Extended phase homogeneity and electrical properties of barium calcium titanate prepared by the wet chemical methods

Ca-substituted BaTiO3 with extended homogeneity range upto ∼50 mol% CaTiO3 have been prepared by three different chemical routes namely carbonate-oxalate (COBCT), gel-carbonate (GCBCT), and gel-to-crystallite conversion (GHBCT) followed by heat treatment above 1150 deg. C. X-ray powder diffraction (XRD) data show continuous decrease in the tetragonal unit cell parameters as well as c0/a0 ratio with CaTiO3 content, which are in accordance with the substitution of smaller sized Ca2+ ions at the barium sites. The microstructure as well as the dielectric properties are greatly influenced by the cationic ratio, α=(Ba+Ca)/Ti. The grain size decreases with CaTiO3 content for the stoichiometric samples (α=1), whereas ultrafine microstructure is observed in the case of off-stoichiometric samples (α>1) for the whole compositional range of CaTiO3 concentrations. Sharper εr-T characteristics at lower calcium content and broader εr-T with decreased εmax, in the higher calcium range are observed in the case of α=1. Whereas nanometer grained ceramics exhibiting diffuse εr-T characteristics are obtained in the case of α>1. The positive temperature coefficient of resistivity (PTCR) is realized for barium calcium titanate ceramics having 0.3 at.% Sb as the donor dopant for higher CaTiO3 (typically 30 mol%) containing samples (α=1), indicating that Ca2+ ions do not behave as acceptors if they were to substitute at the Ti4+ sites. Whereas the off-stoichiometric (α>1) ceramics retained high resistivity, indicative of the Ti-site occupancy for Ca2+ in fine grain ceramics