Structure and chemical composition of planar defects in Sr_0.9La_0.1CuO₂ infinite-layered superconductors by electron spectroscopic imaging

The superconducting infinite-layered compound Sr_0.9La_0.1CuO₂ was prepared by high-pressure synthesis and characterized using HRTEM and electron spectroscopic imaging (ESI). Defect layers in the a-b plane were observed which show an expansion of the adjacent strontium layers along c, similar as in the calcium-doped SrCuO₂ system. Using high resolution ESI, the planar defects were found to be oxygen deficient, whereas no change in the strontium composition was observed. Removing oxygen, the charge may be compensated by reduction of Cu^II to Cu^I or by removal of copper ions, and the possible chemical compositions are discussed. Comparison of lattice images with simulated images clearly shows that the copper ions in the defect layer are displaced from the regular positions they occupy in the bulk.