The Optimal Growth of Single Grain Bulk Y–Ba–Cu–O Superconductors With Nd–Ba–Cu–O Thin Film Seed

The NdBCO thin film on MgO substrate is widely used as a seed for growing large, single grain bulk REBCO superconductors, due to its good epitaxy and superheating effect. While the NdBCO thin film seed is put on YBCO precursor pellets and heated above the peritectic temperature, it will be destroyed by the liquid phase of the Ba-Cu-O component. The exposed MgO substrate is found in the destroyed seed, resulting in the undesirable growth of (001) and (103) c-axis oriented grains. However, this can be avoided by carefully controlling the two steps of cooling during heterogeneous nucleation on the seeds, which also eliminates the homogeneous nucleated subgrains. The optimal growth conditions and morphology diagram of TSMG process by NdBCO thin film seeds are constructed in this work to aid in engineering fabrication, along with the coordinate system of temperature and welding time instead of temperature and degree of overcooling.