crystal K 2 Mn 2 (SO 4 ) 3 have been observed with a special attention to internal modes of SO 4 molecules. At the phase transition temperature, new internal modes appear owing to the inequivalence of the molecular sites in the crystal. Micro-Raman mapping study has been carried out near the transition temperature. The spectra exhibit either the high-temperature structure or the low-temperature structure depending on the observed position. It is concluded that the sample crystal consists of the local regions that have different transition temperatures. This result indicates that not the intermediate phase but the coexistence of two phases appears in the K 2 Mn 2 (SO 4 ) 3 single crystal.