Study Of The Crystallization Of Sodium Niobate Powders

Sodium niobate (NaNbO3) has been drawing intensive interests among researchers and equipment designers during past decades due to its excellent electric and optical properties. A large number of studies show that physical and chemical properties of this material deeply depend on its microscopic morphologies, chemical composition, crystal structures and surface properties. Therefore, it has always been a hot issue to fabricate NaNbO3 powers through facile, environmentally friendly and easily controllable methods, and analyze reaction mechanisms and crystallization process. Focusing on NaNbO3, a novel chemical approach is adopted in this dissertation based on hydrothermal treatments of a novel precursor in different reaction solutions to controllably fabricate NaNbO3 powders with multiple morphologies and surface characteristics.As a highly reactive precursor, niobate acid is designed and synthesized firstly, and then react with relatively dilute NaOH aqueous solution under hydrothermal conditions, taking advantage of selectively coordination of three bidentate organic ligands, i.e. ethylene glycol, ethylene diamine and ethanol amine. After reactions, NaNbO3 powders with cube-based multiple morphologies are obtained. Different organic solvents with different groups and their dosages have close relationship with the morphology of products because they differ in coordination capabilities on the surface of NaNbO3 microcrystals. Moreover, influences of hydrothermal reaction period, concentration of NaOH aqueous solution and different kind of precursor are also discussed. This method provides an effective approach to decorate surfaces and control morphologies of NaNbO3 microcrystals.NaNbO3 cubic microcrystals with concave surfaces are synthesized based on a hydrothermal reaction between niobate acid and NaOH in ethanol/water mixed solution. The experiment results indicate that the concentration of NaOH aqueous solution and the volumetric ratio of ethanol/water deeply impact the concave degree of surfaces; and the addition of several surfactants lead to different shapes of concave. A possible formation mechanism of these cubes with concave surfaces is presented. This result provides a referential example for the manufacture of high quality and defect-free NaNbO3 microcrystals.