Preparation And Performance Of Several Rare-earth Hexaborides Nanomaterials

Rare-earth mental hexaborides(RB6) have extensive application in the civilian and national defense industry because of their especial mechanical, thermal and electrical properties. The structure of the rare earth hexaborides is special, such as LaB6, which is composed of rare earth embedded inside a stable boron octahedron network. There are no hands combined between the B atoms and the rare earth mental atoms, and each B atom with other five B atoms together forming B6.This arrangement allows a unique combination of all desired properties for an excellent field-emitted material, such as low work function, high mechanical strength, high melting point, high conductivity, high Young's modulus, low volatility, high chemical resistance, which these properties seldom coexist in any other materials. So it is very important to research the hexaborides nanometer material.In the desertion, aligned LaB6, LaB6nanorods and PrB6nanowires were prepared by chemical vapor deposition and characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS), X-ray energy spectrum (EDS) and Raman spectrum were used to test the characters of the nanostructures. The growth mechanism of those nanostructures was simply discussed.Large-denomination aligned LaB6nanowires have been successfully fabricated for the first time under the low pressure by using Lanthanum trichloride hydrate (LaCl3-7H2O) solid and boron hydride (B2H6) atmosphere. XRD, FE-SEM, TEM, HRTEM were used to characterize the structures, morphologies and compositions of the nanowires. The results show that a large coverage of nanowire arrays deposited homogeneously on the substrate. A nanowire has a smooth and masonry-towers like morphology with flat top. The diameter and length of the nanowire are well-proportioned. The nanowires generally grow perpendicular to the substrate, and the average length of15μm and the typical diameter of80nm, revealing that the average aspect ratio is estimated200. TEM, SAED and XRD indicate that the high-purity are cubic crystals preferentially in the [100] direction. The growth mechanism of the LaB6nanowires attribute to the vapor-liquid-solid mechanism.nanorods were also prepared by chemical vapor deposition and the self-catalyst process and characterized by X-ray diffraction (XRD),field-emission scanning electron microscopy (FE-SEM),transmission electron microscopy (TEM),high resolution transmission electron microscopy(HRTEM),select area electron diffraction(SAED).The field-emission analysis shows that the PrB6nanorods have lower turn-on voltage, lower field threshold, higher field emission enhancement factor and steady emit current.PrB6nanowires have successfully been obtained by using the simple method by heating praseodymium trichloride hydrate (LaCl3-7H2O) solid and boron hydride (B2H6) gas. XRD, FE-SEM, TEM and HRTEM indicate the nanowires adopt a single structure were purity, smooth, uniformity and the diameter of100nm, the length of several microns. The temperature effect on the morphologies of the nanostructure was studied, simply. It was disadvantageous for the growth of PrB6when the temperature was low or high. A growth mechanism based on the Vapor-Solid process is simply discussed for the formation of the PrB6nanowires.