title: Hydrogen-Substituted Superconductors SmFeAsO(1-x)Hx Misidentified As Oxygen-Deficient SmFeAsO(1-x).
abstract: We investigated the preferred electron dopants at the oxygen sites of 1111-type SmFeAsO by changing the atmospheres around the precursor with the composition of Sm:Fe:As:O = 1:1:1:1 - x in high-pressure synthesis. Under H2O and H2 atmospheres, hydrogens derived from H2O or H2 molecules were introduced into the oxygen sites as a hydride ion, and SmFeAsO(1-x)Hx was obtained. However, when the H2O and H2 sources were removed from the synthetic process, nearly stoichiometric SmFeAsO was obtained and the maximum amount of oxygen vacancies introduced remained x = 0.05(4). Density functional theory calculations indicated that substitution of hydrogen in the form of H(-) is more stable than the formation of an oxygen vacancy at the oxygen site of SmFeAsO. These results strongly imply that oxygen-deficient SmFeAsO(1-x) reported previously is SmFeAsO(1-x)Hx with hydride ion incorporated unintentionally during high-pressure synthesis.
authors.affiliation: Materials Research Center for Element Strategy, Tokyo Institute of Technology , 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8503, Japan.
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Muraba
authors.affiliation: Materials and Structures Laboratory, Tokyo Institute of Technology , 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8503, Japan.
authors.forename: Soshi
authors.initials: S
authors.lastname: Iimura
authors.affiliation: Materials Research Center for Element Strategy, Tokyo Institute of Technology , 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8503, Japan.
authors.forename: Satoru
authors.initials: S
authors.lastname: Matsuishi
authors.affiliation: Materials Research Center for Element Strategy, Tokyo Institute of Technology , 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8503, Japan.|Materials and Structures Laboratory, Tokyo Institute of Technology , 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8503, Japan.
authors.forename: Hideo
authors.initials: H
authors.lastname: Hosono