Abstract
Abstract We recently report that a superconducting transition is invoked by exposure to water vapor in undoped SrFe 2 As 2 , which occurs accompanied by shrinkage of the c -axis length of the unit cell. In this paper, we calculated structures and formation energies of O-/OH-related impurities and vacancies in SrFe 2 As 2 by first-principles calculations in order to find a model that explains the c -axis shrinkage in SrFe 2 As 2 . It was found that the incorporation of an O, OH or H 2 O molecule at an interstitial site cannot explain the c -axis shrinkage, and that formation of an As vacancy needs a large formation energy. While, Sr and Fe vacancies are formed with negative formation energies, and the Fe vacancy can explain the c -axis shrinkage.
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