Cross-sectional microstructure observation of YBa2Cu3O7-δ multifilament films fabricated on Nb stripes

A bottom-up approach was employed to achieve multifilamentation aimed at reducing the alternating current (AC) losses of REBa₂Cu₃O 7-δ coated conductors. Nb stripes were fabricated on SrTiO₃ substrates, followed by the deposition of YBa₂Cu₃O₇ -δ (YBCO) thin films via the metal-organic deposition method. The films were subsequently evaluated and analyzed. Surface observations using scanning electron microscopy revealed a linear dark contrast on the stripes, distinct from the YBCO matrix. Furthermore, selected area electron diffraction patterns and scanning transmission electron microscopy-energy dispersive X-ray spectroscopy analyses confirmed the presence of multiple Y–Cu–O and Cu–O particles in the YBCO phase on a ~4 μm-wide Nb stripe. In addition, the formation of voids and Ba 5 Nb 4 O 15 was observed in the ~4 μm Nb stripe. On a wider Nb stripe (~13 μm), only Y–Cu–O and Cu–O phases and cracks were observed, along with relatively large voids and the formation of Ba 5 Nb 4 O 15 . This study provides a fundamental understanding of multifilamented YBCO thin films and offers important insights into reducing AC losses. • YBa 2 Cu 3 O 7-δ thin films were fabricated by the TFA-MOD method on SrTiO 3 substrates with Nb stripes patterned using photolithography process, and successful multifilamented YBCO was achieved. • Cross-sectional TEM observations of the YBCO thin film with Nb stripes revealed that the reaction between the Nb stripes and the BaO precursor induced a deviation in the local chemical composition ratio of YBCO near the Nb stripes, leading to the formation of non-superconducting Y-Cu-O and Cu-O particles. • Cross-sectional TEM observations near Nb stripes with two different widths revealed that the wider stripe promoted the formation of larger non-superconducting phases, indicating that the stripe width significantly influences the multifilamentation.