Thickness dependence of microstructure and critical current density of YBa₂Cu₃O_7-δ on rolling-assisted biaxially textured substrates

The change in microstructure associated with the decrease in critical current density (J_c) of YBa₂Cu₃O_7-δ (YBCO) films with increasing thickness was examined. Samples of pulse laser deposited YBCO films varying in thickness from 0.19 to 3.0 μm on rolling-assisted biaxially textured substrates with an architecture of CeO₂/YSZ/CeO₂/Ni were prepared by tripod polishing for cross-sectional electron microscopy. More randomly oriented grains in the upper portion of the YBCO film surface were observed with increasing film thickness, resulting in less cube texture. In addition, increases in mismatch across the boundaries of the c-axis grains with increasing time during deposition, along with the development of BaCeO₃ and Y₂BaCuO₅ phases at the YBCO/CeO₂ interface, contributed to the degradation of film properties. Surface outgrowths of the YBCO film were examined as well as the defect structures and second-phase formations within the films.