KF-doped BaTi2O5 ferroelectric ceramics by solid-state reaction of KF and sol–gel-derived BaTi2O5 powders

We report KF-doping work on the recently found ferroelectric material BaTi2O5. The ceramic samples, Ba1-xKxTi2O5-xFx, were synthesized by solid-state reaction of mixed KF and sol–gel-derived BaTi2O5 powders at 1150 °C. An almost pure phase was obtained for nominal composition x≤0.097, while electron probe microanalysis indicated that the real incorporated K and F contents were less than half of the nominal values. It was observed that KF-doping is beneficial in enhancing the ceramic density to some extent, which is a key issue in sol–gel-derived BaTi2O5 ceramics, due to a possible liquid-phase sintering mechanism through the presence of melted KF at the sintering temperature. Scanning electron microscopy images showed that these porous ceramic samples are composed of sub-micron-sized powder aggregates which, with increasing KF-doping, undergo further agglomeration. Dielectric measurement from room temperature to ∼ 560 °C showed a broad ferroelectric phase transition, with TC ∼ 430 °C for the undoped sample. As KF-doping increases, TC decreases, and the magnitude of the dielectric constant maximum also displays a decreasing trend. The strongly reduced dielectric response can be partly understood by regarding the porous ceramic sample as a composite material composed of bulk BaTi2O5 and air, where the porosity has a significant influence on the effective dielectric constant.