Direct observation and analysis of CuO sub 2 shear defects in La sub 2 minus x Sr sub x CuO sub 4

• Published in: Science (American Association for the Advancement of Science) Vol. 247:4942
• Main Authors: Gai, P.L., McCarron, E.M. III
• Format: Journal Article
• Language: English
• Published: United States 02-02-1990
• Subjects: ALKALINE EARTH METAL COMPOUNDS; COPPER COMPOUNDS; CRYSTAL DEFECTS; CRYSTAL STRUCTURE; DATA; EXPERIMENTAL DATA; INFORMATION; LANTHANUM COMPOUNDS; MATERIALS SCIENCE; MECHANICAL PROPERTIES; NUMERICAL DATA; OXYGEN COMPOUNDS; RARE EARTH COMPOUNDS; SHEAR PROPERTIES; STRONTIUM COMPOUNDS; SUPERCONDUCTORS; TRANSITION ELEMENT COMPOUNDS 360602 > Other Materials > Structure & Phase Studies
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.247.4942.553

Direct observations of CuO{sub 2} sheet defect structures in superconducting La{sub 2{minus}x}Sr{sub x}CuO{sub 4}, with x in the range 0.05 {le} x {le} 0.15, are reported. Electron microscopy shows that extended line defects are generated in planes, along crystallographic directions, by a pure shear mechanism along the edge of the octahedral copper-oxygen units The line defects are partial screw dislocations, with characteristic displacement vectors of the type <(a/2), 0, (c/6)>, bounding the stacking faults. The existence of this type of defect demonstrates that there is an oxygen deficiency within the CuO{sub 2} layers. However, unlike the open ReO{sub 3} type-related structures, the packing density of the K{sub 2}NiF{sub 4} structure necessarily requires that anion defects be accompanied by the loss of cations of the A type (lanthanum, strontium). Under identical synthesis conditions, no defects are observed in the parent compound La{sub 2}CuO{sub 4}. 12 refs., 6 figs., 1 tab.