Structural characterization of yttria (Y2O3) inclusions in YBa2Cu3O7-x films : growth model and effect on critical current density

• Published in: Thin solid films Vol. 229; no. 2; pp. 237 - 248
• Main Authors: SELINDER, T. I, HELMERSSON, U, HAN, Z, WALLENBERG, L. R
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier Science 25.06.1993
• Subjects: Chemical Sciences; Condensed Matter Physics; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Den kondenserade materiens fysik; Exact sciences and technology; Fysik; Kemi; Materialkemi; Materials Chemistry; Natural Sciences; Naturvetenskap; Physical Sciences; Physics; Superconducting films and low-dimensional structures; Superconductivity; Critical current density; Inclusion; Precipitate; Experimental study; Sputtering; Thin film; Characterization; Superconducting materials; Transmission electron microscopy; Yttrium Oxides; Microstructure; Structure; Barium Copper Yttrium Oxides Mixed; High temperature superconductor
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/0040-6090(93)90371-U

A higher critical current and enhanced pinning was obtained in c-axis-oriented YBa2Cu3O7−x (YBCO)films having a higher density of semicoherent yttria (Y2O3) inclusions. The films were grown by sputtering and the inclusion density depends on the fraction of N2O in the sputtering gas. The inclusions were studied by transmission electron microscopy, both in planar sections and in cross-sections. They are embedded in the YBCO matrix without disturbing its structure appreciably, and the inclusion density is up to about 1017 cm−3, comprising about 4% of the film volume. From the appearance of moiré fringes and from high resolution transmission electron micrographs, it is concluded that the inclusions are highly oriented and have coherent or semicoherent interfaces towards matrix. A model for formation of the yttria inclusions during film growth is presented, which includes nucleation of epitaxial coherent yttria islands, layer-by-layer growth and finally overgrowth by advancing steps of the YBCO film. The enhanced pinning and transport critical current densities, relation to film microstructure and the possible flux-pinning mechanisms by these yttria inclusions are discussed.