Electrical Characteristics of Boundary Layer-Type Semiconducting SrTiO3 Ceramics

Porous SrTiO3 ceramics containing an MgO-TiO2-SiO2 compound, Nb2O5, ZrO2, and a perovskite compound of Mn, Cu or Co oxide, were prepared. After fired in air, the ceramics were reduced in an N2-H2 atmosphere and then oxidized in air at a temperature between 800° and 1200°C. Grain boundaries were mainly oxidized by the heat treatment and the ceramics exhibited the characteristics of both capacitor and varistor. The apparent value of effective dielectric constant ε decreased with the rise of temperature of heat treatment, and the maximum value 14 of nonlinear exponent α was obtained by the heat treatment at 1000°C. It is concluded that oxygen diffused through pores formed at tripple grain junctions, and oxidized the grain boundaries, thus furnishing the ceramics with the characteristics of capacitor and varistor.