Crystal structure and microwave dielectric properties of (1 − x)NdAlO3–xCaTiO3 ceramics

Crystal structure and microwave dielectric properties of (1−x)NdAlO3–xCaTiO3 ceramics have been investigated. Crystal structure of the specimens changed with the composition. Rhombohedral structure was found for the specimens with x≤0.1. When 0.3≤x≤0.7, the specimens had the tetragonal structure and it changed to the orthorhombic structure as x exceeded 0.7. Two types of the second phases were observed in (1−x)NdAlO3–xCaTiO3 ceramics. For the specimens with x≤0.5, Nd4Al2O9 phase was observed and Al-rich phase was found in the specimens with x≥0.7. The dielectric constant (εr) and the temperature coefficient of the resonant frequency (τf) increased with the increase of x. The Q×f value of the specimen increased with x and exhibited the maximum value when x=0.5. The microwave dielectric properties of Q×f=45,000 GHz, εr=45 and τf=−1.5 ppm/°C were obtained for 0.3NdAlO3–0.7CaTiO3 ceramics.