Structure, bond features, and microwave dielectric properties of Li2(Mg1−xCax)2(MoO4)3 ceramics for ULTCC application

Ultra‐low temperature sintered ceramics, Li2(Mg1−xCax)2(MoO4)3 (x = 0.025–0.100), were synthesized using the solid‐phase method. XRD analysis revealed that adding Ca2+ increased the second‐phase CaMoO4 content. Particularly, Li2(Mg0.975Ca0.025)2(MoO4)3 ceramics exhibited excellent properties: εr = 9.31, Q × f = 55,400 GHz, and τf = −38.9 ppm/°C. Incorporating Ca2+ significantly improved the performance of ceramics. The microwave dielectric properties of Li2(Mg0.9Ca0.1)2(MoO4)3 ceramics sintered at 650°C showed enhancements: εr of 9.55, Q × f of 63,500 GHz, and τf of −10.8 ppm/°C. The rise in εr can be attributed to polarizability, while a higher packing fraction led to a larger Q × f value, and the reduced distortion of the [Li/Mg/CaO6] octahedra enhanced the τf value. Moreover, the increased of CaMoO4 also positively influenced the ceramic's properties. Furthermore, in accordance with the principles of complex chemical bonding, the elevation of ionicity, lattice energy, and bond energy of the Mo–O bond contributed to the enhancement of εr, Q × f, and τf, respectively. Raman spectroscopy showed a positive correlation between dielectric loss and full width at half maximum of the Raman peak. Good chemical compatibility between silver and Li2(Mg0.9Ca0.1)2(MoO4)3 ceramic was demonstrated through our co‐firing experiment.