IMPROVEMENT OF THE THALLIUM CUPRATE THIN FILMS DUE TO AN OPTIMIZATION OF THE DOPING HOLES DENSITIES AS SEEN BY XAS

摘要

T-c optimization of as-synthesized Tl 2212 thin films can be obtained through post-annealing treatments at low temperatures (180 and 220 degrees C). In this paper, the optimization process was controlled by ac magnetic susceptibility measurements for the T-c's and by polarized X-ray absorption spectroscopy measurements for the doping hole densities. The latter technique allows a direct insight into the hole density only in the (a, b) plane of the Tl 2212 structure. All the studied thin films are overdoped with respect to the optimum of 0.12 doping holes per copper defined previously. T-c increases up to 6 K were observed after post-annealing treatments under an argon atmosphere and were correlated with significant reduction of the doping hole density. In contrast to what has been observed on sintered samples, a post-annealing treatment at 220 degrees C resulted in an insufficient doping hole density, below the optimum, probably resulting from the small sample thickness. (C) 1996 Academic Press, Inc. [References: 13]