Yangxian Li

Magnetic field-controlled two-way shape memory in CoNiGa single crystals

A two-way magnetic field controlled shape memory effect has been observed in single crystals of CoNiGa with martensitic transformation temperature ranging from 205 to 341 K. Two-way shape memory with −2.3% strain has been obtained in free samples. By applying a bias field of up to 2 T, the shape memory strain can be continuously controlled from negative 2.3% to positive 2.2% giving it a total strain of 4.5%. The magnetic properties of CoNiGa show that it is a good shape memory material working at relatively high temperature of up to 450 K, and has a lower magnetic anisotropy than NiMnGa.

Giant magnetostriction on Fe85Ga15 stacked ribbon samples

Large magnetostrictions of −1300 and +1100 ppm related in the different directions have been obtained in our stacked Fe85Ga15 ribbon samples. In the case of non-180° domain magnetization in the high anisotropic samples, the magnetostrictions are mainly attributed to the existence of Ga clusters which preferentially orient with the ribbon normal due to the ribbon grain texturing. Forming the modified DO3 structure, the Ga–Ga atom pairs distribute in the matrix and cause the x-ray diffraction peak split in melt-spun ribbons. As a special micromorphology, Ga clusters highly condensed in some nanoscale dots have also been experimentally observed.

Mechanism study of self-organized TiO2 nanotube arrays by anodization

Based on analysis of the current–time curve and observation of surface morphology including top, cross-section, bottom and substrate views by scanning electron microscopy (SEM), a new growth, dissolution–breakdown model, of self-organized titania nanotube arrays is presented. By this model, many phenomena raised during anodization are explained, such as the sharp decrease of current in initial period, current transient, occurring of ridges on tube walls, and formation of not pores but tubes etc. Furthermore, the reason for the occurrence of a porous structure, the balance between internal energy and surface energy, was proposed too. This study may also shed light on the formation of porous oxide films on other valve metals.

Large magnetostriction in Fe100−xAlx(15⩽x⩽30) melt-spun ribbons

Magnetostriction of Fe100−xAlx(15⩽x⩽30) al1oys has been largely improved by using melt-spun method. The large magnetostriction up to −700ppm obtained in Fe81Al19 sample is about 5 times as large as that in conventional bulk samples of Fe–Al composition. It has been ascribed to the high concentration of Al–Al atom pairs created by melting-spinning method and their strongly preferential orientation in [100] textured ribbon plane. The remarkable anisotropic magnetostriction reflects the magnetoelastic competition occurring in those strong textured and thin ribbon samples. The composition dependence of the magnetostriction in ribbon samples has been found to be consistent with bulk materials.

Photoelectrochemical Activities of W-Doped Titania Nanotube Arrays Fabricated by Anodization

Titania nanotube arrays and W-doped (containing 3-wt% W) titania nanotube arrays were obtained using a direct anodization method in ethylene glycol electrolyte containing 0.5-wt% HF at 60 V. Anneal was conducted to get anatase crystals. The microstructure and crystal structure of the nanotubes were characterized by scanning electron microscopy and X-ray diffraction. The ultraviolet-visible diffuse reflectance spectra of the annealed samples show that the addition of W led to the red shift of absorbance edge and a decrease of bandgap energy for about 0.14 ev. The photoelectrochemical behavior of these samples has been also studied. Results show that photocurrent densities of W-doped titania nanotube arrays were much larger than that of the undoped sample.

Preparation and Growth Mechanism of Niobium Oxide Microcones by the Anodization Method

The formation of niobium oxide microcones on niobium substrates was investigated in HF electrolytes. The microstructure of the layers depends strongly on the HF concentration, the formation potential, and the anodization time. Microcones can be formed under a range of experimental conditions. Electrochemical determination and scanning electron microscopy indicate the microcones were formed due to the fast expansion of the oxide volume and the electric break under electric field. X-ray diffraction results verify the formation of Nb 2 O 5 . A possible growth mechanism has also been presented on the basis of experiments.

Preparation and magnetic properties of highly ordered Co/Ag alloy nanowire arrays

Highly ordered Co/Ag nanowire arrays have been successfully prepared by electrochemical deposition method using anodic alumina membranes (AAMS) as template. Electrolytes used in our study were the mixed solution of cobalt sulphate and silver nitrate. Experimental parameters including concentrations of different electrolytes, deposition potential, reaction time, temperature and frequency were investigated in detail. The microstructures and chemical composition of Co/Ag nanowires were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). XRD patterns of Co/Ag nanowires clearly showed that they presented a cubic crystalline structure. Magnetic properties of Co/Ag nanowires were determined by vibrating sample magnetometer (VSM). The hysteresis loops show that all of the nanowires exhibited magnetic anisotropy with the easy axis along the nanowires. In this orientation, the nanowire arrays have large coercive field and high squareness. The hard axis direction is perpendicular to the nanowires. In this orientation, the nanowire arrays have small coercive field and low squareness.