Nanocolumns in YBa₂Cu₃O_{7 −<i>x</i>}<i>/</i>BaZrO₃quasi-multilayers: formation and influence on superconducting properties

Abstract

The magnitude and anisotropy of the critical current density Jc as well as the irreversibility field Hirr of BaZrO3 (BZO)-doped YBa2Cu3O7 − x (YBCO) thin films are determined by both the amount of BZO and the deposition temperature. The influence of these two parameters was investigated on BZO/YBCO quasi-multilayers in two temperature series with different doping amounts (4 and 9 vol% BZO). The deposition temperature was varied between 790 and 850 °C. The samples show an increase in Hirr, logarithmic peaks in Jc(B) and strong c-axis peaks in Jc(θ). Nevertheless, the two series reveal opposite temperature trends for Jc: whereas Jc increases with temperature for 4 vol% BZO, it decreases for 9 vol%. This is explained by a diffusion model for the formation and growth of BZO nanocolumns and an optimum balance between correlated and random pinning centres for high Jc. TEM images support this model.