Phase Transitions in Monoclinic Rubidium Tetraiodozincate Rb2ZnI4

Single crystals of monoclinic Rb 2 ZnI 4 were grown and dielectric properties were measured below room temperature down to 4.2 K. Two phase transitions were newly observed at 62.4 K and 7.5 K. The dielectric constant along the b -direction shows a peak at 62.4 K and a break at 7.5 K. Neither ferroelectric hysteresis loop nor pyroelectricity was, however, found below the 62.4 K transition.