Preparation And Characterization Of Bi₃.15Nd₀.85Ti₃O₁2 Ferroelectric Nanotubes

Because of the miniturization of electronic devices, the low dimensional ferroelectric nanomaterials are drawing great attention. In this dissertation, the main work is the preparation of Bi3.15Nd0.85Ti3O12 (BNT) nanotubes and the study of their crystalline structures and physical properties. On the other hand, a hydrothermal method is developed to fabricate BNT nanotubes, in which BNT nanotubes are obtained by transforming the TiO2 nanotubes into BNT nanotubes. The main research contents and obtained results in this thesis are summarized as follows:1. Sol-gel template synthesis and characterization of BNT nanotube arraysBNT nanotubes with differrent tube wall thicknesses were prepared by changing the immersing time of the AAO template in the different concentrations BNT sol. Scanning electron microscopy (SEM), Energy dispersive spectrometry(EDS), Transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) are used to characterize the microstructures and morphologies of the prepared BNT nanotubes. The results show that the obtained BNT nanotubes are polycrystalline and have a single phase of bismuth-layered perovskite structure. Polarization-electricfield (P-E) response curves of BNT nanotube embedded in AAO template were measured by a ferroelectric test system. And the hysteresis loops illustrate a room temperature ferroelectric characteristic and the values of Pr and Ec of BNT nanotubes are lower than those of thin films. The optical properties of BNT nanotubes have also been investigated by using an ultraviolet-visible (UV-VIS) spectrophotometer. The results showed that BNT nanotubes have a strong intrinsic absorption in the range of 200-350 nm and have a good blue-violet photoluminescence property.2. Synthesis and characterization of BNT nanotube arrays by hydrothermal methodFirstly, self-aligned highly ordered TiO2 nanotube arrays are fabricated by potentiostatic anodization of Ti foil using aqueous organic polar electrolytes. Then the BNT nanotube arrays are obtained by transforming TiO2 nanotube arrays into BNT nanotube arrays using a hydrothermal method. The relationships of the morphologies and structures and the reaction conditions are studied. SEM, EDS, TEM and XRD results show that the obtained BNT nanotubes still contained some TiO2 when the reaction conditions are 200 oC and 12 hours. But when the TiO2 nanotubes are reacted at the same temperature with the longer reaction time of 48 hours and 96 hours respectively, the tubular structures were destroyed and turned to an acicular crystal. Whereas, with the conditions of 250 oC, 12 hours, and 250oC, 24 hours respectively, acicular crystal and granular crystal are obtained, respectively. A further study to investigate the influence of the reaction conditions and the morphologies and structures of the BNT nanotubes is still in progress.