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 two-zone reactor

Abstract

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 °C and boat temperatures of 775–870 °C were investigated. X-ray diffraction analysis of the best samples, which were prepared in an oxygen ambient at sample temperatures of 895–900 °C and boat temperatures of 805–810 °C, revealed the presence of a highly oriented Tl2Ca2Ba2Cu3O10+y phase with a trace of the Tl2CaBa2Cu2O8+y phase. FWHM's of ∼2°θ were obtained in x-ray rocking curve analyses of the oriented 2223 phase. Tc (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 Jc samples reveal a highly textured structure consisting of platelike crystals.