Light scattering studies of phase transitions of (NH4)2SO4-type crystals

The mechanism of the ferroelectric transition of pure and rubidium-doped ammonium sulfate is investigated by means of Raman, Brillouin and dielectric measurements. The study contributes to spectroscopic evidences of temperature anomalies of lattice vibrations in the paraelectric and ferroelectric range. The different behaviour of rubidium-doped crystals with respect to their dielectric and elastic properties at the transition is interpreted as an indication that different order parameters might become active in this first order transformation.