Microwave dielectric properties of ZnO/Al₂O₃ composite coatings

ZnO/Al₂O₃ composite coatings were prepared by plasma spray technology using ZnO powders, Al₂O₃ powders and PVA additives as starting materials. Phase compositions, microstructure of these coatings were analysised. And the influence of the content of ZnO in the absorbing coatings on dielectric property was investigated. The results indicate that new phase ZnAl₂O₄ generated in the progress of spraying, and by increasing the amount of ZnO, the counts of ZnAl₂O₄ increased. The density of coatings depends on the content of ZnO powders. The dielectric constant measurements revealed that when the content of ZnO increases from 60 mol% to 70 mol%, both the real part of permittivity and the loss change greatly over the frequency range 8.2-12.4 GHz. By the increase of frequency, the permittivity decrease when the ZnO content is 65 mol%, which demonstrated the strong frequency dispersion.