Crystal structure and microwave dielectric properties of α-(Ca1-Sr ) SiO3 (x= 1 and 0.8) ring silicates for millimeter-wave applications

Millimeter-wave wireless communications in a high-level information society have been expanding in terms of high-density data transfer and radar for pre-crash safety systems. α-wollastonite (CaSiO 3 ) based and SrSiO 3 based solid solutions (s.s.) in the CaSiO 3 -SrSiO 3 eutectic binary system are expected as millimeter-wave dielectrics because of low dielectric constant as described in a previous paper. In this paper, crystal structures of SrSiO 3 and Ca 0.2 Sr 0.8 SiO 3 compounds are analyzed by Rietveld method using X-ray powder diffraction (XRPD) patterns obtained at the PF-KEK, Tsukuba, Japan. Covalencies of Si O bonds are calculated through the bond strength obtained by the bond length, which at x = 0.8 were higher than that of at x = 1 as (Ca 1- x Sr x )SiO 3 . The lowest dielectric constant ( e r ) and highest Qf value at x = 0.8 with e r = 6.62, Qf = 66,700 GHz and τ f = –40 ppm/°C were explained by the covalencies.