A sol-gel method for preparing oriented YBa2Cu3O7- delta films on silver substrates

Abstract

YBa2Cu3O7- delta (YBCO) superconducting films on polycrystalline silver substrates have been fabricated using a sol-gel/spray pyrolysis method. The sol-gel precursor is composed of yttrium, barium and copper acetates that are dissolved in a minimum amount of water and partially gelled using ethanolamine. Silver substrates were heated to 300 degrees C before spray-coating with the precursor solution. Intermittent treatment of films at 550 degrees C in air between spray coats resulted in dense films. Subsequently, the YBCO films were sintered between 850 and 950 degrees C and oxygen annealed on cool down. Film thicknesses of 1-3 mu m were obtained and were highly oriented with the c axis perpendicular to the silver surface. Critical current densities (Jc) of 200-500 A cm-2 have been measured at 77 K and no applied magnetic field; higher Jc values have been measured on films with many pin holes, which appear to increase the number of oxygen entry points into the oriented films. The Jc rapidly decreases in magnetic field, which indicates that transport properties are dominated by weak-link behaviour.