Effect of oxygen pressure on the synthesis of YBa2Cu3O7−x thin films by post-deposition annealing

Abstract

The effect of ambient oxygen pressure on the synthesis of epitaxial YBa₂Cu₃O_7−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 pO₂−1/T diagram containing recent literature data regarding YBa₂Cu₃O_7−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 pO₂=2.6×10⁻⁴ atm (0.2 Torr). Similar to YBa₂Cu₃O_7−x films produced by in situ laser ablation at the same temperature and oxygen pressure, the films exhibited low ion channeling yields (χ_min2. 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)].