Transformation of in-plane $\rho (T)$ in $YBa_{2}Cu_{3}O_{7-\delta}$ at fixed oxygen content

TL;DR

This study investigates how annealing affects the in-plane resistivity of YBCO thin films with fixed oxygen content, revealing a transition from non-linear to linear temperature dependence due to oxygen redistribution.

Contribution

It introduces a model explaining resistivity changes in YBCO films based on thermally activated oxygen redistribution, supported by experimental data and numerical calculations.

Findings

Annealing increases resistivity and alters temperature dependence of resistivity.

Increased T_c observed in films with higher oxygen content after annealing.

Good agreement between experimental data and the proposed oxygen redistribution model.

Abstract

This paper reveals the origin of variation in the magnitude and temperature dependence of the normal state resistivity frequently observed in different YBCO single crystal or thin film samples with the same $T_{c}$. We investigated temperature dependence of resistivity in $YBa_{2}Cu_{3}O_{7-\delta}$ thin films with 7- $\delta = 6.95$ and 6.90, which were subjected to annealing in argon at 400-420 K ($120-140^{o}C$). Before annealing these films exhibited a non-linear $\rho_{ab}(T)$, with a flattening below 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 non-linear dependence towards a more linear one (less flattening). In films with 7- $\delta = 6.90$ the increase of resistivity is also associated with an increase in $T_{c}$. We proposed the 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. Good agreement between the experimental data for $\rho_{ab}(t,T)$, where t is the annealing time, and numerical calculations was obtained.