Modulation in sintering characteristics and microwave dielectric properties of Ca3Co2SiV2O12 via Li+ inequivalent substitution

Abstract

In this study, the inequivalent substitution of Ca²⁺ by Li⁺ in the Ca₃Co₂SiV₂O₁₂ compound was designed to modulate its sintering characteristics and microwave dielectric properties. The corresponding Ca_3–xLi_2xCo₂SiV₂O₁₂ (CCSV-xLi, 0.01≤ x ≤ 0.07) ceramics were prepared via the conventional solid-state phase method, which could be densely sintered at a temperature below 1140 °C. Rietveld refinement results suggested that all the doped Li occupied the Ca-site as x ≤ 0.05 while superfluous Li positioned at the Co-site of CCSV when x = 0.07. This atomic occupancy had a remarkable effect on the degree of “rattling effect” and thus modulated the relative permittivity of ceramics, constantly increasing at x = 0.01–0.05 and slightly decreasing at x = 0.07. Raman spectra revealed that Q×f value was closely related to Raman shift and FWHM. Also, the Q×f value was partly influenced by oxygen vacancy concentration. The τ_f demonstrated an opposite tendency to the bond valence of the A-site and was affected by the “rattling effect”. The CCSV-0.05Li ceramic sintered at 1120 °C possessed excellent microwave dielectric properties: ε_r = 12.17, Q×f = 56,220 GHz, and τ_f = −8.5 × 10⁻⁶ °C⁻¹.