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 Condensed Matter Tuesday, April 11, 2017 3:30 PM Physics Building, Room 204 Chunruo Duan [Host: Despina Louca] "The Effects of Annealing on Fe Vacancy and Superconductivity in K_xFe_{2-y}Se_2" ABSTRACT:The unique Fe vacancy ordering in alkali metal doped iron selenide $$A_xFe_{2-y}Se_2$$ (A=K, Rb, Cs, $$\cdots$$) has drawn a lot of attention among the Fe-based superconductor community. In this work we investigated the effects of annealing on Fe vacancy in $$K_xFe_{2-y}Se_2$$ single crystal samples by high energy X-ray diffraction and Monte Carlo simulation. The X-ray results indicated that the I4/mmm phase volume fraction decreased after annealing, while the simulation results demonstrated that this shrink of I4/mmm phase is accompanied with a expand of the Fe vacancy disordered area at the domain boundaries. Together with the well known annealing induced superconductivity enhancement, we found that superconductivity in this system is most likely related to the Fe vacancy disordered region.