Zhiqiang Mao

Preparation and phase research of the 110 K high-Tc superconductor Bi2Sr2Ca2Cu3Oy doped with Sb and Pb

Abstract A nearly pure 110 K phase of the ceramic superconductor Bi1.92Pb0.38,0.3SbxSi2Ca2Cu3.2O10-δ was obtained by codecomposition of coprecipatated oxalate technique. These samples with Sb=0.1, Pb=0.38 had zero resistance temperature at 102 K. For those samples with Sb=0.3, Pb=0.3, Tco was equal to 90 K. Their magnetic susceptibility all dropped sharply at 110 K and it does not change at 80 K. X-ray diffraction revealed that there was no 80 K or 20 K phase but the 110 K and an unknown phase. This unknown phase itself is not superconducting above 77 K. The average composition of the unknown phase is given as Bi32Pb3Sb7Sr29Cu7Ox.

Structure and transport properties of Cr doped La214 system

Abstract The structure and normal state transport properties of La 1.85− x Sr 0.15+ x Cu 1− x Cr x O 4 (0≤ x ≤0.30) have been investigated by means of XRD, resistivity and thermoelectric power. The analysis of experimental results indicates that Cr doping introduces disorder into the system, which causes an obvious metal–insulator (MI) transition in the samples with high doping level. This MI transition can be well interpreted in the context of the Anderson theory of disorder-induced localization. In addition, Cr doping leads to the broad peaks in the S – T curves shifting up to high temperature, which is in contrast to that of the non-magnetic element, Al, doped system. This discrepancy is analyzed in terms of the changes of d–p hybridization and spin correlation.

Study on Bi(Pb,Sb)SrCaCuO superconductors prepared by the oxalate co-precipitation technique

A nearly pure 110 K phase of the ceramic superconductor Bi1.92Pb0.38,0.3SbxSr2Ca2Cu3.2O10- delta was obtained by the technique of co-decomposition of co-precipitated oxalate. Those samples with Sb=0.1, Pb=0.38 had a zero-resistance temperature of 102 K. For those samples with Sb=0.3, Pb=0.3, Tco was equal to 90 K. Their magnetic susceptibilities all dropped sharply at 110 K and did not change at 80 K. X-ray diffraction revealed that there was no 80 K or 20 K phase but a 110 K phase and a new phase. This new phase itself is not superconducting above 77 K, and it belongs to the monoclinic system. The average composition of the new phase is given as Bi32Pb3Sb7Sr29Ca23Cu7Ox.

Crystal structure and transport properties of La1.75Sr0.25Cu0.9M0.1O4 (M=Cr, Mn, Fe, Co, Ga and Al)

Abstract The structure and transport properties of samples of La 1.75 Sr 0.25 Cu 0.9 M x O 4 (M=Cr, Mn, Fe, Co, Ga and Al) were investigated by means of X-ray diffraction (XRD) analysis, resistivity and thermoelectric power. The experimental results indicate that Mn doping causes the strongest lattice deformation among these dopants and leads to the largest change in the transport properties. A different change in TEP was observed between magnetic ion doping and nonmagnetic ion doping, which was analyzed in terms of d–p hybridization state and spin correlation.

Growth of 1212 phase PbSrYCaCuO single crystals

Relatively large single crystals of 1212 phase PbSrYCaCuO have been grown by spontaneous nucleation from a eutectic melt. Pure phase 1212 single crystals up to 5 × 4 × 3 mm3 were obtained. The length of the c-axis of the as-grown single crystals is 11.784 A. The crystals have been characterized by X-ray fluorescence spectrometry, X-ray diffraction data (rocking curves), multiple order (001) diffraction and back-reflection Laue photography. The results indicate that the crystals are highly oriented.

A NEW PHASE IN Pb AND Sb DOPED Bi–Sr–Ca–Cu–O SYSTEM

In this paper, a new phase in the Pb and Sb doped Bi–Sr–Ca–Cu–O system with Tc about 140 K is identified by electron diffraction. The transition temperature is determined by the susceptibility measurement. There may exist some connections between the new phase and the 110 K phase. The connections are considered to be the key to the improvement of Tc.

Distortion of the microstructure in Bi1.8Pb0.2Sr2−xCuOy system

Abstract We investigate the Raman scattering and electron diffraction (ED) for the nominal composition of Bi 1.8 Pb 0.2 Sr 2− x CuO y samples. It is found that the Sr vacancies bring about the distortion of Sr–O bond as well as the reduction of the incommensurate modulation with decreasing Sr content in Bi 1.8 Pb 0.2 Sr 2− x CuO y samples. Our analysis indicates that the characteristics in Raman scattering spectra can be explained well by the crystal misfit model.

Crystal growth and physical properties of ternary bismuth molybdenum oxides BixMoOy (x=0.21, 0.25; y=3 + δ)

Large purple-brown crystals of two reduced bismuth molybdenum oxides have been grown from the MoO3–Bi2O3 system by electrolytic reduction of the molten salts. The unit cell parameters and the compositions have been determined by X-ray diffraction and XPS microprobe analysis, respectively. The empirical formulae were refined to Bi0.25MoO3.1 and Bi0.21MoO3.2. Transport measurements (the resistivity and the thermoelectric power) showed that both crystals are semiconductors with p-type carriers, and the thermally activated energy gaps are respectively about 0.296 eV and 0.30 eV. The EPR spectra, the XPS core-level spectra and possible structural features were also considered.

Study on the transport properties in Bi2−xPbxSr1.65La0.35CuOy system

Abstract Two series of samples of Bi2−xPbxSr1.65La 0.35 CuOy (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.6) system with different oxygen concentration were obtained. By means of XRD, resistivity and Raman spectrum, we studied the relation between structure and superconductivity. Pb doping can increases T c onset and T c o to 45K and 37K. Our experimental results indicate that besides carrier concentration, the crystal microstructural characteristic has strong influence on the normal-state transport properties and superconducting transitions.

Anomalous normal-state transport property in Bi-2201 single crystals

Abstract Four samples of Bi2201 single crystals with various carrier concentration were prepared and the electrical resistivity were measured. An interesting phenomenon in the ϱ ab (T)−T curves is that for the sample annealed in vacuum a downward deviation of the resistivity from T-linearity at 160K is observed, which has been revealed to be associated with the opening of a spin gap by means of the measurement of thermoelectric power. The scattering of spin fluctuation as the origin of the T-linear resistivity in Bi2201 system is discussed.