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

Abstract

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.