Ferroelectricity and Successive Phase Transitions in (NH4)2ZnBr4

Dielectric and thermal properties of (NH 4 ) 2 ZnBr 4 were studied. It was found that (NH 4 ) 2 ZnBr 4 undergoes phase transitions at about -56.5°C and 166°C on warming. The crystal becomes ferroelectric below the lower transition temperature where a small stepwise anomaly in the dielectric constant along the a axis is observed. Spontaneous polarization obtained is 0.22 µCoul/cm 2 at -140°C.