Semiconducting barium titanate

Barium titanate, which is well known as a basic ferroelectric material, is also of interest when doped because of the interaction between semiconductivity and ferroelectricity. The resistance of blocking layers at surfaces and grain-boundaries is governed mainly by the ferroelectric properties, so that a resistance jump of four decades is observed on heating above the Curie temperature. A survey of the chemical and physical properties of such blocking layers both at surfaces and interfaces is presented. Doped titanates have been used as the basis of two new types of material:

1. Semiconductors with high positive temperature-coefficient of resistivity in special temperature ranges suitable for temperature-sensors and stabilisers.
2. Dielectrics with extremely high dielectric constant, used in so-called barrier-layer condensers.