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

(1- x )MgAl 2 O 4 - x MgTa 2 O 6 composite ceramics based on the MgO-Al 2 O 3 -Ta 2 O 5 pseudoternary phase diagram were prepared by the solid-state reaction. MgAl 2 O 4 and MgTa 2 O 6 could coexist due to their different crystal structures. MgAl 2 O 4 inhibited the rapid growth of MgTa 2 O 6 grains, and dense microstructures ( ρ  > 95%) with a uniform grain size distribution was obtained, with an optimal densification temperature of 1550 - 1575 °C. The temperature coefficient of resonant frequency ( τ f ) and quality factor ( Q × f ) were optimized by introducing MgTa 2 O 6 phases with low dielectric loss and positive τ f . In addition, the partial solid solutions of Al 3+ into Ta 5+ sites resulted in loosening bonds within [Al/TaO 6 ] octahedra and abnormally large polarizabilities, which was confirmed by the decrease in V Ta-O and the redshift of A 1 g (Ta-O) mode. Consequently, the relative permittivity ( ε r ) and τ f values o f MgAl 2 O 4 -MgTa 2 O 6 composite ceramics were further enhanced, exceeding the predicted ones. The 0.6MgAl 2 O 4 -0.4MgTa 2 O 6 composition sintered at 1550 °C achieved excellent performance, with a near-zero τ f value of 3.3 ± 1.7 ppm/°C, a low ε r of 16.4 ± 0.3 and an ultra-high Q × f 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.