Dicaesium hexa­mercury hepta­sulfide

The title compound, Cs2Hg6S7, crystallizes in a new structure type that is closely related to that of K2Zn6O7. The structure comprises a three-dimensional mercury sulfide network that is composed of channels. These channels, which are along [001], are of two different diameters. The crystal structure contains one Cs, two Hg, and three S atoms in the asymmetric unit. The Cs, one Hg, and one S atom are at sites of symmetry m, whereas a second S atom is at a site of symmetry 2mm. The Hg atoms are bound to the S atoms in both three- and four-coordinate geometries. The caesium cations occupy the central spaces of the larger diameter channels and exhibit a coordination number of 7

Flux Crystal Growth of the RE2Ru3Ge5 (RE = La, Ce, Nd, Gd, Tb) Series and Their Magnetic and Metamagnetic Transitions

Previously synthesized only as powders, single crystals of the RE2Ru3Ge5 (RE = La, Ce, Nd, Gd, Tb) series of compounds have now been obtained from molten In. These materials crystallize with the U2Co3Si5-type structure in orthorhombic space group Ibam with lattice parameters a ≈ 10.00–9.77 Å (La–Tb), b ≈ 12.51–12.35 Å, and c ≈ 5.92–5.72 Å. The structure is a three-dimensional framework consisting of RuGe5 and RuGe6 units, as well as Ge–Ge zigzag chains. This structure type and those of the other five (Sc2Fe3Si5, Lu2Co3Si5, Y2Rh3Sn5, Yb2Ir3Ge5, and Yb2Pt3Sn5) to compose the RE2T3X5 phase space are discussed in depth. For the three compounds with RE = Nd, Gd, Tb, multiple magnetic transitions and metamagnetic behavior are observed. Electronic band structure calculations performed on La2Ru3Ge5 indicate that these materials have a negative band gap and are semimetallic in nature

Local orthorhombicity in the magnetic C4C_4 phase of the hole-doped iron-arsenide superconductor Sr1−x_{1-x}Nax_{x}Fe2_2As2_2

We report temperature-dependent pair distribution function measurements of Sr$_{1-x}$Na$_{x}$Fe$_2$As$_2$, an iron-based superconductor system that contains a magnetic phase with reentrant tetragonal symmetry, known as the magnetic $C_4$ phase. Quantitative refinements indicate that the instantaneous local structure in the $C_4$ phase is comprised of fluctuating orthorhombic regions with a length scale of $\sim$2 nm, despite the tetragonal symmetry of the average static structure. Additionally, local orthorhombic fluctuations exist on a similar length scale at temperatures well into the paramagnetic tetragonal phase. These results highlight the exceptionally large nematic susceptibility of iron-based superconductors and have significant implications for the magnetic $C_4$ phase and the neighboring $C_2$ and superconducting phases

Investigation of the High-Temperature Redox Chemistry of Sr\u3csub\u3e2\u3c/sub\u3eFe\u3csub\u3e1.5\u3c/sub\u3eMo\u3csub\u3e0.5\u3c/sub\u3eO\u3csub\u3e6-δ\u3c/sub\u3e\u3ci\u3e via In Situ\u3c/i\u3e Neutron Diffraction

Crystallographic structural changes were investigated for Sr2Fe1.5Mo0.5O6−δ, an electrode material for symmetric solid oxide fuel cells. The samples of this material were heated and cooled in wet hydrogen and wet oxygen atmospheres, to simulate the reducing and oxidizing conditions experienced under actual fuel cell operating conditions, and their structures and oxygen contents were determined using in situ powder neutron diffraction. The existence of a reversible tetragonal to cubic phase transition was established to occur between room temperature and 400 °C, both on heating and cooling in either oxygen or hydrogen. The oxygen content reaches a low value of 5.50(2) at 850 °C in wet hydrogen. Excellent correlations are observed between the oxygen content of the structure and the conductivities reported in the literature

Ba₈Hg₃U₃S₁₈: A Complex Uranium(+4)/Uranium(+5) Sulfide

The compound Ba₈Hg₃U₃S₁₈ was obtained from the solid-state reaction at 1123 K of U, HgS, BaS, and S, with BaBr₂/KBr or BaCl₂ as a flux. This material crystallizes in a new structure type in space group <i>P</i>6̅ of the hexagonal system with three formula units in a cell of dimensions <i>a</i> = 27.08(1) Å, <i>c</i> = 4.208(2) Å, and <i>V</i> = 2673(2) ų. The structure contains infinite chains of US₆ octahedra and nearly linear [S–Hg–S]^2– dithiomercurate anions, separated by Ba²⁺ cations. In the temperature range 100–300 K, the paramagnetic behavior of Ba₈Hg₃U₃S₁₈ can be fit to the Curie–Weiss law, resulting in μ_eff = 5.40(4) μ_B, or 3.12(2) μ_B/U. The compound displays an antiferromagnetic transition at <i>T</i>_N = 59 K. Although the formal oxidation states of Ba, Hg, and S can be assigned as +2, +2, and –2, the oxidation state of U is less certain. On the basis of interatomic distance arguments and the magnetic susceptibility data, the compound is proposed to contain U in both +4 and +5 formal oxidation states