Characterization of films prepared by laser ablation of precursor targets and<i>ex situ</i>thalliation

Abstract

Thin films of (Tl-2212) were grown on (001) single crystals by excimer laser ablation using Tl-free targets and subsequent ex situ thalliation. The thalliation process of the film precursor () took place in an crucible containing the precursor and Tl-2212 powder. The procedure was carried out at a temperature and under a reduced oxygen pressure = 20 - 400 Torr. The resulting Tl-2212 films were characterized by XRD, AES, EDAX, ECP, Raman spectroscopy and a.c. susceptibility measurements. The films exhibited epitaxial, c-axis-oriented growth with critical temperatures = 98 - 106.5 K, transition widths = 0.5 - 1 K, and critical current densities at 77 K of . EDAX measurements showed that the films were as a rule somewhat Tl and Ba deficient but Ca rich . AES depth profiling revealed a noticeable depth dependence of the Ca and Ba distribution, though the combined concentration of these elements (Ba + Ca) was fairly constant throughout the whole film thickness. It is postulated that cation disorder (Ba Ca substitution) is responsible, at least in part, for the high critical current density observed in the Tl films. These point defects would contribute to the strong pinning of the flux lines in the films by creating a dense network of pinning centres.