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

Two garnet-structured ceramics, Ca 3 B 2 GeV 2 O 12 (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 ( ε r ) of 9.75 (Ca 3 Mg 2 GeV 2 O 12 ) and 11.06 (Ca 3 Mn 2 GeV 2 O 12 ), quality factor ( Q  ×  f ) of 54,000 GHz (Ca 3 Mg 2 GeV 2 O 12 ) and 30,240 GHz (Ca 3 Mn 2 GeV 2 O 12 ), and temperature coefficient of resonant frequency ( τ f ) of −61.2 ppm/ ° C (Ca 3 Mg 2 GeV 2 O 12 ) and −66.4 ppm/ ° C (Ca 3 Mn 2 GeV 2 O 12 ) were obtained. The ε r value was correlated with the sum of the ionic polarization per unit volume. The Q  ×  f value was associated with the part with a fully filled 3 d orbit, un-paired d electrons of B-site ion, and magnetic loss. The τ f was correlated to the bond valance at the A- and C-sites. Moreover, the fitting analysis of the far-infrared reflectance spectra of Ca 3 Mg 2 GeV 2 O 12 revealed that the active vibration modes in the low wave number range (100 - 400 cm -1 ) contributed mainly to the intrinsic microwave dielectric polarization.