The superconductors (Tl, Pb)Sr2CaCu2O7 and (Tl, Pb)Sr2Ca2Cu3O9: neutron powder diffraction, high resolution electron microscopy and x-ray absorption studies

Parise, J. B. ; Gai, P. L. ; Subramanian, M. A. ; Gopalakrishnan, J. ; Sleight, A. W. (1989) The superconductors (Tl, Pb)Sr2CaCu2O7 and (Tl, Pb)Sr2Ca2Cu3O9: neutron powder diffraction, high resolution electron microscopy and x-ray absorption studies Physica C: Superconductivity, 159 (3). pp. 245-254. ISSN 0921-4534

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Official URL: http://linkinghub.elsevier.com/retrieve/pii/092145...

Related URL: http://dx.doi.org/10.1016/0921-4534(89)90376-6

Abstract

The structures of (Tl, Pb)Sr2CaCu2O7 (Tc=85 K) and (Tl, Pb)Sr2Ca2Cu3O9 (Tc=122 K) have been investigated using neutron powder diffraction and electron microscopy. They are isostructural (14/mmm) with the corresponding thallium/barium end members of compositions (TlBa2Can-1CunO2n+3), possessing two or three CuO2-sheets separated by (Tl, Pb)O- and Sr2O2-sheets. X-ray microanalysis and neutron diffraction are consistent with fully occupied strontium sites in both materials. However, the diffraction results suggest considerable site disorder in the (Tl, Pb) and Ca-sites. High resolution electron microscope images indicate occasional defects and, in the case of (Tl, Pb)Sr2Ca2Cu3O9, occasional intergrowth of a structure containing 4-layers of copper. X-ray absorption measurements are consistent with formal oxidation states of 4+ for Pb and 3+ for thallium in these materials.

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