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

• TEM images show that Sm 2 O 3 admixture significantly changes the morphology of the MgB 2 wires. • TEM images point out that Sm 2 O 3 doping accelerates the formation of the MgB 2 phase. • TEM images show that Sm 2 O 3 admixture does not form rectangular MgB 2 crystallites, does not leave pure Mg. • TEM images indicate that Sm 2 O 3 doping forms Sm 2 O 3 areas of 10 nm and 20 nm (point pinning centers). • The TEM images show that rectangular MgB 2 crystallites are formed in undoped MgB 2 wires. This study reports results for the morphology, crystal structure and critical parameters of Sm 2 O 3 -doped MgB 2 wires with low and high initial filling densities. The transmission electron microscope (TEM) images were done for the longitudinal section of MgB 2 wires. The results show that the Sm 2 O 3 admixture significantly changes the morphology of the MgB 2 material, accelerates the formation of the MgB 2 phase, does not form rectangular MgB 2 crystallites, does not leave pure Mg, and forms Sm 2 O 3 areas of 10 nm and 20 nm. The effects of Sm 2 O 3 addition on MgB 2 formation in superconducting wires were revealed in detail in this study. Additionally, Sm 2 O 3 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 MgB 2 crystallites are formed in undoped MgB 2 wires, which have not been previously reported. XRPD results showed that short-term heating allowed obtaining a larger amount of MgB 2 phase for the MgB 2 wire with high initial filling density. On the other hand, long heating time and high initial density slow down the creation of MgB 2 phase when the Mg is in the solid state.