Achieving High Jc in High Fields in Multilayer BZO/YBCO Thick Films

Abstract

Improved pinning efficiency of c-axis-aligned BaZrO ₃ nanorods (BZO-NRs) in BZO/YBa ₂ Cu ₃ O ₇ nanocomposite thin films was obtained recently using a multilayer (ML) approach, in which diffusion of Ca ions from two thin (Ca _0.3 Y _0.7 )BCO spacers (10 nm in thickness) sandwiched with three BZO/YBa ₂ Cu ₃ O ₇ layers. The subsequent Ca (30% larger)/Cu substitution at the Cu-O planes of YBCO was found energetically preferable by inducing c-axis elongation of the YBa ₂ Cu ₃ O ₇ lattice near the BZO-NRs/YBa ₂ Cu ₃ O ₇ interface to enable a coherent interface via reducing the BZO/YBCO lattice mismatch from originally 7.7% to 1.4%, leading to significantly enhanced J _c ( B ) and F _p in thin ML films of 150 nm in thickness. This work investigates whether improved pinning could be achievable in thicker BZO-NRs/YBa ₂ Cu ₃ O ₇ ML films with the thickness increased to 1000 nm. Interestingly, similar pinning enhancement has been observed in thick BZO-NRs/YBa ₂ Cu ₃ O ₇ ML films across a wide temperature range of 20–80 K. In particular, the thicker BZO-NRs/YBa ₂ Cu ₃ O ₇ ML films outperform their thinner counterparts in both higher value and less anisotropy of J _c ( B ). At 1000 nm thickness, I _c (30 K, 9T) reaches up to ∼680 A/cm-width with a variation of ∼85% over the entire angular range of B field orientations. This result illustrates the critical role of Ca diffusion at the BZO-NRs/YBCO interface for improving pinning efficiency of BZO-NRs in a wide range of temperatures and B fields.