The crystal structure of 3-R Nb1.06S2

The X-ray single crystal structure of 3-R Nb_1.06S₂ has been determined. The material crystallizes in the space group R_3m with a = 3.3285(4) and c = 17.910(4) Å when indexed on a hexagonal lattice. The structure was refined by full matrix least squares procedures to a final residual of R = 0.026 based on 79 observed (I > 3σ_I) reflections. The sulfurs form closest-packed layers with the majority of the metal in sheets of trigonal prismatic sites. A small portion of niobium was found to occupy octahedral sites, between the van der Waals gaps of the sulfur lattice. Niobium in the van der Waals region is trigonally distorted from octahedral symmetry, with niobium-sulfur distances of 2.234(8) and 2.577(11) Å, because of repulsion from niobium in adjacent trigonal prismatic layers.     

Crystal structures of V3S4 and V5S8

Crystal structures of the ordered phases of V₃S₄ and V₅S₈ were refined with single crystal data. Both are monoclinic. Chemical compositions, space groups and lattice constants are as follows: VS_1.47, $\text{I2}\text{m}$ (No. 12), a = 5.831(1), b = 3.267(1), c = 11.317(2)Å, β = 91.78(1)° and VS_1.64, $\text{F}\text{2}\text{m}$ (No. 12), a = 11.396(11), b = 6.645(7), c = 11.293(4), Å, β = 91.45(6)°. In both structures, short metal-metal bonds were found between the layers as well as within them. In comparison with the structure of Fe₇S₈, the stability of NiAs-type structure was discussed based on the detailed metal-sulfur distances.     

The crystal structure of niobium trisulfide,NbS3

The crystal structure of NbS₃ was determined from single-crystal diffractometer data obtained with MoKα radiation. The compound is triclinic, space group $\text{P}\text{1}$, with: a 4.963(2) Å; b = 6.730(2) Å; c = 9.144(4)Å; α = 90°; β = 97.17(1)°; γ = 90°. The structure is closely related to the ZrSe₃ structure type; it shows that the compound can be formulated as Nb⁴⁺(S₂)^2?S^2?, in agreement with XPS spectra. The main difference with ZrSe₃ is that the Nb atoms are shifted from the mirror planes of the surrounding bicapped trigonal prisms of sulfur atoms to form NbNb pairs (NbNb = 3.04 Å); this causes a doubling of the b axis relative to ZrSe₃ and a decrease of the symmetry to triclinic.     

The preparation and properties of BaTa0.8S3, BaNb0.8S3, and BaTa0.8Se3

Compounds of the formulas BaTa_0.8S₃, BaNb_0.8S₃, and BaTa_0.8Se₃ were prepared by two methods: reaction of the elements in evacuated silica tubes and reaction of H₂S over mixtures of BaCO₃ and 0.4Ta(Nb)₂O₅. They have the hexagonal BaNiO₃-type structure and are diamagnetic semiconductors. From the stoichiometries and properties we conclude that Nb and Ta are pentavalent.     

High-pressure syntheses of TaS3, NbS3, TaSe3, and NbSe3 with NbSe3-type crystal structure

Transition metal trichalcogenides TaSe₃, TaS₃, NbSe₃ and NbS₃ were prepared under the reaction conditions of 2 GPa, 700°C, 30 min. NbSe₃ is exactly the same as that obtained in the usual sealed-tube method. The other products are modifications of each usual phase. They have crystal structures very similar to that of NbSe₃. The lattice parameters are a = 10.02Å, b = 3.48 Å, c = 15.56 Å, β = 109.6° for TaSe₃, a = 9.52 Å, b = 3.35 Å, c = 14.92 Å, β = 110.0° for TaS₃, and a = 9.68 Å, b = 3.37 Å, c = 14.83 Å, β = 109.9° for NbS₃. In spite of the similarity in their crystal structures, these high-pressure phases show a variety of electrical transport properties. TaSe₃ is a superconductor having T_c at 1.9 K. TaS₃ is a semiconductor with two transitions at 200 and 250 K. NbS₃ is a semiconductor with E_a = 180 MeV.     

The crystal structure of Lu3S4: A new population wave structure

The monosulfide of lutetium loses lutetium preferentially upon vaporization in vacuo at 1750°C, and the quenched samples exhibit a new structure which is formed by an ordering of metal vacancies on the rock-salt type lattice.     

SnSbBiS4-SnS and SnSbBiS4-Sn2Sb6S11 sections of the SnS-Sb2S3-Bi2S3 ternary system

SnSbBiS₄-SnS and SnSbBiS₄-Sn₂Sb₆S₁₁ sections were studied by physicochemical methods (DTA, X-ray powder diffraction, microstructure observation, and microhardness measurements). These sections were found to be eutectic quasi-binary sections of the SnS-Sb₂S₃-Bi₂S₃ ternary system. Solid solution regions based on the initial components were found on either side of the sections. Alloys in the solid solution region are p-type semiconductors.     

