Research On Fabrication And Performance Of Ti₆O₁₁ Nanofibers

Magneli phases materials are a series of sub-stoichiometric titanium oxides of the general formula TinO2n-1, where n is between 4 and 10. They are of interest in a variety of applications, such as electrochemistry, due to their high electrical conductivity and chemical resistance. Electrospinning was used to fabricate long and fine nanofiber with high aspect ratio. It is readily to control the morphology and implement directional arrangement which has good prospects in nanomaterials device assembly applications. In this paper, based on the electrospinning technology, we fabricated pure Magneli phase Ti₆O₁₁ nanofiber using high temperature H2 reduction, characterized the phase,microstructure and morphology, and tested the electrical, electrochemical and optical properties of the nanofibers. Finally, we explored the applications of TinO2n-1 fibers in resistance random access memory, super capacitors and transparent conducting films. The main research results are as follows.The pure phase Ti₆O₁₁ and Ti₉O₁₇ fibers were fabricated by reducing TiO2 precursor fibers, produced by electrospinning, at 900 and 1000 C, respectively. The Ti₆O₁₁ nanofibers remained intact and continuous with high aspect ratio. After coated by carbon, the grain size of the Ti₆O₁₁ nanofibers reduced from 350 nm to about 100 nm, and the length of the nanofibers was up to several millimeters.By controlling the electrospinning process, the ordered Ti₆O₁₁ fibers were directly arranged on a Si/SiO2 wafer and Au/Ti₆O₁₁/Au memory cells were assembled through depositing gold electrodes. Without electrical forming process excitation, the Au/Ti₆O₁₁/Au memory cells showed a behavior of bipolar resistance switching with counter clockwise polarity, caused by the presence of the higher density of the oxygen vacancies in Ti₆O₁₁ fibers. The resistance change is due to the change in Schottky barrier height or width by trapping/detrapping electric charge at Au/Ti₆O₁₁ interface oxygen vacancies. The memorycells, however, after electric forming process with a large bias, showed a bipolar resistance switching with clockwise polarity. The switching with opposite polarity resulted from the conductive channel caused by the oxygen vacancies in Ti₆O₁₁ nanofibers moved in electric field.Cyclic voltammogram?CV? measurements of the Ti₆O₁₁ fiber as electrode materials were performed in a three electrode cell configuration. The morphology of CV curves showed good capacitive performance of Ti₆O₁₁ fiber, and the highest capacitance achieved148.6 F/g at 2 mV/s voltage sweep rate. The electrochemical performances of solid-state supercapacitor assembled by using Ti₆O₁₁ fibers were evaluated by cyclic voltammogram,galvanostatic charge-discharge and AC impedance in two-electrode cell configuration. The resulting Ti₆O₁₁ nanofiber delivered a high energy density?0.365 mWh/cm3? and power density?1.7 W/cm3?. This work is expected to expand the application of Ti₆O₁₁ nanofibers in the field of supercapacitors.By controlling the electrospinning deposition cycle index, the conductive films with porous network structure were prepared by multiple aligned Ti₆O₁₁ fibers. The effects of the density of nanofibers on optical transmittance and sheet resistance were investigated. When the electrospinning cycle was four, the sheet resistance of Ti₆O₁₁ nanofiber network was165 ?/sq at a optical transmittance of 86%, which indicated that Ti₆O₁₁ nanofibers could be used as a new type of transparent conductive materials.