Effect of non-stoichiometry on the microstructure and microwave dielectric properties of Ca₅Mg_4+xV₆O₂₄ (− 0.05 ≤ x ≤ 0.15) ceramics

Ca₅Mg_4+xV₆O₂₄ (− 0.05 ≤ x ≤ 0.15) ceramics were prepared via a conventional solid-state reaction route. XRD patterns and Raman spectra confirmed that a single garnet phase was formed in all samples. The full-width-at-half maximum of Raman peaks revealed that an appropriate excess of magnesium ions improves the ordering degree of cations and quality factor (Q × f) value. The dielectric constant (ε_r) was closely correlated with the relative density and ion polarizability. The connections among the Q × f value, lattice energy, and packing fraction were discussed. As for the variation of the temperature coefficient of resonant frequency (τ_f), it was explained by the bond energy of V–O. Ca₅Mg_4+xV₆O₂₄ (x = 0.05) ceramic sintered at 825 °C achieved optimal microwave dielectric properties: ɛ_r = 9.93, Q × f = 56192 GHz, and τ_f = − 48.3 ppm/°C.