Direct observation and analysis of CuO2 shear defects in La(2-x)Sr(x)CuO4

Direct observations of CuO2 sheet defect structures in superconducting La(2-x)Sr(x)CuO4, 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 line crystallographic directions, by a pure shear mechanism along the edge of the octahedral copper-oxygen units. The line defects are partial screw dislocations, bounding the stacking faults. The existence of this type of defect demonstrates that there is an oxygen deficiency within the CuO2 layers. Under identical synthesis conditions, no defects are observed in the parent compound La2CuO4.