The influence of grain boundary i c on the macroscopic strain effect of i c in BHO-doped GdBCO-coated conductors

Abstract

The effect of strain in REBa2Cu3Oy (REBCO: RE = Y, Gd, Sm, Eu) coated conductors (CCs) on the critical current (I c) is one of the most fundamental factors for superconducting coil applications because CCs experience a variety of stresses. In this study, we carried out bending tests and measured the peak strain and the strain sensitivity of I c (a-value) for GdBCO CCs at 77 K under self-field. These values were evaluated for pure GdBCO CCs and BaHfO3 BHO-doped GdBCO CCs, which had oxide buffer layers with varying in-plane grain alignments of the CeO2 top layer. As a result, the peak strains and a-values for the BHO-doped GdBCO CCs depended on the FWHM of the CeO2 220 reflection in the φ-scan profile (Δφ), and decreased monotonically with decreasing Δφ. On the other hand, the peak strain and a-value were nearly independent of Δφ in the pure-GdBCO CCs. The change in peak strains for the BHO-doped GdBCO CCs are discussed on the basis of the relative contribution of intra-grain I c and inter-grain I c to the macroscopic strain effect of I c in the CCs.