Jipeng Miao

Enhancement of low-field magnetoresistance in polycrystalline Sr2FeMoO6 with Al doping

Polycrystalline Sr2Fe1−xAlxMoO6 compounds with x=0, 0.05, 0.10, 0.15, and 0.30 were fabricated and their low-field magnetoresistance (LFMR) performance studied. The LFMR was greatly enhanced as x increased from nil to 0.15, and its origin was found to be intragranular spin-dependent scattering. The replacement of Fe by Al weakened the antiferromagnetic exchange in the antiphase boundary arising from the antisite defect and acted as a barrier for electron transport along the Mo–O–Fe–O–Mo–O–Fe chain in the ferromagnetic segregation and weakened the ferromagnetic exchange. When the external magnetic field was applied, the spin in the antiphase boundary appeared to align more easily to the external field after Al doping and the transport of the electron was easier due to the weakening of the double exchange barrier.

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.

Enhanced low field magnetoresistance in Sr2FeMoO6-glass composites

In this paper, we report the enhancement of the low field magnetoresistance in Sr2FeMoO6-glass composites with different wt % percents of glass. The crystal structure of Sr2FeMoO6 does not change by adding glass, and the glass is most likely located at the grain boundaries. The low field magnetoresistance up to 1 T of Sr2FeMoO6-glass composites at 10 K all shows obvious butterfly-shaped field dependence other than the pure Sr2FeMoO6 bulk sample. The magnetoresistance of Sr2FeMoO6-glass composites at 10 K is enhanced gradually with increasing the glass concentration and reaches 39% with a wt % of 50%. The enhancement of low field magnetoresistance in Sr2FeMoO6-glass composites can be well explained by the spin-dependent tunneling at the glass boundaries, and it also allowed us to conclude that the spin polarization of Sr2FeMoO6 is at least 80% at low temperature

The Pr4+ ions in Mg doped PrGaO3 perovskites

In this study, the valence state of Pr in Mg doped PrGaO3 perovskites was investigated. It is found that Pr4+ ions are created in samples doped with low-valence ions, for example, with Mg2+. The color of the doped samples changes from black to light green after being treated in H-2 atmosphere, which shows that the Pr4+ ions in the sample are reduced to Pr3+ ions. The open circuit voltage of the solid oxide fuel cell (SOFC) using PrGa0.95Mg0.05O3 as the electrolyte increases with time and the X-ray photoelectron spectroscopy (XPS) data of PrGa0.9Mg0.1O3 also show the existence of Pr4+ ions in Mg doped PrGaO3

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

Influence of nonmagnetic Al ions on magnetoresistance of double-perovskite Sr2Fe1−xAlxMoO6 (0≤x≤0.30)

The structural, magnetic, and magnetoresistance properties of the double-perovskite series Sr2Fe1-xAlxMoO6 (0 <= x <= 0.30) were systematically investigated in order to clarify the influence of nonmagnetic Al ions on the magnetoresistance. The structural refinements of these samples show that the degree of cationic order increases gradually from 88.5% for x=0 to 92% for x=0.30 without any change in the crystal structure. The magnetization measurements reveal that the substitution of nonmagnetic Al ion for Fe ion enhances the magnetic moment per Fe ion significantly. In addition, the magnetic-field dependence of magnetization and magnetoresistance of these Sr2Fe1-xAlxMoO6 samples were all fitted excellently by taking into account the contributions from ferromagnetic-coupled Fe-O-Mo region and nonferromagnetic-coupled regions. The fitting results indicate that the low-field magnetoresistance can be greatly enhanced due to the separation of the cationic-ordered Fe-O-Mo regions by the paramagnetic Mo-O-Al-O-Mo chains introduced through Al doping. Furthermore, doping nonmagnetic Al ions also suppress the formation of antiferromagnetic Fe-O-Fe antiphase boundaries, and then lead to the improvement of cation ordering and the reduction of magnetoresistance under high field. (c) 2005 American Institute of Physics.