Resonant ultrasound spectroscopy investigation of a first‐order structural phase transition in LiKSO4.

Abstract

Lithium potassium sulphate (LiKSO4) exhibits a rich variety of structural phase transitions. Ten different phases have been reported over the temperature range from approximately 4 to 1000 K. The room temperature phase is hexagonal P63. On cooling, the room temperature phase transforms at approximately 205 K to another phase which is now believed to be trigonal P31c, although the symmetry of this phase has been controversial. Resonant ultrasound spectroscopy has been used to measure the complete set of elastic constants of LiKSO4 over the temperature range of 200 to 300 K. The room temperature elastic constants are accurately described by hexagonal symmetry. At approximately 213 K on cooling there are large abrupt changes of as much as 80% in many elastic constants. The elasticity of this phase cannot be described by hexagonal symmetry, but trigonal symmetry fits the data well. The elastic constants return to the hexagonal values at approximately 243 K on warming. The results will be discussed in terms of Landau theory. [Research supported by NSF under Grant No. DMR‐9501550.]