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Spectrophotometric method for rapid estimation of the oxygen stoichiometry in YBCO superconducting samples

100%
Georgieva S., Nedeltcheva T., Vladimirova L., Stoyanova-Ivanova A.
Open Chemistry
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2013
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vol. 11
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issue 3
381-387
EN
Abstract Detailed investigations on the possibility for determination of the oxygen stoichiometry in YBa2Cu3Oy superconducting samples by measuring the absorbance of the colored Co(III)-EDTA and Cu(II)-EDTA complexes in one solution have been performed. The absorptivity of the complexes at pH 2.5 and 4.9 as well as Beer’s law have been studied. The content of the solution for the sample dissolving has been established. The stoichiometry of the oxidation-reduction reaction between Cu(III) from the sample and Co(II) in the solution has been proved. The possibility to dissolve the sample in air has been tested. As a result a simple and rapid spectrophotometric method for the determination of the δ non-stoichiometric oxygen coefficient in YBa2Cu3O6.5+δ samples has been developed without precise measurement of the sample mass. The standard deviation of the δ- and y-coefficient results is 0.017. The reproducibility of the y-values in relative units (sr ) is 0.2%. The accuracy of the results has been confirmed by the method, which is based on the absorbance measurement of the I 3−-starch compound. Graphical abstract [...]
2
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Spectrophotometric determination of oxygen content in calcium substituted RBCO (R=Eu, Gd, Er) superconductors

100%
Stoyanova-Ivanova A., Nedeltcheva T., Vladimirova L.
|
EN
The oxygen stoichiometry in R1−x CaxBa2Cu3Oy (R=Eu, Er, Gd; x=0, 0.2, 0.25, 0.3) superconducting bulk samples was determined spectrophotometrically. The dependence of the critical temperature on the y-oxygen coefficient and the x-coefficient of the included calcium was studied.
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Synthesis and superconducting properties of Nd0.33Eu0.08Gd0.58Ba2Cu3Oz materials

88%
Stoyanova-Ivanova A., Terzieva S., Shivachev B., Mikli V., Vladimirova L.
Open Physics
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2008
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vol. 6
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issue 1
76-79
EN
We have studied the effect of the ratio of different rare-earth element on the superconducting properties and phase formation of (Nd0.33Eu0.08Gd0.58)Ba2Cu3Oz ceramic. Bulk NEG samples were prepared using the solid-state reaction process. The superconducting transition for Nd0.33Eu0.08Gd0.58Ba2Cu3Oz is T c ≈90 K and the value of the critical current density (J c) is 13.9 A/cm2 at 77 K under zero magnetic fields. This value is twice as high when compared with the (J c) value of YBCO systems (J c = 7.31 A/cm2). The obtained bulk sample was used for the production of superconducting Ag-sheathed tapes by OPIT method including hot rolling. The critical current density of the obtained tape (337 A/cm2) is one order higher than the one of the bulk sample.
4
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Microstructure and thermal properties of quasi-equal rare earth substitution Y0.5Gd0.5Ba2Cu3O6.94 superconductor

76%
Terzieva S., Stoyanova-Ivanova A., Shivachev B., Terzijska B., Zaleski A., Misiorek H., Mikli V.
Open Physics
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2009
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vol. 7
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issue 1
84-88
EN
Sintering effects in YBa2Cu3Oz samples with quasi-equal rare earth substitution have been investigated. It has been shown that the Y-123 type compound can be formed when gadolinium is partially substituted (in this case 50% atomic substitution) for yttrium. The superconducting compound was obtained by the optimized ceramic method, including solid-state reaction, melting and sintering, controlled by X-ray diffraction. The microstructure was investigated by SEM and energy dispersive X-ray analyses. An AC susceptibility measurement has shown that T c =93 K. Temperature-dependece of the thermal conductivity (4.5–300 K) of the polycrystalline Y0.5Gd0.5Ba2Cu3O6.94 sample was also measured.
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