Preparation and Microstructure Characterization of Anodic Spark Deposited Barium Titanate Conversion Layers

Anodic spark deposition (ASD) is an advanced plasma-electrochemical coating process to prepare polycrystalline, ceramic-like conversion coatings on metal surfaces. As an example, polycrystalline barium titanate (BaTiO₃) phases have been prepared by the anodic conversion of metal substrate and the metal ions in the electrolyte. By a combination of various characterization techniques, the configuration of the coating was elucidated. On the metal substrate a thin (~50 nm) passivating amorphous film of titania (TiO₂) first forms, which subsequently changes to anatase and rutile structures. With increasing anodic potentials, a plasma-chemical conversion reaction starts, leading to the heterogeneous formation of BaTiO₃layers of 2–10 μm thickness. The results of this study lead to the formulation of a model describing a polycrystalline and inhomogeneous layer configuration.