Study On Controllable Synthesis And Properties Of One - Dimensional Nanostructures Of Ternary Rare Earth Compounds

In this dissertation, a series of rare earth oxysulfide (Ln2OS2, Ln= Y, Gd, Dy, Ho, Er, Yb) ultrathin nanowires and rare earth orthoferrite (LnFeO3, Ln= Tb, Dy) one-dimensional nanostructures have been successfully synthesized by choosing appropriate structure directing reagents in non-hydrolytic and aqueous system, respectively. These strutures have been characterized by X-ray diffraction (XRD), X-ray energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), Ultraviolet-visible spectrometer (UV-vis), Fourier transform infrared Spectroscopy (FT-IR), laser Raman scattering spectroscopy, fluorescence spectroscopy. Some new and interesting physicochemical properties are found in the obtained nanostructures. The main results are as follows:1.By using 1-octadecene as solvent, oleic acid and dodecylamine as surfactants, and rare earth nitrates and thiourea as source materials, a series of rare earth oxysulfide (Ln2OS2,Ln= Y, Gd, Dy, Ho, Er, Yb) ultrathin nanowires have been successfully synthesized under mild conditions. The diameters of the obtained nanowires are about 2 nm and their length is up to micrometer scale.Those nanowires are found to be dynamic stable, not thermodynamic stable, which will be transformed into sphere-like nanostructures by prolonging the time of thermal treatment. Moreover, the obtained nanowires can be self-organized into novel tube-like or belt-like superstructures by controlling reaction parameters. Based on time-dependent experimental results and combined with FT-IR as well as TG-DTA analysis, a possible mechanism for formation of those ultrathin nanowires is provided. UV-vis results demonstrate that the obtained rare earth oxysulfide ultrathin nanowires not only exhibit strong optical absorption band in ultraviolet region but also shows the transition absorption of f-f electrons in some oxysulfide compounds due to the difference of f electron configuration on rare earth elements. Furthermore, owing to the presence of many structural defects, the obtained rare earth oxysulfide nanowires emit strong blueviolet fluorescence excited by the light with a special wavelength.2. In aqueous system, a series of perovskite-type rare earth orthoferrite (LnFeO3, Ln= Tb, Dy) one- dimensitional nanomaterials have been prepared by using hydrothermal- crystallization method under mild conditions. The suberic acid is selected as the structure directing reagent. The rare earth nitrates and iron nitrate are chosen as the source materials. And NaOH is used as the additive reagent. XRD analysis shows that the obtained samples are pure orthorhombic phase product. No yttrium aluminum garnet (Ln3Fe5O12) compounds and Fe3O4 by-products are detected in the obtained samples, resolving the phase structure purity problem in the current synthesis of rare earth orthoferrites fields. FT-IR and Raman experimental results reveal that the obtained LnFeO3 1-D nanostructures exhibit different vibration and scattering features compared with that of their bulk - counterparts. Furthermore, the ferroelectric performance of the synthesized LnFeO3 1-D nanostructures are measured on the RT6000HVS apparatus. The obvious electric hysteresis loops are observed in the DyFeO3 and TbFeO3 nanobelt samples, indicating that they possess ferroelectric behaviour at room temperature. These results show that the design and synthesis of complex ternary rare earth oxide low-dimensional ferroelectric nanomaterials is feasible), which paves the way for exploring and designing high density rare earth based ferroelectric storage device , high efficiency non-linear optical devices, thermoelectric materials and novel high-performance heterogeneous catalysts.