Z. W. Ouyang

Structural transition and atomic ordering in the non-stoichiometric double perovskite Sr2FexMo2-xO6

The structural transition and atomic ordering of a new series of ordered double perovskite oxides Sr2FexMo2-xO6 (0.8 less than or equal to x less than or equal to 1.5) have been studied by X-ray powder diffraction (XRD). Rietveld refinement of the powder diffraction profiles indicates that the crystal structure of the compounds Sr2FexMo2-xO6 changes from a tetragonal I4/mmm lattice to a cubic Fm(3)over-bar-m lattice around x = 1.2 and the lattice parameters decrease slightly as Fe content increases. The degree of ordering in Sr2FexMo2-xO6 exhibits a maximal at x = 0.95 and decreases as x deviates from 0.95

Structure and magnetoresistance of the double perovskite Sr2FeMoO6 doped at the Fe site

The structural, magnetic and transport properties of the compounds Sr2(Fe1−xMnx)MoO6 (0 ≤ x ≤ 0.45) have been studied. The saturated magnetization, Curie temperature and low-field magnetoresistance of the compounds decrease with x, while the resistivity increases by several orders of magnitude when x exceeds a critical value. A positive magnetoresistance has been observed for x = 0.45. A possible percolation mechanism is proposed to elucidate the observations; it also suggests a coexistence of (Mn3+, Mo5+) and (Mn2+, Mo6+) valence pairs and a saturated substitution of Mn3+ for Fe3+.

Crystal structure and phase relationships in the pseudobinary system Pr5Si4–Pr5Ge4

Phase relationships at ambient temperature in the pseudobinary system Pr5Si4-Pr5Ge4 were studied by X-ray powder diffraction (XRD). Three structurally distinct phase regions exist in this system. The Pr5Si4-based solid solution where Ge statistically substitutes for Si crystallizes in the Zr5Si4-type tetragonal structure with space group P4(1)2(1)2. The Pr5Ge4-based solid solution where Si statistically substitutes for Ge crystallizes in Sm5Ge4-type orthorhombic structure with space group Pnma. The crystal structure of a ternary intermediate phase, which exists between 1.65 less than or equal to x less than or equal to 2.6, is determined for the first time, and shown to be the Gd5Si2Ge2-type monoclinic structure with space group P112(1)/a. The Rietveld powder diffraction profile fitting technique was used for the refinement of crystal structure. The lattice parameters, atomic occupations, interatomic distances of the Pr5Si4, Pr5Ge4 and Pr5Si2Ge2 compounds were derived

Atomic ordering and magnetic properties of non-stoichiometric double-perovskite Sr2FexMo2-xO6

The crystal structure and magnetic properties of a new series of ordered double-perovskite oxides Sr2FexMo2-xO6 (0.8 less than or equal to x less than or equal to 1.5) have been studied. The crystal structure changes from a tetragonal I4/mmm lattice to a cubic Fm (3) over barm lattice around x = 1.2. The degree of ordering in Sr2FexMo2-xO6 exhibits a maximal at x = 0.95 and decreases as x deviates from 0.95. The saturated magnetization increases from x = 0.8 to 0.95 and then decreases from x = 0.95 to 1.5. The Curie temperature exhibits an abrupt drop around x = 1.2, where the structural transition takes place. These complex behaviours are strongly correlated to antisite defect concentration in the compounds.

The crystal structure of La5Si4 and Nd5Si4

0The crystal structures of La5Si4 and Nd5Si4 were studied by X-ray powder diffraction (XRD). Both of these compounds crystallize in the tetragonal Zr5Si4 type structure with space group P4(1)2(1)2. The Rietveld powder diffraction profile fitting technique was used for the refinement of the crystal structure. The lattice parameters are a=8.0467(0) Angstrom, c=15.4476(1) Angstrom for La5Si4 and a=7.8694(0) Angstrom, c=14.8077(1) Angstrom for Nd5S4. Atomic occupations, interatomic distances and coordination polyhedra in La5Si4 and Nd5Si4 were derived

Metal–semiconductor transition in non-stoichiometric double perovskite Sr2FexMo2−xO6

