Interface microstructure between Ni base-metal electrode and BaTiO3 dielectric

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The interface microstructure in a simulated sandwich structure of Ni base-metal electrode and BaTiO3 dielectric has been studied by transmission electron microscopy. Some Ni grains have been oxidized to NiO; most of them although coarsened and poorly densified remained Ni metal. NiO formed during the reoxidation step at 1000 °C because the partial pressure of oxygen (pO2 ≈ 10−6 atm) in the controlled-sintering atmosphere was higher than the thermodynamic equilibrium value of pO2 = 4.68 × 10−11 atm. Crystallographic orientation relationships between NiO and BaTiO3 at the interface were determined. The BaTiO3–NiO interface was both twist and tilt boundaries that are characterized by dislocations of a mixed nature with Burgers vectors b = ½ ⟨0 0 1⟩ and ½ ⟨1 1 0⟩ and ⟨1 1 1⟩, described in the indices of pseudo-cubic BaTiO3. Dislocation loops were also found in BaTiO3 as well as along the NiO–BaTiO3 interface; the latter with was a vacancy loop formed by condensation of intrinsic Schottky defects. The Ni–BaTiO3 interface is built on and a configuration with opposite-charged ions stacked upon each other was energetically more favourable. The lattice mismatch was accommodated by misfit partials with b = ½ ⟨1 1 0⟩ that were dissociated from perfect dislocations with b = ⟨1 1 0⟩ probably by glide in on the metal–dielectric interface.