Tuning of microwave dielectric properties of garnets Ca3Mg2CV2O12 (C = Si, Ti) through compression and expansion effects

摘要

? 2022 Elsevier Ltd and Techna Group S.r.l.Two novel low-εr Ca3Mg2CV2O12 (C = Si, Ti) ceramics with the garnet structure were synthesized by a traditional solid-state reaction method. Rietveld refinements based on XRD patterns show both the compounds crystallized into a cubic structure with the Ia-3d space group. Outstanding microwave dielectric properties (εr = 9.70, Q × f = 35,680 GHz, and τf = ?60.1 ppm/°C for Ca3Mg2SiV2O12 ceramic; εr = 11.70, Q × f = 48,530 GHz, and τf = ?43.7 ppm/°C for Ca3Mg2TiV2O12 ceramic) were obtained at 1240 °C and 1260 °C, respectively. The bond valence calculations reveal that Ca2+ at the A-site and Mg2+ at the B-site are slightly compressed, in combination with “rattling” Si4+ and “compressed” V5+ in the C-site of Ca3Mg2SiV2O12 compared to “rattling” V5+and “compressed” Ti4+ in Ca3Mg2TiV2O12, resulting in a negative deviation of ?7.16% for Ca3Mg2SiV2O12 and a positive value of 5.66% for Ca3Mg2TiV2O12 between the porosity corrected εr(Corr) (10.11 and 11.95) and theoretical εth (10.89 and 11.31) calculated by the C-M equation. The overall “rattling” effect in Ca3Mg2TiV2O12 results in a higher εr and a nearer to zero τf compared to Ca3Mg2SiV2O12. Besides, the Q × f values of Ca3Mg2CV2O12 (C = Si, Ti) ceramics were correlated with relative density and Raman mode (A1g).