Preparation and characteristics of Bi-Pb-Sr-Ca-Cu-O superconducting films by spray pyrolysis and post-annealing

Abstract

Two kinds of high-T-c superconducting films, Bi1.8Pb0.2Sr2Ca2Cu3Oy and Bi2PbSr2Ca2Cu3Oy, were prepared by spray pyrolysis and postannealing with the aid of Bi-based bulk. Highly c-oriented and nearly single-phase 2223 high-T-c Bi-based superconducting films can be achieved for the as-sprayed Bi1.8Pb0.2Sr2Ca2Cu3Oy and the Bi2PbSr2Ca2Cu3Oy films annealed at 845 degrees C for 20 h. X-ray diffraction (XRD) patterns exhibit amorphous-like phases with microcrystals for the as-sprayed films and the transformation of amorphous-like phase into crystalline high-T-c (2223), low-T-c (2212) and Ca2PbO4 phases for the resultant films. For as-sprayed films, post-annealing in the closed system with Bi-based bulk sources is favourable to the formation of 2223 phase; on the contrary, the 2212 phase is formed in the open system, as demonstrated by XRD and scanning electron microscopy (SEM). SEM and XRD analyses show a plate-like microstructure for the 2223 phase and a needle-like one for the 2212 phase. This phenomenon explains that compensation and diffusion of Bi-based bulk sources into the as-sprayed films help in the formation of 2223 phase and these processes are more efficient in the closed system. The resultant film shows a high critical transition temperature (T-c,T-zero) of 104 K and a critical current density (J(c)) of 1.8 x 10(4) A/cm(2). (C) 1998 Elsevier Science S.A. All rights reserved.