Cao Liezhao

Zero resistance at 132K in the multiphase system of Bi1.9−xPbxSb0.1Sr2Ca2Cu3Oy with x=0.3, 0.4

Abstract Superconducting properties of the multiphase compounds of ( Bi 1.9− x Pb x Sb 0.1) Sr 2 Ca 2 Cu 3 O y have been investigated. Zero resistance at 132K has been observed with x =0.3 and 0.4. Two samples with 132K zero resistance were stable in low temperature circling (77K to 200K). Zero resistance were down to 112K( x =0.3) and 106K( x =0.4), but the a.c susceptibilities of the two samples still have large drop at 132K after several circles from 77K to room temperature.

Enhancement of Critical Current Density in Graphite Doped MgB2 Wires

Graphite doped MgB2−xCx (x = 0.00, 0.05, 0.10) wires were fabricated via the in situ powder-in-tube method in flowing argon by using low carbon steel tubes as the sheath materials. With the increase of graphite concentration, the amount of unreacted graphite in the core area increases, and the average grain size of MgB2 decreases. It is found that the critical current density Jc can be significantly improved by graphite doping. The MgB2 wire with x = 0.05 exhibits the best Jc value of 16710 A/cm2 at 6 K, 4.5 T, but the MgB1.9C0.1 wire has the highest Jc value of 2060 A/cm2 at 6 K, 8 T. It is suggested that the enhancement of Jc is due to not only the improvement of the microstructure features but also the introduction of pinning centres.

Superconductivity in Sr-Y-Cu-O system

Abstract A stable and reproducible superconductivity transition has been observed through a.c. magnetic susceptibility and electrical resistivity measurements in the (Srx Y1−x)CuO3−Y with x=0.375, 0.4, and 0.5. The highest Tc(π=0) is 90.5K and the width of transition δTc=1.5K.

SUPERCONDUCTIVITY AT 27-K IN NB-1222 CUPRATE - NBSR2(GDCE)2CU2OY

Samples of NbSr2Gd2-xCexCu2Oy have been prepared by solid state reaction. The X-ray powder diffraction patterns show that a single phase can be formed in the composition range of 0.49 < x< 0.51 that has the TaSr2 (NdCe)2Cu2Oy Structure [ 11, the cell para

Study on the specific heat anomalies of La2−xSrxCuO4−δ polycrystalline samples

Abstract The specific heat anomalies of La 2− x Sr x CuO 4− δ polycrystalline samples ( x =0.25, 0.20, 0.16, 0.15, 0.14, 0.12, 0.10, 0.08) were measured. The specific-heat jump at the superconducting transition temperature changes systematically with Sr substitution. The maximum specific-heat jump corresponds to the sample with Sr content x = 0.16. The bulk superconducting phase diagram is similar to that deduced from resistivity measurement. The measurement shows that only the sample with x = 0.16 presents optimal electronic single phase properties and the superconducting transition temperature T c directly related to the electron density of states at the Fermi level N ( E F ).

High Tc superconductivity in single crystal YBa2Cu3O7-δ

Abstract We report the structure and superconductivity of single crystal YBa2Cu3O7−δ. The maximum dimensions of single crystal are 2.5×2.5×1.5 mm3. It is orthorhombic structure with space group Pmmm, cell parameters are a =3.88 A , b =3.82 A , c =11.68 A . The superconducting critical temperature is Tc=91 K. And a resistance anomalous phenomenon is also observed at 280 K.

Electronic properties of superconducting Pb-doped YBa2Cu3O7-y system

Abstract The relationships between the granular structure, normal state resistivity and the superconductivity were systematically investigated in YBa 2 Cu 3-x Pb x O y system. We find that the normal state resistivity and the critical current density are sensitive to the amount of lead. Especially, the critical current density of the sample with x =0.1 is more twice higher than that of the sample with x =0 at liquid nitrogen temperature. The effects of the weak-link structure of sintered bulk samples on the electronic properties are discussed with the theories of Mcmillan and Ambegaokar-Barataff.

Zero resistance above 90K in superconducting oxides ErBaCuO and YbBaCuO

Abstract Superconductivity transition has been observed by electrical resistance and a.c. magnetic susceptibility measurements in ErBaCuO and YbBaCuO systems. The highest T c ( ϱ =0) is 90.3K for ErBaCuO and 91K for YbBaCuO.

The specific heat of BSCCO (2201) single crystal at low temperatures

Abstract We report on the specific heat of a Bi 2 Sr 2 CuO y single crystal measured between 0.1K and 5K. The measurements were carried out with the single crystal first in the semiconducting state and then, after oxygenation in a superconducting state. The specific heat of the latter showed a well defined peak centred at 4.1K associated with the superconducting transition. At low temperatures both states exhibited a 1/T 2 term associated with the nuclear spins of the copper ions. In addition both could be fitted well to a function which includes a residual term of the form αT n where n is less than unity. The exponent n is smaller for the superconducting state than for the semiconducting state, as is found in some other systems.

The influence of Pb on the stability of the Bi-type modulated structure

Abstract The mechanism of the Bi-type modulated structure was studied in Bi-based high-temperature superconductors with nominal compositions of Bi2Sr2CaCu2Oy, Bi1.85Pb0.15Sr2CaCu2Oy and Bi1.8Pb0.35Sr2Ca2Cu3O y. It was found that the three samples annealed in oxygen flow showed the presence of Bi-type modulation in electron diffraction patterns; after the samples were annealed in nitrogen atmosphere the Bi-type modulation still existed for the sample Bi2Sr2CaCu2Oy but disappeared completely for the Pb- doped samples Bi1.85Pb0.15Sr2CaCu2Oy and Bi1.8Pb0.35Sr2Ca2Cu3Oy. This suggests that doping Pb in the Bi-Sr-Ca-Cu-O system strongly changes the stability of the Bi-type modulation. It is confirmed that the driving force of Bi-type modulation is not the consequence of extra oxygen for the charge balance, but the adjustment of the BiO layer to the lattice mismatch.