Synthetic design and analysis on microwave dielectric properties of novel garnet-type Ca3MTiGe3O12 (M = Co, Ni) ceramics

In this paper, novel Ca 3 CoTiGe 3 O 12 (CCTG) and Ca 3 NiTiGe 3 O 12 (CNTG) ceramics with transition metal elements and Ti co-occupying the B-site were designed by calculating the tolerance factor of the garnet structure. CCTG and CNTG ceramics sintered at optimal temperatures exhibit excellent microwave dielectric properties with ε r = 11.64, Q×f = 45474.73 GHz, τ f = −42.01 ppm/°C and ε r = 11.58, Q×f = 41346.11 GHz, τ f = −45.53 ppm/°C, respectively. X-ray diffraction analysis shows that the CCTG is single phase while secondary phase is present in CNTG. The analysis of density and surface micromorphology for the ceramics synthesized in this study reveals that both possess high densities. Raman analysis shows that the half-width (FWHM) corresponding to the peak of the A 1g mode is closely related to the dielectric loss of both ceramics. The lattice energy and packing fraction are both critical factors that influence the Q×f value of CCTG ceramics. The influence of the secondary phase on the Q×f value of CNTG ceramics cannot be ignored. Both the bond valence and bond energy of the B-site cation are factors that affect τ f . In conclusion, the two ceramics studied in this paper have great application prospects in the field of microwave communications.