Enhancement of local microstructural distortions, boundary weak-interactions and crucial defeats performed via Bi+3/La+3 partial substitution in the Bi-2212 matrix
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Tarih
2016
Dergi Başlığı
Dergi ISSN
Cilt Başlığı
Yayıncı
Elsevier Science Sa
Erişim Hakkı
info:eu-repo/semantics/closedAccess
Özet
This exhaustive study examines not only the decrement in characteristic two-stage (pairing and coherence) transitions but also the characteristic variation of the mechanical performance with the partial substitution level of homovalent La nanoparticles on Bi sites in the Bi-2212 crystal structure with the aid of the detailed dc resistivity (rho-T), bulk density, Vickers microhardness (H-v) experimental findings and evaluated theoretical calculations. The experimental results obtained show that both the electrical and superconducting properties being responsible for the potential technological and industrial applications degrade consistently with the increment of the La inclusions in the Bi-2212 superconducting matrix. In fact, the crucial characteristics disappear completely after the critical dopant value of x = 0.20 as a result of the full deformation between the Bi-2212 planes and grain boundaries. In other words, the excess La impurities lead to the disorder and hole localization (filling) problem in the system due to the normal-state electrical resistance transition from the truly-metallic state to the disordered metallic state, and the electrical and superconducting properties demolish totally due to the metal to insulator transition (MIT). In this paper, we focus only on the (Bi, La)-2212 materials exhibiting superconducting behavior to reveal granular superconducting nature of Bi1.6-xLaxPb0.5Sr2.0Ca1.1Cu2.1Oy. As for the theoretical values deduced from the resistivity curves, temperature derivatives of the sample resistivities (d rho/dT) confirm characteristic two-stage transitions in all the samples prepared and both the pairing (bulk genuine) and coherence transitions tend to suppress with the increase of the La inclusions inserted in the Bi-2212 superconducting core as a consequence of the presence of the increased structural inhomogeneities (distribution of oxygen) and grain boundaries. Moreover, Percolation model confirms that the decrease in the coherence transitions with the dopant level is explained with the enhancement of Josephson coupled energy and the degradation of coupling probability. The existence of the relationship between microstructure and strength of interaction between the grains is also confirmed by the bulk density and porosity surveys. As for the load dependent microhardness parameters deduced from Vickers measurements, the pure sample exhibits the Indentation Size Effect (ISE) behavior whereas the La nanoparticles inserted in the Bi-2212 superconducting system make the materials present Reverse Indentation Size Effect (RISE) feature. This is attributed to the fact that the local structural distortions and boundary weak-interactions between the superconducting grains enhance dramatically with the La doping. In other words, plastic (irreversible) deformation becomes a much more dominant character in the materials as a result of the loss of the elastic recovery. At the same time, we analyze the microhardness experimental findings with the aid of the available models such as Meyer's law, proportional sample resistance (PSR), modified PRS (MPSR), Elastic-Plastic Deformation (EPD), Hays-Kendall (HK) and Indentation-Induced Cracking (IIC) approach for the first time. The results determined show that HK approach is found to be the best descriptor to examine the mechanical performance of the pure sample, showing ISE nature while the IIC model is observed to be the most successful model in understanding the mechanical properties of the Bi-site La substituted Bi-2212 superconducting compounds, obeying RISE nature. (C) 2015 Elsevier B.V. All rights reserved.
Açıklama
Anahtar Kelimeler
Bi-Site La Substituted Bi-2212 System, Pairing Transition, Coherence Transition, Percolation Model, Mechanical Performance and Modeling
Kaynak
Journal Of Alloys And Compounds
WoS Q Değeri
Q1
Scopus Q Değeri
Q1
Cilt
658