Oxygen nonstoichiometry and dielectric evolution of BaTiO₃. Part II—insulation resistance degradation under applied dc bias

The microchemical and microstructural origins of insulation-resistance degradation in BaTiO₃-based capacitors are studied by complementary impedance spectroscopy and analytical transmission electron microscopy. The degradation under dc-field bias involves electromigration and accumulation of oxygen vacancies at interfaces. The nonstoichiometric BaTiO_3-δ becomes locally more conducting through increased oxygen vacancy concentration and Ti ion reduction. The symmetry across the dielectric layer and locally across each grain is broken during the degradation process. Locally, the nonstoichiometry becomes so severe that metastable lattice structures are formed. The degradation in insulation resistance at the grain boundaries and electrode interfaces is associated with the double Schottky-barrier potential lowering and narrowing. This may correlate with an effective decrease in net acceptor charge density at the grain boundaries.