Crystal structures, chemical bond features and Raman vibrations of Li₂Co₂Mo₃O₁₂ microwave dielectric ceramics with low sintering temperature

Abstract

Li₂Co₂Mo₃O₁₂ (LCMO) ceramics were synthesized using the solid‐state reaction method. XRD analysis results indicated that the sole crystalline phase present in the ceramics was Li₂Co₂Mo₃O₁₂, which belongs to the orthorhombic structure of the Pnma space group. The sample, which was sintered at 850°C, demonstrated outstanding microwave dielectric properties, with an ε_r value of 8.95, a Q × f value of 43200 GHz, and a τ_f value of ‐71.3 ppm/°C. It was found that while the main factor influencing ε_r was ionic polarizability, sintering density had a lesser effect on it. Furthermore, Q × f was primarily affected by relative density, and there was no significant relationship between packing fraction and this property. The higher the degree of distortion of [Li/CoO₆] octahedron, the poorer the τ_f value of LCMO ceramics. Additionally, the microwave dielectric properties of LCMO ceramics were intrinsically linked to ionicity, lattice energy, bond energy, and thermal expansion coefficient of chemical bonds, with Mo‐O bonds being the primary factor affecting these properties as supported by analysis using chemical bonding theories. Mo‐O bond vibration dominated the Raman spectra. Good chemical compatibility between silver and LCMO ceramics was demonstrated through our co‐firing experiment.

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