Crystal structures of CsFe2S3 and RbFe2S3: synthetic analogs of rasvumite KFe2S3

The isostructural alkali thioferrate compounds CsFe₂S₃, RbFe₂S₃ and KFe₂S₃ have been synthesized by reacting Fe and S with their corresponding AFeS₂ (A=K, Rb, Cs) precursors. The crystal structures of these and binary compounds of intermediate composition were determined by Rietveld analysis of laboratory powder X-ray diffraction patterns. All of the synthesized compounds adopt the space group Cmcm (#63), Z=4 with: a=9.5193(8) Å, b=11.5826(10) Å, c=5.4820(4) Å for CsFe₂S₃; a=9.2202(7) Å, b=11.2429(9) Å, c=5.4450(3) Å for RbFe₂S₃; and a=9.0415(13) Å, b=11.0298(17) Å, c=5.4177(6) Å for KFe₂S₃. These mixed valence alkali thioferrates show regular changes in cell dimensions, AS₁₀ (A=K, Rb, Cs) polyhedron volumes, polyhedron distortion parameters, and calculated oxidation state of Fe with respect to increasing size of the alkali element cation. The calculated empirical oxidation state of iron varies from +2.618 (CsFe₂S₃), through +2.666 (RbFe₂S₃) to +2.77 (KFe₂S₃).     

四硫化三铁纳米粒子的制备及应用

近年来,Fe₃S₄磁性纳米粒子由于其独特的物理化学性质,如量子尺寸效应、电磁学特性,在环境治理、能源储存、催化剂、生物医学应用等方面展示出巨大的潜力。本文总结了近10年来国内外Fe₃S₄纳米粒子的制备方法,包括共沉淀法、水热法(溶剂热法)、热分解法和模板法等,并对比了不同合成方法的优缺点;随后介绍了Fe₃S₄纳米材料在环境治理、能源储存、生物医学等方面的应用;最后,分析了Fe₃S₄纳米材料在制备中存在的一些问题,并对其的发展方向进行了展望。     

Crystal Structures and Magnetic Properties of the Two Misfit Layer Compounds: [SrGd0.5S1.5]1.16 NbS2 and [Sr(Fe,Nb)0.5S1.5]1.13 NbS2

Crystal structures of two new misfit compounds, [SrGd_0.5S_1.5]_1.16NbS₂ and [Sr(Fe,Nb)_0.5S_1.5]_1.13NbS₂, were determined through the composite approach, i.e., by refining each subpart (Q, H-parts, and the common part) of these composite materials, separately. The Q-part is a three-atom-thick layer, with the NaCl-type structure, where external SrS planes enclose the inner GdS or (Fe,Nb)S plane; the structural difference between these two compounds lies in the central layer within the Q-part: Gd and S atoms are in special positions (octahedral coordination), while Fe and S atoms are statistically distributed on split (×4) positions (tetrahedral coordination) around a central unique site (=special position occupied by Nb). The H-part is a sandwich of sulfur planes enclosing the inner Nb plane as observed for the structure of the binary compound NbS₂ itself. The Sr-Gd derivative shows a paramagnetic behavior in the whole studied temperature range (2-300 K). On the other hand, antiferromagnetic interactions occur in the Sr-Fe derivative; the complex magnetic behavior of this compound is related to the statistical distribution of Fe atoms which leads to frustration of the magnetic interactions. At room temperature, experimental values obtained from Mössbauer spectrum correspond to Fe³⁺ in tetrahedral sulfur environment: isomer shift δ=0.32 mm s⁻¹, and quadrupole splitting ΔE=0.48 mm s⁻¹.     

Charge-density waves in pure and intercalated Nb3Te4

High-resolution transmission electron microscopy (HRTEM), resistivity measurements and electronic band structure calculations performed by means of the extended Hückel tight-binding method are presented for the quasi one-dimensional compounds A_xNb₃Te₄ (A = In, Tl, Zn, Ag, Hg). HRTEM and electron diffraction performed on pure Nb₃Te₄ at room- and liquid nitrogen temperatures, reveal both the basic structure and the low-temperature charge-density waves (CDWs) modulation. Resistivity vs. temperature plots show characteristic CDW anomalies, dependent on the type and concentration of the atoms, intercalated into the large hexagonal tunnels of the host structure. It is shown that intercalation of Tl and In results in a flattening of the corresponding Fermi surfaces and that CDW formation is largely dependent on the coincidence between the Fermi level E_F and a small peak in the density of states spectrum, mainly developed from the Nb dz² orbitals. This peak is positioned in a minimum between the filled and empty states of the spectrum and tends to split into a doublet as a consequence of intercalation.     

New SbS2 strings in the BaSb2S4 structure

The new compound BaSb₂S₄ crystallizes in the monoclinic system (space group: $\text{P2}{}_1\text{c}$, No. 14) with a = 8.985(2) Å, b = 8.203(3) Å, c = 20.602(5) Å, β = 101.36(3)°. SbS₃ ψ tetrahedra and ψ-trigonal SbS₄ bipyramids are connected by common corners and edgers to infinite strings. These are arraged cross-wise in sheets perpendicular to the c axis.     

