Micro-Raman scattering study of the phase transition of K2Mn2(SO4)3

Raman scattering spectra of the langbeinite-type crystal K2Mn2(SO4)(3) have been observed by using a micro-Raman scattering technique with a special attention to internal modes of SO4 molecules. At the phase transition temperature, new internal modes appear owing to the inequivalence of the molecular sites in the crystal. Micro-Raman spectra just at the transition temperature exhibit either the high-temperature structure or the low-temperature structure as a function of the observed position. Therefore, the sample single-crystal consists of local regions which have different transition temperatures. This result indicates that the intermediate phase is absent in the K2Mn2(SO4)(3) crystal.