Phase development of Tl2Ba2CaCu2O8 thin films on LaAlO3 substrates

Abstract
The evolution of phases leading to the formation of epitaxial films of nominal composition Tl2Ba2CaCu2O8 on (100) LaAlO3 by post‐deposition annealing of amorphous precursor films has been investigated by examining interrupted heat‐treatment samples using analytical microscopy and x‐ray diffraction. The superconductor, with a composition of Tl1.8Ba2Ca0.94Cu2.6O x , forms from a melt, which itself formed from intermediary crystalline phases during the continual loss of Tl2O. It is concluded that Tl1.8Ba2Ca0.94Cu2.6O x , Cu2O, and Tl3Ca5O x are in subsolidus equilibrium and that a melt phase exists between at least 780 and 860 °C under reducing conditions controlled by the Tl2O vapor.