Nanostructures and flux pinning properties in YBa_2Cu_3O_(7-y) thin films with double perovskite Ba_2LuNbO_6 nanorods

摘要

Double perovskite Ba_2LuNbO_6 (BLNO)-doped YBa_2Cu_3O_(7-y) (YBCO) thin films are fabricated on a SrTiO_3 (001) substrate by pulsed laser deposition, and their nanostructures are characterized by transmission electron microscopy and scanning transmission electron microscopy. Cross-sectional observations and elemental mapping reveal that BLNO self-assembles during thin film deposition, and consequently, nanorods extending straight from the substrate to the surface are formed in the YBCO thin films. It is confirmed that stacking faults perpendicular to the growth direction disturb the formation of BLNO nanorods. Strain maps extracted by geometric phase analysis reveal that the tensile strain occurs in the YBCO matrix around the BLNO nanorods. Misfit dislocations are periodically introduced at the interface between the nanorod and the matrix, which results in the inhomogeneous strain of YBCO around the BLNO nanorods. The superconducting properties of the YBCO + BLNO thin films are compared with those of other previously reported YBCO thin films with normal perovskite and double perovskite nanorods.