Seeing the Unseen: The Structural Influence of the Lone Pair Electrons in PbWO4

Pair distribution function (PDF) analysis of the scheelite-type material PbWO4reveals previously unidentified short-range structural distortions in the PbO8polyhedra and WO4tetrahedra not observed in the similarly structured CaWO4. These local distortions are a result of the structural influence of the Pb2+6s2lone pair electrons. These are not evident from the Rietveld analysis of synchrotron X-ray or neutron powder diffraction data, nor do they strongly influence the X-ray PDF (XPDF). This illustrates the importance of neutron PDF (NPDF) in the study of such materials. First-principles density function theory (DFT) calculations show that the Pb2+6s2electrons are hybridized with the O2–2p electrons near the Fermi level. The presence of local-scale distortions has previously been neglected in studies of structure–functionality relationships in PbWO4and other scheelite-structured photocatalytic materials, including BiVO4, and this observation opens new avenues for their optimization.