High-pressure Raman spectroscopy and lattice-dynamics calculations on scintillating MgWO4: Comparison with isomorphic compounds

Raman scattering measurements and lattice-dynamics calculations were performed on magnesium tungstate (MgWO4) under high pressure up to 41 GPa. Experiments were carried out on a selection of pressure media. The influence of nonhydrostaticity on the structural properties of MgWO4 and isomorphic compounds is examined. Under quasihydrostatic conditions, a phase transition was found at 26 GPa in MgWO4. The high-pressure phase is tentatively assigned to a triclinic structure similar to that of CuWO4 . We also report and discuss the Raman symmetries, frequencies, and pressure coefficients in the low- and high-pressure phases. In addition, the Raman frequencies for different wolframites are compared and the variation of the mode frequency with the reduced mass across the family is investigated. Finally, the accuracy of theoretical calculations is systematically discussed for MgWO4, MnWO4, FeWO4, CoWO4, NiWO4, ZnWO4, and CdWO4.