The influence of Sm₂O₃ dopant on structure, morphology and transport critical current density of MgB₂ wires investigated by using the transmission electron microscope

This study reports results for the morphology, crystal structure and critical parameters of Sm₂O₃-doped MgB₂ wires with low and high initial filling densities. The transmission electron microscope (TEM) images were done for the longitudinal section of MgB₂ wires. The results show that the Sm₂O₃ admixture significantly changes the morphology of the MgB₂ material, accelerates the formation of the MgB₂ phase, does not form rectangular MgB₂ crystallites, does not leave pure Mg, and forms Sm₂O₃ areas of 10 nm and 20 nm. The effects of Sm₂O₃ addition on MgB₂ formation in superconducting wires were revealed in detail in this study. Additionally, Sm₂O₃ causes the formation of point pinning regions that significantly increase the critical transport current density at the temperature range from 15 K to 30 K. The TEM images point out that rectangular MgB₂ crystallites are formed in undoped MgB₂ wires, which have not been previously reported. XRPD results showed that short-term heating allowed obtaining a larger amount of MgB₂ phase for the MgB₂ wire with high initial filling density. On the other hand, long heating time and high initial density slow down the creation of MgB₂ phase when the Mg is in the solid state.