Defect pinning and oxygen vacancy engineering in Ta2O5-doped CaTiO3-SmAlO3 ceramics for enhancing microwave dielectric and mechanical performances

The miniaturization and high-performance optimization of microwave dielectric ceramics are crucial for modern communication technologies. Doping with oxides is an important method to enhance the properties of the microwave dielectric ceramics. Herein, we used Ta₂O₅ doping and constructed defects and oxygen vacancies to significantly optimize the microwave dielectric and mechanical properties of 0.7CaTiO₃-0.3SmAlO₃ (CTSA) ceramics. The Ta⁵⁺ substitution for B-site ions (Ti⁴⁺/Al³⁺) caused lattice expansion (from 445.43 to 446.32 Å³) for the Ta₂O₅-doped CTSA (T-CTSA) ceramics. Furthermore, the Ta⁵⁺ doping can cause the increase of oxygen vacancies. Low doping suppressed lattice disorder, while high doping led to loss dominated by oxygen vacancies. As a result, the T-CTSA ceramic has a uniform grain size and minimized porosity at 1.5 wt% doping, with a density of 4.84 g/cm³ and flexural strength of 234 MPa. Furthermore, the optimal sintering conditions were 1450 °C for 2 h for the T-CTSA-1.5 ceramic, yielding a dielectric loss of 1.28 × 10⁻⁴. Meanwhile, the T-CTSA-1.5 ceramic exhibits significantly enhanced dielectric properties: εᵣ = 43, Q × ƒ = 46875 GHz, and τ_ƒ = 3.5 ppm/°C. Therefore, the excellent performance of T-CTSA ceramics offers broad prospects in communication devices and provides new insights for future high-performance microwave dielectric ceramics.