X-Ray Spectroscopic And First-Principles Investigation Of Lead Tungstate Under Pressure

High-energy-resolution fluorescence-detected (HERFD) near-edge x-ray-absorption fine-structure measurements performed at the Pb and W L-3 absorption edges have been used to study the pressure dependence of the local atomic structure of PbWO4 from 1 bar up to 22 GPa. Comparison of measured spectra with density-functional theory structural calculations and simulations based on solution of the Bethe-Salpeter equation establish an unambiguous PbWO4-I to PbWO4-III phase transition around 7 GPa. No evidence of either the Raspite or Fergusonite structures is found. The smaller core-hole lifetime broadening afforded by HERFD allows unique experimental determination of crystal-field splitting and its sensitivity to the oxygen cage geometry surrounding the Pb and W atoms thus giving definitive identification of the high-pressure phase of PbWO4.