Barrier Layers in Semiconducting Barium Titanate Glass-Ceramics

Methods were developed for the reduction and subsequent oxidation of glass-crystallized barium titanate for obtaining surface and grain-boundary barrier-layer dielectrics, together with the solid state chemistry compatible with glassmelting, crystallization, and the diffusion processes involved. The material obtained can be described as an interconnected dispersion of semiconducting BaTiO₃ crystallites sealed in a mostly glassy silicate matrix. Oxidation of this semiconductor leads to surface layers with very high dielectric strength, up to 10⁶ V/cm, and resistivity of the order of 10¹⁴ω·cm. The properties of compound barriers consisting of a space charge layer and a thin insulating film are also described and conditions leading to glass-ceramic materials having a positive temperature coefficient of resistance (PTCR) by the use of an anionic dopant are discussed.