Temperature-dependent Raman scattering study of K 2MoO 4

Abstract

This research reports a temperature-dependent Raman scattering study of dipotassium molybdate (K 2MoO 4) in the 18–913 K temperature range. This study indicates that K 2MoO 4 crystal exhibits a temperature-induced first-order phase transition at around 578 K from monoclinic phase to incommensurate phase. The phase transition is connected with tilting and/or rotations of the MoO 4 tetrahedra that lead to a disorder in the MoO 4 sites. An orthorhombic phase (α′-phase) of K 2MoO 4 was obtained when the low-temperature monoclinic structure was heated or when high-temperature hexagonal structure was cooled. A lattice dynamic calculation was performed by using the classical rigid ion model, in order to predict both wavenumbers and atomic displacements (eigenvectors) for the vibrational modes of the monoclinic phase of K 2MoO 4 and K 2WO 4.