Role of Y substitution for Ca-site on magneto-resistivity properties of Bi-2212 superconductor rods prepared by LFZ

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Highlights

  • Well-textured Y-substituted Bi-2212 rods are successfully produced using LFZ method.

  • The applied magnetic field up to 5T mostly affects intergranular regions rather than intra-grain ones.

  • The magnetic field and temperature dependence of U(H,T) is found to be U(H,T)∼ΔT H−η where η = β+n.

Abstract

This comprehensive study delves into the effect of partial Y3+ substitution for Ca2+ in Bi2Sr2CaCu2O8+y superconducting rods prepared by the laser floating zone method (LFZ). The critical transition temperatures (Tconset, Tc, Tcoffset), activation energy (U), irreversibility field (Hirr), upper critical magnetic field (Hc2), coherence length (ξ), and penetration depth (λ) are determined by means of magneto-resistivity measurements performed between 0 and 5 T. According to the resistivity-temperature graph for zero fields, Tcoffset values tend to decrease regularly from 90.8 K to 87.1 K, and the residual resistivity values increase steadily from 0.14 to 9.7 mΩ .cm with the Y-content. The change of these two parameters is a sign that Y-introduction into the Bi-2212 matrix undermines the inter-grain coupling and increases the level of permanent-defects in the crystalline structure. However, the relatively high Tcoffset values and extremely low residual resistivity, especially in the pure and low Y-substituted samples, reflect the success of the LFZ process in growing homogeneous and well-oriented Bi-2212 grains. The resistivity transition broadening is observed when the applied field increases and Tcoffset values decrease dramatically, i.e. from 90.8 K to 72.1 K for the pure sample and from 87.1 K to 48.2 K for the 0.20Y-substituted ones. The calculated U values using the TAFF model decrease with the increase of the Y-content and the magnetic field. In addition, the magnetic field and temperature dependence of U is expressed by using U(H,T) ΔT H−η equation. Deduced parameters of Hirr and Hc2 from magneto-resistivity curves and theoretical findings of ξ and λ also favor the degradation of U values with the augmentation of Y-content in the Bi-2212 rods.

Introduction

Bi–Sr–Ca–Cu–O (BSCCO) system with the general formula of Bi2Sr2Can-1CunO2n+4+y is one of the most studied materials among high-temperature superconductors (HTSCs). The n value indicates the number of copper-oxide layers in the crystal structure, describing three different phases in the BSCCO family, namely Bi-2201, Bi-2212 and Bi-2223, with 20, 85, and 110 K critical temperatures (Tc), respectively [1,2]. The BSCCO family is characterized by high critical magnetic field (Hc), and critical current density (Jc), which allow its application in areas such as high field magnets [3], power cables [4], magnetic resonance imaging systems [5], or resistive fault current limiters [6]. Among the phases of in the BSCCO family, Bi-2212 one is the good candidate for these technological applications due to its high thermodynamic stability over a wide temperature range, lower fabrication cost, and lesser weak link problems compared to Bi-2223 phase [[7], [8], [9]]. On the other hand, an adequate grain orientation is necessary in these bulk materials to be used in the above-mentioned technological applications. This necessity gave birth to various methods such as the micro-pulling down [10], the hot uniaxial pressing [11], the laser floating zone (LFZ) [12], or the electrically assisted laser floating zone (EALFZ) [13]. Among these methods, LFZ stands out as a useful method for very rapidly growing well textured Bi-2212 rods from the melt, with the c-axis of grains perpendicular to the growth direction and, consequently, conducting CuO2 planes grow quasi-parallel to the rods axis [14]. In these growth conditions, transport properties along the fiber axis are maximized as a result of the reduction of high angle grain boundaries [15]. As it is known for HTSCs, when the magnetic field is between the lower critical field (Hc1), and upper critical field (Hc2), they are in the so-called mixed state, where the magnetic field penetrates the superconducting material in the form of quantized magnetic vortices. When a current is passed through a superconducting material in a mixed state, the Lorenz force emerges, consuming energy by forcing the magnetic vortices into motion. The mechanisms opposing the Lorentz force in these materials are the pinning forces created by pinning centers. In general, pinning centers in the material can be naturally formed in grain boundaries and crystal defects, or by artificial methods such as chemical doping or neutron radiation [16]. In fact, chemical doping is of great interest because it is an easily controlled, not destructive and efficient method to improve mechanical, structural and superconducting properties of the HTSCs [8]. In particular, the substitution of rare-earth elements (Re) for Ca in Bi-2212 phase leads to structural stability and helps in understanding the nature and variation of charge carries with substitution [17]. To this end, looking at Bi-2212 in particular, the chemical substitution of Ca2+ by Y or lanthanides (Ln) is frequently preferred [[18], [19], [20], [21], [22], [23], [24], [25], [26]]. Most of these studies show that superconductivity is suppressed, and metal-insulator transition takes place at high level of Y or Ln substitutions [[22], [23], [24], [25]]. Resistivity versus temperature measurement under different magnetic fields (magneto-resistivity) is a very useful method to determine the effect of doping elements on the pinning properties. In the current study, the resistive transition broadening as a function of magnetic field and temperature in Bi2Sr2Ca1-xYxCu2O8+y with x = 0.0, 0.05, 0.10, 0.15 and 0.20 superconductors fabricated by laser floating zone method (LFZ) is examined on the basis of thermally activated flux flow model (TAFF).

