PHASE DEVELOPMENT OF TL2BA2CACU2O8 THIN-FILMS ON LAALO3 SUBSTRATES

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 examin ing interrupted heat-treatment samples using analytical microscopy and x-ray diffraction. The superconductor, with a composition of Tl1.8Ba2 Ca0.94CU2.6Ox, forms from a melt, which itself formed from intermediar y crystalline phases during the continual loss of Tl2O. It is conclude d that Tl1.8Ba2Ca0.94CU2.6Ox, CU2O, and T13Ca5Ox are in subsolidus equ ilibrium and that a melt phase exists between at least 780 and 860-deg rees-C under reducing conditions controlled by the Tl2O vapor.