G.A. Wiegers

Chalcogenide misfit layer compounds

Abstract Misfit layer chalcogenides (MX)1+x(TX2)m (M  Sn, Pb, Sb, Bi, rare earth; T  Ti, V, Cr, Nb, Ta; X  S, Se; 0.08

MISFIT LAYER COMPOUNDS (MS)NTS2 (M = SN, PB, BI, RARE-EARTH ELEMENTS - T = NB, TA - N = 1.08 - 1.19), A NEW CLASS OF LAYER COMPOUNDS

Abstract A study by X-ray diffraction and electron microscopy is reported of the type of compounds that is usually designated as ternary sulphides “MTS 3 ” ( M = Sn, Pb, Bi, rare earth metals; T = Nb, Ta). They are misfit layer compounds built of alternating double layers of MS with M in distorted square pyramidal coordination by sulphur and sandwiches TS 2 with T is distorted trigonal-prismatic coordination by sulphur. One intralayer lattice constant of MS is incommensurate with that of TS 2 . Recent progress in the understanding of the crystallographic description is discussed and a unifying view based on about ten compounds is presented. Results of electrical transport measurements are briefly summarized.

The crystal structure of some rhenium and technetium dichalcogenides

Abstract The crystal structures of ReSe., ReS., ReSSe and TeS2 are determined using single crystal X-ray diffraction. The compounds are triclinic with space groupPl. ReSe., ReS, and ReSSe have a distorted CdCl2-type structure: TeS2 has a distorted Cd(OH)-type structure. In the case of ReS, there are two sandwiches in the unit cell, related by symmetry centers. The other compounds have one sandwich per unit cell and the centers of symmetry are within the Re (Tc)-layer. In all compounds the Re (Te) atoms in each layer form parallelogram-shaped connected clusters with Re Re (Te Te) distances of ca. 2.7–2.8A, in the cluster and ca. 2.9A, between clusters. The chains of clusters run along the a-axis. Unit cell dimensions and structure of ReS, differ from the one reported recently by Murray et al.Inorg. Chem., 33 (1994) 4418) where only one sandwich is present and the centers of symmetry are in the Re layer. The structure of ReSe2 differs from that reported by Alcock and Kjekshus (Acta Chem. Scand., 19 (1965) 79), in the sense that these authors interchanged inversion-centers and pseudo-centers.

The preparation and crystal structure of gold monochloride, AuCl

Abstract Large single crystals of AuCl were prepared by a vapour-transport method. AuCl is tetragonal, a = 6.734, c = 8.674 A , space group 141/amd, Z = 8. The structure consists of zig-zag chains of Au and Cl; Au is linearly coordinated by Cl at distances of 2.36 A, the bond angles Au-Cl-Au are 92 °.

The system titanium-sulfur. II. The structures of Ti3S4 and Ti4S5

Abstract The crystal structures of rhombohedral Ti 3 S 4 and hexagonal Ti 4 S 5 were determined by X-ray powder diffraction methods. The structures are based on close packings of sulfur atoms of the types ( chchchh ) 3 and ( chchh ) 2 , respectively; the metal atoms lie in part of the octahedral holes of these packings. The occupancies of the various metal positions were determined; they can be described by occupation waves . Correlations of the compositions of titanium sulfides in the range Ti 2 S 3 TiS with the observed interatomic distances, stacking sequences and occupation waves are given and discussed.

Structure, electrical transport, and magnetic properties of the misfit layer compound (PbS)1.13TaS2

Abstract (PbS)1.13TaS2, formerly designated “PbTaS3,” has been found by single-crystal X-ray diffraction to be a misfit layer compound characterized by two face-centered orthorhombic unit cells each with space group Fm2m. One belongs to the PbS part of the structure (a = 5.825A, b = 5.779A, c = 23.96A, Z = 8), the other belongs to the TaS2 part of the structure (a′ = 3.304A, b′ = 5.779A, c′ = 23.96A, Z = 4). The corresponding axes are parallel; the ratio of the lengths of the misfit a axes, a a′ is irrational, but close to 7 4 . The compound is built of alternately double layers of PbS with distorted NaCl-type structure and TaS2 sandwiches, with Ta in distorted trigonal prisms of sulfur. Along the c axes of length 23.96 A, four units are stacked; units of the same type but ( 1 2 )c apart are displaced with respect to each other over ( 1 2 )b . The symmetry of the complete structure is analyzed in terms of a four-dimensional superspace group. The electrical transport and magnetic properties are related to those of 2HTaS2. The conduction is metallic and strongly anisotropic, the in-plane resistivity being about 105 smaller than the resistivity along the c axis. The Hall coefficient, with positive sign, corresponds with an electron donation from PbS to TaS2. The Seebeck coefficient is negative like that in other intercalates of 2HTaS2. The compound is Pauli-paramagnetic.

