Yanting Yang

Highly improved ethanol gas-sensing performance of mesoporous nickel oxides nanowires with the stannum donor doping

Mesoporous nickel oxides (NiO) and stannum(Sn)-doped NiO nanowires (NWs) were synthesized by using SBA-15 templates with the nanocasting method. X-ray diffraction, transmission electron microscope, energy dispersive spectrometry, nitrogen adsorption/desorption isotherm and UV-vis spectrum were used to characterize the phase structure, components and microstructure of the as-prepared samples. The gas-sensing analysis indicated that the Sn-doping could greatly improve the ethanol sensitivity for mesoporous NiO NWs. With the increasing Sn content, the ethanol sensitivity increased from 2.16 for NiO NWs up to the maximum of 15.60 for Ni0.962Sn0.038O1.038, and then decreased to 12.24 for Ni0.946Sn0.054O1.054 to 100 ppm ethanol gas at 340 °C. The high surface area from the Sn-doping improved the adsorption of oxygen on the surface of NiO NWs, resulting in the smaller surface resistance in air. Furthermore, owing to the recombination of the holes in hole-accumulation lay with the electrons from the donor impurity level and the increasing the body defects for Sn-doping, the total resistance in ethanol gas enhanced greatly. It was concluded that the sensitivity of Sn-doped NiO NWs based sensor could be greatly improved by the higher surface area and high-valence donor substitution from Sn-doping.

Strange critical behaviors of ferromagnetic to paramagnetic transition in La0.5Ca0.5MnO3 nanowires bundles

Highly ordered La0.5Ca0.5MnO3 nanowires bundles are synthesized using mesoporous SBA-15 silica as the hard template. The magnetic properties and critical behaviors of the ferromagnetic–paramagnetic (FM–PM) phase transition of the La0.5Ca0.5MnO3 nanowires bundles are investigated through isothermal magnetization methods. The calculated results show that the FM–PM transition is second order and the magnetic interaction has some deviations from the mean-field model. Though the obtained critical parameters of β = 0.596 ± 0.009, γ = 1.131 ± 0.008 and δ = 2.99 ± 0.05 follow the Widom scaling relation δ = 1 + γ/β and the single scaling equation M(H,|e|) = eβf±(H/|e|β+γ), the critical exponents do not obey the magnetization entropy scaling theory, indicating that the nanometer-size effect play a significant role on the magnetic phase transition and magnetic entropy for La0.5Ca0.5MnO3 nanowires bundles.

Synthesis of fine α″-Fe16N2 powders by low-temperature nitridation of α-Fe from magnetite nanoparticles

α″-Fe16N2 nanoparticles were produced from starting Fe3O4 powders via hydrogen reduction and low temperature nitridation. Influences of both reduction and nitridation conditions on the synthesis of α″-Fe16N2 were investigated in detail. The magnetic properties of the nitrided products were also studied. The results show that the combination of 4-h reduction at 400 °C and 16-h nitridation at 170 °C gives the highest yield of α″-Fe16N2 up to 59.8 wt. %, which exhibits a saturation magnetization of about 207.3 emu/g.

FeSiAl soft magnetic composites with NiZn ferrite coating produced via solvothermal method

NiZn ferrites were selected as coating agents to prepare NiZn/FeSiAl soft magnetic composites (SMCs) in order to improve the soft magnetic property. It is based upon the higher permeability of magnetic NiZn ferrites than that of traditional nonmagnetic coatings, and also relative higher resistance than that of MnZn ferrites. The effects of molding pressure, annealing temperature, and content of insulation on the magnetic properties were studied. As molding pressure increases, the effective permeability increases firstly and then decreases, while the core loss shows a reverse trend, and both get the best performance at 1.6 GPa. With increasing temperature, the permeability increases, reaches the maximum value at 660 °C and then decreases, while the core loss has a reverse trend, and both get the minimum value at 700 °C. The permeability increases with increasing NiZn from 0.1% to 3%, and then decreases. The D-C bias property of FeSiAl SMCs increases with increasing both mica and NiZn content. The larger re...

Large magnetostrain in magnetic-field-aligned Mn0.965CoGe compound

By applying external stimulus (temperature or magnetic field), MnCoGe-based compounds undergo a martensitic transformation from hexagonal Ni2In-type to orthorhombic TiNiSi-type structure accompanied with a giant negative thermal expansion, which suggests a large magnetic-field-induced strain. However, these compounds naturally collapse into powders and are difficult to be oriented, which hinder their applications for magnetostrain. In this paper, a magnetic-field-aligned Mn0.965CoGe compound was prepared by bonding with epoxy resin and orientating in a magnetic field. The XRD patterns revealed the texture in this sample. By introducing vacancies of Mn element, the magnetostructural transformation temperature of Mn0.965CoGe compound was shifted down to 278 K. The magnetostrain was measured at some selected temperatures and the maximal strain could reach up to 925 ppm at 270 K.