Abstract
The attenuation of a longitudinal ultrasonic wave propagating in the [111] direction in CdF 2 is studied as function of temperature from 300K to 1030K. An ultrasonic attenuation peak has been observed for the first time near 983K. This peak is used to define the diffuse transition temperature (T c = 983 K) in CdF 2 which is well below its melting temperature of 1372K. The Arrhenius activation energy of anion motion above T c was obtained from the temperature dependence of the attenuation and the theory of the dynamics of the coupled crystalline-cage-charged-liquid fluctuations. The elastic constant, C 11+2 C 12+4 C 44) 3 , measured simulataneously with the ultrasonic attenuation displays a large decrease near 983K in addition to the nearly linear decrease in the elastic constant with temperature.
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