Substrate strain effect of EuBa 2Cu 3O 7− δ film: interplay between dislocations, precipitates and superconductivity

Abstract

Our previous study showed that there is always a substantial resistive tail below the bulk T C of EuBa 2Cu 3O 7− δ and SmBa 2Cu 3O 7− δ (RBCO) films deposited on nearly perfect lattice matched SrTiO 3 (STO) substrates, which is in contrast to the same films deposited on less well-matched substrates, e.g., LaAlO 3 (LAO), under similar conditions. Although the lattice match is poorer, the latter films have a sharp resistive transition without any tail. The present study examines the evolution of precipitate density and intergranular coupling with increasing film thickness, revealing that dislocations induced from the release of strain affect the precipitation of off-stoichiometric phases. We propose a model that indicates induced dislocations attract off-stoichiometric phases and thus lead to tower-like precipitates. The precipitates segregate the potential impurities out from grain boundaries. Therefore, the intergranular coupling of RBCO film grown on LAO improves with increasing thickness. Meanwhile, in the absence of precipitates, off-stoichiometric materials in the film on STO coat each columnar grain. This model is consistent with the observed evolution of film morphology, T C and J C with thickness, and the theoretical fitting of the measured χ( t) curves.