Defect chemistry of nano-grained barium titanate films

Polycrystalline barium titanate thin films have been prepared with 100 ppm of B-site acceptor dopants Ca, Mg, and Mn via chemical solution deposition on base metal substrates. The films are fired in low pO₂ atmospheres at 900 °C to prevent substrate oxidation. All dopant species produce low loss, space-charge free material without secondary reoxidation anneals. We note that the dopant concentrations required to compensate for oxygen non-stoichiometry are substantially greater than expected by equilibrium thermodynamic calculations. This observation is rationalized in the context of a composite oxygen defect model with differing reduction enthalpies for grain interiors and surfaces.