Liang Jing-Kui

The preparation, superconductivity and thermal characteristics of the Tl−Ba−Ca−Cu oxide superconductor

The high-Tc Tl-Ba-Ca-Cu oxide superconductor with a critical current density Jc=1630 A cm-2 at 77 K has been prepared and high-Tc properties have been observed in this system. The zero-resistance transition temperatures T(c0)=120.3 K and Tc(AC chi )=119 K were observed by resistance and magnetic susceptibility measurements, respectively. The stability and reproduction of the materials are absolutely necessary. Thermal characteristics were investigated.

EFFECT OF HIGH-ANGLE DIFFRACTION DATA ON RIETVELD STRUCTURE REFINEMENT

By utilizing the powder x-ray step-scanning diffraction data of PbSO4, we have studied the effect of the diffraction data (with different high-angle upper-limit: 2θm = 160, 140, 120, 100, 80, 70 and 60°) on the precision of the Rietveld refined lattice constants, structure parameters, and agreement indices. These refined results are compared with those obtained from the single crystal data. It is revealed that the deviations of the refined lattice constants, atomic positions and isotropic temperature factors decrease, and agreement indices become smaller with the increase of 2θm. But when 2θm > 120°, the deviations and agreement indices decrease very slowly. Therefore, in general cases, 2θm should be taken to be 120° or larger in order to get satisfactory refined results in the Rietveld crystal structure refinement.

Thermodynamic study on the Sm-Ba-Cu-O system

The assembly for EMF measurement with CaF2 single crystal or MgO partially stabilized zirconia as solid state electrolyte has been constructed. From the EMF data, the standard Gibbs energies, standard enthalpies of formation and standard entropies of six complex oxides in the Sm-Ba-Cu-O system were calculated. The decomposition pressures of these complex oxides were derived.

Structure and magnetic properties of LaCo13-based alloys

The structure and magnetic properties of two series of LaCo13-based alloys, LaCo13-xFex (0 ≤ x ≤ 6) and La1-xRx(Co, Fe)13 (x = 0.1, 0.2; R=Y, Ge, Pr, Nd Sm, Gd, Tb, Dy, Ho, Er, and Yb), are studied by x-ray diffraction and magnetic measurements. In the above-mentioned composotions, all the samples display a structure of NaZn13 type (space group: Fm3c). In LaCo13-xFex system, as the iron content increases, its Curie temperature decreases, while the magnetic moment per 3d atom increases. This may be explained by a rigid band model. In the other alloy system, the Curie temperature goes through a maxium at R=Gd, and this reflects the influence of R - T interaction. It is also observed that saturation magnetization varies with R and gets lower when R is a heavy rare earth element. The contribution of R is close to that of a free-ion moment. La0.9Pr0.1Co9Fe4 has the largest value 29μB/f.u.