Microstructure characteristics and microwave dielectric properties of calcium apatite ceramics as microwave substrates

Apatite structure of CaLa4Si3O13 ceramics was prepared by the conventional solid-state reaction route. The Rietveld refinement of powder X-ray diffraction (XRD) and analysis of scanning electron microscope images demonstrated that CaLa4Si3O13 belonged to a hexagonal structure with space group of P63/m (No. 176) and grew in a shape of hexagonal prism. The effects of crystallinity, porosity, grain morphology, grain size distribution, and oxygen vacancy on the microwave dielectric properties were investigated in detail as a function of sintering temperature. The existence of Oxygen vacancies and the stretching and bending modes of SiO4 tetrahedral units were discussed by Raman spectra. Excellent microwave dielectric properties were obtained with εr = 14.5, Q × f = 31,100 GHz (at 9.05 GHz), τf = −22 ppm/°C, indicating possible potential applications for microwave substrate applications.