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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 [...]
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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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Spectrophotometric study of competitive complexation equilibria involving overlapped spectral responding species: Determination of the stability constant of bismuth-pyrophosphate complex

88%
Nedeltcheva T., Surleva A., Nikolova L., Borissova R., Georgieva S.
Open Chemistry
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2012
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vol. 10
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issue 6
1875-1881
EN
Spectrophotometric study of competitive complex formation equilibria involving overlapped spectral responding species applying a simple and versatile algorithm was carried out. The algorithm involves multivariable regression for calculation of equilibrium concentrations from multiwavelength data and mass action law for the stability constant calculation. The used regression functions are part of common statistical software. Stability constants and complex stoichiometry of competing equilibria were simultaneously determined. The species concentration profiles at several spectral overlapping and α-coefficient of competing reaction were obtained. Non-absorbing bismuth - pyrophosphate (PPh) system was studied as a competitive reaction of bismuth - 4-(2-Pyridylazo) resorcinol (PAR) complex. The formation of Bi-PPh complex with 1:1 stoichiometry was proved in the studied concentration region (CBi = 1×10−5 mol L−1; CPPh = 5×10−6 − 1×10−4 mol L−1). The stability constant of the complex at pH 1 and µ = 1.0 have been determined: logβ = 4.2±0.2. [...]
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