Enabling coherent BaZrO₃nanorods/YBa₂Cu₃O_7-x interface through dynamic lattice enlargement in vertical epitaxy of BaZrO₃/YBa₂Cu₃O_7-x nanocomposites

One-dimensional c-axis-aligned BaZrO3 (BZO) nanorods are regarded as strong one-dimensional artificial pinning centers (1D-APCs) in BZO-doped YaBa2Cu3O7-x (BZO/YBCO) nanocomposite films. However, a microstructure analysis has revealed a defective, oxygen-deficient YBCO column around the BZO 1D-APCs due to the large lattice mismatch of ∼7.7% between the BZO (3a = 1.26 nm) and YBCO (c = 1.17 nm), which has been blamed for the reduced pinning efficiency of BZO 1D-APCs. Herein, we report a dynamic lattice enlargement approach on the tensile strained YBCO lattice during the BZO 1D-APCs growth to induce c-axis elongation of the YBCO lattice up to 1.26 nm near the BZO 1D-APC/YBCO interface via Ca/Cu substitution on single Cu-O planes of YBCO, which prevents the interfacial defect formation by reducing the BZO/YBCO lattice mismatch to ∼1.4%. Specifically, this is achieved by inserting thin Ca0.3Y0.7Ba2Cu3O7-x (CaY-123) spacers as the Ca reservoir in 2-6 vol.% BZO/YBCO nanocomposite multilayer (ML) films. A defect-free, coherent BZO 1D-APC/YBCO interface is confirmed in transmission electron microscopy and elemental distribution analyses. Excitingly, up to five-fold enhancement of J c (B) at magnetic field B= 9.0 T//c-axis and 65 K-77 K was obtained in the ML samples as compared to their BZO/YBCO single-layer (SL) counterpart's. This has led to a record high pinning force density F p together with significantly enhanced B max at which F p reaches its maximum value F p,max for BZO 1D-APCs at B//c-axis. At 65 K, the F p,max ∼158 GN m-3 and B max ∼8.0 T for the 6% BZO/YBCO ML samples represent a significant enhancement over F p,max ∼36.1 GN m-3 and B max ∼5.0 T for the 6% BZO/YBCO SL counterparts. This result not only illustrates the critical importance of a coherent BZO 1D-APC/YBCO interface in the pinning efficiency, but also provides a facile scheme to achieve such an interface to restore the pristine pinning efficiency of the BZO 1D-APCs.