Preparation of High-Tc Films via Flaming Solvent Spray

Thick films of the high-temperature superconductors YBa2Cu3O7−x and Bi1.7Pb0.3Sr2Ca2Cu3O10 have been prepared by spraying an ignited ethanol, ethylene glycol, or liquid ammonia solution of stoichiometric amounts of the metal nitrates (or acetates) onto polycrystalline MgO. The flaming spray is mechanically forced to traverse a region directly in front of the substrates. This new method is simple and inexpensive, and eliminates the problem of substrate cooling encountered in normal spray pyrolysis methods. Since decomposition of the solvent and metal salts occurs before deposition, the resulting films are relatively free of craters and nonuniformities common with spray methods. The method can be adapted to coat large areas and irregular or nonplanar shapes (i.e., cylinders), which could have useful magnetic shielding properties. The films were characterized by XRD and show single-phase material with preferredc-axis orientation. For YBa2Cu3O7−x , resistance vs. temperature measurements show aT c onset at 90 K and aT c 0 at 76 K. Silver nitrate has been added to some of the solutions in an attempt to improve contact among individual grains