MICROSTRUCTURAL STUDIES OF SUPERCONDUCTING OXIDE THIN FILMS AND MULTILAYERS A. Vailionis, A. Brazdeikis, A.S. Flodström, Department of Physics, Materials Physics, Royal Institute of Technology, S-100 44 Stockholm, Sweden

Superconducting properties of the layered cuprate thin films and multilayers are known to be very sensitive to the microstructural quality such as intergrowth defects, interface roughness and substitutional disorder in a unit cell. An extensive structural analysis is often required before the physical properties are measured. We will present the microstructural studies of MBE-grown "infinite-layer" structure, (Sr,Ca)CuO₂, films as well as Bi₂Sr₂Ca_n-1Cu_nO_y films and multilayers using x-ray diffraction (XRD) and extended x-ray absorption fine structure (EXAFS) techniques. To obtain a quantitative information of the thin film microstructure a general one- dimensional kinematic x-ray diffraction model has been applied to these complex layered oxides. Structure of Bi-based cuprates was determined by comparing the measured XRD spectra of the MBE-grown samples with the calculated x-ray diffraction profiles of the model structure. The interplanar distances and cationic substitutions within the unit cell and number of stacking faults were used as fitting parameters. The iterative fitting procedure revealed a substitutional disorder present in the average unit cell as well as stacking defects. The high-resolution transmission electron microscopy confirmed a presence of both Bi₂Sr₂Cu₁O_y and Bi₂Sr₂Ca₂Cu₃O_y phases as intergrowths in the Bi₂Sr₂Ca₁Cu₂O_y film matrix. For Bi₂Sr₂Ca₁Cu₂O_y/Bi₂Sr₂Cu₁O_y multilayers the randomly distributed stacking faults were distinguished from those localized at the interface. Local environment of the copper atoms in the layered unit cell was analyzed by EXAFS. The Cu-Sr, Cu-Ca, Cu-Cu distances and Cu-O bond lengths were determined from Cu K-edge absorption spectra. CuO₂-CuO₂ and CuO₂-SrO interplanar distances obtained from XRD data are compared with those from EXAFS data. The relations between structural quality and growth parameters are discussed. The origin of structural disorder is interpreted as being caused by growth kinetics that plays a major role in film formation.