Spinel Mg(Al, Ga) 2 O 4 Solid Solution as High‐Performance Microwave Dielectric Ceramics

Spinel Mg ( Al 1− x Ga x ) 2 O 4 ( x  =   0–1) solid solutions were synthesized via solid‐state method. Replacement of Al 3+ by Ga 3+ in MgAl 2 O 4 gave rise to the expansion of the lattice, as well as blueshifts of FT ‐ IR and Raman peaks. The homogeneous solid solutions, high relative densities, large grain sizes, and compact microstructures resulted in excellent microwave dielectric properties for spinel Mg ( Al 1− x Ga x ) 2 O 4 ( x  =   0.6) ceramics sintered at 1485°C: that is, ε r  = 8.87, Q × f = 107 000 GHz (at 14.8 GHz), and τ f  = −16 ppm/°C. Spinel‐structured Mg ( Al 1− x Ga x ) 2 O 4 ( x  =   0–1) solid solutions possessed low sintering temperatures, wide temperature regions (~100°C), and small negative τ f values. These outstanding performance make Mg ( Al , Ga ) 2 O 4 a promising candidate material for millimeter‐wave devices.