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

Apatite structure of CaLa 4 Si 3 O 13 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 CaLa 4 Si 3 O 13 belonged to a hexagonal structure with space group of P 6 3 / 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 SiO 4 tetrahedral units were discussed by Raman spectra. Excellent microwave dielectric properties were obtained with ε r  = 14.5, Q × f = 31,100 GHz (at 9.05 GHz), τ f  = −22 ppm/°C, indicating possible potential applications for microwave substrate applications.