Ferroelastic phase transition in crystalline K3Na(CrO4)2: Acoustic studies

Ultrasonic studies of the temperature behavior of the velocity and damping of sound for the xx and zz longitudinal and yx and zx transverse waves in K3Na(CrO4)2 have been carried out in the temperature interval 185–295 K, which includes the region of the ferroelastic phase transition. The acoustic parameters for both shear and longitudinal waves were found to have anomalies in the region of the phase transition with a Curie temperature of 235.5 K. A theoretical analysis of the softening of the elastic moduli c44 and c66 was performed on the basis of the Landau expansion in terms of the strain tensor components ɛ4 and (ɛ2-ɛ1)/2 considered as the linearly coupled primary and secondary order parameter, respectively. The absolute values of the elastic moduli c11, c33, c44, c66, c12, and c14 at 295 K were calculated.