Preparation of high-Tc superconducting thin films of Tl-Ca-Ba-Cu-O by the chemical spray pyrolysis technique

Abstract

Thin films of the Tl-Ca-Ba-Cu-O system have been prepared on MgO and YSZ single-crystal substrates by a simple chemical process (the spray pyrolysis technique). Since Tl is toxic, the Tl-Ca-Ba-Cu-O films were prepared by a two step process. Firstly, precursor (Ca-Ba-Cu-O) films were prepared followed by diffusion of Tl derived by vaporizing Tl2O3 in a closed system under oxygen flow. A new feature found in the present investigation is that the Tc (R=0) of the Tl-Ca-Ba-Cu-O films has been found to depend upon the microstructural characteristics of the precursor films which can be varied by annealing these films. The Tc (R=0) of the Tl-Ca-Ba-Cu-O HTSCs films prepared from the annealed precursor films has been found to be higher than in the films prepared from the as-deposited precursor films. As, for example, in the case of a film on a MgO substrate, the Tc (R=0) has been enhanced from approximately 90 K to approximately 98 K. The highest Tc obtained by the authors for the films synthesized from the annealed precursor films on YSZ substrates corresponds to approximately 103 K. The XRD reveals the biphasic (2223/2122) nature of the films. The microstructural characteristics of the films as monitored by SEM reveals the partially oriented nature of the Tl-Ca-Ba-Cu-O film.