W. F. Liu

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

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.

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−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.

Valence transition and low field magnetoresistance in (Sr2-xBax)FeMoO6

The crystal structure, electronic transport and magnetic properties of double perovskite (Sr2−xBax)FeMoO6 () are investigated. These compounds exhibit a metal–insulator transition as a function of doping x. The valence transition from Fe3+–Mo5+ to Fe2+–Mo6+ when x exceeds the critical concentration x = 1.6 can lead to a localization of the itinerant electrons and plays a key role in the metal–insulator transition. The bond distance data and composition dependence of the Curie temperature and magnetoresistance suggest this valence transition. The Curie temperature TC shows an enhancement on the Ba-poor side and decreases monotonically with x on the Ba-rich side, which can be understood in terms of two competing effects: anti-site defects and chemical pressure. The low field magnetoresistance shows a close correlation with the Curie temperature of the compounds.

Crystal structure and phase relationships in the pseudobinary system RE5Si4-RE5Ge4 (RE=Nd and Pr) at 1273 K

High-temperature (1273 K) phase relationships in the pseudobinary system RE5Si4-RE5Ge4 (RE=Nd and Pr) were studied by X-ray powder diffraction (XRD). Three structurally distinct phase regions exist in the Nd5Si4-xGex system: the Nd5Si4-based solid solution crystallizing in the tetragonal Zr5Si4-type Structure with space group P4(1)2(1)2, the Nd5Ge4-based solid solution crystallizing in the orthorhombic Gd5Ge4-type structure with space group Pnma and a ternary intermediate phase crystallizing in the monoclinic Gd5Si2Ge2-type structure with space group P112(1)/a. In the Pr5Si4-xGex system, there are only two structurally distinct phase regions: the Pr5Si4-based solid solution crystallizing in the tetragonal Zr5Si4-type structure with space group P4(1)2(1)2 and the Pr5Ge4-based solid solution crystallizing in the orthorhombic Gd5Ge4-type structure with space group Pnma. The Rietveld powder diffraction profile fitting technique was used for the refinement of crystal structures. The lattice parameters, atomic positions and interatomic distances in the high-temperature Nd5Si2.8Ge1.2, Nd5Si2Ge2 and Pr5Si2Ge2 compounds were derived

Enhanced micro-vibration sensitive high-damping capacity and mechanical strength achieved in Al matrix composites reinforced with garnet-like lithium electrolyte

A novel micro-vibration sensitive-type high-damping Al matrix composites reinforced with Li7-xLa3Zr2-xNbxO12 (LLZNO, x = 0.25) was designed and prepared using an advanced spark plasma sintering (SPS) technique. The damping capacity and mechanical properties of LLZNO/Al composites (LLZNO content: 0-40 wt.%) were found to be greatly improved by the LLZNO addition. The maximum damping capacity and the ultimate tensile strength (UTS) of LLZNO/Al composite can be respectively up to 0.033 and 101.2 MPa in the case of 20 wt.% LLZNO addition. The enhancement of damping and mechanical properties of the composites was ascribed to the intrinsic high-damping capacity and strengthening effects of hard LLZNO particulate. This investigation provides a new insight to sensitively suppress micro-vibration of payloads in the aerospace environment.

Preparation and enhancement of ionic conductivity in Al-added garnet-like Li6.8La3Zr1.8Bi0.2O12 lithium ionic electrolyte

Garnet-like Li6.8La3Zr1.8Bi0.2O12 (LLZBO) + x mol.% Al2O3 (x = 0, 1.25, 2.50) lithium ionic electrolytes were prepared by conventional solid state reaction method under two different sintering temperatures of 1000°C and 1100°C. XPS, induced coupled plasma optical emission spectrometer (ICP-OES), XRD and AC impedance spectroscopy were applied to investigate the bismuth valance, lithium concentration, phase structure and lithium ionic conductivity, respectively. Electrical measurement demonstrated that ionic conductivity of Al-added LLZBO compounds could be obviously improved when the sample sintering temperature increased from 1000°C to 1100°C. The highest ionic conductivity 6.3×10-5 S/cm was obtained in the LLZBO-1.25%Al sample sintered at 1100°C, in consistent with the lowest activation energy 0.45 eV for the lithium ion migration. The mechanism related with good ionic conductivity in the Al-added LLZBO sample was attributed to the lattice distortion induced by the partial Al substitution at Zr sites, which is helpful to improve the migration ability of Li ions in lattice.

The effect of Y substitution on the magnetic properties of the compound NdCo9.5V2.5

The Nd1-xYxCo9.5V2.5 compounds with x = 0-1 crystallize in the tetragonal ThMn12 structure. The lattice parameters a, c and the cell volume V decrease with increasing Y content. The Curie temperature increases for x less than or equal to 0.2, then decreases with increase of the Y content. The exchange field coefficient n(RCo) was derived from the Curie temperature and follows the general trend of rare-earth-3d intermetallic interaction exchange. The high field saturation magnetization decreases with increase of the Y content. A domain wall pinning phenomenon was observed in all of the compounds and the substitution of Y for Nd makes this phenomenon less obvious. High field measurements of the magnetization show a field induced metamagnetic transition in each compound and the critical field H-crit(H) decreases with increase of the Y content.