Low temperature sintering process, phase evolution and dielectric properties of BaTi₄O₉-filled B–La–Mg–Ti–O glass/ceramic composites

Low temperature co-fired ceramics composite is fabricated by mixing B₂O₃–La₂O₃–MgO–TiO₂ (BLMT) glass matrix with BaTi₄O₉ ceramic filler and the influence of the filler on sintering behavior, phase composition, microstructure and dielectric properties of the composite is investigated. The results show that the densification of composites can be achieved at 860 °C for 20 min by three-stage reactive liquid assisted sintering process, consisting of glass redistribution and local grains rearrangement, viscous flow, and solid state sintering and closure of pores. The XRD patterns exhibit that the main phase of all samples is LaBO₃ phase formed from the crystallization of BLMT glass and the secondary phases have changed due to chemical reaction between BLMT glass and BaTi₄O₉ forming two new phases BaTi(BO₃)₂ and TiO₂ during sintering. Meanwhile, the microstructure results indicate that the reaction helps to eliminate the closed pores in composites. As the filler is increased, the dielectric constant and quality factor firstly increases and then decreases, while the temperature coefficient of resonant frequency increases. Typically, the 30 wt% BaTi₄O₉-filled BLMT glass composite sintered at 860 °C for 20 min displays dielectric properties of εε_r = 20.49, Q × f = 24000 GHz and ττ_f = +145 ppm/°C.