Curie Point of Barium Titanate

Abstract

The Curie point, that is, the transition temperature between the ferro-electric and the non-ferro-electric structures of barium metatitanate, BaTiO₃, is characterized by a marked peak in the permittivity v. temperature curve and has recently received much attention, though reported values^1–4 for the temperatures of maximum permittivity show in some cases considerable discrepancies. This may be due to the effect of impurities or the firing conditions employed. It has also been reported⁵ that there is a second-order phase transition from a tetragonal structure to a cubic structure at about 120° C. The identity of the temperature of this transition with that of the permittivity peak has been regarded as uncertain, and we have, therefore, determined the Curie point by two non-electrical methods, namely, X-ray structure determinations and specific heat measurements, and compared these with the permittivity using a material containing more than 99 per cent BaTiO₃. That these effects occur at the same temperature has now been established, but a further complexity has, been revealed on detailed examination of the tetragonal to cubic transition.