CURRENT-LIMITING ACTION OF MIXED-PHASE BATIO3 CERAMIC SEMICONDUCTORS

Stable and highly reproducible current-limiting characteristics are observed for polycrystalline ceramics prepared by sintering mixtures of coarse-grained, donor-doped BaTiO3 (tetragonal) as the major phase and ultrafine, undoped cubic perovskite such as BaSnO3, BaZrO 3, SrTiO3, or BaTiO3 (cubic). The linear current-voltage (I-V) relation changes over to current limiting as the field strength increases, when thermal equilibrium is attained. The grain-boundary layers with low donor and high Sn, Zr, or Sr have depleted charge carrier density as compared to that in the grain bulk. The voltage drop at the grain-boundary layers diminishes the temperature gradient between the interior and surface regions.