Unusual crystal structure of non-superconducting Y1Ba2Cu3O7-x films on buffered silicon substrates

Superconducting common c-axis oriented YBCO films as well as non-superconducting films epitaxially grown at significantly reduced substrate temperatures were deposited by laser ablation on CeO2/YSZ buffered silicon substrates. The crystal structure of the non-superconducting films measured by XRD is collapsed from the original orthorhombic one, whereas the chemical composition detected using RES and EDX remains identical, Especially the oxygen content in the non-superconducting material is as high as in the common 90 K superconductor. Thus, the change in the electrical behaviour is only due to a structural modification. The crystallographic model of a simple cubic YBCO perovskite unit cell does not represent completely our experimental results measured on the non-superconducting YBCO. A modified model based on detailed TEM and XRD measurements and known crystal defects of orthorhombic YBCO is proposed. (C) 1997 Elsevier Science B.V.