Spinel-trirutile microwave dielectric ceramics with high Q and excellent temperature stability based on MgO-Al₂O₃-Ta₂O₅ ternary systems

(1-x)MgAl2O4-xMgTa(2)O(6) composite ceramics based on the MgO-Al2O3-Ta2O5 pseudoternary phase diagram were prepared by the solid-state reaction. MgAl2O4 and MgTa2O6 could coexist due to their different crystal structures. MgAl2O4 inhibited the rapid growth of MgTa2O6 grains, and dense microstructures (rho > 95%) with a uniform grain size distribution was obtained, with an optimal densification temperature of 1550 - 1575 degrees C. The temperature coefficient of resonant frequency (tau(f)) and quality factor (Qxf) were optimized by introducing MgTa2O6 phases with low dielectric loss and positive tau(f). In addition, the partial solid solutions of Al3+ into Ta5+ sites resulted in loosening bonds within [Al/TaO6] octahedra and abnormally large polarizabilities, which was confirmed by the decrease in VTa-O and the redshift of A(1 g)(Ta-O) mode. Consequently, the relative permittivity (epsilon(r)) and tau(f) values o(f) MgAl2O4-MgTa2O6 composite ceramics were further enhanced, exceeding the predicted ones. The 0.6MgAl(2)O(4)-0.4MgTa(2)O(6) composition sintered at 1550 degrees C achieved excellent performance, with a near-zero tau(f) value of 3.3 +/- 1.7 ppm/degrees C, a low epsilon(r) of 16.4 +/- 0.3 and an ultra-high Qxf of 179,000 +/- 6700 GHz @ 8.94 +/- 0.04 GHz. These findings hold promising applications in the field of 5 G/6 G high-frequency communication.