Relationship between the structure and microwave dielectric properties of garnet ceramics Ca3B2GeV2O12 (B = Mg, Mn)

Two garnet-structured ceramics, Ca3B2GeV2O12 (B = Mg, Mn), were synthesized using a traditional solid-state reaction method, and their sintering behavior, structures, vibrational spectra, and magnetic and microwave dielectric properties were characterized. Low permittivity (er) of 9.75 (Ca3Mg2GeV2O12) and 11.06 (Ca3Mn2GeV2O12), quality factor (Q x f) of 54,000 GHz (Ca3Mg2GeV2O12) and 30,240 GHz (Ca3Mn2GeV2O12), and temperature coefficient of resonant frequency (Tf) of -61.2 ppm/degrees C (Ca3Mg2GeV2O12) and -66.4 ppm/degrees C (Ca3Mn2GeV2O12) were obtained. The er value was correlated with the sum of the ionic polarization per unit volume. The Q x f value was associated with the part with a fully filled 3d orbit, un-paired d electrons of B-site ion, and magnetic loss. The Tf was correlated to the bond valance at the A- and C-sites. Moreover, the fitting analysis of the far-infrared reflectance spectra of Ca3Mg2GeV2O12 revealed that the active vibration modes in the low wave number range (100 - 400 cm-1) contributed mainly to the intrinsic microwave dielectric polarization.