Light scattering study of the onset of disorder in solid electrolytes at high temperatures

Certain solids exhibit anomalously high ionic conductivities at temperatures appreciably below their melting points; this phenomenon is sometimes referred to as superionicity, and is associated with development of disorder in a component sublattice. This effect has been studied in the fluorites SrCl 2 , BaF 2 and PbF 2 and in AgI, using Raman and Brillouin scattering. In the fluorites the disorder occurs in the anion sublattice and in AgI in the cation sublattice. At the transition to the highly conducting phase, the emergence of a broad low-frequency response has been observed; simultaneously, there is a dramatic softening of elastic constants.