The role of F-doping and oxygen vacancies on the superconductivity in SmFeAsO compounds

By investigating the F-doping effect in the SmFeAsO1-xFx, SmFeAsO1-xF0.20 and SmFeAsO0.90Fx systems as well as the oxygen vacancy effect in the SmFeAsO1-y superconductors, we obtained the following results: (a) the substitution range of F for oxygen in the SmFeAsO1-xFx system prepared by the ambient pressure method is 0 < =x < =0.125; (b) F cannot substitute for oxygen in samples without oxygen vacancies; (c) the oxygen-deficient SmFeAsO1-y superconductor cannot be prepared by the ambient pressure method; and (d) F-doping and oxygen vacancies both lead to lattice shrinkage. Oxygen-deficient SmFeAsO0.85 and F-doped SmFeAsO0.85F0.15 prepared by the high pressure method have higher superconducting transition temperature compared to SmFeAsO0.85F0.15 prepared by the ambient pressure method.