Influence of Stoichiometry on the Microstructure and Positive Temperature Coefficient of Resistivity of Semiconducting Barium Titanate Ceramics

Abstract

The influence of stoichiometry, i.e., Ba/Ti ratio, on the microstructure and positive temperature coefficient of resistivity (PTCR) characteristics of BaTiO 3 was investigated. Fine‐grain microstructures are obtained for Ba‐rich, stoichiometric, low‐temperature‐sintered, Ti‐rich materials. The room‐temperature resistivities ( ρRT ) of the fine‐grain Ti‐rich samples are large (>10 8 Ω·cm). Excess Ba 2+ ions can decrease the ρRT , by more than 2 orders of magnitude, because of the compensation of barium vacancies near the grain‐boundary regions. Rapid cooling after sintering can also decrease ρRT (⋍100×) and is ascribed to the suppression of reoxidation. Large‐grain microstructures and low ρRT , on the other hand, are generally observed for Ti‐rich and Al 2 O 3 ‐SiO 2 ‐TiO 2 ‐added samples after sintering at a temperature higher than the corresponding eutectic point.