Sr-substitution limit at 760-800 degrees C in epitaxial Yb(Ba1-xSrx)(2)Cu4O8 films prepared by coating-pyrolysis process

Epitaxially grown c-axis-oriented and 'single phase' Yb(Ba1-xSrx)(2)Cu4O8 ( x = 0-0.1) films were successfully fabricated on SrTiO3 (001) substrates by a coating-pyrolysis process. The substitution limit of Sr decreased with i ncreasing temperature in the range from 760 to 800 degrees C. The films pre pared at 780 degrees C in flowing O-2 at ambient pressure were found to con sist of an almost single phase of c-axis-oriented Yb(Ba1-xSrx)(2)Cu4O8 and a trace amount of c-axis YbBa2Cu3O7-y. The reciprocal-map analysis of the f ilms showed that the Yb(Ba1-xSrx)(2)Cu4O8 phase is pseudotetragonal. The su perconducting transition temperatures increased by Sr-substitution and T-c, T-zero (r) = 81 K by dc-resistance and T-c,T-onset (s) = 81 K by ac-suscept ibility measurements were obtained for the Yb(Ba0.9Sr0.1)(2)Cu4O8 film. The film with x = 0.1, quenched from 600 degrees C, also showed metallic behav ior with T-c,T-zero (r) = 76 K. (C) 1999 Published by Elsevier Science B.V. All rights reserved.