The Li 2 Mg 3 Ti 1 − x Al 4 x /3 O 6 (0 ≤ x ≤ 0.1) ceramics are synthesized using the solid phase method, showing excellent microwave dielectric properties with ε r = 14.05, Q × f = 144 500 GHz, and τ f = −43 ppm/°C at x = 0.04. Rietveld refinements, based on the XRD data, reveal that the Li 2 Mg 3 Ti 1 − x Al 4 x /3 O 6 ceramics crystallize in the rock salt structure with Fm-3m space group. The relationship between the crystal structure and intrinsic microwave dielectric properties is studied in detail. The variation in...