Preparation and characterization of Tl-Ba-Ca-Cu-O superconducting films by spray pyrolysis and Tl-diffusion technique

The present work reports that highly c-axis-oriented T1-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 t1-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 - 400 C) MgO(001) single-crystal substrate. The presence of the superconducting phases of he resultant films depended strongly on the types of T1 sources used. The results showed that the formation of the superconducting phases could be achieved more readily by using the bulk T1-Ba-Ca-Cu-O rather than T12O3 as a T1 source. In other words, the low T1 content in the T1BaCaCuO bulk source with a resulting low T1-vapor pressure is favorable for the formation of a higher Tc superconducting phase. The dominant phases in the prepared films were mainly T1Ba2Ca2Cu3Oy(1223 phase) and T12Ba2CaCu2Oy (2212 phase). The critical current density of a film with a nearly single-phase (1223) structure was measured to be 1.2 X 104 A/cm2 at 77 K under zero magnetic field