Phase composition, crystal structures and enhanced microwave dielectric properties of Mg2+/Zr4+ co-doped Al2Mo3O12 ceramics

In this work, the substitution of Al3+ by Zr/Mg in Al2Mo3O12 was designed to enhance the quality factor while simultaneously adjusting the thermal stability of the resonant frequency. The Al2-2x(Zr0.5Mg0.5)2xMo3O12 (AMZM) (0.1 ≤ x ≤ 0.5) ceramics were synthesized using a simple solid-state method, resulting in all components exhibiting single-phase crystallinity and a dense structure. A phase transition temperature below room temperature was observed when x ≥ 0.4. Furthermore, the quality factor of the synthesized samples, compared to pure-phase Al2Mo3O12 (εr = 6.79, Q×f = 28471 GHz, τf = -48.77 ppm/℃), increased by nearly threefold. A detailed investigation of the crystal structure of the samples was conducted through Rietveld refinement. The composition with x = 0.3 (monoclinic phase) exhibited optimal dielectric performance after sintering at 800 ℃ for 6 h: εr = 7.84, Q×f = 86511 GHz, τf = -42.08 ppm/℃. By forming a composite ceramic with (Li1/2Sm1/2)MoO4, the negative τf value was further adjusted to near zero.