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

Two novel low- ε r Ca 3 Mg 2 CV 2 O 12 (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 ( ε r = 9.70, Q × f = 35,680 GHz, and τ f = −60.1 ppm/°C for Ca 3 Mg 2 SiV 2 O 12 ceramic; ε r = 11.70, Q × f = 48,530 GHz, and τ f = −43.7 ppm/°C for Ca 3 Mg 2 TiV 2 O 12 ceramic) were obtained at 1240 °C and 1260 °C, respectively. The bond valence calculations reveal that Ca 2+ at the A-site and Mg 2+ at the B-site are slightly compressed, in combination with “rattling” Si 4+ and “compressed” V 5+ in the C-site of Ca 3 Mg 2 SiV 2 O 12 compared to “rattling” V 5+ and “compressed” Ti 4+ in Ca 3 Mg 2 TiV 2 O 12 , resulting in a negative deviation of −7.16% for Ca 3 Mg 2 SiV 2 O 12 and a positive value of 5.66% for Ca 3 Mg 2 TiV 2 O 12 between the porosity corrected ε r (Corr) (10.11 and 11.95) and theoretical ε th (10.89 and 11.31) calculated by the C-M equation. The overall “rattling” effect in Ca 3 Mg 2 TiV 2 O 12 results in a higher ε r and a nearer to zero τ f compared to Ca 3 Mg 2 SiV 2 O 12 . Besides, the Q × f values of Ca 3 Mg 2 CV 2 O 12 (C = Si, Ti) ceramics were correlated with relative density and Raman mode (A 1g ).