Superconducting cuprates of the series Bi2Ca1-xLnxSr2Cu2O8+δ (Ln=rare earth or Y)

Rao, C. N. R. ; Nagarajan, R. ; Vijayaraghavan, R. ; Vasanthacharya, N. Y. ; Kulkarni, G. V. ; Rao, G. Rango ; Umarji, A. M. ; Somasundaram, P. ; Subbanna, G. N. ; Raju, A. R. ; Sood, A. K. ; Chandrabhas, N. (1990) Superconducting cuprates of the series Bi2Ca1-xLnxSr2Cu2O8+δ (Ln=rare earth or Y) Superconductor Science and Technology, 3 (5). pp. 242-248. ISSN 0953-2048

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Official URL: http://iopscience.iop.org/0953-2048/3/5/006

Related URL: http://dx.doi.org/10.1088/0953-2048/3/5/006

Abstract

A systematic investigation of the properties of the series Bi2Ca1-xLnxSr2Cu2O8+ delta (Ln-rare earth or Y) of superconducting cuprates has been carried out by employing a variety of techniques. In these cuprates, the a and b parameters of the unit cell increase with x while the c parameter decreases. These cuprates show interesting superlattice modulation with both 4b and 8b periodicity depending on the rare earth when x=1.0. This observation suggests that the superlattice modulation has nothing to do with superconductivity, but may be determined by the oxygen stoichiometry. The oxygen excess, delta , increases linearly with x, but the hole concentration shows a maximum around x=0.25 or delta approximately=0.225+or-0.025. Interestingly, Tc also shows a maximum around x=0.25. The authors have examined the nature of copper by XANES and Cu core level spectra. The relative intensity of the satellite in the Cu(2p) spectrum shows a minimum at x=0.25. The Raman band around 630 cm-1 due to the oxygen atoms in Bi-O layers decreases with increase in x, as does the a parameter.

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