Optimizing BaHfO₃ Nanocrystal Size and Concentration to Enhance MOD-YBCO Film Performance

The flux pinning of metal-organic deposition-REBa₂Cu₃O_7-δ (MOD-REBCO) coated conductors can be effectively enhanced through a BaHfO₃ (BHO) nanocrystal addition strategy. The present research explores the performance enhancement achieved by BHO additions with different concentrations and the BHO sizes. BHO nanocrystals with size of 5.5 nm and 6.5 nm were respectively added to REBCO at concentrations ranging from 0 to 15 mol%, resulting in significant increase in the in-field critical current density (J_c) of the BHO-REBCO films at low temperatures. At 30 K and 3 T, the 15 mol% BHO-REBCO film exhibited a 2.94-fold enhancement in J_c compared to the pristine film. For the two different sizes of BHO addition, the REBCO films with 5.5 nm-BHO exhibited lower in-field performance than those with 6.5 nm-BHO. This is attributed to instability-induced coarsening of smaller BHO nanocrystals in 5.5 nm case, leading to reduced flux pinning efficiency. The results demonstrate that optimizing the size of BHO nanocrystals can significantly enhance the in-field performance of REBCO films.