PTC behavior in yttria doped BaTiO3 as related to grain boundary structure

Lattice structure and phase distribution along the grain boundaries in Y₂O₃-doped BaTiO₃, with Zr⁴⁺ as a counterdopant were investigated with respect to their impact on PTC (positive-temperature-coefficient) behavior. This doping, related to A and B-site occupancy, creates ionic defect states which segregate during annealing to different morphological regions along the grain boundaries, identified as nondomain and domain regions. TEM (transmission electron microscope) high-resolution imaging, and HOLZ pattern and EDS (electron diffraction spectroscopy) analysis of these regions showed differences in composition, lattice parameters, and lattice plane coherency across the grain boundaries. Optimum doping in light of these structural changes resulted in lower resistivity and enhanced PTC effects, the stress release being the driving force for sharp PCT transitions