Sol-hydrothermal synthesis of Na_0.5Bi_0.5TiO₃ powders and corresponding ceramics prepared by traditional and flash sintering

In this paper, a new wet chemical route named sol-hydrothermal method was used to synthesize Na_0.5Bi_0.5TiO₃ (NBT) nanopowders. The effects of hydrothermal reaction conditions such as temperature, time and NaOH concentration on the properties of the powder were studied in detail. The results showed that as-synthesized NBT powders with were perovskite structure with rhombohedral symmetry and had submicron size (200 nm ∼ 800 nm). The morphology of NBT powders was mainly spherical and they had good dispersibility. NBT powders with homogeneous size and pure phase were synthesized under the optimum condition of hydrothermal reaction at 200 °C for 24 h. It is worth noting that pure NBT ceramic could not be obtained by traditional sintering at 1100 °C for 2 h. However, the relatviely dense ceramic with a relative density of 95.8% and an apparent porosity of 1.8% was obtained by electric field assisted flash sintering for only 3 s at 700 °C. Therefore, the very short time flash sintering method was suitable for the preparation of volatile NBT ceramic. In particular, a mechanism named Electric Field Assisted Solid Crystal Growth (EFASCG) was proposed to explain sintering process.