Three Dimensional Observation of Flux Pinning Centers in Dy-doped YBa_2Cu_3O_(7-x) Coated Superconductors by STEM Tomography

摘要

The spatial distribution of flux pinning centers in YBa_2Cu_3O_7 (YBCO) coated conductors significantly affects the conductive properties. Nanoparticles acting as pinning centers can be intentionally introduced into the structure by chemical doping. In this study, a Dy-doped YBa_2Cu_3O_(7-x) coated superconductor was investigated and the particle composition was found to be as (Y_sDy_(1-s))_2Cu_2O_5 with s ～0.6. A tomographic tilt series was acquired using a scanning transmission electron microscope (STEM) to determine the 3-D distribution of nanoparticles. In the investigated sample area, 71 particles were located with a particle size distribution ranging between 13 and 135 nm. The distribution uniformity and size of the particles appeared to be dependent on the grain boundary network structure. Large particles were observed to be located on grain boundaries indicating that fast grain boundary diffusion may determine the particle size.