Effect of growth conditions on the properties and morphology of chemically derived epitaxial thin films of Ba2YCu3O7−x on (001) LaAlO3

Publisher Website
Google Scholar
Abstract
Epitaxial thin films of Ba2YCu3O7−x (BYC) were prepared on (001) LaAlO3 single‐crystal substrates by metalorganic deposition of metal trifluoroacetate precursors. This is an ex situ process that requires high‐temperature annealing in a humid atmosphere to produce stoichiometric BYC thin films. The chemically derived superconducting films were found to have high critical temperatures and high current densities when crystallized under low‐oxygen partial pressures. Superconducting films of 70 nm thickness with zero‐field critical current densities greater than 5×106 A/cm2 at 77 K and zero resistance at 92 K were prepared by annealing at 780 and 830 °C in 2.5 × 10−4–1 × 10−3 atm oxygen furnace atmospheres. As the film thickness was increased, the superconducting properties and surface smoothness of the films tended to degrade. This behavior was consistent with a microstructural model in which the films are composed of a dense slab of c‐axis normal BYC near the film/substrate interface with the overlying material dominated by grains with c‐axis in‐plane crystallographic orientation. The transport Jc fell to 2–3×106 A/cm2 for films of 200–250‐nm thickness annealed at 780 °C in 1 × 10−3 atm oxygen. As the P(O2) was raised to 0.032 atm at 780 °C, for films of the same thickness, the Jc at 77 K decreased to 0.7 × 106–1 × 106 A/cm2 and the Tc(R = 0) dropped to 89 K. Increasing the furnace P(O2) was also found to degrade the crystalline quality of the films, as characterized by ion channeling Rutherford backscattering spectroscopy.