Influence of ZnO content and annealing temperature on the dielectric properties of ZnO/Al2O3 composite coatings

ZnO/Al2O3 coatings were prepared by atmospheric plasma spraying (APS) using ZnO powders and Al2O3 powders as starting materials. The dielectric properties of these coatings were discussed. Both the real part of permittivity and the energy loss increase greatly with increasing ZnO content over the frequency range 8.2–12.4 GHz, which can be ascribed to orientation polarization and relaxation polarization due to a higher ZnO content. The frequency-dependent maximum of the loss tangent is found to obey Debye theory. In addition, annealing temperature which leads to the change of ZnO content also plays an important role in the dielectric performance.

► Crystalline phase, morphology and EDX analysis of the sprayed coatings. ► Effect of ZnO content on the dielectric property of ZnO/Al2O3 coatings. ► Effect of annealing temperature on the dielectric property of ZnO/Al2O3 coatings.