Crystal structure and microwave dielectric properties of Li-modified BaSi2O5 ceramics

Ba1-xLixSi2O5-x/2 (x = 0–0.5) ceramics were prepared by solid-state reaction method. The occupation tendency of Li+ was well explained based on First-principle calculation and unit cell volume changes. Li+ non-equivalent substitution for Ba2+ considerably reduced the sintering temperature to 975 °C, in comparison with 1225 °C for pure BaSi2O5. Single phase solid solution with orthorhombic structure was observed with x = 0–0.1. Nevertheless, trace amounts of unexpected secondary phases Li2Si2O5 and SiO2 were detected for higher Li-containing samples. Notably, the Q×f significantly enhanced up to 58.16% from 16,134 GHz (x = 0) to 25,518 GHz (x = 0.01), which predominantly depended on the structural characteristics, such as packing fraction and bond covalence. Increase x from 0 to 0.5 led to the reduction of dielectric constant εr from 7.11 to 5.95. The resonant frequency temperature coefficient τf was directly dominated by oxygen bond valence (VO), rather than VBa and VSi. Ba0.99Li0.01Si2O4.995 ceramic sintered at 1050 °C for 4 h exhibited a high Q×f value of 25,518 GHz, and the εr and τf values were 6.94 and −29.46 ppm/°C, respectively