Crystal structure, sintering characteristics, and dielectric properties of low-permittivity garnet-type Ca1.5Y1.5Al3.5Si1.5O12 microwave ceramics

Garnet-structured ceramics are of particular strategic importance in the development of wireless communications due to their complex elemental composition and high quality factor and frequency ( Q × f ) values. In this paper, an investigation is conducted into the composition-optimized garnet-structured Ca 1.5 Y 1.5 Al 3.5 Si 1.5 O 12 , which was demonstrated by X-ray diffraction analyses to be a pure phase that is well-matched with PDF#00-033-0040 throughout the entire sintering temperature interval. Rietveld refinement has confirmed the garnet structure of the sample, which is consistent with the space group of Ia-3d . The sample prepared at 1465 °C exhibited highest bulk density (3.81 g cm −3 ), relative density (94.49 %) and excellent performances, including relative permittivity ( ε r ) = 8.34, Q × f = 41,616 GHz, and temperature coefficient of resonance frequency ( τ f ) = −43.6 ppm/°C. Furthermore, the packing fraction and the full width at half maximum of the T 2g Raman spectra are found to be highly correlated with the Q × f values. It is also evident that the Al(2)/Si-O bond valence exerts an influence on the τ f values of the samples. In conclusion, the Ca 1.5 Y 1.5 Al 3.5 Si 1.5 O 12 ceramics demonstrate considerable potential for further development and application in wireless communication devices.