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

✍ Scribed by J.B. Parise; P.L. Gai; M.A. Subramanian; J. Gopalakrishnan; A.W. Sleight

• Publisher: Elsevier Science
• Year: 1989
• Tongue: English
• Weight: 881 KB
• Volume: 159
• Category: Article
• ISSN: 0921-4534
• DOI: 10.1016/0921-4534(89)90376-6

✦ Synopsis

The structures of (T1, Pb)Sr2CaCu207 (To= 85 K) and (T1, Pb)Sr2Ca2Cu309 ( To= 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 (T1Ba2Can_ ~Cu,Oz, + 3 ), possessing two or three CuO2-sheets separated by (T1, Pb )O-and Sr202sheets. 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 (TI, Pb ) and Ca-sites. High resolution electron microscope images indicate occasional defects and, in the case of (T1, Pb)SrzCa2Cu309, 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.