Calcium as an Acceptor Impurity in BaTiO3

The equilibrium electrical conductivity of polycrystalline, calcium-doped BaTiO₃ was studied over the oxygen partial pressure range 10^-13 to 10⁵ Pa and the temperature range 800° to 1000°C. There is little effect if CaO is substituted for a corresponding amount of BaO, i.e., Ba, _1-xCa_xTiO₃. If CaO is substituted for a corresponding amount of the TiO₂ content, i.e., BaTi_1-xCa_xO_3-x, the equilibrium conductivity shows strong evidence of acceptor-doped behavior. If the corresponding amount of excess CaO is added to stoichiometric BaTiO₃, i.e., BaCa_xTiO_3+x, the conductivity profiles are very close to those for samples with TiO₂ replaced by CaO, and show highly acceptor-doped behavior. This is in agreement with the replacement of a small amount of Ti by Ca²⁺ on the octahedral B-sites of BaTiO₃, where it acts as an acceptor center, Ca_T