Transformation of in-plane ρ(T) in YBa2Cu3O7-δ at fixed oxygen content -: art. no. 184515

This paper reveals the origin of a variation in magnitude and temperature dependence of the normal-state resistivity frequently observed in different YBa2Cu3O7-delta (YBCO) single-crystal or thin-film samples with the same T-c. We investigated temperature dependence of resistivity in YBa2Cu3O7-delta thin films with 7-delta between 6.80 and 6.95, which were subjected to annealing in argon at 400-420 K (120-140 degreesC) or aging at room temperature in air. Before annealing (or aging) these films exhibited a nonlinear rho(ab)(T), with a flattening [superlinear rho(ab)(T)] below 220-230 K, similar to rho(b)(T) and rho(ab)(T) observed in untwinned and twinned YBCO crystals, respectively. For all films the annealing causes an increase of resistivity and a transformation of rho(ab)(T) from a nonlinear (superlinear) dependence towards a more linear one (less flattening). For films annealed in argon with 7-delta=6.90 the increase of resistivity is also associated with an increase in T-c. We proposed a model that provides an explanation of these phenomena in terms of thermally activated redistribution of residual O(5) oxygens in the chain layer of YBCO. A good agreement between the experimental data for rho(ab)(t,T), where t is the annealing time, and numerical calculations was obtained.