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

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 T_c (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 T_c (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 T_c (R=0) has been enhanced from approximately 90 K to approximately 98 K. The highest T_c 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.