  The effect of pressure on the Raman spectrum of PbWO4 has been investigated
up to 48 GPa in a diamond-anvil cell using neon as pressure-transmitting
medium. Changes are detected in the Raman spectrum at 6.8 GPa as a consequence
of a structural phase transition from the tetragonal scheelite structure to the
monoclinic PbWO4-III structure. Two additional phase transitions are detected
at 15.5 and 21.2 GPa to the previously unknown crystalline phases IV and V. The
last one remains stable up to 43.3 GPa. At 47.7 GPa all Raman modes disappear,
which could be caused by a pressure-induced amorphization. All structural
changes are reversible, being the scheelite phase recovered at ambient
pressure. However, the two most intense modes of the PbWO4-III phase are still
present after full decompression, indicating that this phase coexists as a
minority metastable phase with the scheelite phase after pressure release. The
wavenumber of the Raman modes and their pressure dependencies are reported for
the four crystalline phases. The present reported results are compared with
previous studies.
