Enhanced mechanical, dielectric, and microwave absorption properties of ZnO/ZrSiO₄ composite ceramics by adding Al₂O₃ powders

The ZnO/ZrSiO₄ composite ceramics with different Al₂O₃ additions are fabricated by pressureless sintering method. The addition of Al₂O₃ contributes to the formation of ZnAl₂O₄, which results in the enhancement of bulk densities as well as flexural strengths of the ceramics by promoting the mass transportation movement. Both the complex permittivity and dielectric loss increase firstly then decrease as the Al₂O₃ content enhances from 0 to 7 wt%. The bulk density and ZnO content are the main factors to affect the dielectric performance of the ceramics. Owing to the higher dielectric loss, the ceramic with 3 wt% Al₂O₃ addition presents the better microwave absorption property. The effective absorption bandwidth of the ceramic in 2.4 mm thickness is 8.8-11.9 GHz, with a minimum reflection loss of -25.36 dB at 10.4 GHz. As the thickness of the ceramic increases, the absorption peak shifts toward the lower frequency region, which indicates the absorption bandwidth can be tailored by changing the thickness.