Ruibin Zhu

Temperature- and magnetic-field-induced magnetization reversal in perovskite YFe0.5Cr0.5O3

Perovskite YFe0.5Cr0.5O3 exhibits magnetization reversal at low applied fields due to the competition between the single ion magnetic anisotropy and the antisymmetric Dzyaloshinsky–Moriya interaction. Below a compensation temperature (Tcomp), a tunable bipolar switching of magnetization is demonstrated by changing the magnitude of the field while keeping it in the same direction. The present compound also displays both normal and inverse magnetocaloric effects above and below 260 K, respectively. These phenomena coexisting in a single magnetic system can be tuned in a predictable manner and have potential applications in electromagnetic devices.

Anode-Supported Micro-SOFC Stacks Operated under Single-Chamber Conditions

A micro solid oxide fuel cell (SOFC) stack with two series-wound single fuel cells was fabricated and operated successfully under single-chamber conditions. In this stack, the single cells were based on Ni/yttria-stabilized zirconia (YSZ) anode-supported YSZ membrane and were arranged with an anode-facing-cathode configuration in diluted methane and oxygen mixture gas between 600 and 750 degrees C. The performances of the stack were affected by the flow rate, gas composition, and furnace temperature. The effects of the narrow path between two cells on the electrodes and cells were discussed in detail, according to the open-circuit voltages (OCVs) and impedance spectra of each cell. At 700 degrees C, the maximum OCV of the whole stack was larger than 2.0 V at CH4/O-2=1.75 and 2, while the maximum power output of stack was about 371 mW at CH4/O-2=1 with a mass specific power of 552 mW/g. The performance indicates that such microstacks have potential for portable applications. (c) 2007 The Electrochemical Society.

Magnetic and magneto-transport properties of double perovskite Sr2FeMoO6 with Co doping

The electrical, magnetic and magnetoresistance properties of polycrystalline Sr2Fe1-xCoxMoO6 compounds with x = 0.0, 0.05, 0.15 and 0.25 were investigated. With increasing Co content, both the degree of cationic order and the saturation magnetic moment per formula unit of these compounds increase, while their resistivity decreases monotonically and exhibits an enhanced metallic behaviour for x >= 0.15. The low-field magnetoresistance was greatly enhanced at x = 0.15, and the field dependence of magnetoresistance for x >= 0.15 almost saturates above 1.5 T. These results can be well explained by the change of magnetic structure of Sr2FeMoO6 after replacing partial Fe ions by Co ions. The enhanced metallic behaviour and low-field magnetoresistance also suggest a great application potential in spin electronic devices.

An anode for solid oxide fuel cells: NiO+(Ce0.9Ca0.1O1.9)0.25(YSZ)0.75 solid solution

A (CCO)(0.25)(YSZ)(0.75) solid solution (YSZ is Y2O3-stabilized ZrO2; CCO is an abbreviation of Ce0.9Ca0.1O1.9) was successfully synthesized by a solid-state method. A composite anode material, NYCx (60 wt% NiO+40 wt% (CCO)(x)(YSZ)(1-x)), for SOFCs (solid oxide fuel cells) was prepared. XRD results suggest that a solid solution reaction occurs between YSZ and CCO after sintering at 1400 degreesC for 10 h. From the impedance results, the conclusion can be drawn that the (CCO)(0.25)(YSZ)(0.75) solid solution is a mixed conductor (ionic and electronic). Its total conductivity is greater than that of YSZ. The NYCx (x>0) anodes exhibited better performance than the commonly used Ni+YSZ anode with regards to overpotential and anode interfacial impedance, with the NYC0.25 anode exhibiting the best performance (C) 2003 Elsevier B.V. All rights reserved.

Evidence of two distinct dynamical freezing processes in single-layered perovskite La0.7Sr1.3CoO4

The static and dynamic features of magnetization have been investigated in terms of dc magnetization, ac susceptibility, and memory effects on single-layered perovskite La(0.7)Sr(1.3)CoO(4). The results indicate that short-range ferromagnetic clusters coexist with the glassy magnetic state, i.e., a cluster-glass phase between T(f) and T(G) and a spin-glass-like phase below T(f). The clear evidence of memory effects in the dc magnetization is also observed below T(f) and T(G), respectively. These two glassy states with cooperative relaxation processes may derive from the different interaction processes among nanoscale ferromagnetic clusters mediated by the matrix, which is influenced by changing the spin state of Co(3+) ions in spontaneously phase-separated cobaltite.

A Ni/YSZ composite containing Ce0.9Ca0.1O2−δ particles as an anode for SOFCs

A composite material (hereafter referred to as NYC) containing Ni, Y2O3-stabilized ZrO2 (YSZ) and Ce0.9Ca0.1O2-delta (CC10) particles was prepared and used as the anode of solid oxide fuel cells (SOFCs). The performance of NYC was better than that of conventional Ni/YSZ anodes in terms of anodic overpotential and interface impedance. The additional CC10 particles improved the anode properties. XRD results suggest that a solid solution of YSZ and CC10 was produced. From impedance measurements, it is concluded that the solid solution exhibits substantial electronic conduction. Ni/YSZ/15 wt% Ce0.9Ca0.1O2-delta anodes exhibited the best properties over the experimental temperature range. A SOFC with an anode of Ni/YSZ/15 wt% Ce0.9Ca0.1O2-delta provided the maximum power density and current density. Addition of CC10 with an average particle size of 0.3 mum was more advantageous than that with an average size of 3 mum

Effect of solvent on absorption spectra of all-trans-β-carotene under high pressure

The absorption spectra of all-trans-beta-carotene in n-hexane and carbon disulfide (CS(2)) solutions are measured under high pressure at ambient temperature. The common redshift and broadening in the spectra are observed. Simulation of the absorption spectra was performed by using the time-domain formula of the stochastic model. The pressure dependence of the 0-0 band wavenumber is in agreement with the Bayliss theory at pressure higher than 0.2 GPa. The deviation of the linearity at lower pressure is ascribed to the reorientation of the solvent molecules. Both the redshift and broadening are stronger in CS(2) than that in n-hexane because of the more sensitive pressure dependence of dispersive interactions in CS(2) solution. The effect of pressure on the transition moment is explained with the aid of a simple model involving the relative dimension, location, and orientation of the solute and solvent molecules. The implication of these results for light-harvesting functions of carotenoids in photosynthesis is also discussed.

Influence of hot pressure on the magnetoresistance of CrO2

In this paper, we investigate the influence of high temperature and high pressure (hot pressure) on the magnetic and transport properties of polycrystalline CrO2 samples compacted under high pressure and high temperature of up to 5GPa and 600°C, respectively. The magnetic moment increases with compacting temperature, and a metal-semiconductor transition is observed in hot-pressed samples, different from the cold-pressed samples. These results indicate that the formation of Cr2O3 at the grain boundaries of CrO2 is suppressed by hot pressure. The magnitude of low field magnetoresistance of up to 1T at 5K is enhanced first with the increase of compacting temperature and then decreased under higher compacting temperature. This result can be well explained by the change of spin-dependent tunneling at the modulated grain boundaries of CrO2 due to the transformation from Cr2O3 to CrO2 under hot pressure.