Evidence of non‐linear to linear transformation of the normal state resistivity in YBCO at constant oxygen content

Abstract

AbstractWe studied the origin of variation in the magnitude and temperature dependence of the normal state resistivity frequently observed in different Y Ba2Cu3O7–δ (YBCO) single crystal or thin film samples with the same T C. We investigated the temperature dependence of resistivity in YBCO thin films, which were subjected to annealing in argon at 120 – 140 °C or aging at room temperature in air. Before annealing (or aging) these films exhibited a non‐linear in‐plane resistivity ρ a b (T), with upward deviation (flattening) in ρ a b (T) from the linear high temperature behavior below 220‐230 K. For all films the annealing causes an increase of resistivity and a transformation of ρ a b (T) from a non‐linear dependence towards a more linear one (less flattening). Our proposed model provides explanation of these phenomena based on the thermally activated redistribution of residual O(5) oxygen in the chain‐layer of YBCO without any change in the overall oxygen content within the sample. The results show that a perfectly linear ρ (T) can be observed in YBCO of oxygen content 7 – δ as low as 6.8. The agreement between the our data for ρ a b (T; t) and the proposed model was very good. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)