Influence of Al2O3 addition on the microstructure and microwave dielectric properties of α-CaSiO3 ceramics

The effects of Al2O3 additives on the sintering behavior, microstructures, and microwave dielectric properties of α-CaSiO3 ceramics have been investigated. The X-ray diffraction analysis indicated that the crystal phase of α-CaSiO3–Al2O3 ceramics was α-CaSiO3 with trace amounts of Ca2Al2SiO7, which could inhibit the growth of α-CaSiO3 grains by surrounding their boundaries and also improve the bulk density of α-CaSiO3–Al2O3 ceramics. However, excessive additives (≥3 wt%) of Al2O3 undermined the microwave dielectric properties of α-CaSiO3–Al2O3 ceramics because of the poor quality factor of Ca2Al2SiO7. The optimal Al2O3 addition was found to be 2 wt%, and the α-CaSiO3-2 wt%Al2O3 ceramic sintered at 1,250 °C showed excellent microwave dielectric properties with an εr of 7.39, a quality factor Q × f of 39,523 GHz and a τf of −13.28 ppm/°C.