Structural Phase Transition in Hexagonal Barium Titanate

Abstract

Distinct dielectric anomalies have been found in the hexagonal modification of BaTiO₃ at 60 K and 222 K. X-ray studies have revealed that a structural distortion from the prototypic hexagonal structure occurs at T₀=222 K. Below T₀, a very weak diffraction line has been detected, which is the forbidden line for the hexagonal space group of P6₃/mmc; and the diffraction intensity I in the new phase is given approximately by I∝T₀−T. The transition at 222 K is very probably of the second order. A possibility is speculated that a ferroic transition takes place below T₀.