Effect of MgO/La₂O₃ co-doping on the microstructure, transmittance and microwave dielectric properties of translucent polycrystalline alumina

In this paper, a systematic experimental design is used to study the influence of different content ratios of MgO/La₂O₃ co-doping on the microstructure, real inline transmittance (RIT) and microwave dielectric properties of translucent polycrystalline alumina (PCA). Compared with those doped only with MgO, translucent PCA co-doped with different ratios of MgO/La₂O₃ demonstrates a higher and more stable Q×f value. The increased solubility of La in alumina and the elimination of the second phase are possible reasons for the decrease in dielectric loss. An optimized Q×f value of~300,000 GHz could be attained for samples co-doped with 1500 ppm MgO/300 ppm La₂O₃. Besides, a high RIT of~30% at a wavelength of 600 nm could be achieved when 500 ppm MgO/500 ppm La₂O₃ was co-doped, the reasons for these phenomena are also discussed in the paper.