Phase evolution and enhanced Q×f in BaSi2O5 ceramics with Co2O3 substitution

Abstract

According to the chemical formula Ba1-xCoxSi2O5, low permittivity ceramics were prepared using BaCO3, Co2O3 and SiO2. Orthorhombic structured BaSi2O5 limited solid solution was obtained at x≤0.1. It coexisted with BaCo2Si2O7 and SiO2 in the range of 0.3≤x≤0.5. While x=0.7, the three-phase equilibrium was destroyed, accompanied by BaSi2O5 vanishing. At x=1, all Si existed in the form of Co2SiO4 and SiO2. Co2O3 melting decreased the sintering temperature from 1200 °C to 1025 °C. Because of the dielectric polarizability decrease, Co introduction brought in low dielectric constant εr. Notably, the quality factor Q×f was boosted to 60,340 GHz, which was almost 4 times than the original (∼16,526 GHz). This occurred because the intrinsic loss and extrinsic loss were significantly reduced by the average bond covalence increase and SiO2 generation (Q×f∼80,400 GHz), respectively. The variation of resonant frequency temperature coefficient τf was explained from the view of the change in the bond valence of oxygen. When x=0.5, the system with a high relative density of 98.63% exhibited superior microwave dielectric properties: εr=6.77, Q×f=60,340 GHz, and τf=-47.11 ppm/°C.