Acoustic phonon softening in KH3(SeO3)2

Abstract

Ultrasonic velocities of centrosymmetric KH3(SeO3)2 were measured along with additional measurements of the transition entropy and spontaneous strains. The ultrasonic velocity of the transverse wave with the wave number q//[010] and the polarization ε//[001] tends to approach nearly zero at the transition point (Tc) on approaching Tc from both sides of Tc. The basic experimental results are analyzed by a phenomenological theory and are discussed.