Controllable Synthesis And Characterization Of Bi₄Ti₃O₁₂ Nanostructure By Hydrothermal/Solvothermal Methods

Ferroelectric nanostructures become a hot topic of materials science and technology due to their novel properties and potential applications for nanoscale devices, including memorizers, transducers, sensors, and energy-harvesting devices. In nanostructures, morphology details such as size, shape, and aggregation form have a significant effect on the properties. Therefore, the controlled synthesis of ferroelectric nanomaterials has long been important topics of determining their properties and applications.Bismuth titanate (Bi4Ti3O12) has attracted growing attention from researchers due to their great properties and widely applications. As far as we know, there is no systemic study on controllable synthesis and growth mechanism of Bi4Ti3O12nanostructures. Herein, we demonstrate the effects of the kinds of precursor, the types and concentration of mineralizer, the surfactant and the reaction temperature and time on the shapes and structures of Bi4Ti3O12samples. Various single-crystalline Bi4Ti3O12nanostructures have been controllably synthesized by tuning the reaction parameters. The formation mechanisms of Bi4Ti3O12with different shapes are also investigated. Moreover, Bi4Ti3O12nanostructures with different shape have been firstly applied in the dye-sensitized solar cells (DSSCs). The main contents andresults results have been presented as follows.1、Bi4Ti3O12nanostructures were synthesized by hydrothermal process based on coprecipitation precursorBi4Ti3O12nanoplates were synthesized through hydrothermal process based on coprecipitation precursor. The effects of the kinds and concentration of mineralizer, the reaction temperature and time on the shapes and structures of Bi4Ti3O12samples have been analyzed. The formation mechanisms of the obtained hollow microspheres constructed by single-crystalline Bi4Ti3O12nanoplates are proposed to be Ostwald ripening. The characterization results show the surface of Bi4Ti3O12hollow microspheres exist the oxygen vacancies and the surface absorption, which will directly impact the atomic polarization for surface atoms and red-shift behavior. Piezoresponse Force Microscopy (PFM) was applied to explore the ferroelectric properties of Bi4Ti3O12nanoplates. The measurement showed that apparent ferroelectric properties of Bi4Ti3O12nanoplates and an enhanced piezoelectric coefficient d*33(58pm/V) of Bi4Ti3O12nanoplates than that of the BIT bulk single crystal. The possible reasons for such a large piezoelectric coefficient were analyzed by surface effects and nanodomain structures.2、Various morphologies of Bi4Ti3O12nanostructures were synthesized by a modified hydrothermal methodA modified hydrothermal method was applied to synthesize Bi4Ti3O12nanostructures. Single-crystalline Bi4Ti3O12nanostructures with various morphologies including nanoplates, lamellas, nanobelts and nanorods have been controllably synthesized. The effects of the kinds and concentration of mineralizer, the reaction time on the shapes and structures of Bi4Ti3O12samples have been analyzed. The kinds of mineralizers and their concentrations play important roles on the structure and morphology of Bi4Ti3O12products. A possible growth mechanism has been proposed by time-dependent experiments. In addition, PFM was applied to confirme the ferroelectric properties of Bi4Ti3O12nanoplates. Local piezoresponse force measurements display a typical butterfly curve and180o phase transition, indicating good ferroelectric property of the Bi4Ti3O12nanoplates and lamellas. UV/Vis absorption spectra have shown that the as-synthesized Bi4Ti3O12samples have a slightly red-shift behavior.3、Bi4Ti3O12nano-and micro-structures were controlly synthesized by a solvothermal methodA solvothermal method was applied to synthesize Bi4Ti3O12nanostructures. The effects of the kinds of solvent, the proportion of solvent and water, the kinds of surfactant, the reaction time on the shapes and structures of Bi4Ti3O12samples have been analyzed. Novel hierarchical Bi4Ti3O12micro-cross spheres with a diameter of about5μm were obtained. The hierarchical Bi4Ti3O12micro-cross spheres are consisted of nano-sheets which assemble into a cross intercalated structure. Moreover, the morphological evolution process indicates that the type and concentration of surfactant can adjusted the shape of Bi4Ti3O12nanostructures and the cetyltrimethylammonium bromide is important in determining the self-assembling process of Bi4Ti3O12micro-cross spheres. In addition, UV/Vis absorption spectra show that the as-synthesized Bi4Ti3O12samples have a slightly red-shift behavior and exhibit different band gaps with different morphologies.4、Morphology effects of Bi4Ti3O12nanostructures on the photoelectrochemical properties The morphology-dependent photoelectrochemical properties of Bi4Ti3O12nanostructures including nanoplates, lamellas, nanobelts, nanorods, hollow microspheres and micro-cross spheres were studied by applying for dye-sensitized solar cells (DSSCs). The results showed that the crystal facets of the Bi4Ti3O12nanostructure play important roles in the photoelectrochemical properties. The Bi4Ti3O12nanoplates with exposed {101} facets possessed the highest short circuit current density of5.02mA cm-2, fill factor of0.66, photovoltaic efficiency of2.56%. It is explained that the Ti-O-Ti-O bond chains are greatly enhanced the transfers of the photogenerated electron-hole pairs. This study demonstrates that Bi4Ti3O12nanostructure is a promising candidate as a DSSC.5、Ferroelectric nanorod arrays synthesized by a new acid vapor hydrothermalA new growth approach, acid vapor hydrothermal was adopted to fabricate ferroelectric nanorod arrays. The effects of the thickness of ferroelectric thin fims with different kinds of ferroelectric materials, the concentration of hydrochloric acid and the reaction time on the shapes and structures of ferroelectric thin films have been analyzed. The formation mechanisms of ferroelectric nanorod arrays Bi4Ti3O12have been proposed.