Hongjian Guo

Novel permanent magnetic material: Sm3(Fe,Ti)29Ny

Abstract The X-ray diffraction pattern of the novel Sm 3 (Fe 0.933 Ti 0.067 ) 29 compound was indexed on the basis of monoclinic symmetry with the lattice parameters a = 1.065 nm, b = 0.858 nm, c = 0.972 nm and β = 96.98°. The Sm 3 (Fe 0.933 Ti 0.067 ) 29 compound exhibits ferromagnetic ordering with T C = 486 K and a planar anisotropy. The new interstitial nitride of the Sm 3 (Fe 0.933 Ti 0.067 ) 29 N 5 compound was obtained by gas-solid phase reaction. The nitride has the same structure as the parent compound. The introduction of nitrogen leads to an increase in the Curie temperature to 750 K. The saturation magnetization values σ s = 160 A m 2 kg −1 at 4.2 K and 140 A m 2 kg −1 at 293 K. The anisotropy was changed from planar to uniaxial upon nitrogenation. The anisotropy field B a values were 18.1 T at 4.2 K and 12.8 T at 293 K. The hard magnetic properties of the Sm 3 (Fe 0.933 Ti 0.066 ) 29 N 5 compound have been studied. A coercivity μ 0i H c value of 0.83 T and a maximum energy product ( BH ) max of 105 kJ m −3 at 293 K have been achieved. The Sm 3 (Fe 0.933 Ti 0.067 ) 29 Ny compound is a promising material for permanent magnetic applications.

Microstructures, mechanical and tribological properties of VN films deposited by PLD technique

Consistent stoichiometric FCC structured vanadium nitride (VN) films were fabricated by the pulsed laser deposition (PLD) technique at room temperature and 300 °C, for which the microstructures and mechanical and tribological properties were systematically investigated. The results indicated that the films deposited at 300 °C displayed a denser structure and possessed higher hardness and elastic modulus values than the films deposited at room temperature that exhibited a columnar structure. The wear behaviors of VN films were investigated at elevated temperature to 900 °C against an alumina ball under an ambient atmosphere. Due to the densified structure and excellent mechanical properties, the VN films deposited at 300 °C held lower friction coefficients over the investigated temperature range compared to those of the films deposited at room temperature and registered the lowest friction coefficient of about 0.21 at 900 °C. According to the XRD and Raman spectroscopy results, the oxidation behaviors of VN films at elevated temperatures formed a series of vanadium oxides, such as V2O5, V3O7, V6O11 and V6O13, which displayed easy crystallographic shear planes with reduced binding strength and influenced the tribological properties significantly. Moreover, liquid self-lubrication existed in the tribology process above 700 °C due to the melting of V2O5 that registered low melting points of 680 °C. Combining the vanadium oxides phase and lubrication phases with the lubricious oxide layer, as well as the liquid lubrication in the contact area, can cause decreased friction coefficients at higher temperatures.

Controllable coverage of Bi2S3 quantum dots on one-dimensional TiO2 nanorod arrays by pulsed laser deposition technique for high photoelectrochemical properties

In this work, the pulsed laser deposition (PLD) technique is applied for direct physical deposition of narrow bandgap semiconductor Bi2S3 quantum dots (QDs) on one-dimensional TiO2 nanorod arrays to fabricate quantum dots sensitized solar cells (QDSSCs). Without regard for any protective packaging or surface treatment process for binding QDs, the QDSSCs exhibit excellent stability and high energy conversion efficiency in ambient air. Through varying the laser ablation pulses, the controlled coverage of QDs on nanorods is realized and an optimal energy conversion efficiency of 3.06% is obtained under one sun illumination (AM 1.5, 100 mW cm−2). The enhanced absorption in an extended wavelength range, quick interfacial charge transfer and few recombination chances for electrons with holes are believed to contribute to the improved performance of Bi2S3 QD-sensitized solar cells. Moreover, a sputtered plasma at high velocity can collide intensely with the surface of TiO2, which enables direct atomic contact and endows the QDSSCs with high stability. These promising results provide a potential option of using the PLD technique for the fabrication of QD-based solar cells or other thin film photo-absorption materials.