B.L. Gu

Effect of Li doping on structure and superconducting transition temperature of Mg1-xLixB2

Abstract We report the preparation of Mg 1− x Li x B 2 compounds. Nearly single phase samples were obtained for x ⩽0.3. The in-plane lattice parameter a decreases with Li doping, while the lattice parameter c does not show obvious change. The superconducting transition temperature of Mg 1− x Li x B 2 decreases with Li doping and loss of superconductivity occurs for x =0.5 sample. The results were discussed in terms of the T c dependence on hole doping and contraction of the lattice parameter a .

Investigation on the Structure and Superconducting Properties of Mg1 − xMxB2 (M = deficiency or Ca)

We report the preparation of Mg1 − xMxB2 (M = deficiency or Ca) compounds and their structure and superconducting properties. For Mg1 − xB2, although nearly single-phase samples can be obtained for x = 0, MgB4 coexists with the MgB2 phase and some minor impurity phases, and the amount of MgB4 increases with x for 0 < x ≤ 0.5. The lattice parameters a and c of MgB2 decreases and increases, respectively, with the increase of x, and Tc also decreases. While for Mg1 − xCaxB2, the superconducting transition temperature remains unchanged for x ≤ 0.3 and loss of superconductivity occurs for x > 0.3. X-ray diffraction patterns for x ≤ 0.3 samples show that MgB2 phase coexists with CaB6, Mg, and MgO. With increasing x, the amount of CaB6, Mg, and MgO increases, while the amount of MgB2 decreases. The lattice parameters of MgB2 phase do not show any obvious change in contrast to Mg1 − xB2. The results were discussed by considering some possible contributions.

The influence of many-body interaction on the oxygen ordering of the CuO plane in YBaCuO superconductors

Abstract The oxygen ordering in the Cu O plane of YBa2Cu3O7-y is investigated by introducing three-body interaction (TBI) based on the two-dimensional Ising model with the asymmetric next nearest neighbor interaction. The correlation of two neighbor Cu O chains is discussed and phase diagrams are calculated by application of the cluster variation method ( CVM ). The double-cell structure at high temperature can be stabilized by the TBI. The average of the pair probabilities along the Cu O chains shows a smooth plateau in the range of 0.3

Study of synthesis of Pr1−xCexBa2Cu3O7-δ and its transport and magnetic properties

Abstract The synthesis of Pr 1−x Ce x Ba 2 Cu 3 O 7-δ was studied. The results indicated possible doping of Ce into the PBCO structure. Electrical transport and magnetic properties were also investigated, which indicated their insensitivity to Ce doping.

Positron annihilation study of Y1−xPrxBa2Cu3O7

Abstract A positron annihilation study of Y 1− x Pr x Ba 2 Cu 3 O 7 was performed. The results showed that charge transfer between the CuO 2 planes and 1D CuO chains upon Pr doping, as proposed in the literature, did not occur. Pr doping suppressed the anomaly of positron annihilation lifetime near and below T c which has been observed in YBa 2 Cu 3 O 7 . The perfection of the 1D CuO chains was reduced by Pr doping and this may be partly responsible for the increase of resistivity with Pr doping, and finally the semiconducting behaviour of DC resistivity in Y 1− x Pr x Ba 2 Cu 3 O 7 with x > 0.6.

Theoretical study on order-disorder phase transition in the YBa2Cu3O7−x

Abstract The YBa 2 Cu 3 O 7−x undergoes order-disorder phase transitions between orthorhombic and tetragonal structure. This transition modifies both the long-range and short-range order order of the Cu O plane as a function of composition (7−x). This affects thermodynamic quantities such as the order parameter, entropy, and phase diagram as well as lattice parameters. These quantities are calculated with the Kikuchi approximation. The results are in good agreement with experiment.

Power dependence of radiation efficiency of circularly polarized YBa2CU3O7 microstrip antennas

The power dependence of radiation efficiency of two circularly polarized superconducting microstrip antennas, fabricated from YBCO/LaAlO3 films, was investigated. The study showed that this kind of HTS antennas could withstand 5W input power level, beyond which a sharp drop in the radiation efficiency was observed.

Effect of precursor and annealing on the quality of Bi2Sr2CaCu2Ox/Ag thick films

Abstract The effect of precursor and annealing on the quality of Bi 2 Sr 2 Ca 2 Cu 2 O x /Ag thick films was studied. The precursor and annealing treatment were optimized to improve the quality of the thick films.