The microwave dielectric properties of transparent ZnAl2O4 ceramics fabricated by spark plasma sintering

The transparent ZnAl2O4 ceramics were fabricated by spark plasma sintering. The effects of sintering temperature on the microstructure, optical, microwave dielectric and mechanical properties of ZnAl2O4 ceramics were investigated. With increasing temperature from 1240 to 1280 degrees C, the average grain size increased from 0.35 to 0.76 mu m, and the in- line transmittance increased first and then decreased. The highest in- line transmittance of 64% at 550 nm was obtained at 1260 degrees C. The quality factor (Q.f) and dielectric constant (epsilon(r)) values increased to the maximum and then decreased with the increase of temperature. The optimal microwave dielectric properties were achieved by sintered at 1260 degrees C with er value of 8.71, Q.f value of 64,395 GHz, and tau(f) value of -68 ppm/degrees C. The Vickers hardness depended on the relative density and the grain size, and the maximum value of 16.3 GPa was achieved at the sintering temperature of 1260 degrees C. The transparent ZnAl2O4 ceramics with good microwave dielectric properties would be a new optical-electronic integration material.