Structural defects which formed on the {111} planes of BaTiO3 during the degradation of high-performance multi-layer Ni–BaTiO3 capacitors were studied by using transmission electron microscopy and electron energy loss spectroscopy. Normal pseudocubic titanate grains were present in as-produced capacitors. There was a coexistence of regular, modulated and long-range ordered structures in intentionally electrically degraded devices. The electron energy-loss spectroscopic analysis demonstrated that the concentration of O vacancies in titanate having modulated or ordered structures was higher than that in normal perovskite grains. The clustering or accumulation of O vacancies in the framework of BaTiO3 gave rise to the formation of new metastable structures. These observations were consistent with earlier models for degradation, but demonstrated that the details of the process might be more complex than originally assumed. New details of the nature of the reduction process were introduced with regard to the manner in which the lattice accommodated the enhanced O vacancy concentration in the failed regions of the capacitor.

Modulated and Ordered Defect Structures in Electrically Degraded Ni–BaTiO3 Multilayer Ceramic Capacitors. G.Y.Yang, E.C.Dickey, C.A.Randall, M.S.Randall, L.A.Mann: Journal of Applied Physics, 2003, 94[9], 5990-6