In this paper we report our results on the effect of Sb-doping on the superconducting properties of the compound Bi 1.6- x Sb x Pb 0.4 Sr 2 Ca 2.2 Cu 3.5 O y for x =0.0, 0.1 and 0.2. Through a series of experiments it is shown that the small addition of Sb ( x =0.1) increases the 2223 phase fraction and enhances T c as well as intergrain J c , provided that the sintering parameters are carefully optimized. Thus, for example, the composition Bi 1.5 Sb 0.1 Pb 0.4 Sr 2 Ca 2.2 Cu 3.5 O y sintered at 830°C for 12 h has a T c0 (zero resistivity) = 108 K, a drop in the χ'- T plot at 108 K and in intergrain J c =695 A/cm 2 (as estimated on the basis of Clem's model). Any lowering of sintering temperature below 830°C or prolonging of sintering at 830°C leads to a degradation in the superconducting parameters. Similarly, a reduction in T c and J c is observed if Sb concentration is increased to 0.2. The sintering parameters (temperature and duration) thus appear to be critical for a given composition.

Effect of Sb doping on critical current density in Bi (Pb)-Sr-Ca- Cu-O high-Tc superconductors

In an attempt to increase the volume fraction of the high Tc phase Bi2Sr2Ca2Cu3Oy(2223), mixed doping of Pb+Sb was performed in a Bi superconducting system. A stoichiometric starting composition with Bi partially replaced by Sb+Pb was found to result in a system with an unusually high value (>or=140 K) of onset transition temperature (Tcon). A Tco of 111 K could be achieved with about 75 to 80% 2223 content, as calculated from the XRD data, for annealing duration of about 100 h, which is much less than in an undoped or Pb-doped Bi system. The most important characteristic of this system is the presence of a 'new phase' with its strong and sharp reflections near 2 theta =30 degrees in the XRD pattern. Such a phase could never be detected in the Bi system doped only with Pb. Interestingly, the 'new phase' is found to be present even in the calcined material and its existence has been shown at all stages of annealing. R-T characteristics and XRD analysis have revealed the development of the low Tc phase Bi2Sr2Ca1Cu2Oy (2212) at a very early stage of annealing, and further the transformation of 2212 into 2223, always in coexistence with the 'new phase' and CuO. Incorporation of Sb resulting in the formation of the 'new phase' appears to be responsible for Tcon values that are unusually high and also for making the kinetics of the solid state reaction of 2223 formation much faster.

http://iopscience.iop.org/article/10.1088/0953-2048/4/1/003/pdf

Enhancement of Tcon, appearance of a 'new phase' and faster kinetics in Pb+Sb doped Bi2Sr2Ca2Cu3Oy

The superconducting properties and microstructure evolution of Hg doped Bi based compounds with the nominal composition of Bi 1.7 (Pb 0.3 )Hg x Sr 2 Ca 2 Cu 3 O δ (0⩽ x ⩽0.4) were investigated as a function of the doping level and sintering temperature. The transition to the superconductive state was observed at 94 K in the Hg doped samples sintered for 4 h and the addition of Hg increased the onset transition temperature to ≈ 118 K. Aligned grain structures and improved inter-grain linkage were observed in all the microstructures by scanning electron microscopy (SEM). The density of the Hg doped samples also increased with increasing the Hg content.

Superconductivity and microstructure in the Bi1.7(Pb0.3)HgxSr2Ca2Cu3Oδ (0⩽x⩽0.4) system

The effect of a small amount of Sb doping (5%) on the formation of the high temperature superconducting phase has been investigated on the Bi1.5Pb0.5Sr2Ca2Cu3Oy compound. It is observed that at 860°C the Tc zero value depends on the sintering time. It first increases to a maximum value of 96 K and then decreases to a stable lowest value of 88 K. The samples have been characterized by X-ray diffraction (XRD), four probe electrical resistance and current density measurements. The XRD revealed the presence of two phases: an orthorhombic high-Tc 2223 phases with lattice constants a = 5.395 A, b = 5.508 A, c = 37.0422 A and another tetragonal low-Tc 2212 phase with lattice constants a = b = 5.419 A, c = 30.832 A.

THE EFFECT OF 5% Sb DOPING ON HIGH Tc SUPERCONDUCTIVITY IN (Bi, Pb)2Sr2Ca2Cu3Oy COMPOUND

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.

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

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 .

https://iopscience.iop.org/article/10.1088/0953-2048/3/2/008/pdf

Fan Chengao

Papers

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

The study on the structures of nonsuperconducting Bi2Sr2CaGa0.6Co1.4Oy phases