The soft optic mode in ferroelastic Rb4LiH3(SO4)4

Raman scattering measurements were performed on the ferroelastic compound Rb4LiH3(SO4)(4) to determine the nature of the structural transition observed at T-c = 134 K. A double-grating spectrometer was used to obtain the Raman active B modes of Rb4LiH3(SO4)(4). Back-scattering measurements, as a function of temperature, reveal that the 31 cm(-1) mode shows softening consistent with that of an order parameter. As a result, our investigation indicates that the structural transition in Rb4LiH3(SO4)(4) should be cataloged as a pseudo-proper ferroelastic transition rather than a proper ferroelastic one.