Study of the elastic stiffness constants of thiourea by Brillouin scattering

All the elastic stiffness constants of thiourea have been measured at room temperature. The value of C₆₆(0.7 × 10¹⁰dynes/cm²) is very low. The C₁₁ and C₃₃ constants exhibit discontinuities at 169 and 202 K. The longitudinal acoustic phonons propagating in the c direction are very strongly damped in the vicinity of 202 K.