No abstract

Thin films in the Bi-Sr-Ca-Cu-0 system have been synthesized from liquid ethylhexanoate precursors by spin pyrolysis. An extensive solid-solution range was found for the two-Cu-layer phase through the study of c-axisoriented, single-phase thin films fabricated on singlecrystal, (100)-oriented, MgO substrates. All two-layer compositions were excess in Bi and deficient in Sr + Ca relative to the ideal 2212 composition and showed an overall cation deficiency. The solidus temperature and c lattice parameter were found to vary systematically with composition. Sharp superconductive transitions were obtained in the case of a number of different compositions with T, varying between 72 and 84 K. Evidence for significant compositional heterogeneities within single-phase two-layer thin films was found and the implications for superconductivity are discussed. Compositions within the solid-solution range gave singlephase, c-axis-oriented films over a wide temperature range extending from 730°C to an upper, solidus (or peritectic) temperature (780" to 840°C) which is dependent on the initial starting composition. A model has been developed that describes the formation of the two-layer phase from a fugitive liquid. [

The microstructure of YBa2Cu3O7−δ (YBCO) materials, melt-textured in air and quenched from the temperature range 900–;990 °C, has been characterized using a combination of x-ray diffractometry, optical microscopy, scanning electron microscopy, transmission electron microscopy, and energy dispersive x-ray spectrometry. BaCu2O2 and BaCuO2 were found to coexist in samples quenched from the temperature range 920–960 °C. The formation of BaCu2O2 preceded the formation of YBCO. Once the YBCO had formed, BaCu2O2 was present at the solidification front filling the space between nearly parallel platelets of YBCO. Large Y2BaCuO2 particles at the solidification front appeared divided into smaller ones as a result of their dissolution in the liquid that quenched as BaCu2O2.

Superconducting thin films of the two Cu-layer phase in the Pb-doped Bi-Sr-Ca-Cu-O system have been fabricated on {100} LaAlO3 single crystals by the metalorganic deposition from ethyl hexanoate precursors. Thin films given heat treatments in air at 850–860 °C had resistive transitions with a Tc of 86–89 K. The zero-field transport critical current densities were in the range of 2–4×105 A/cm−2 at 77 K and 106 A cm−2 at 45 K in 200–300-nm-thick films. In contrast to c-axis oriented films grown on {100} MgO, x-ray pole figures show that the films grown on {100} LaAlO3 are epitaxial, a result confirmed by electron channeling patterns.