The effects of substrate temperature on the superconducting properties of Tl₂Ca₂Ba₂Cu₃O₁₀ films sputter-deposited from stoichiometric oxide targets

Abstract

The annealing characteristics and the superconducting properties of Tl2Ca2Ba2Cu3O10 thin films sputter-deposited onto yttrium- stabilized ZrO2 substrate at up to 500°C from two stoichiometric oxide targets are reported. The films deposited at 400-500°C were found to require a lower post-annealing temperature than the films deposited at lower temperatures to attain the highest Tc superconducting state, due to a more pronounced Ba diffusion toward the substrate as indicated by their secondary ion mass spectrometry depth profiles. The highest Tc achieved tends to degrade with increasing substrate temperatures, a zero resistance Tc of 121 and ≈90 K, respectively, being observed for the films deposited at ∼-ambient temperature and at 500°C. The formation of the highest Tc phase (Tl2Ca2Ba2Cu3O10) generally is associated with a sheet type of crystal growth morphology with smooth and aligned surfaces which can be obtained only from the films capable of sustaining prolonged annealing at 900°C. Annealing at lower temperatures (≈860°C) results in the formation of rod or sphere type of morphologies with rough and randomly oriented crystals and the lower Tc phases such as Tl2Ca1Ba2Cu2O8. © 1989.