In order to study metal fluorides of the fluorite structure at temperatures greater than 650 °K using ultrasonic techniques, several previously reported acoustic bonds were found to be inadequate. DuPont 9770 silver–platinum paste has been found to act as an effective acoustic bond for longitudinal ultrasound in contrast to the usual high temperature oxide acoustic bonds which break because they interact strongly with fluoride materials. Measurements of longitudinal ultrasonic velocities have been made up to 796 °K in [110] oriented CdF2and up to 850 °K in [100] oriented BaF2. In neither of these measurements did the bonds break at the highest temperatures.