Low temperature preparation and superconductivity of F-doped SmFeAsO

A low temperature (1100 °C) process of preparing F-doped SmFeAsO samples has been developed using SmF₃ with nanometer scale as the source of fluorine. A series of the SmFeAsO_1−xF_x (x = 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3) samples have been prepared using the present method. Compared with previous reports, the present SmF₃ is more effective to introduce F into SmFeAsO system in which a transition temperature of 39 K can be observed when x = 0.05. The superconductivity is definitely enhanced with the increasing F-doping level. All the samples presented to be layered structure and the crystal particle size is about three times larger with sintering time increasing from 36 h to 48 h. Except for the nanometer scale of SmF₃, the flux effect of SmF₃ is recognized to be another reason for the decrease of the sintering temperature. Further more, a relatively large amount of SmF₃ was also employed in the raw materials to introduce excessive F and this has induced higher T_c (55 K) in SmFeAsO_0.8F_0.2+δ system.