Evolution of Phase Transformation on Microwave Dielectric Properties of BaSixO1+2x Ceramics and Their Temperature-Stable LTCC Materials

BaSixO1+2x (1.61 ≤ x ≤ 1.90) and LiF-doped BaSi1.63O4.26 ceramics were prepared by using a traditional solid-state method at the optimal sintering temperatures. The evolution of phase compositions of BaSixO1+2x (1.61 ≤ x ≤ 1.9) ceramics was revealed. The coexistence of Ba5Si8O21 and Ba3Si5O13 phases was obtained in BaSixO1+2x (1.61 ≤ x ≤ 1.67) ceramics. The BaSi2O5 phase appeared inBaSixO1+2x (1.68 ≤ x ≤ 1.90) ceramics. At 1.68 ≤ x ≤ 1.69, only BaSi2O5 and Ba3Si5O13 phases existed. With the further increase in x, the Ba5Si8O21 phase appeared, and BaSi2O5, Ba5Si8O21 and Ba3Si5O13 phases coexisted in BaSixO1+2x (1.70 ≤ x ≤ 1.90) ceramics. The phase compositions of BaSixO1+2x (1.61 ≤ x ≤ 1.90) ceramics were controlled by the ratio of Ba:Si. The BaSixO1+2x (x = 1.68) ceramics with 98.15 wt% Ba3Si5O13 and 1.85 wt% BaSi2O5 phases exhibited a negative τf value (−37.53 ppm/°C), and the good microwave dielectric properties of εr = 7.51, Q × f = 13,038 GHz and τf = +3.95 ppm/°C were obtained for BaSi1.63O4.26 ceramics with 70.05 wt% Ba5Si8O21 and 29.95 wt% Ba3Si5O13 phases. The addition of LiF sintering aids were able to reduce the sintering temperatures of BaSi1.63O4.26 ceramics to 800 °C. The phase composition of BaSi1.63O4.26 ceramics was affected by the sintering temperature, and the coexistence of Ba5Si8O21, Ba2Si3O8, BaSi2O5 and SiO2 phases was achieved in BaSi1.63O4.26-3 wt% LiF ceramics. The BaSi1.63O4.26-3 wt% LiF ceramics sintered at 800 °C exhibited dense microstructures and excellent microwave dielectric properties (εr = 7.10, Q × f = 12,463 GHz and τf = +5.75 ppm/°C), and no chemical reaction occurred between BaSi1.63O4.26-3 wt% LiF ceramics and the Ag electrodes, which indicates their potential for low-temperature co-fired ceramic (LTCC) applications.