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Issue 18, 2016
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The preparation and phase diagrams of (7Li1−xFexOD)FeSe and (Li1−xFexOH)FeSe superconductors

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We report the phase diagram for the superconducting system (7Li1−xFexOD)FeSe and contrast it with that of (Li1−xFexOH)FeSe both in single crystal and powder forms. Samples were prepared via hydrothermal methods and characterized by laboratory and synchrotron X-ray diffraction, high-resolution neutron powder diffraction (NPD), and high intensity NPD. We find a correlation between the tetragonality of the unit cell parameters and the critical temperature, Tc, which is indicative of the effects of charge doping on the lattice and formation of iron vacancies in the FeSe layer. We observe no appreciable isotope effect on the maximum Tc in substituting H by D. The NPD measurements definitively rule out an antiferromagnetic ordering in the non-superconducting (Li1−xFexOD)FeSe samples below 120 K, which has been reported in non-superconducting (Li1−xFexOH)FeSe. A likely explanation for the observed antiferromagnetic transition in (Li1−xFexOH)FeSe samples is the formation of impurities during their preparation such as Fe3O4 and LixFeO2, which express a charge ordering transition known as the Verwey transition near 120 K. The concentration of these oxide impurities is found to be dependent on the concentration of the lithium hydroxide reagent and the use of H2O vs. D2O as the solvent during synthesis. We also describe the reaction conditions that lead to some of our superconducting samples to exhibit ferromagnetism below Tc.

Graphical abstract: The preparation and phase diagrams of (7Li1−xFexOD)FeSe and (Li1−xFexOH)FeSe superconductors

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Publication details

The article was received on 30 Nov 2015, accepted on 26 Feb 2016 and first published on 29 Feb 2016

Article type: Paper
DOI: 10.1039/C5TC04041H
J. Mater. Chem. C, 2016,4, 3934-3941

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    The preparation and phase diagrams of (7Li1−xFexOD)FeSe and (Li1−xFexOH)FeSe superconductors

    X. Zhou, C. K. H. Borg, J. W. Lynn, S. R. Saha, J. Paglione and E. E. Rodriguez, J. Mater. Chem. C, 2016, 4, 3934
    DOI: 10.1039/C5TC04041H

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