Near-zero temperature coefficient in Mg²⁺–Ti⁴⁺ co-doped Sm₂O₃–CaSmAlO₄ microwave dielectric ceramics

The practical application of CaSmAlO₄ microwave dielectric ceramics is limited by its low quality factor (Q×f) value and non-zero temperature coefficient resonant frequency (τ_f) value. In this study, we introduced Mg²⁺–Ti⁴⁺ ionic pairs into CaSmAlO₄, along with an excess of 9% Sm₂O₃. The Mg²⁺–Ti⁴⁺ ionic pairs substituted Al³⁺, and two phases simultaneously coexisted in the ceramics: CaSmAlO₄ and Sm₂O₃. As the doping concentration of Mg²⁺–Ti⁴⁺ ionic pairs increased, the relative permittivity exhibited an upward trend, while the quality factor and resonant frequency temperature coefficient first rose and then descended. Remarkably, 0.09Sm₂O₃–0.91CaSmAl_0.7Mg_0.15–Ti_0.15O₄ sintered at 1450 °C yielded excellent dielectric properties: ε_r = 19.72, Q × f = 72,936 GHz, and τ_f = –0.044 ppm·°C^− 1. The factors influencing the microwave dielectric properties of 0.09Sm₂O₃–0.91CaSmAlO₄ ceramics were further examined by considering the crystal structure, grain size, Lichtenecker logarithmic rule, tolerance factor and packing fraction.