Zhaojia Chen

Microstructure and Superconductivity in Bi?Sr?Ca?Cu?O System Doped with Pb and Sb

A series of samples BixPbySb0.1Sr2Ca2CuzOw has been produced by two methods. X-ray diffraction patterns revealed that there was a nearly single 2223 phase with a small amount of monoclinic phase in both two kinds of samples. The samples made by the oxalate coprecipitation technique had TCO=102 K. The A.C. magnetic susceptibility showed only one sharp transition at 110 K. For samples prepared by a mixture of powders, the electrical resistance began to drop at 140 K, reaching zero at 92 K. Their A.C. magnetic susceptibility showed sharp transition at 135 K, and no transition at 110 K. The monoclinic particles were segregated on the surface of the samples. The intergrowth of 2223 and monoclinic phases at their boundaries caused the partial distortion of the 2223 phase. The distorted 2223 phase might be responsible for the 130 K superconductivity.

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.

A structural change at 110 K of single-phase Bi(Pb)-Sr-Ca-Cu-O ceramic superconductor

Elastic modulus softening and a corresponding internal friction peak occur at 110 K in 2223 single-phase samples of Bi(Pb)-Sr-Ca-Cu-O superconductor prepared by the sol-gel method. The sudden change in internal friction has the characteristics of a structural transition. There is a clear, anomalous peak with Delta Cp=1.8 mJ g-1 K-1 in the specific heat versus temperature curve, corresponding to a superconducting transition. This indicates that some kind of structural readjustment occurs before the superconducting transition.

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.

Characterization and properties of YBCO samples containing metastannate inclusion

As is well known, it is possible to increase the critical current density of type II superconductors by creating defects in the matrix [1, 2]. Many researchers have tried to increase the defect density by irradiation and cation substitution [3]. Others have obtained highly dense crystal defects such as dislocations and stacking faults around 211 particles by precipitation of the 211 phase from the melt [4]. Because the strain generated by precipitates or inclusions in the neighbouring matrix will interact more strongly with the magnetic flux line as the magnitude of the strains increases [5]. This suggests that stronger pinning might be obtained through the presence of inclusions due to the existence of strains resulting from the mismatch of lattice parameters or phase transformations of inclusions. Following from the above, we attempted to increase the critical current density, and not to decrease superconducting transition temperature, by the addition of perovskite structure particles, which would produce some kind of defects in 123 matrix to enhance the interaction with a magnetic flux. The samples were prepared from the decomposed powders of citric gel [6] with the nominal composition of Y:Ba:Cu as 2:1:1 and 0:1:1, CuO and the powders of BaSnO3, CaSnO3 and SrSnO3, respectively, which were prepared from the decomposition of BaSn(OH)6, SrSn(OH)6 and CaSn(OH)6 coprecipitation powders. The 211 and 011 powders were calcined at 900 °C for 10 h, mixing 211,011 and CuO with nominal composition Y:Ba:Ca = 1:2:3:, adding 5 wt % metastannate, ground and pressed at 40 kgmm -2 into pellets 13 mm in diameter. The pellets were sintered at 920 °C for 20 h in air and cooled in a furnace. X-ray powder diffraction was measured using CuK~ radiation at 40 kV and 100 mA to identify the various phases. The a.c. magnetic susceptibility of samples was measured employing a mutual inductance bridge with precision of 0.1/xV. A Hitach X-650 scanning electron microscope (SEM) equipped with a wavelength-dispersive meter (WDM) was used to observe fracture sections and elemental analysis. An H-800 transmission electron microscope (TEM) was used to determine the structure of phases. Fig. 1 shows the X-ray diffraction patterns of a Y B a C u O sample with BaSnO3 addition. It can be seen that some characteristic diffraction peaks of 211 (20=29 .3 , 30.5 and 31.6 ° ) and BaSnO3

Electro-magnetic properties of the La2-xMxCuO4 (M=Sr, Ba) and La1.85Sr0.15Cu1-xMxO4 (M=Mn, Mg, Ni and Zn)

Abstract The structural, resistivity, and DC susceptibility of the mixed compounds La 2−x M x CuO 4 (0.07 1.85 Sr 0.15 Cu 1−x M x O 4 (0

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.

ZERO RESISTANCE AT 113 K IN THE (Bi1.9−xPbxSb0.1)Sr2Ca2Cu3Oy SYSTEM (x=0.1, 0.2, 0.3, 0.4)

The 110 K superconducting transition in Bi-Pb-Sr-Ca-Cu-O system has been observed by S.M. Green et al.1 However, Tc, zero was 107 K. We have achieved zero resistance at temperature 113 K in Bi-Pb-Sb-Sr-Ca-Cu-O system, higher than that of Bi-Pb-Sr-Ca-Cu-O by more than 6 K. At room temperature, this high temperature phase is steady. After several heating-cooling circle, Tc, zero decreases slowly.

EVIDENCE FOR THE EXISTENCE OF 90º CRYSTAL DOMAINS IN 1212 PbSrYCaCuO SINGLE CRYSTALS

Single crystals of pure phase 1212 with dimensions up to 5×4×3 mm3 have been successfully grown from a starting composition of Pb0.5Sr2.5Y0.75Ca0.25Cu2Ox by the spontaneous nucleation method. 1212 single crystals have an orthorhombic structure with a=5.466 A, b=5.378 A, and c=11.784 A. X-ray transmission scanning measurements were first carried out for as-grown 1212 single crystals. The measurements indicated the existence of many crystal domains formed by the rotation by 90o of one domain relative to another. The sizes of the domains are relatively large as estimated by θ−2θ scans for various conditions.

The superconductivity of La1.8 5Sr0.1 5Cu1−xMxO4−y (0<x<0.03) (M=Mg,Mn)

The structure analysis and superconductivity in the mixed compounds La1.8 5Sr0.1 5Cu1−xMxO4−y (0<x<0.03) (M=Mg,Mn) were studied. It is observed that the crystal structure is not distorted. The Superconducting transition temperature Tc drops linearly with the increase of the M(M=Mg,Mn) content. Superconductivity is suppressed above x=0.022 for Mg doping and x=0.012 for Mn doping, respectively. The difference of doping results for magnetic and nonmagnetic ions is given, and the origin of the depression on Tc is discussed in this paper.