Six different sound velocities of ammonium sulfate in GHz region have been measured from room temperature to –70°C by Brillouin scattering method utilizing a differential type of Fabry-Perot interferometer. Sound velocities, v 1 , v 4 and v 5 show a softening in the disordered phase near the transition temperature, T c =-49.5^° C . All the sound velocities show an abrupt fall at T c . The change amounts to 70% of the velocity at room temperature in the case of v 1 . A new anomaly is observed at T c - 8^° C on v 1 , and no remarkable effect of depolarization field on v 3 is observed in the ordered phase. It is attempted to interpret the phase transition of ammonium sulfate by the model of an improper ferrielectric type with a non-polar or weak-polar soft mode.
No takes yet. Share an insight, caveat, or question.
Yoshihara et al. (1978) studied this question.