Charge compensation mechanism in yttria-doped barium titanate

A commercial TiO2-excess BaTiO3 powder doped with Y2O3 has been pressureless-sintered using conventional tube furnace and CO2-laser, and the room-temperature electrical conductivity determined. Grain-growth inhibition is found to occur at ∼0.40 mol% Y2O3 where the refined microstructure of an average grain size of ∼1 μm is obtained from sintering at 1215 °C. The principal charge compensation mechanism in Y2O3-doped BaTiO3 depending upon temperature can be divided into three characteristic regimes. The mechanism is predominantly of the cation vacancy compensation at temperatures <1210 °C, a mixed mode at 1210-1500 °C, and the electron compensation when sintering temperature exceeds 1500 °C. Sintering using the CO2-laser has enabled the retention of the high temperature defect equilibrium which renders the room-temperature conductivity of ∼10−2 (Ω mm)−1 to the ceramics. The sintering of Y2O3-doped BaTiO3 ceramics is improved since densification is enhanced by faster barium diffusion via the extrinsic cation vacancy and coarsening suppressed by high Y2O3-content due to reduced grain-boundary mobility by second-phase (Y2Ti2O7) pinning.