Electronic structure, galvanomagnetic and magnetic properties of the bismuth subhalides Bi4I4 and Bi4Br4

Two bismuth-rich subhalides, Bi₄Br₄ and Bi₄I₄, featuring extended quasi one-dimensional metallic fragments in their structures, have been investigated. The gas-phase technique of crystal growth has been refined for obtaining large (up to 5 mm long) single crystals. Electronic structure calculations on three-dimensional structures of both compounds have been performed (DFT level, hybrid B3LYP functional), predicting a semiconducting behavior for both compounds, with an indication of possible directional anisotropy of electric conductivity. Galvanomagnetic (resistance, magnetoresistance, Hall effect, thermopower) and magnetic (temperature and field dependence of magnetization) properties have been measured experimentally. Both compounds are found to be diamagnetic, room-temperature semiconductors with n-type conductivity. While Bi₄Br₄ demonstrates a typical case of one dimensionality, the difference in magnetoresistivity between Bi₄Br₄ and Bi₄I₄ indicates some weak interactions between isolated bismuth metallic fragments within the bismuth substructures.     

A CNDO/2 approach to electron delocalization in N4S4 and N4S4F4

The electronic structure of N₄S₄ and N₄S₄F₄ molecules is investigated within the framework of the CNDO/2 approximation. A pure alternated system is obtained for the fluorinated compound with respect to the Wiberg bond populations. On the other hand, the N₄S₄ molecule appears to be composed of three highly delocalized “islands”, as defined by Dewar in the case of cyclophosphazenes. The “tub form” of N₄S₄ is due to a strong spatial interaction between non-bonded sulphur atoms and, for this reason, the N₄S₄ molecule may be called the “inorganic cyclooctatetraene”.     

Preparation and crystal structure of Na2Mn2S3

Na₂Mn₂S₃ was prepared by reacting manganese powder with an excess of anhydrous sodium carbonate and elemental sulfur at 870 K. Extraction of the solidified melt with water and alcohol yielded well developed, bright red crystals. Na₂Mn₂S₃ crystallizes with a new monoclinic structure type, space group $\text{C2}\text{c}\text{, Z = 8}$, with a = 14.942(2)Å, b = 13.276(2)Å, c = 6.851(2)Å, and β = 116.50(1)°. The crystal structure was determined from single crystal diffractometer data and refined to a conventional R value of 0.026 for 1613 observed reflections. The atomic arrangement shows sulfur-manganese-sulfur slabs which are separated from each other by corrugated layers of sodium atoms. A prominent feature of the crystal structure is the formation of short, four-membered zigzag chains built up by MnS₄ tetradedra sharing edges. These chains are further connected by the remaining apices to form an infinite sheet. Short MnMn distances (3.02 and 3.05 Å, respectively) are found within the four membered chains. Susceptibility measurements show antiferromagnetic interactions between the Mn atoms.     

Synthesis of Co4S3/Co9S8 nanosheets and comparison study toward the OER properties induced by different metal ion doping

Regulation of chemical composition and nanostructure, such as the introduction of dopant into twodimensional nanomaterials, is a general and valid strategy for the efficient electrocatalyst design. In this work, Co₄S₃/Co₉S₈ nanosheets, with an ultrathin layer structure, were successfully synthesized via an efficient solvothermal process combined with ultrasonic exfoliation. Different metal ions(M = Fe³⁺,Cr³⁺, Mn²⁺ and N...     

Vaporization chemistry and thermodynamics in the CdGa2S4-Ga2S3 system

The chemistry and thermodynamics of vaporization of CdGa₂S₄(s), CdGa₈S₁₃(s), and Ga₂S₃(s) were studied by computer-automated, simultaneous Knudsen-effusion and torsion-effusion, vapor pressure measurements in the temperature range 967–1280 K. The vaporization was incongruent with loss of Cd(g) + 1/2 S₂(g) and production of CdGa₈S₁₃(s), a previously unknown compound, in equilibrium with CdGa₂S₄(s), until the solid became CdGa₈S₁₃ only. Then, incongruent vaporization continued with production of Ga₂S₃(s) until the solid was Ga₂S₃ only. The latter vaporized congruently. The ΔH°(298 K) of combination of one mole of CdS(s) with one mole of Ga₂S₃(s) to give CdGa₂S₄(s) was ?22.6 ± 0.9 kJ mole^?1. The 2H2(298 K) of combination of one mole of CdS(s) with four moles of Ga₂S₃(s) to give CdGa₈S₁₃(s) was ?25.5 ± 1.1 kJ mole^?1. The 2H2(298K) of CdGa₈S₁₃(s) with respect to disproportionation into CdGa₂S₄(s) and 3 Ga₂S₃(s) was ?2.8 ± 0.6 kJ mole^?1. CdGa₈S₁₃(s) was not observed at room temperature. The 2H2(298 K) of vaporization of the residual Ga₂S₃(s) was 663.4 ± 0.8 kJ mole^?1, which compared well with a value of 661.4 ± 0.3 kJ mole^?1 already available from the literature. Implications of small variations in stoichiometry of compounds in this study were observed and are discussed.