High velocity oxy-fuel and plasma deposition of BaTiO₃ and (Ba,Sr)TiO₃

High velocity oxy-fuel (HVOF) spraying has been successfully optimized for the deposition of BaTiO₃ as dense thick (25-150 μm) dielectric layers. These deposits have been compared with layers of BaTiO₃ and (Ba,Sr)TiO₃ produced by plasma spraying. The production of prototype conformal electronic components of these HVOF sprayed deposits by multilayering with thermally sprayed MgAl₂O₄ spinel and conductor thick films has been achieved. Parameter optimization has been shown to play a critical role in the deposition of these materials as thin structurally homogeneous deposits. The effect of standoff distance and combustion chamber size on the phase structure of the coatings have been studied and related to the dielectric properties of the layer. The proportion of crystalline-to-amorphous phase was found to be critically dependent upon the degree of melting of the particles in the flame and the rate of cooling of the deposits. The crystalline/amorphous ratio is directly related to the dielectric properties of the layer, with greater crystallinity giving higher values of dielectric constant. Microcracks and splat/splat interfaces are also believed to adversely affect the dielectric properties. The maximum dielectric constant (k) values achieved using the HVOF method for deposition are in the range 70-115. Plasma spraying of these materials has produced layers with k values close to 200.