6533b7d7fe1ef96bd126825a

RESEARCH PRODUCT

Lattice dynamics study of scheelite tungstates under high pressure I.BaWO4

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Room-temperature Raman scattering has been measured in lead tungstate up to 17 GPa. We report the pressure dependence of all the Raman modes of the tetragonal scheelite phase PbWO4-I or stolzite, space group I41 /a, which is stable at ambient conditions. Upon compression the Raman spectrum undergoes significant changes around 6.2 GPa due to the onset of a partial structural phase transition to the monoclinic PbWO4-III phase space group P21 /n. Further changes in the spectrum occur at 7.9 GPa, related to a scheelite-to-fergusonite transition. This transition is observed due to the sluggishness and kinetic hindrance of the I → III transition. Consequently, we found the coexistence of the scheelite, PbWO4-III, and fergusonite phases from 7.9 to 9 GPa, and of the last two phases up to 14.6 GPa. We have performed ab initio latticedynamics calculations, which have greatly helped us in assigning the Raman modes of the three phases and discussing their pressure dependence. The Raman modes of the free WO4 molecule are discussed.