Ferroelectric Behavior in Hexagonal Type Barium Titanate

An investigation on dielectric anomalies in a hexagonal modification of barium titanate has revealed that this crystal is also ferroelectric as in the well known perovskite type barium titanate. The hexagonal single crystals have been grown successfully. The dielectric constant along c-axis ec shows two distinct peaks at 222 K and 74 K; a general feature of ec vs temperature relation is in agreement with that of ceramic samples (J. Phys. Soc. Jpn. 54 (1985) 480). Above 74 K Curie-Weiss law holds with the curie constant C=1.2×104 degrees. The dielectric constant perpendicular to c-axis is constant e⊥~70. Below about 74 K ferroelectric hysteresis loop occurs. The c-component of the spontaneous polarization is ~2×10-2 C/m2 at 5 K. Barium titanate affords a rare and an interesting example that both polymorphic states show strong ferroelectric activity despite the quite difference in crystal structures.