Effect of high pressure on the Raman and electronic absorption spectra ofPbMoO4andPbWO4

The effect of pressure on the Raman spectrum of scheelite-structure compounds ${\mathrm{PbMoO}}_4$ and ${\mathrm{PbWO}}_4$ has been investigated, with use of a diamond-anvil cell. The electronic absorption edge in ${\mathrm{PbMoO}}_4$ was also studied up to 100 kbar. Both in ${\mathrm{PbMoO}}_4$ and in ${\mathrm{PbWO}}_4$, new Raman peaks appear at 90 and 45 kbar, respectively, due to first-order phase transition. The electronic absorption edge in ${\mathrm{PbMoO}}_4$ decreases in energy at the rate of 5 meV/kbar. These results are discussed in terms of the crystal chemistry and electronic structure of AB${\mathrm{O}}_4$ (oxide) compounds.