Brillouin scattering of thiourea under hydrostatic pressure

Abstract

Brillouin scattering study of thiourea under hydrostatic pressure shows that some elastic constants exhibit strong variations at the different transitions. C₆₆ increases of 150% at the transition from the phase V to the plase VI. C₃₃ decreases at the transition from phase V to the incommensurate phase and the corresponding Brillouin line is broadened. The temperature of this transition, the diminution of C₃₃ and the line width depend strongly of the pressure. The results are explained by coupling between the order parameter and the S₃ deformation.