Structure, bond features, and microwave dielectric properties of Li ₂ (Mg ₁₋ <i> _x </i> Ca <i> _x </i> ) ₂ (MoO ₄ ) ₃ ceramics for ULTCC application

Abstract Ultra‐low temperature sintered ceramics, Li 2 (Mg 1− x Ca x ) 2 (MoO 4 ) 3 ( x = 0.025–0.100), were synthesized using the solid‐phase method. XRD analysis revealed that adding Ca 2+ increased the second‐phase CaMoO 4 content. Particularly, Li 2 (Mg 0.975 Ca 0.025 ) 2 (MoO 4 ) 3 ceramics exhibited excellent properties: ε r = 9.31, Q × f = 55,400 GHz, and τ f = −38.9 ppm/°C. Incorporating Ca 2+ significantly improved the performance of ceramics. The microwave dielectric properties of Li 2 (Mg 0.9 Ca 0.1 ) 2 (MoO 4 ) 3 ceramics sintered at 650°C showed enhancements: ε r of 9.55, Q × f of 63,500 GHz, and τ f of −10.8 ppm/°C. The rise in ε r 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/CaO 6 ] octahedra enhanced the τ f value. Moreover, the increased of CaMoO 4 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 ε r , Q × f , and τ f , 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 Li 2 (Mg 0.9 Ca 0.1 ) 2 (MoO 4 ) 3 ceramic was demonstrated through our co‐firing experiment.