Influence of thickness on the microstructure and performance of BaHfO3-doped EuBa2Cu3O7-δ layers grown by ultra-fast PLD techniques

Abstract

The thickness effect in rare-earth barium cuprate thick superconducting layers is one of the main issues for achieving high-efficiency large-scale production. In this work, the evolution of the microstructure and current-carrying capacity was investigated on two tapes with different superconducting layer thicknesses. Both layers, composed of BaHfO3 (BHO)-doped EuBa2Cu3O7-δ (EuBCO), were deposited by an industrial multi-pulse and multi-turn pulsed laser deposition facility. XRD results indicate that both layers predominantly consist of c-axis-oriented EuBCO grains. Cross-sectional TEM images show that the EuBCO matrix exhibits columnar growth in both layers. Some misoriented EuBCO grains are found growing on Cu-O particles in the thick layer, while such defect regions are scarcely observed in the thin one. It is likely related to the deviation of growth conditions from the EuBCO growth window as the layer thickness increases. Additionally, the BHO distribution within the EuBCO matrix in the thick layer becomes more splayed and exhibits varying morphologies along the thickness direction. In terms of superconductivity, although both layers exhibit similar Tc around 97 K and similar ΔTc of 0.6 K, the Jc of the thin layer is nearly double that of the thick layer at 77 K and 4.2 K, self-field. However, under the perpendicular field (B//c-axis), the Jc(B) of the thick layer decreases more slowly than that of the thin layer, particularly at 4.2 K, resulting in the Jc values of two layers close to approximately 5 MA/cm2 at 4.2 K and 14 T. Moreover, the thick layer exhibits lower anisotropy in Jc (θ) compared to the thin one at 30 K, 5 T and 50 K, 3 T. These observations are associated with the highly splayed BHO nanocolumns and numerous natural defects in the thick layer, which act as effective pinning centers. This work provides clues for enhancing the in-field performance of tapes with thick superconducting layers.