Abstract: Selective ion doping is a promising approach to boost dielectric properties in perovskite ceramics. However, challenges remain in leveraging the clash of the dielectric properties with the dielectric constant and quality factor. To balance this trade-off, A/B-site co-doping could be a potentially ideal solution. Unfortunately, effective co-doping strategies have been overlooked owing to the absence of rational A-site cation selection, significantly hindering the optimization of material properties. Here, we fabricated Sr_1-1.5xCe_xTi_1-y(Al_0.5Ta_0.5)_yO₃ co-doped materials with varying compositions using Ce at the A-site and Al/Ta at the B-site. A controlled decrease in ionic polarizability coupled with enhanced octahedral distortion enables the material to maintain an ε_r> 110 while significantly lowering the τ_f from +1472 to +330 ppm/°C. The markedly suppressed Ti⁴⁺ reduction elevates the overall quality factor beyond 15,000 GHz, while a substantial rise in lattice and bond energy confirms the reduction of intrinsic loss in the material. Most importantly, a comparison with La-co-doped samples exhibiting similar phase composition and microstructure reveals that the valence transition of Ce and synergistic electron pinning effect with Al/Ta effectively immobilizes free electrons, significantly suppressing carrier migration and thereby enhancing the dielectric properties of the material. Benefiting from the synergistic effect, Sr_0.625Ce_0.25Ti_0.95(Al_0.5Ta_0.5)_0.05O₃ achieved excellent properties with ε_r=127, Q×f=16,367 GHz and τ_f=+380 ppm/°C. A miniaturized cylindrical dielectric resonator antenna was also designed, maintaining high performance with reduced size and demonstrating significant application potential. This work demonstrates that the rational A/B-site co-doping is an advanced method for the development of high-performance microwave dielectric ceramics and enables miniaturized device applications.

Key words: Dielectric constant, Co-doping, Octahedral distortion, Synergistic effect, DFT calculation