Compositional design, structure stability, and microwave dielectric properties in Ca3MgBGe3O12 (B = Zr, Sn) garnet ceramics with tetravalent cations on B-site

Two garnet-structured Ca 3 MgBGe 3 O 12 (B = Zr, Sn) ceramics with tetravalent cations at B-site were prepared by conventional solid state reaction. The crystal structure, microstructure evolution, and microwave dielectric performance were investigated using X-ray powder diffraction, Rietveld refinement , scanning electron microscopy, Raman spectroscopy , and infrared spectroscopy techniques . Dense Ca 3 MgZrGe 3 O 12 and Ca 3 MgSnGe 3 O 12 ceramics were obtained at sintering temperatures of 1420 and 1400 °C, respectively. The dielectric constant, unloaded quality factor, and temperature coefficient of resonance frequency of Ca 3 MgZrGe 3 O 12 were 10.80 ± 0.2; 79,600 ± 1000 GHz ( f  = 12.61 GHz); and −66.8 ± 1 ppm/°C, respectively, and the corresponding values for Ca 3 MgSnGe 3 O 12 were 9.68 ± 0.2; 83,400 ± 1000 GHz ( f  = 14.19 GHz); and −57.9 ± 1 ppm/°C, respectively. The dielectric performances of the two ceramics were compared by analyzing the ionic polarizability, packing fraction, and bond valence. The intrinsic dielectric properties were predicted by fitting the infrared reflectivity spectra.