The Phase Transition of (ND 4 ) 3 D(SO 4 ) 2 Studied with Raman Scattering

Ferroelectric phase transition is studied with observing the x 2 and x 4 modes of SO 4 ions. Discussion about the change of spectra with decreasing temperature is given. According to this discussion, it is concluded that the phase transition to the ferroelectric phase VI is caused by the ordering of ions other than deuteriums and the ferroelectric phase VII is triggered by the order of deuteriums in dimmers.