Minfeng Lv

Preparation of ferrite MFe2O4 (M = Co, Ni) ribbons with nanoporous structure and their magnetic properties.

Spinel ferrite, MFe 2O 4 (M = Co, Ni), ribbons with nanoporous structure were prepared by electrospinning combined with sol-gel technology. The ribbons were formed through the agglomeration of magnetic nanoparticles with PVP as the structure directing template. The length of the polycrystalline ribbons can reach millimeters, and the width of the ribbons can be tuned from several micrometers to several hundred nanometers by changing the concentration of precursor. The nanoporous structure was formed during the decomposition of PVP and inorganic salts. The ribbons exhibited weak saturation magnetizations and low coercivities at room temperature, but at low temperature, saturation magnetizations and coercivities increased a lot, especially for CoFe 2O 4 ribbons, reaching 72 emu/g and 1.45 T at 2 k, respectively. These novel magnetic ribbons can potentially be used in micro/nano electronic devices, gas-sensors, and catalysts.

Electrical conductivity optimization in electrolyte-free fuel cells by single-component Ce0.8Sm0.2O2-δ–Li0.15Ni0.45Zn0.4 layer

Single-component electrolyte-free fuel cells possess a similar function to the traditional fuel cells with a complex three-component structure. However, how to enhance their electrical properties for practical industrial applications remains a timely and important issue. Here, we report the manipulation of concentration ratios of ionic to electronic conductors in an electrolyte-free Ce0.8Sm0.2O2-δ–Li0.15Ni0.45Zn0.4 by adjusting the relative weight between its two inside compositions. Our systematic investigations reveal that the fuel cell with 30% in weight of Li0.15Ni0.45Zn0.4 exhibits an almost uniform distribution of the two compositions and has a total conductivity as high as 10 × 10−2 S cm−1 at 600 °C. Such an enhancement is found to be attributed to the established balance between the numbers of its inside ionic and electronic conductors. These findings are relevant for the technological improvement of this new species of electrolyte-free fuel cell and represent an important step toward commercialization of this single-component fuel cell.

Facile Synthesis of Porous Fe7Co3/Carbon Nanocomposites and Their Applications as Magnetically Separable Adsorber and Catalyst Support

A facile co-gelation route has been developed to synthesize novel porous Fe(7)Co(3)/carbon composites with Fe(7)Co(3) nanoparticles embedded in the porous carbon matrix. The sol-gel process of this route simultaneously involves the hydrolysis of tetraethylorthosilicate (TEOS) and the polymerization of furfuryl alcohol (FA) within an ethanol solution containing TEOS, FA, and metal nitrates, which led to the inorganic/organic hybrid xerogel, accompanying metal salts spontaneously captured in the xerogel, mostly in the framework of poly(furfuryl alcohol) (PFA). Compared to the nanocasting route, the advantage of this method is that the formation of silica template and the impregnation of carbon precursor and metal salts were simultaneously carried out in one co-gelation process, which makes the synthesis very simple and eliminates the time-consuming synthesis of the silica template and multistep impregnation process. Different amounts of Fe(7)Co(3) can be introduced into the composites, which led to different pore structures and magnetic properties. The composites have large surface areas (as high as 651.4 m(2)/g) and high saturation magnetizations (as high as 31.2 emu/g). The Fe(7)Co(3)/carbon composites prepared were successfully applied to the removal of dyes from water and catalysis of hydrogenation as efficient magnetically separable adsober and catalyst support. The facile co-gelation route makes the scalable synthesis of magnetic porous carbon possible for application, and it also provides a promising path to the synthesis of nanoscale metal or alloy embedded in the porous carbon materials.

Charge, orbital, and magnetic ordering in YBaFe2O5 from first-principles calculations.

First principles calculations using the augmented plane wave plus local orbitals method, as implemented in the WIEN2k code, have been used to investigate the electronic and magnetic properties of YBaFe2O5, especially as regards the charge-orbital ordering. Although the total 3d charge disproportion is rather small, an orbital order parameter defined as the difference between t2g orbital occupations of Fe2+ and Fe3+ cations is large (0.73) and gives unambiguous evidence for charge and orbital ordering. Strong hybridization between O2p and Fe e g states results in the nearly complete loss of the separation between the total charges at the Fe2+ and Fe3+ atoms. Furthermore, the relationship between the orbital ordering and charge ordering is also discussed. The dxz orbital ordering is responsible for the stability of the G-type antiferromagnetic spin ordering and the charge ordering pattern.

Magnetic structure and orbital ordering in tetragonal and monoclinic KCrF3 from first-principles calculations

KCrF(3) has been systematically investigated by using the full-potential linearized augmented plane wave plus local orbital method within the generalized gradient approximation and the local spin density approximation plus the on-site Coulomb repulsion approach. The total energies for ferromagnetic and three different antiferromagnetic configurations are calculated in the high-temperature tetragonal and low-temperature monoclinic phases, respectively. It reveals that the ground state is the A-type antiferromagnetic in both phases. Furthermore, the ground states of the two phases are found to be Mott-Hubbard insulators with the G-type orbital ordering pattern. In addition, our calculations show the staggered orbital ordering of the 3d(x(2) ) and 3d(y(2) ) orbitals for the tetragonal phase and the 3d(z(2) ) and 3d(x(2) ) orbitals for the monoclinic phase, which is in agreement with the available data. More importantly, the relationship between magnetic structure and orbital ordering as well as the origin of the orbital ordering are analyzed in detail.