Structural Phase Transition in Hexagonal Barium Titanate

Distinct dielectric anomalies have been found in the hexagonal modification of BaTiO 3 at 60 K and 222 K. X-ray studies have revealed that a structural distortion from the prototypic hexagonal structure occurs at T 0 =222 K. Below T 0 , a very weak diffraction line has been detected, which is the forbidden line for the hexagonal space group of P6 3 /mmc; and the diffraction intensity I in the new phase is given approximately by I ∝ T 0 - T . The transition at 222 K is very probably of the second order. A possibility is speculated that a ferroic transition takes place below T 0 .