Sintering behavior and PTCR properties of stoichiometric blend BaTiO3

Donor doped positive temperature coefficient of resistivity barium titanate is highly sensitive to minor changes in processing conditions, Ba/Ti ratio, and dopant concentration. This leads to a lack of reproducibility of properties and microstructure. This study was performed in an effort to obtain a more microstructurally stable PTCR material. Barium titanate ceramics were prepared by blending Ba-excess BaTiO₃ powder with Ti-excess powder, in different ratios. Such donor modified blended systems display uniform, medium grain size (4-6 μm), high-density microstructures which are more stable to changes in processing parameters. The microstructures are characterized by flat grain edges, large grain-to-grain contact area and high degree of domain coherence across grain boundaries. The PTCR effect was, however, measured to be nominal in these samples. This has been attributed to the presence of a smaller barrier potential, and such microstructural features as strong domain coherence across grain boundaries, large grain-to-grain contact area, and high density. It was found that the simple act of blending donor doped BaTiO₃ powders of different Ba/Ti ratios drastically changes both microstructure and electrical properties. Blending results in the suppression of liquid-phase induced anomalous grain growth, suppressing grain growth processes and allowing sintering processes to go to a greater degree of completion. The proposed mechanism whereby this happens is that the presence of the donor in blended systems either changes the kinetics of liquid-phase formation and/or the wettability of grains, affecting liquid-phase distribution.