Role of the extra Fe in K2−xFe4+ySe5 superconductors
A paper resulted from PhD student Chih-Han Wang, advised by Professor Maw-Kuen Wu, in collaboration with Dr. Ming-Jye Wnag of ASIAA, Dr. Hwo-Shuenn Sheu and Dr. Jey-Jau Lee of NSRRC, has published in PNAS. This paper presents the results of a detailed structural study using synchrotron X-ray diffraction at various temperatures up to 850 °C on K2-xFe4+ySe5 superconductors. The results confirm that extra Fe atoms begin to fill the empty 4d site and stabilize the structural-phase I4/m symmetry so that the lattice size remains the same even above the order–disorder temperature. The results show that the addition of extra Fe suppresses the Fe vacancy long-range order and the accompanied magnetic order so that superconductivity emerges. The significance of this research is that it demonstrates unambiguously the structural origin for superconductivity in the K2−xFe4+ySe5 superconducting system.
Figure: Evolution of the temperature-dependent X-ray powder diffraction pattern and refined lattice parameters of (a) K2Fe4Se5 parent compound and (b) K1.9Fe4.2Se5 superconductor.
WebSite: https://www.pnas.org/cgi/doi/10.1073/pnas.1815237116