Effect of oxygen pressure on the synthesis of YBa2Cu 3O7-x thin films by post-deposition annealing

Abstract

The effect of ambient oxygen pressure on the synthesis of epitaxial YBa2Cu3O7-x films on (100) SrTiO3 substrates by post-deposition annealing of amorphous precursor films was studied for oxygen partial pressures pO2 between 1.0 and 8.0×10 -5 atm and annealing temperatures between 890 and 650°C. A p O2-1/T diagram containing recent literature data regarding YBa 2Cu3O7-x oxygen stoichiometry, phase stability, and liquid-phase formation was compiled to provide guidance for the selection and interpretation of annealing conditions. The results evidence a strong dependency of growth properties on the oxygen pressure with enhanced c-oriented epitaxy at lower pO2 values. A particularly interesting result is the formation of predominantly c-oriented films at 740°C and p O2=2.6×10-4 atm (0.2 Torr). Similar to YBa 2Cu3O7-x films produced by in situ laser ablation at the same temperature and oxygen pressure, the films exhibited low ion channeling yields (χmin<0.1) and a dense (smooth) surface morphology, while critical currents at 77 K were well in excess of 1 MA/cm 2. From the observed systematic variation of structural film properties with synthesis conditions, annealing lines were derived indicating (T-pO2) combinations for either c- or a-oriented epitaxial growth. A comparison is made between these lines and synthesis conditions for in situ film growth as compiled recently by Hammond and Bormann [Physica C 162-169, 703 (1989)].