Microstructure of coated conductors with La- or Nb-doped SrTiO₃ conductive buffer

A novel configuration for coated conductors (CCs) was proposed to reduce material cost and consisted of YBa₂Cu₃O_y (YBCO) / conductive buffer(s) / Ni-electroplated {100} <001> textured Cu, and SUS316 lamination tape. Conductive buffers are a key subject to reduce material cost of CCs. In the CC using the conductive buffer of Nb-doped SrTiO₃ (Nb-STO), a high-J_C YBCO (2.5 MA/cm² at 77 K and self-field) was successfully obtained. Moreover, a clean interface between the buffer and the metal tape without oxides was confirmed using TEM analysis. However, the resistivity of the Nb-STO buffer increased to be several Ω·cm after the YBCO deposition, which was beyond expectations. Therefore, the La-doped STO (La-STO) conductive buffer was incorporated into CCs as a novel conductive buffer. Two CCs with the different conductive buffers were compared in terms of microstructure analysis using transmission electron microscopy.