Synergistic A/B-site co-doping strategy for achieving high dielectric constant and enhanced comprehensive performance in perovskite ceramics

Microwave dielectric ceramics with high dielectric constant and low dielectric loss are essential for miniaturized communication devices, yet their further optimization is hindered by inherent trade-offs among intrinsic properties. While A-site rare-earth doping or B-site complex-ion doping has been explored to enhance perovskite performance, such approaches still encounter limitations stemming from suboptimal selection of A-site and B-site ions. Here, we fabricating B-site doped and A/B-site co-doped SrTiO₃-based microwave dielectric ceramics selectively using Ga/Ta complex ions and Ce ions, respectively. Phase analysis confirms that both materials retain a single-phase cubic perovskite structure. Notably, the B-site doped ceramic develops exceptionally large grains, which elevate its quality factor (Q×f) beyond 10,000 GHz despite incomplete densification, underscoring the dominant role of grain size. With Ce incorporation, a dense microstructure is achieved, accompanied by a marked reduction in Ti3+ content. Crucially, DFT calculation verifies that the valence transition of Ce, in synergy with the Ga/Ta complex ions, creates a cooperative electron-pinning effect that localizes free electrons and markedly suppresses Ti4+ reduction. This synergistic mechanism boosts the Q×f value to over 15,000 GHz. Furthermore, by coordinating the reduction in ionic polarizability with enhanced octahedral distortion, the dielectric constant (ε_r) is maintained above 120 while the temperature coefficient (τ_f) is drastically improved from +1431 ppm/°C to +336 ppm/°C. Therefore, at a Ce doping level of 0.25, the co-doped material exhibits outstanding comprehensive performance: ε_r = 128.8, Q×f = 15,919 GHz, and τ_f = +381 ppm/°C. This study demonstrates the considerable potential of a rational co-doping strategy for enhancing material properties.