Chen Zhao-Jia

Phase identification of 140 K superconducting Bi2Sr2Ca2Cu3O10-δ doped with Sb and Pb

The Tc=140 K superconductor Bi2Sr2Ca2Cu3O10- delta doped with Sb and Pb was characterised by powder X-ray diffraction, electron diffraction and electron probe microanalysis. It was observed in the specimen that there was a new phase Bi3Sb0.8Pb0.2Sr4.1Ca3.9CuO15+ delta besides 2212, 2223 and a little CuO. The new phase belongs to the monoclinic system with cell dimensions a=22.14, b=5.902, c=19.91 AA and beta =99.7 degrees .

Superconducting properties in Bi2−x−yPbxSbySr2Ca2Co3Oz (x=0, 0.1, 0.3, 0.5; y=0, 0.1)

Abstract The temperature of zero resistance of the previously reported 120K superconductor in the Biue5f8Sbue5f8Srue5f8Caue5f8Cuue5f8O system was 75 K. We added Pb to the Biue5f8Sbue5f8Srue5f8Caue5f8Cuue5f8O system, so that the temperature of zero resistance was raised to 108 K.

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.

La2−xSrxCuO4: Low temperature specific heat and thermal conductivity

Abstract We present simultaneous measurements of the low temperature (0.04K to 1.2K) specific heat and thermal conductivity for a series of four sintered samples from the La 2−x Sr x CuO 4 system. By systematically varying the strontium (hole) concentration from x =0.05 (near-insulator) through to x =0.27 (near-metallic), we were able to study the thermal properties of the different superconducting regimes in this cuprate system. The thermal conductivity data are characterised by a weakening of the temperature dependence from T =3 to T =1 , observed in all the samples below 1K. A linear temperature variation in the specific heat data for the two most inhomogeneous superconductors ( x =0.05 and 0.27) was replaced by a T 0.5 dependence for the samples with the higher transition temperatures ( x =0.1 and 0.15). The specific heats of all the samples showed a large upturn (proportional to T −2 ) at the lowest temperatures. The coefficients of this T −2 term were found to have a minimum for x =0.15. We discuss these effects in terms of possible transport mechanisms.

Two lower critical fields Hc1(0) in the high-Tc superconducting Bi2-xPbxSr2Ca2Cu3Oy system

Magnetization curves for the Bi2-xPbxSr2Ca2Cu3Oy system at different temperatures are reported. There are two phases with different critical temperatures. Corresponding to the two phases, two lower critical fields Hc1(0) are obtained.

Spin fluctuation effects in the specific heat of CnNi alloys

Abstract The electronic specific heat of paramagnetic and weakly ferromagnetic CuNi in the temperature range 1.5 K to 240 K is shown to be strongly enhanced at very low temperatures by spin fluctuations, and to approach the unenhanced band value at high temperature.