Tuning the electrical conductivity of Rare Earth-doped BaTiO3 using Gd2O3 as an exemplar

The electrical properties of Gd-doped BaTiO3 ceramics prepared by various doping mechanisms have been investigated using Impedance Spectroscopy and correlated with the proposed doping mechanisms observed from phase diagram studies and with solution energies obtained from atomistic simulations. Undoped BaTiO3, BaTi1-xGdxO3-x/2, Ba1-y/2Ti1-y/2GdyO3 and Ba1-zGdzTi1-z/4O3 were prepared. The first two series and y < 0.10 samples possess extrinsic p-type conduction due to oxygen gain (oxidation) associated with the presence of oxygen vacancies. A core-shell microstructure causes electrical heterogeneity where y < 0.10. For y ≥ 0.10, oxygen vacancies are eliminated by substitution of a small excess of Gd3+ at the Ba-site leading to intrinsic (band-type) conduction. All Ba1-zGdzTi1-z/4O3 ceramics processed in air exhibit n-type semiconductivity that is attributed to a small amount of oxygen loss (reduction) during sintering. The oxygen loss can be prevented by processing ceramics in a flowing O2 atmosphere.