Raman spectroscopic study of structural disordering in YVO4, GdVO4, and CaWO4 crystals

The Raman spectra of single-crystal YVO₄, GdVO₄, and ZrSiO₄ with a zircon structure, as well as CaWO₄ and BaWO₄ with a scheelite structure, are studied in detail over a wide temperature range 14–800 K. An inhomogeneous splitting of the A _1g (ν₂) vibrational lines in the Raman spectra of YVO₄ and GdVO₄ and the A _g (ν₁) vibrational lines in the spectrum of CaWO₄ is detected. It is shown that the profiles of these lines can be decomposed into two components, whose integrated intensities are redistributed with temperature and also depend on the matrix kind in which they are detected. The phenomenon observed is associated with the thermally activated processes of disorientation of the tetrahedral anions in the zircon and scheelite structures.