Influence of TiO2 additive on the microwave dielectric properties of α-CaSiO3–Al2O3 ceramics

The effects of TiO2 additives on microstructure and microwave dielectric properties of α-CaSiO3–2 wt%Al2O3 ceramics have been investigated in detail. Specifically, the TiO2 addition results in the presence of two distinct phases, e.g. CaTiO3 and CaTiSiO5, which can inhibit the growth of α-CaSiO3 grains by surrounding their boundaries and also improve the bulk density of α-CaSiO3–2 wt%Al2O3 ceramics. However, the TiO2 addition undermines the microwave dielectric properties of the title ceramics because the derived phases of CaTiO3 and CaTiSiO5 have poor quality factor. The τf value is strongly correlated to the compositions and can be controlled through the compositional ratio. The α-CaSiO3–2 wt%Al2O3 ceramics containing 2.5 wt% of TiO2 sintered at 1250 °C showed excellent microwave dielectric properties (εr=7.88, Q×f=24,412 GHz and τf=−0.52 ppm/°C).