Structure-dielectric property relations in (Al_0.5Nb_0.5)⁴⁺ co-doped Ca_0.8Sr_0.2TiO₃ ceramics with excellent temperature stability

Ca_0.8Sr_0.2Ti_1-x(Al_0.5Nb_0.5)_xO₃ (abbreviated as CSTAN_x) microwave dielectric ceramics were synthesized through the solid-state reaction. The effects of (Al_0.5Nb_0.5)⁴⁺ co-doping on the microstructure and dielectric behavior were systematically investigated, and the relationship between structure and property was discussed. All compositions exhibited a single orthorhombic phase with dense morphology. The doping of (Al_0.5Nb_0.5)⁴⁺ was beneficial to increasing the ordering at the B-site and inhibiting the reduction of Ti⁴⁺, which in turn reduced the dielectric loss. In addition, the temperature stability of relative permittivity and resonant frequency was significantly improved due to the limitation of relative permittivity as well as the distortion and tilting of BO₆ octahedron. At 1 MHz, the variation of the relative permittivity (ε_r) for x = 0.6 composition was only 1% from 25 to 350 °C, and the loss angle tangent (tanδ) was below 0.003. Also, the x = 0.6 composition had the optimum microwave dielectric properties (ε_r = 45.7, Qf = 24,930 GHz, τ_f = + 3.1 ppm/°C). The results reveal that CSTAN_0.6 ceramics can be used for communication devices such as resonators and filters.