Improvement in high-Tc phase formation in (thallium–antimony) doped bismuth-based superconducting materials

https://doi.org/10.1016/j.jallcom.2008.10.006Get rights and content

Abstract

Doping of a combination of Tl0.3−xSbx is found to promote the formation of high-Tc (Bi-2223) superconducting phase in Bi1.7Pb0.4Sr2Ca2Cu3Oy compound which consequently results in enhancement of the critical temperatures, i.e. Tc(0) and Tc(onset). The structural information about the samples is retrieved through powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) whereas the critical temperature are determined through measurement of electrical resistivity and magnetic susceptibility. Various proportions of both the high-Tc (Bi-2223) and the low-Tc (Bi-2212) phases are present in the synthesized samples. However, the sample containing a dopant content x = 0.06 exhibits comparatively the lowest value of the ΔT = 5 K and the highest content (82.5%) of the high-Tc phase and zero resistivity critical temperature Tc(0) = 109 K.

Introduction

Bi–Sr–Ca–Cu–O with an orthorhombic structure is an important member of the metal oxide high-Tc superconductor compound (HTSC) family. It can be regarded as a model system for investigation of the appearance of the superconducting state by doping with different elements. A lot of interest is focused on the Bi(2223) phase and substitution of several cations, such as Pb+2, Sb+3, Mg+2, Nb+3, Ga+3, Mo+3 Au+3 and V+5, Pb+2Sb+3, Pb+2Sn+4 and Nd+3Tb+3 at different sites has already been investigated [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15].

It has been reported that the addition of Pb in the Bi(2223) matrix greatly facilitates the formation of the high-Tc domain [1], eases the diffusion of elements to form the high-Tc phase [2] and promotes the stability and abundance of the transient partially melted phase [3]. Addition of antimony is reported to exert a stabilizing influence on the formation of the 2223 phase [4] and believed to play an important role in enhancing the kinetics of especially the decarbonation reaction, as well as the promotion of the high-Tc phase [5]. Increasing annealing time from 10 to 50 h (at 1103 K) of Au-doped Bi(2223) system results in increase in the values of the critical transition temperature, Tc(0) (from 100 to 106 K) and the transport critical current density [6], [7]. On the contrary, the addition of Nb, Ga and Mo results in lowering the zero resistivity critical temperature, Tc(0) of the material [8], [9], [10]. Substitution Mg in place of Ca decreases the critical current density [11]. Higher Tc(0) value of 103 K together with the first Tc(onset) = 102 for the high-Tc phase and second Tc(onset) = 78 K for low-Tc phase have been observed in the bismuth based system doped with vanadium [12]. Doping with a lead–tin combination is reported to be effective in promoting the 110 K phase as compared to doping with Pb and Sn separately [13], [14]. A value of Tc(0) of 108 K has been reported for Nd–Tb doped material, i.e. Bi1−(x+y)NdxTbyPbSr2Ca2Cu3O10 [15].

In the present study, an enhancement of 3 K in the value of the Tc(0) and a regular increase in the magnitude of high-Tc (Bi-2223) phase has been achieved as a result of the addition of a certain concentration range of binary mixture of antimony and thallium.

Section snippets

Experimental detail

The samples with the nominal composition Bi1.7Tl0.3−xSbxPb0.4Sr2Ca2Cu3Oy (x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10 and 0.20) are prepared by the conventional solid-state reaction method [16]. The stoichiometric amounts of high purity Bi2O3 (99.9%) PbO (99.9%), Sb2O3 (99.9%) and SrCO3 (99.9%) supplied by Aldrich and CuO (>99%), CaCO3 (99.9%) and Tl2O3 (>99%) supplied by Fluka are used as starting materials. The required quantities of the materials are weighed, mixed and ground for 1 h in an

Results and discussion

Fig. 1 shows the room temperature X-ray diffraction patterns of bismuth based superconducting materials containing different Tl:Sb ratios, i.e. Bi1.7Tl0.3−xSbxPb0.4Sr2Ca2Cu3Oy (x = 0.00, 0.02, and 0.04, 0.0.6 0.08, 0.10 and 0.20). The intensity of characteristic reflection peak (1 1 5) at 2θ  27° corresponding to the low-Tc phase (2212) decreases regularly from 919.65 cps to 545.56 cps, 276.09 cps, 182.79 cps and 131.71 cps for x = 0.00, 0.02, 0.04, 0.06 and 0.08, respectively, and then increases to 651.18 

Conclusions

Of all the synthesized materials, the sample with an Sb content of x = 0.06 exhibits the highest Tc(0) value (109 K), the highest percentage of Bi(2223) phase (82.45%) and the lowest ΔT value (5 K). However, the entire set of samples shows a constant value of Tc(onset) = 114 K. A gradual decrease in peak intensity corresponding to the low-Tc phase at 2θ between 27 and 28° and regular increase in peak intensity corresponding to the high-Tc phase at 2θ near to 29° with increasing Sb-content in a certain

Acknowledgement

This work has been supported by the Higher Education Commission Pakistan through indigenous scholarship scheme under the grant contact.

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