FABRICATION OF BA5NB4O15 CERAMICS BY FLUX-ASSISTED ULTRA-LOW SINTERING TEMPERATURE TECHNIQUE

Ba5Nb4O15 ceramic is a promising dielectric material for microwave frequencies. One of the factors that affects its dielectric properties is density, which can be controlled by fabrication processes such as sintering. Normally, conventional sintering requires high sintering temperature (T?> 1,200ºC) to produce grain coarsening and pore reduction which consumes high energy. However, there has been growing interest in low-temperature ceramic processing due to its potential to revolutionize the way ceramic materials are manufactured. Cold sintering is a new sintering technique that can be used to fabricate dense ceramics below 300°C. It can be applied to a variety of compounds, and the densification process is driven by the dissolution-precipitation mechanism, with the aid of a congruent solvent, pressure, and temperature. Herein, Ba5Nb4O15 ceramics are prepared by cold sintering technique using hydrated barium hydroxide (Ba(OH)2-8H2O) as a flux to reduce sintering temperature and introduce densification process. The effects of processing parameters, including sintering temperature, dwelling time, pressure, and flux concentration, on the density and dielectric properties of sintered samples were investigated. Phase formation and electrical properties were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and an LCR meter. Under the sintering conditions T = 150°C, pressure = 7,000 kPa, and t = 60 min, the obtained Ba5Nb4O15 ceramic exhibited a relative density of ˜80% which closes to the ceramics obtained from conventional sintering. These results suggest that sintering temperature has little influence on sample density, while applied pressure is the dominant factor in improving density. The mechanism of flux-assisted cold sintering and dielectric properties are also discussed.