Huge dielectric constant of Rb2CdI4 and K2ZnI4 crystals grown by Czochralski method

Temperature and frequency dependences of the dielectric constant and the spontaneous polarization were measured for crystals of Rb2CdI4 and K2ZnI4 obtained by the Czochralski method. The dielectric constant of both crystals shows a huge sharp peak just below the Curie point T C and the peak value is 57,000 at T C = 210.3 K of Rb2CdI4 and 27,000 at T C = 272.5 K of K2ZnI4. Below T C, it shows a shoulder-like dielectric dispersion, which is connected to ferroelectric domain motions. The spontaneous polarization of K2ZnI4 was measured by the pyroelectric method and is about 3.9 × 10–2 C m−2 at 4 K. The effects of dc field application on the dielectric properties are also discussed.