Phase transition and vibrational properties of A2(BO4)3 compounds (A=Sc, In; B=Mo, W)

IR and Raman studies have been performed for Sc2(MoO4)3, Sc2(WO4)3, In2(MoO4)3 and In2(WO4)3 compounds belonging to the group of materials exhibiting negative thermal expansion. Moreover, temperature-dependent spectra have been measured for Sc2(MoO4)3 in the 290-8 K temperature range. The assignment of the observed vibrational modes to respective vibrations of atoms has been proposed and the observed changes due to first-order ferroelastic phase transition has been analyzed.