Microstructures of YBa_(1.85)Eu_(0.15)Cu_2O_(7-δ) superconducting films grown on SrTiO_3 and YSZ substrates

摘要

A detailed atomic scale microstructure analysis of Eu-doped YB_(1.85)Eu_(0.15)Cu_3O_(7-δ) (YEBCO) thin films with 100 nm in thickness has been carried out by a combination of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Interesting regular-like arranged network of nanoscale undulations is observed on the surface of YEBCO film on (0 0 1) SrTiO_3 substrate. TEM image clearly indicates that the film is always c-axis oriented, but lots of natural precipitates of Y_2O_3 are involved both at the interface and deep in the film. Desirable size and number density of Y_2O_3 are thought to be important for acting as efficient flux pinning centers. In the case of YEBCO film on (0 01) yttrium stabilized ZrO_2 (YSZ) substrate, few cracks and outgrowths appear due to much larger lattice mismatch and dissimilar crystal structure between the film and substrate, but surface quality is still much better compared to the parent YBaCu_3O_(7-δ) film. Besides, highly textured BaZrO_3 layer at the interface and a-axis grains with small dimensions in the film are formed. Interface stability of two kinds of films studied, namely YEBCO/STO and YEBCO/YSZ, is also assessed comprehensively by first principle calculations.