Enhanced dielectric properties of tungsten bronze Ba6FeNb9O30 prepared by microwave hydrothermal method

In the present study, pure tungsten bronzes structural Ba6FeNb9O30 powders were synthesized by a standard solid-state reaction process (BFN-S) and a microwave hydrothermal method (BFN-W), respectively. The structure and dielectric properties of the BFN-S ceramics and BFN-W ceramics were investigated and discussed thoroughly. Comparing the two kinds of ceramics, the dielectric constant of BFN-W ceramics was significantly increased, while temperature stability also was improved. It was due to the larger degree of the octahedral tilting in BFN-W ceramics which had more polarization microregions and structural fluctuation and perturbation. The fluctuation of tetragonal tungsten bronze structure leads to differences in the sources and values of dielectric relaxation in BFN-S ceramics and BFN-W ceramics. The relaxation of BFN-S ceramics mainly originated from grain effect, and the relaxation of BFN-W ceramics mainly originated from the effect of grain boundary. Also, impedance spectra were analyzed to determine high dielectric constant contributions. In conclusion, grain boundaries become more insulated as compared to grains, so the enhanced dielectric response should be benefited from the strengthened grain boundary layer capacitor effect in BFN-W ceramics, thus the dielectric constant of BFN-W ceramics increased obviously. This paper provides an effective way to improve the dielectric constant and temperature stability of tungsten bronze structural ceramics. (c) 2018 Elsevier B.V. All rights reserved.