## 5aPA9. Resonant ultrasound spectroscopy investigation of a first-order structural phase transition in LiKSO[inf 4].

### Session: Friday Morning, May 17

### Time: 11:10

**Author: F. A. Willis**

**Author: R. G. Leisure**

**Location: Dept. of Phys., Colorado State Univ., Ft. Collins, CO 80523**

**Abstract:**

Lithium potassium sulphate (LiKSO[inf 4]) 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 P6[inf 3]. 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
LiKSO[inf 4] 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.]

from ASA 131st Meeting, Indianapolis, May 1996