High-resolution XRD study of stress-modulated YBCO films with various thicknesses

摘要

High-quality epitaxial YBa_2Cu_3O_(7-δ) (YBCO) superconducting films with thicknesses between 0.2 and 2 μm were fabricated on (0 01) LaAlO_3 with direct-current sputtering method. The influence of film thickness on the structure and texture was investigated by X-ray diffraction conventional θ-2θ scan and high-resolution reciprocal space mapping (HR-RSM). The films grew with strictly c-axis epitaxial, and no α-axis-oriented growth was observed up to a thickness of 2 μm. Lattice parameters of the YBCO films with different thicknesses were extracted from symmetry and asymmetry HR-RSMs. The X-ray lattice parameter method was used to determine the residual stress in YBCO films by measuring the α-, b-, c-axis strains, respectively. The results showed that YBCO films within thinner than 1 μm were under compressive stress, which was relieved increasing of film thickness. However, beyond 1 μm in thickness, YBCO films exhibited a tensile stress. Based on the experimental analysis, the variety of residual stresses in the films is mainly attributed to oxygen vacancies with thickness of YBCO film increasing.