Dielectric Studies of Monoclinic Rb 1− x Cs x D 2 PO 4 on the Phase Transitions

Dielectric, pyroelectric and thermal properties of the crystals of monoclinic Rb 1- x Cs x D 2 PO 4 system were studied from -190°C to 120°C. The phase diagram of the system was established in the whole range of x . The crystal of x =0 has three phases denoted as I, II and III in order of the descending temperature. As x increases from zero, a ferroelectric IV phase appears between the phases III and II, and the temperature range of the phase TV spreads. The III–IV and IV–I transition entropies are distinctly small in comparison with those for the III–II, II–I and IV–II transitions.