Sprayed Tl-1223 films: formation kinetics and superconducting properties

TlBa/sub 2/Ca/sub 2/Cu/sub 3/O/sub 9/ superconducting films, 0.5 to 1 (mu)m in thickness, have been prepared in a two step process. Using a nitrate solution, a precursor layer with composition Ba/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ is first sprayed on a LaAlO/sub 3/ heated substrate and then thallinated, following a procedure established for bulk samples. The critical temperature of the films ranges from 108 to 113 K, and the critical current density of the best samples reaches 0.7 AMA/cm/sup 2/. The reaction kinetics for the formation of the Tl-1223 phase between 880 (degree)C and 910 (degree)C has been studied for a better control of the grain growth and texture. The effect of fluorine addition on both the microstructure and superconducting properties have been also analyzed.