MgF2 Doping of SmFeAsO Superconductors Prepared by Mechanical Alloying and Rapid Annealing

Magnesium and fluorine codoped Sm1–x/2Mg x/2FeAsO1–x F x (x = 0 – 0.3) superconductors were prepared by the process of mechanical alloying and subsequent rapid sintering. The transition temperature (T c) increases with x and reaches 53.3 K at x = 0.3, accompanied by decreased lattice parameters. Electron-type conduction in the MgF2-doped samples was found by Hall-effect measurements. The higher T c value of Sm1–x/2Mg x/2FeAsO1–x F x was attributed to the larger disorder and a higher internal pressure from the Sm and O sites, similar to the case of (Ln1–x M x )2CuO4 superconductors (where Ln is a rare-earth element and M = Ca, Sr, Ba).