Study of chemical bond characteristics and microwave dielectric properties in Al2O3-substituted BaSi2O5 ceramics

BaSi 2- x Al x O 5- x /2 ( x = 0-0.05) low-dielectric ceramics were prepared by the solid-phase method. The effects of heterovalent ion substitution on the crystal structure and microwave dielectric properties were studied. X-ray (XRD) diffraction revealed that they formed single-phase solid solution with orthorhombic structure. Appropriate amount of Al 3+ doping decreased the sintering temperature from 1225 °C to 1150 °C. The change in dielectric constant ( ε r ) resulted from the combined effects of the ionic nature of chemical bonds ( f i ave ) (internal factor) and the relative density (external factor). Si-O bonds contributed more significantly to the ceramic dielectric polarization. The increase in packing density and lattice energy ( U Total ) enhanced the quality factor ( Q×f ), which nearly tripled compared with the undoped case. The resonant frequency temperature coefficient ( τ ƒ ) was dominated by oxygen bond valence ( V o ). When sintered at 1150 °C for 4 h, BaSi 1.98 Al 0.02 O 4.99 exhibited optimal performance: ε r = 7.56, Q×f = 41,878 GHz, τ f = -17.65 ppm/°C. This study offered a new approach to modifying BaSi 2 O 5 ceramics.