Phase transitions at low temperatures in A2BX4-type halide substances

The temperature and frequency dependences of the dielectric constants of A2BX4-type halide dielectrics, K2ZnBr4, K2CoBr4, K2ZnI4, Rb, MnI4, Rb2ZnI4 and Rb2CoI4, all of which take crystal structure of Sr:GeS4-type at room temperature, were investigated. It was found that there is a common nature in the temperature dependence of the dielectric constants, namely, all substances show a ferroelectriclike dielectric anomaly with X-type shape below room temperature but this is followed by a stepwise anomaly with frequency dispersion, which occurs at a little lower temperature than the λ-type dielectric anomaly.