Effect of high pressure on the Raman and electronic absorption spectra of PbMoO₄ and PbWO₄

The effect of pressure on the Raman spectrum of scheelite-structure compounds PbMoO4 and PbWO4 has been investigated, with use of a diamond-anvil cell. The electronic absorption edge in PbMoO4 was also studied up to 100 kbar. Both in PbMoO4 and in PbWO4, new Raman peaks appear at 90 and 45 kbar, respectively, due to first-order phase transition. The electronic absorption edge in PbMoO4 decreases in energy at the rate of 5 meV/kbar. These results are discussed in terms of the crystal chemistry and electronic structure of ABO4 (oxide) compounds