[High temperature Raman spectra and structure study of stolzite-structured PbWO4 crystals and its melt]

Raman spectra of stolzite-structured PbWO4 crystal were recorded from 298 to 1 473 K. All the appearing vibrational modes were interpreted and assigned. The most intense mode at 902.7 cm(-1), which is identified as the internal mode upsilon1(Ag) of symmetrical stretching attributed to the vibration of [WO4]2- tetrahedron. Temperature dependent characteristics of the Raman spectra of the crystal were investigated. Band half-widths widened accompanied by the relative intensity decreased, and the lattice became more disorder with the increase in temperature. As being heated up to 1 398 K, PbWO4 crystals began to be melting and have completely transformed to liquid state at 1 473 K, while the internal vibrational modes of isolated [WO4]2- tetrahedron have appeared and the symmetry of vibrational modes transformed from S4 in crystal into Td of [WO4]2- in melt. It suggested that the isolated [WO4]2- structure unit exists in the melt.