The electronic transport properties of the ordered double perovskite oxides Sr2FexMo2-xO6 (0.8 less than or equal to x less than or equal to 1.5) have been investigated. In this system, the samples (x greater than or equal to 1.2) are semiconducting in the temperature range of 4.2 less than or equal to T less than or equal to 300 K. A metal-semiconductor transition occurs when x < 1.2 and the transition temperature T-MS decreases obviously as the Fe, content decreases. Rietveld refinement of the X-ray powder. diffraction profiles indicates that the crystal structure of the compounds Sr2FexMo2-xO6 changes from a tetragonal I4/mmm lattice to a cubic Fm (3) over barm lattice around x = 1.2

Crystal structures of compounds in the pseudobinary system Gd5Ge4-La5Ge4

Crystal structures of compounds at ambient temperature in the pseudobinary system Gd5Ge4-La5Ge4 were studied by X-ray powder diffraction (XRD). There exist three single-phase regions in this system. The crystal structure of Gd5Ge4, La5Ge4 and Gd3La2Ge4, which are prototype compounds in three phase regions, respectively, were reported. The Gd5Ge4 and La5Ge4 crystallize in the orthorhombic Sm5Ge4-type structure with space group Pnma. The ternary intermediate compound Gd3La2Ge4, which is determined for the first time, crystallizes in the monoclinic Gd5Si2Ge2-type structure with space group P112(1)/a. The Rietveld powder diffraction profile fitting technique was used for the refinement of crystal structure. The lattice parameters, atomic occupations, interatomic distances of the Gd5Ge4, La5Ge4 and Gd3La2Ge4 compounds were derived

Mixing effects of light and heavy rare earths in the Laves phase compounds Nd1−xTbxCo2

The lattice constant and magnetic properties of compounds Nd1-xTbxCo2 were investigated by x-ray power diffraction and magnetic measurements. The lattice constant and Curie temperature show linear variations with the Tb concentration, while the saturation moment exhibits an anomaly at a critical concentration x(c)approximate to0.33. The compounds exhibit a field-induced metamagnetic transition from a weak ferrimagnetism to a strong ferrimagnetism in the vicinity of x(c)

Mixing effects of light and heavy rare earths in the Laves phase compounds Nd1−xHRxCo2 (HR = Gd,Tb)

The mixing effects of light and heavy rare earths in cubic Laves phase compounds Nd1-xHRxCO2 (HR = Gd, Tb) have been investigated by means of x-ray powder diffraction and magnetic measurements. In Nd1-xTbxCo2, the saturation moment M-S exhibits in anomaly and could be ascribed to an abrupt jump of the Co moment at a critical concentration x approximate to 0.33, whereas, in Nd1-xGdxCo2, M-S does not show such an anomaly and a relatively simple magnetic behaviour is observed at x(c) approximate to 0.43. The different behaviours of these two systems can be understood by considering the structural distortion of a cubic unit cell at low temperature. A field-induced metamagnetic transition from weak ferrimagnetism to strong ferrimagnetism is observed in both systems. This can be interpreted by the evolution of magnetization with the help of percolation theory. The compensation points are observed in both systems, which are well explained within the two-sublattice model. A double peak of the AC susceptibility observed in Nd1-xTbxCo2 near x(0) approximate to 0.19 does not necessarily mean the occurrence of a first-order phase transition. The observed second-order magnetic phase transition near x(0) can be well described by Landau theory of the phase transition.

Crystal structure and magnetic properties of Pr5Si4−xGex compounds

The magnetic properties of Pr5Si4-xGex (x = 0.0, 1.0, 2.0, 2.5, 3.0, 3.5, 4.0) were investigated by magnetic measurements. The compounds Pr5Si4-xGex crystallize in the tetragonal Zr5Si4-type structure for x = 0.0 and 1.0, in the monoclinic Gd5Si2Ge2-type structure for x = 2.0 and 2.5; and in the orthorhombic Sm5Ge4-type structure for x = 3.0-4.0. Unlike the heavy rare earth RE5Si4-xGex (RE = Gd, Tb, Dy) system, the Curie temperature of this system exhibits the following features: the Curie temperature of the compound increases with the increasing of the Ge content in the tetragonal phase region, whereas it shows a weak dependence on the Ge content in the monoclinic phase region and decreases in the orthorhombic phase region. All of the compounds in this system may have a canted magnetic structure