Physical Properties and DiffusionCoefficient Calc

Authors: O Ozturk E Asikuzun S Kaya M Coskunyurek G Yildirim M Yilmazlar C Terzioglu

Publish Date: 2012/06/09

Volume: 25, Issue: 7, Pages: 2481-2487

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Abstract

This study includes two parts I investigation of the effect of different annealing time 10 h 30 h and 60 h on physical superconducting and microstructural properties of Fediffused Bi2223 superconductor ceramics prepared by the conventional solidstate reaction method with the aid of the Xray diffraction XRD scanning electron microscopy SEM dc resistivity ρ–T and transport critical current density J c measurements and II determination of the diffusion coefficient and the activation energy of iron in the Bi2223 system In the former part the zeroresistivity transition temperature T c phase purity volume fraction holecarrier concentration lattice parameters surface morphology texturing crystallinity grain connectivity grain size and room temperature resistivity values of the bulk samples are found and compared with each other The results obtained show that both the zero resistivity transition temperature T c and transport critical current density J c regularly enhance with the increment in the diffusionannealing time The maximum T c of 107±02 K and J c of 500 A cm−2 are observed for the sample annealed at 830 °C for 60 h As for the XRD investigations according to the refinement of cell parameters done by considering the structural modulation the enhancement in the diffusionannealing is confirmed by both a decrease of the cell parameter a and an increase of the lattice parameter c of the samples meaning that the greatest Bi2223 phase fraction belongs to the sample annealed at 830 °C for 60 h Moreover SEM images display that the sample has the best crystallinity grain connectivity and largest grain size Based on the results the superconducting and microstructural properties improve with the increase in the diffusionannealing time In the latter part Fe diffusion in the Bi2223 system is examined in a range of 500–830 °C by the variation of the lattice parameters evaluated from the XRD patterns The temperature dependence of the Fe diffusion coefficient is described by the Arrhenius relation D=427×10−5exp−127±010 eV/kBT and the related activation energy of the iron in the Bi2223 system is found to be about 127 eV The relatively low value of activation energy obtained illustrates that the migration of the Fe ions primarily proceeds through defects such as pore surfaces and grain boundaries in the polycrystalline structure leading to the improvement of the microstructural and superconducting properties of the samples supported by the results of part I All in all the aim of the present study is not only to analyze the role of diffusionannealing time on superconducting and microstructural properties of Fediffused Bi2223 superconductors but also to find the diffusion coefficient and activation energy of Fe in the Bi2223 system

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