No abstract

Novel BiS2-based superconductors LaO1−xFxBiS2 prepared by a high-pressure synthesis technique were systematically studied. It was found that the high-pressure annealing strongly shrank the lattice as compared to the LaO1−xFxBiS2 samples prepared by conventional solid-state reaction at ambient pressure. Bulk superconductivity was observed within a wide F concentration range of x = 0.2-0.7. On the basis of those results, we have established a phase diagram of LaO1−xFxBiS2.

Phase diagrams of as-grown and O 2 -annealed FeTe 1-x Se x determined from magnetic susceptibility measurement were obtained. For as-grown samples, the antiferromagnetic order was fully suppressed in the range region x ≥ 0.15, and weak superconductivity appeared when x ≥ 0.1.Beginning at x = 0.5, weak superconductivity was found to evolve into bulk superconductivity.Interestingly, for O 2 -annealed samples, complete suppression of magnetic order and the occurrence of bulk superconductivity were observed when x ≥ 0.1. We found that O 2 -annealing induces bulk superconductivity for FeTe 1-x Se x . Oxygen probably plays a key role in the suppression of the magnetic order and the appearance of bulk superconductivity.

We show the observation of the coexistence of bulk superconductivity and ferromagnetism in CeO 1-x

The Phase diagram of SmFeAsO 1-x F x in terms of x is exhibited in this study. SmFeAsO 1-x F x from x = 0 to x = 0.3 were prepared by low temperature sintering with slow cooling. The low temperature sintering suppresses the formation of the amorphous FeAs, which is inevitably produced as an impurity by using high temperature sintering. Moreover, slow cooling is effective to obtain the high fluorine concentration.The compositional change from feedstock composition is quite small after this synthesis. We can reproducibly observe a record superconducting transition for an iron based superconductor at 58.1 K.This achievement of a high superconducting transition is due to the success in a large amount of fluorine substitution. A shrinking of the a lattice parameter caused by fluorine substitution is observed and the substitutional rate of fluorine changes at x =0.16.