Tl-Ba-Ca-Cu-O superconducting thin films with postdeposition processing using Tl-containing thin films as Tl source

We describe a new method of processing Tl-Ba-Ca-Cu-O (TBCCO) superconducting thin films. In this method, two identical elemental multilayer films containing Tl layers were prepared using an electron-beam deposition technique. The thin-film samples were then placed in face-to-face contact in a quartz crucible and heat treated at 740 °C for 10 min in flowing air. The x-ray microanalysis of the bottom sample indicates promising results for obtaining the desired chemical composition. Random characterization from different sections of the sample showed that the microanalysis values had less scatter than those for samples prepared using the usual bulk postdeposition method. The average chemical composition of the 13 points obtained from the random section is Tl1.8Ba1.8Ca1.9Cu2.0Ox. However, oxygen analysis showed that the concentration of oxygen is low and poorly distributed, presumeably attributable to the low oxygen flow. This method has several advantages over the conventional Tl-O vapor processing using pure metallic thallium, thallium oxide or bulk TBCCO. These advantages include: (a) increase in uniformity of thallium deposition, (b) safer processing as a result of a smaller release of thallium, and (c) reduction of processing cost.