# Superconducting cuprates of the series $Bi_2Ca_{1-x}Ln_xSr_2Cu_2O_{8+\delta}$ (Ln=rare earth or Y)

Rao, CNR and Nagarajan, R and Vijayaraghavan, R and Vasanthacharya, NY and Kulkarni, GV and Umarji, AM and Rao, Rango G and Somasundaram, P and Subbanna, GN and Raju, AR and Sood, AK and Chandrabhas, N (1990) Superconducting cuprates of the series $Bi_2Ca_{1-x}Ln_xSr_2Cu_2O_{8+\delta}$ (Ln=rare earth or Y). In: Superconductor Science and Technology, 3 (5). pp. 242-248.

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## Abstract

A systematic investigation of the properties of the series $Bi_2Ca_{1-x}Ln_xSr_2Cu_2O_{8+\delta}$ (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 $\delta \simeq$=0.225+or-0.025. Interestingly, $T_c$ 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.

Item Type: Journal Article Copyright of this article belongs to Institute of Physics cuprates;superconductivity;Raman band Division of Chemical Sciences > Solid State & Structural Chemistry Unit 03 Dec 2007 19 Sep 2010 04:41 http://eprints.iisc.ernet.in/id/eprint/12710