Low-temperature synthesis of SmO0.8F0.2FeAs superconductor with Tc = 56.1 K

Abstract

We report a systematic study on the effect of sintering temperatureon the structural and superconducting properties of nominalSmO0.8F0.2FeAs fabricated by a simple one-step solid state reaction method. A detailed correlationbetween the sintering temperature, structure, onset transition temperature (Tc) and criticalcurrent density (Jc) has been found in all samples of each batch. Most importantly,samples sintered at a low temperature clearly show highTc, for example theTc of the samplessintered at 850 °C is even above 53 K, and the samples prepared at1000 °C display thehighest Tc of 56.1 K reported so far. Furthermore, the samples sintered at1000 °C also show the highestRRR and the lowest ρ(57 K), indicating the low impurity scattering and enhanced carrier density. However, the maximumJc of10 510 A cm − 2 at 5 K in the self-field was achieved in the samples sintered at1100 °C. Thedependence of Tc on the a-axis lattice constant indicates that the sintering temperature has a strong influence on theeffective substitution level of F for O. This result suggests that annealing at a temperature of ∼ 1000 °C seems much better for obtaining high quality 1111 phaseoxypnictides, compared to the commonly used temperatures of around1200 °C.