Brillouin-scattering and computer-simulation studies of fast-ion conductors: a review

Experimental Brillouin-scattering studies of fast-ion conductors at high temperatures and complementary computer simulations are reviewed. Several different compounds are considered: fluorites, cubic zirconias and rare-earth trifluorides. The behaviour of the acoustic-mode frequencies and elastic constants below and above the transition temperature to the state of high-ionic conductivity is examined. Static-lattice and defect-energy calculations which provide theoretical insights into the diffuse-phase transition, and provide explanations of the anharmonic and defect contributions to the observed reductions in elastic constants, are discussed.