Synthesis, X-ray absorption (Xanes) and transport studies of some cuprate superconductors

In some selective substituted cuprate superconductors studies of phase purity, TC behaviour, lattice oxygen content and electronic structure have been carried out using XRD, R vs. T, X vs. T, iodometric titration and X-ray absorption near edge structure (XANES) measurements. The study is aimed at understanding the structure property correlations. Cu K-XANES features of YBa2-x SrxCu3O7-d; X<=1.00 (1-2-3 phase) superconducting (SC) compounds show that peak at Cu+ grows, while the white line intensity falls with increasing, Sr content (x). This is attributed to .increase in oxygen vacancies causing a decrease in hole carriers and, thereby, fall in Tc with x. The XRD and SEM data show that the solubility of Sr in normal pressure synthesised 1-2-3 is <= 1.15; this finding resolves the existing controversy. Cu K-XANES studies on argon, au and oxygen annealed SC Lu0.7Ca0.3Ba2Cu3O7-d (Lu,Ca) 1-2-3 compounds lead to an important finding that the value of effective charge (n) >2 on Cu of the Cu(2) sheets is essential for superconductivity. More Info

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