Mg3B2O6 microwave dielectric ceramics fabricated by combining cold sintering with post-annealing process

It is difficult to get pure-phase Mg3B2O6 (abbreviated as MBO) ceramics by the traditional high-temperature solid-state reaction method. In this paper, pure-phase MBO ceramics were successfully densified and obtained by combining the cold sintering and post-annealing process. The relative density of MBO ceramics was similar to 80% cold sintered at 150 degrees C/90 min/800 MPa, which was further improved to similar to 91% by post-annealing at 900 degrees C, 400 degrees C lower than that of the traditional high-temperature sintering process (similar to 1300 degrees C). X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and Raman results demonstrated that the secondary phase of MgO was effectively eliminated, and dense microstructure was observed by the cold-sintering process plus post-annealing treatment. Finally, the microwave dielectric properties of MBO were evaluated with epsilon(r): 5.15-6.37, Qxf: 5942-16 686 GHz, tau(f): -48.45-69.72 ppm/degrees C.