Section snippets

Experimental procedure

Polycrystalline Bi2Sr2Ca1-xYxCu2O8+y (x = 0.0, 0.05, 0.10, 0.15 and 0.20) ceramics are prepared by the classical solid state reaction technique from commercially available of Bi2O3 (Sigma-Aldrich 99.9%), SrCO3 (Sigma-Aldrich 98+%), CaCO3 (Sigma-Aldrich 99%), Y2O3 (Sigma-Aldrich 98+%), and CuO (Sigma-Aldrich 99%) powders. Initially, the chemicals are weighed according to stoichiometric proportions, mixed and ball milled in acetone media at 300 rpm for 30 min. Later, the slurry is dried using

Results and discussion

The electrical resistivity versus temperature curves (in the absence of magnetic field) of the Bi2Sr2Ca1-xYxCu2O8+y superconducting rods with x = 0.0, 0.05, 0.10, 0.15 and 0.20 are given in Fig. 1. Before moving on to detailed discussions, it should be noted that a two-step resistance transition (like a good example given in Fig. 1) is generally observed in HTSCs. Accordingly, three parameters can be obtained, namely onset critical temperature (Tconset), mid critical temperature (Tcmid) and

Conclusion

In this study, the electrical, and superconducting properties, as well as activation energies of Bi2Sr2Ca1-xYxCu2O8+y (0 00.20) superconducting rods obtained by the LFZ technique have been investigated with the help of magneto-resistance measurements performed between 0 and 5 T. The residual resistivity (ρ0) determined from the resistivity-temperature curves measured at 0 T have increased steadily from 0.14 to 9.7 mΩ cm with the Y-content. Although these values have increased with the

CRediT authorship contribution statement

M. Gürsul: Writing – original draft, Writing – review & editing, Data curation, Formal analysis, Visualization. C. Özçelik: Contributor, Data curation, Formal analysis, Visualization. I. Ergin: Contributor, Data curation, Formal analysis, Visualization. M.A. Madre: Writing – original draft, Contributor, Visualization. A. Sotelo: Leader, Writing – original draft, Writing – review & editing, Visualization. B. Özçelik: Leader, Writing – original draft, Writing – review & editing, Visualization.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

A. Sotelo and M.A. Madre acknowledge the Spanish MINECO-FEDER project (MAT2017-82183-C3-1-R) and the Aragón Government (Research Group T54-20R) for financial support. Authors would like to acknowledge the use of Servicio General de Apoyo a la Investigación-SAI, Universidad de Zaragoza.

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