Hydrothermal Synthesis And Characterization Of BNT Lead-free Piezoceramics

With the development of human science and society, people pay more and more attention on environment protection. Lead-free piezoelectric ceramics become a "rising star" in the piezoelectric ceramic gradually, which get the attention of the researchers. For the deeply study of lead-free piezoelectric ceramics, more and more efforts have been made to develop lead-free piezoelectric ceramics to replace PZT based ceramics. Which will not only reduce the use of toxic lead and emissions, it can also make the green manufacture and green application come ture, and it will have a significant influence to sustainable development of eco-environment.Hydrothermal method is a kind of chemical synthesis method, there are many advantages than other methods, for example, the small grain size, good uniformity and a low reaction temperature and so on. In this paper, by controlling the mineralizer concentration of NaOH and reaction time, we successfully synthesize BNT nanostructures with plate-, cubic- and wire-like morphologies, and we describe the different growth mechanism of BNT nanocrystalline. The influence of different BNT nanocrystalline on BNT ceramics’ morphology and electrical properties, and the influence of diffrernt sintering temperature on BNT ceramics’ properties.Based on the growth behavior of nanocrystalline and thermomechanical analysis, There are two formation mechanisms used to explain the growth mechanism of BNT nanocrystalline in the hydrothermal reaction, one is an in situ transformation process, the other is a recrystallization mechanism. When the Na OH concentration is low, the particles grow along the preferential direction(a/b axis), which lead to formation of plate-like nanostructure. With the increase of NaOH concentration, the dissolution–crystallization dominates reaction process, resulting in the formation of cubic-like nanostructure. The formation of BNT nanowires needs not only a high NaOH concentration but a long enough reaction time. In a word, the concentration of NaOH plays a vital role in the morphology of BNT nanocrystalline.By studying the influence of different sintering temperature on BNT ceramics’ morphology and electrical properties, the BNT ceramic of plate-like nanostructure has the larger density, the bigger grain size, and good uniformity. As can be seen, the microstructure and grain size were strongly influenced by the NBT nanocrystalline morphologies, the BNT ceramic of plate-like nanostructure is conducive to formation of the homogeneous microstructure and well-grown grain. the BNT ceramic of plate-like nanostructure has the best electrical properties in three nanocrystallines, concluding the larger remnant polarization and dielectric constant, the optimized values of d33 were obtained for BNT ceramic of plate-like nanostructure, the d33=87 pC/N is superior to the reported values in the NBT system.Through the analysis of the influence of diffrernt sintering temperature on BNT ceramics’ properties, we find 1150℃ is the best sintering temperature, because under this sintering temperature, the BNT ceramic has the larger density, and the better electrical properties in the five sintering temperature.