  Raman scattering measurements and lattice-dynamics calculations have been
performed on magnesium tungstate under high pressure up to 41 GPa. Experiments
have been carried out under a selection of different pressure-media. The
influence of non-hydrostaticity on the structural properties of MgWO4 and
isomorphic compounds is examined. Under quasi-hydrostatic conditions a phase
transition has been found at 26 GPa in MgWO4. The high-pressure phase has been
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.
