DIRECT OBSERVATION AND ANALYSIS OF CUO2 SHEAR DEFECTS IN LA2-XSRXCUO4

Direct observations of CuO2 sheet defect structres in superconducting La2-xSrxCuO4, with x in the range 0.05≤×≤0.15, are reported. Electron microscopy shows that extended line defects are generated in {010} planes, along 〈206〉 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 CuO2 layers. However, unlike the open ReO3 type-related structures, the packing density of the K2NiF4 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 La2CuO4.