Comprehensive study on the performance evolution of BaHfO₃-added metal-organic decomposition YBCO-coated conductors with different sizes and concentrations

YBa₂Cu₃O_7−δ (YBCO)-coated conductors based on colloidal precursor solutions containing preformed nanocrystals by metal-organic decomposition (MOD) are promising, cost-effective and reproducible superconducting films with high critical current density (J_c). Although the preformed nanocrystal addition technology has achieved great success in improving the performance, the relationship between particle sizes and concentrations and the performance of BMO (BaMO₃, M = Hf, Zr) added to MOD-YBCO-coated conductors still needs systematic study. In the present work, the performance evolutions of BaHfO₃ (BHO)-added YBCO thick films of 2.4 µm with pristine sizes of 3.0 nm, 5.5 nm, 8.0 nm and 10 nm, respectively, were comprehensively studied at concentrations of 5-20 mol%. The size evolution results reveal that the coarsening of BHO nanocrystals after high-temperature treatment depends on the pristine size. BHO with a pristine size of 3.0 nm was enlarged by 6.3 times to 20 ± 13 nm due to the instability of small BHO particles. Meanwhile, the smallest final size achieved was 7.0 ± 3 nm for a pristine size of 5.5 nm, resulting in the largest enhancement in the in-field performance of the BHO-YBCO films, especially at low temperatures. The results indicate that the pristine size and final size of BHO nanocrystals are both very important and provide great guiding value for promoting preformed nanocrystal addition technology.