Properties and mechanisms of surface doped barium titanate sintered in reducing atmospheres

Barium titanate-based dielectric compositions for Multilayer Ceramic Capacitor (MLCC) applications that are properly formulated can maintain acceptable dielectric properties after firing in a reducing atmosphere. The data to be presented relates to the application of an experimental scheme to probe the fundamental nature of doped BaTiO₃-based dielectrics exposed to low pO₂ sintering atmospheres. Specifically, the effect of Y and Rare Earth dopants Nd, Dy, Ho, and Er and donor dopants Nb, and V have been studied for compositions in the system BaTi(Mn)O₃ + SiO₂. All dopants were applied to high purity barium titanate as chemical surface coatings.; Each coated formulation was evaluated after firing under three different atmospheric conditions. These conditions were comprised of firing in air at 1250°C for 2 hours, firing at 10−10 atm pO₂ at 1250°C for 2 hours, and firing at 10−10 atm pO₂ at 1250°C for 2 hours with an anneal at 10 −9 atm pO₂ at 1000°C for 1 hour. This testing method was useful in gaining insight into the mechanism of the dopant interaction and/or the compensation of the oxygen vacancy concentration.; As a donor addition, vanadium was observed to produce the highest dissipation factor when sintered under oxidizing conditions and the lowest dissipation factor when sintered under reducing conditions. The V-doped formulations exhibited satisfactory basic MLCC electrical properties when sintered under reducing conditions. Niobium was observed to impart strong donor character to the dielectric formulations sintered under reducing conditions suggesting that it was unlikely that compensatory A-site cation vacancies were induced.; For Y and Rare Earth doped formulations there was an observed shifting and suppression of the Curie Peak that seemed to be attributable to electrostrain effects, related to the ionic radius of the dopants. The observed difference in the TCC behavior of the Nd-doped formulations illustrated two possible effects of Nd doping. One is the effect of grain growth on Nd diffusion into the BaTiO₃. The second is a possible effect of a change in the dopant solubility in regions of highly acceptor-rich oxygen vacancies. This result stresses the possible significance of surface coating powders to achieve carefully controlled chemical gradients.