Dielectric properties of polycrystalline CaTiO3 doped with yttrium oxide

Y³⁺ was substituted for Ca²⁺ in polycrystalline CaTiO₃ in amounts up to 15 at %. Sintering conditions (1450° C, 15 h) were such that grain sizes were > 25 m. Stoichiometry was adjusted on the assumption that the excess charge of the dopant was compensated by the creation of calcium vacancies. This assumption was supported by measurements of the Ca/Ti ratio in the grains by electron-probe microanalysis. Unlike yttrium-doped SrTiO₃, material sintered in air was light-coloured with no evidence of semiconductivity. On the other hand, when sintering was done in nitrogen, dielectric relaxation characteristic of boundary layers was observed for dopant levels > 1 mol %. The experimental data support the view that dielectric relaxation in SrTiO₃ and CaTiO₃ results from semiconducting grains with resistive surface layers and that the semiconductivity arises because oxygen loss from the grains during sintering is increased by donor doping.