Dielectric properties of CaZrO3 coatings made by plasma spraying and bulks fired by spark plasma sintering

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In this study, water stabilized plasma spraying (WSP) was used to prepare CaZrO3 coatings, whereas CaZrO3 bulk samples were fired using spark plasma sintering (SPS). The spraying feedstock was prepared from fine CaZrO3 powder by agglomeration (spray drying) and sintering. The initial fine CaZrO3 powder was used for SPS. In case of plasma sprayed materials, the influence of spraying process on the coating structure was studied. Differences in the structure of plasma sprayed thick coatings and SPS compacts were characterized using microscopy, density and porosity measurements. The deposits were striped-out from the substrate, ground and polished in order to produce samples in a shape of planparallel plates with a smooth surface. These samples – in principle monoblock capacitors – were subjected to low voltage alternating electric field with a frequency range from 1 kHz to 1 MHz and their capacitance and loss factor were measured. Relative permittivity was calculated afterwards from the measured capacitance. Dependences of permittivity and losses were also studied for varying temperatures in a range 20–150 °C. Volume resistivity was measured in direct electric field at a room temperature. Influence of the SPS process and subsequent annealing on the microstructure and dielectric properties was studied as well. Decrease of porosity and rearrangement of grains after proper annealing brought improvements in the dielectric characteristics.