THE SYNTHESIS OF SUPERCONDUCTING TL-CA-BA-CU-OXIDE FILMS BY THE REACTION OF SPRAY DEPOSITED CA-BA-CU-OXIDE PRECURSORS WITH TL2O VAPOR IN A 2-ZONE REACTOR

Superconducting Tl-Ca-Ba-Cu-oxide films have been prepared on yttria stabilized zirconia substrates via the reaction of Tl2O vapor with precursor Ca-Ba-Cu-oxide films prepared by the spray pyrolysis of a solution of the metal nitrates. The vapor reaction process, evaluated in both air and oxygen ambients, was carried out in a two-zone reactor which permitted the independent control of the temperatures of the sample and of a boat containing thallium oxide. Sample temperatures of 865-905-degrees-C and boat temperatures of 775-870-degrees-C were investigated. X-ray diffraction analysis of the best samples, which were prepared in an oxygen ambient at sample temperatures of 895-900-degrees-C and boat temperatures of 805-810-degrees-C, revealed the presence of a highly oriented Tl2Ca2Ba2Cu3O10+y phase with a trace of the Tl2CaBa2Cu2O8+y phase. FWHM's of approximately 2-degrees theta-were obtained in x-ray rocking curve analyses of the oriented 2223 phase. T(c) (0) values of 95-105 K were measured for the better samples, and a zero field critical current density of 28 800 amps/cm2 was measured at 77 K for the best sample. SEM micrographs taken of the highest J(c) samples reveal a highly textured structure consisting of platelike crystals.