PREPARATION AND CHARACTERIZATION OF TL-BA-CA-CU-O SUPERCONDUCTING FILMS BY SPRAY-PYROLYSIS AND TL-DIFFUSION TECHNIQUE

Abstract

The present work reports that highly c-axis-oriented Tl-Ba-Ca-Cu-O superconducting films with zero-resistance temperature up to 112 K were successfully prepared using the spray pyrolysis technique with a subsequent Tl-diffusion treatment. The insulating Ba-Ca-Cu-O precursor films (Ba:Ca:Cu = 2:2:3) were made by spray deposition of the related metal nitrate solution on a preheated (300-degrees-400-degrees-C) MgO(001) single-crystal substrate. The presence of the superconducting phases of the resultant films depended strongly on the types of Tl sources used. The results showed that the formation of the superconducting phases could be achieved more readily by using the bulk Tl-Ba-Ca-Cu-O rather than Tl2O3 as a Tl source. In other words, the low Tl content in the TlBaCaCuO bulk source with a resulting low Tl-vapor pressure is favorable for the formation of a higher T(c) superconducting phase. The dominant phases in the prepared films were mainly TlBa2Ca2Cu3Oy(1223 phase) and Tl2Ba2CaCu2Oy(2212 phase). The critical current density of a film with a nearly single-phase(1223) structure was measured to be 1.2 X 10(4) A/cm2 at 77 K under zero magnetic field.