Novel low-permittivity microwave dielectric ceramics in garnet-type Ca4ZrGe3O12

Abstract Novel low-permittivity microwave dielectric ceramics Ca4ZrGe3O12 with garnet structure were fabricated by a traditional solid-state route. A part of the Ca2+ cations are located at the octahedral sites, a quite unusual coordination for this cation in oxygen compounds. The structural characteristics and vibrational modes for the ceramics were studied based on structure refinement and Raman spectra analysis. Owning to the octahedral site is occupied by equivalent Ca2+ and Zr4+ simultaneously, the deviation between etheo and er could be related to the rattling effect of smaller Zr4+ in the octahedron. Optimum microwave dielectric properties were obtained for Ca4ZrGe3O12 ceramic sintered at 1340 °C with er = 10.68, Q × f = 76900 GHz, and τf = −41.3 ppm/°C.