In situ fabrication of epitaxial YBa₂Cu₃O₇ films on lattice-mismatched (100) YS-ZrO₂ substrates by the pulsed laser evaporation method

The formation of good quality epitaxial c-axis-perpendicular YBa ₂ Cu₃ O₇ superconducting thin films on (100) yttria-stabilized-zirconia (YSZ) substrates in the temperature range of 550-650 °C by a biased laser deposition method is reported. However, below 550 °C, the epitaxial quality of the films decreased appreciably with corresponding changes in the superconducting properties. For temperatures much below the critical temperature, the critical current density showed a linear variation with temperature, with a value of 1.0×10⁶ A/cm ² at 77 K and zero magnetic field. Because of the lattice mismatch between the substrate and the film, the interface was found to be highly strained in the presence of a large number of defects. The epitaxial nature and the crystalline quality of the films were determined by a number of techniques including Rutherford backscattering/channeling, electron channeling, cross-section transmission electron microscopy (TEM), and x-ray diffraction techniques. Rutherford backscattering channeling showed a minimum channeling yield of about 18%-25% for films deposited at and above 550 °C. Cross-section TEM and x-ray diffraction revealed the following thin film and substrate relationships: [001]_film ∥[001]_YSZ and [110]_film ∥[100]_YSZ. The electron channeling pattern taken from a large area confirmed the epitaxial relationship. The lattice parameters mismatch in this orientation has been found to gives rise to stresses near the interface.