Synthesis Of Na_0.5tio₃ Powders Through Hydrothermal Method And The Investagation Of Effect Factors On The Morphology

Sodium bismuth titanate,Na0.5Bi0.5TiO3 (NBT),is considered to be an excellent candidate for use in leadfree piezoelectric ceramics.However, due to the high coercive field, it's difficult to polarize the NBT ceramic sufficiently. Thus, most researchers focus on the improvement of piezoelectric properties from two aspects. One is through substitution of NBT in A and B site and the other is to develop new synthesis methods.Synthesis of ceramic powder through hydrothermal method has gained considerable popularity because it has potential to yield high-purity, homogeneous,fine crystalline powders at moderate conditions.Therefore, hydrothermal method has been chosen to synthesis of NBT powders.In this study, Ti(OC4H9)4 and TiCl4 were used as titanium resources,respectively, and many kinds of morphologies had been got through changing reactive parameters. The effect of reactive parameters on the powders morphologies were studied, including solvent type, NaOH concentration, reaction temperature, reaction time, Ti/ Bi molar ratio,reagent concentration and precipitant type, and the reaction mechanisms also been discussed. The results are listed as follows.1)Ti(OC4H9)4 was used as titanium resources, increase the concentration of NaOH, or reaction temperature, or reaction time could improve the crystallinity of NBT powders.2) TiCl4 was used as titanium resources and many kinds of NBT morphologies had been got through changing reactive parameters in hydrothermal method. In the hydrothermal process, within a certain rage, increase of NaOH concentration, or reaction temperature, or Ti/Bi molar ratio,or start reagent concentration, the morphology of obtained NBT powders changed from spherical shape to the mixture of spherical/cubic shape as well as nariowhisker-like shape.3)Two mechanisms of In situ transformation and dissolution and recrystallization were proposed for the hydrothermal reactions.The two mechanisms affect the morphology of the NBT product by influencing the supersaturation of the hydrothermal system.When the supersaturation was in low level (less than the critical supersaturation),in situ transformation was dominant, the product was mainly spherical particles;When the supersaturation was in high level (more than the critical supersaturation),dissolution and recrystallization mechanism was dominant, the product include spherical and cubic particles as well as nanowhiskers.4) There were other factors such as reaction time, precipitant type and solvent type which contribute to the morphology of the final hydrothermal products.In this process,prolong of reaction time could improve the recrystallization of NBT powders, which could make the size of the products even. Besides, precipitant and solvent also play an important role in the process, which affect the morphology of precursor, and then influence the morphology of product.