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

Novel BaZr(Si 1- x Ge x ) 3 O 9 (0 ≤ x  ≤ 1.0) microwave dielectric ceramics were prepared by solid-state reaction sintering at 1200–1450 °C for 5 h Ge 4+ ions occupied the Si 4+ positions, and BaZr(Si 1- x Ge x ) 3 O 9 solid solutions were obtained. The BaZr(Si 1- x Ge x ) 3 O 9 (0 ≤ x  ≤ 1.0) ceramics exhibited hexagonal structures with P -6 c 2 space groups and octahedral layers and [Si/Ge 3 O 9 ] 6- rings. Owing to these structural characteristics, the ceramics exhibited low permittivity. With an increase in x , the relative permittivity ( ε r ) values of the BaZr(Si 1- x Ge x ) 3 O 9 (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 BaZrSi 3 O 9 ( x  = 0) ceramic improved with the substitution of Si 4+ by Ge 4+ . A high Q  ×  f value (36,100 GHz at 13.81 GHz) was obtained for the BaZr(Si 1- x Ge x ) 3 O 9 ( x  = 0.2) ceramic, and the Q  ×  f values of the BaZr(Si 1- x Ge x ) 3 O 9 ceramics could be controlled by varying the Si/Ge-site bond valence. The temperature coefficient of resonance frequency (τ f ) values of the BaZr(Si 1- x Ge x ) 3 O 9 ceramics were mainly affected by the O2-site bond valence, and the optimum τ f value (−22.8 ppm/°C) was achieved for the BaZrSi 3 O 9 ceramic. The BaZr(Si 1- x Ge x ) 3 O 9 ( x  = 0.2) ceramic showed the optimum microwave dielectric properties ( ε r  = 8.36, Q  ×  f  = 36,100 GHz at 13.81 GHz, and τ f  = −34.5 ppm/°C).