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

Abstract

BaSi_2-xAl_xO_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 Al³⁺ 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_iave) (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_1.98Al_0.02O_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 BaSi₂O₅ ceramics.