Brillouin and ultrasonic studies of the ferroelastic phase transition in [N(CH3)4]2ZnBr4

Abstract

The temperature dependence of the elastic stiffness constant c55 in [N(CH3)4]2ZnBr4 single crystals has been measured using Brillouin scattering and the ultrasonic pulse echo overlap technique. The elastic constant c55 was found to soften strongly in both the paraelastic and ferroelastic phases. Despite the ferroelastic transition being an order-disorder type, no elastic dispersion was observed in the frequency range below ∼2 GHz. Hence the frequency of the susceptibility of the order parameter, inducing this transition, is expected to be above ∼2 GHz.