Dielectric Study of Phase Transitions in Cs3H(SeO4)2and Its Isotope Effect

The dielectric constants along the c ' axis of Cs 3 H(SeO 4 ) 2 and its deuterated crystal were measured in a temperature range from 5 K to 460 K. It was found that Cs 3 H(SeO 4 ) 2 undergoes three phase transitions at 451 K, 364 K and 50 K. The dielectric constant of Cs 3 H(SeO 4 ) 2 shows a small peak at 50 K, and it obeys the Curie-Weiss law above 50 K. The transition temperature (50 K) is increased to 168 K by deuteration, showing a large isotope effect, while other two transition temperatures do not change appreciably.