title: Phase separation and suppression of the structural and magnetic transitions in superconducting doped iron tellurides, Fe(1+x)Te(1-y)S(y).
abstract: Single crystal and powder samples of the series of iron chalcogenide superconductors with nominal composition, Fe((1.15))Te((1-)y)S(y), are found to form for 0 ≤ y ≤ 0.15. They crystallize in the tetragonal anti-PbO structure, which is composed of layers of edge-shared Fe(Te, S)(4) tetrahedra. For y = 0, Fe(1+x)Te (x ≈ 0.12(1)) is nonsuperconducting and undergoes a tetragonal (P4/nmm) to monoclinic (P2(1)/m) structural transition at ∼65 K, associated with the onset of commensurate antiferromagnetic order at q = (0.5 0 0.5). We show that on sulfur substitution, Fe(1+x)Te(1-y)S(y) becomes orthorhombic (Pmmn) at low temperature for 0 ≤ y ≤ 0.015, where the greatly suppressed magnetic scattering is now incommensurate at q = (0.5-δ 0 0.5) and possesses short ranged magnetic correlations that are well fitted with a two-dimensional Warren peak shape. At much higher concentrations of S (y ≥ 0.075), there is suppression of both the structural and magnetic transitions and a superconducting transition at 9 K is observed. Between these two composition regimes, there exists a region of phase separation (0.025 ≤ y ≤ 0.05), where the low temperature neutron diffraction data is best refined with a model containing both the tetragonal and orthorhombic phases. The increase in the amount of sulfur is found to be associated with a reduction in interstitial iron, x. Microprobe analysis of a single crystal of composition Fe((1.123(5)))Te((0.948(4)))S((0.052(4))) confirms the presence of compositional variation within the crystals, rationalizing the observed phase separation.
authors.affiliation: NIST Center for Neutron Research, NIST, 100 Bureau Drive, Gaithersburg, Maryland 20878, USA.
authors.forename: Pawel
authors.initials: P
authors.lastname: Zajdel
authors.forename: Ping-Yen
authors.initials: PY
authors.lastname: Hsieh
authors.forename: Efrain E
authors.initials: EE
authors.lastname: Rodriguez
authors.forename: Nicholas P
authors.initials: NP
authors.lastname: Butch
authors.forename: Jeff D
authors.initials: JD
authors.lastname: Magill
authors.forename: Johnpierre
authors.initials: J
authors.lastname: Paglione
authors.forename: Peter
authors.initials: P
authors.lastname: Zavalij
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Suchomel
authors.forename: Mark A
authors.initials: MA
authors.lastname: Green