Crystal structure, far-infrared spectra, and microwave dielectric properties of bazirite-type BaZr(Si1-Ge )3O9 ceramics

Abstract

Novel BaZr(Si1-xGex)3O9 (0 ≤ x ≤ 1.0) microwave dielectric ceramics were prepared by solid-state reaction sintering at 1200–1450 °C for 5 h Ge4+ ions occupied the Si4+ positions, and BaZr(Si1-xGex)3O9 solid solutions were obtained. The BaZr(Si1-xGex)3O9 (0 ≤ x ≤ 1.0) ceramics exhibited hexagonal structures with P-6c2 space groups and octahedral layers and [Si/Ge3O9]6- rings. Owing to these structural characteristics, the ceramics exhibited low permittivity. With an increase in x, the relative permittivity (εr) values of the BaZr(Si1-xGex)3O9 (0 ≤ x ≤ 1.0) ceramics increased from 7.68 (x = 0) to 9.45 (x = 1.0), while their quality factor (Q × f) values first increased and then decreased. The Q × f value (10,300 GHz at 13.43 GHz) of the BaZrSi3O9 (x = 0) ceramic improved with the substitution of Si4+ by Ge4+. A high Q × f value (36,100 GHz at 13.81 GHz) was obtained for the BaZr(Si1-xGex)3O9 (x = 0.2) ceramic, and the Q × f values of the BaZr(Si1-xGex)3O9 ceramics could be controlled by varying the Si/Ge-site bond valence. The temperature coefficient of resonance frequency (τf) values of the BaZr(Si1-xGex)3O9 ceramics were mainly affected by the O2-site bond valence, and the optimum τf value (−22.8 ppm/°C) was achieved for the BaZrSi3O9 ceramic. The BaZr(Si1-xGex)3O9 (x = 0.2) ceramic showed the optimum microwave dielectric properties (εr = 8.36, Q × f = 36,100 GHz at 13.81 GHz, and τf = −34.5 ppm/°C).