Liquid phase sintering and microwave dielectric properties of NdAlO₃ ceramics

The effects of CuO addition on the microstructures and microwave dielectric properties of NdAlO₃ ceramics were investigated. CuO was selected as a liquid-phase-sintering aid to lower the sintering temperature of NdAlO₃ ceramics. With CuO addition, the sintering temperature of NdAlO₃ can be effectively reduced from 1650°C to 1410-1430°C. The crystalline phase exhibited no phase differences at a low addition level while Nd₄Al₂O₉ and NdAl₁₁O₁₈ were presented as second phases at the addition level higher than 0.5 wt%. The quality factors Q × f were strongly dependent upon the CuO concentration. The Q × f value of 63000 GHz was obtained at 1410-1430°C with 0.25 wt% CuO. For all levels of CuO concentration, the relative dielectric constants were not significantly different and ranged from 21.5 to 22.6. The temperature coefficients varied from -30 ppm/°C to -45 ppm/°C. Results of X-ray diffraction analysis and scanning electron microscopy are also presented.