Vibrational spectra of crystals with scheelite structure and the solid solutions on their basis

IR-reflection spectra of scheelite-type crystals, XMeO4, where X = Ca, Pb; Me = Mo, W, and solid solutions on their basis are investigated. The obtained spectra are treated under the program: dispersion oscillator model - Kramers-Kronig analysis. Frequency evolution and the decay of natural vibrations by substituting the metal atoms both inside the MeO42- tetrahedron and beyond of it are also studied. It is shown that the IR-active vibrational spectrum of scheelite-type crystals considerably depends on X-type atoms (Ca or Pb). In solid solutions, while substituting Ca or Pb, some of the vibrations in the spectrum reveal two- or three-mode character of rearrangement. But the replacement of Mo by W does not lead to the formation of local vibrations, and the spectrum is found to be rearranged as a spectrum of single-mode character. (author)