The incommensurate misfit layer structure of (SnS)1.17NbS2, `SnNbS3'. I. A study by means of X-ray diffraction

(SnS)1.17NbS2, Mr = 334.92, is a compound with misfit layer structure consisting of two-atom-thick layers of SnS and three-atom-thick sandwiches of NbS2 which alternate along the c axis. The lattices of SnS and NbS2 both have C-centered orthorhombic unit cells which match along the b and c axes but not along the a axes. The unit cells and space groups are a = 5.673 (1), b = 5.750 (1), c = 11.760 (1) A, space group C2mb (no. 39), Z = 4, for SnS; a = 3.321 (1), b = 5.752 (1), c = 11.763 (1) A, space group Cm2m (no. 38), Z = 2, for NbS2. From the ratio of the lengths of the a axes of the two parts of the complete structure (5.673/3.321 = 1.708 being irrational) one obtains a composition (SnS)1.17NbS2. The structure determination consisted of three parts: the structures of the SnS and NbS2 parts separately and their relative position. Intensities were measured with Mo K{\bar \alpha} radiation (λ = 0.71073 A) at T = 293 K, μ = 102.3 cm-1. For the SnS part RF = 0.088 for 306 unique reflections; for the NbS2 part RF = 0.031 for 329 unique reflections (for both cases 0kl reflections excluded). The relative position of these two lattices was determined from the common reflections 0kl: RF = 0.072 for 98 reflections. The SnS part of the structure consists of deformed slices of SnS with a thickness of half the cell edge of (hypothetical) NaC1-type SnS. Each Sn atom is in this way coordinated by five sulfur atoms; four sulfur atoms are in a plane perpendicular to the c axis with SnS distances 2.74 (1) (1×), 2.913 (1) (2×) and 3.01 (1) A (1×), whereas the fifth Sn-S bond with length 2.695 (9) A is approximately along the c axis. The NbS2 part of the structure is that of NbS2-2H with Nb in trigonal prisms of sulfur; the Nb-S distances are 2.473 (1) A. From refinement of the common 0kl reflections the relative y and z positions of the two sublattices were found; along the common a direction the lattices of SnS and NbS2 are incommensurate.

Structure and phase transitions of molybdenum(III) sulfide and some related phases

Molybdenum(III) sulfide, Mo2.06S3, is monoclinic with a = 6.092A; b = 3.208A; c = 8.6335A; β = 102.43°. The structure has been determined and refined from X-ray powder data. The metal atoms lie in octahedral holes of a chh close packing of sulfur, but they are displaced from the octahedron centers in such a way that zigzag MoMo chains are formed (MoMo = 2.86 A). Blow + 37°C the structure is a superstructure of the one described, all axes being doubled. At −80°C the lattice of Mo2.06S3 undergoes a distortion to triclinic symmetry. In solid solutions (Mo1−x,Nbx)2.06S3 with 0.025 < x ⩽ 0.50 no superstructures are observed; the structure remains monoclinic down to low temperatures. The compounds previously regarded as Mo2Se3 and Mo2Te3 are better designated as Mo3Se4 and Mo3Te4. The low-temperature Guinier camera used in this investigation is described.

Determination of the modulated structure of the inorganic misfit layer compound (PbS)1.18TiS2

Single-crystal X-ray diffraction results (Mo K-alphaBAR radiation, lambda = 0.71073 angstrom) are presented for the inorganic misfit layer compound titanium sulfide (PbS)1.18TiS2 which can be described as a two-component structure. The first subsystem (TiS2, nu = 1) has space-group symmetry C2(1)/m, and a basic structure unit cell given by a11 = 3.409 (1), a12 = 5.880 (2), a13 = 11.760 (2) angstrom and alpha-1 = 95.29 (2)-degrees. The modulation wavevector is q1 = a21* = alpha-a11*, with alpha = 0.5878 (3). Its subsystem superspace group is [GRAPHICS] (alpha, 0, 0). The second subsystem (PbS, nu = 2) has space group C2/m and a basic structure unit cell given by a21 = 5.800 (2), a22 = 5.881 (2), a23 = 11.759 (2) angstrom and alpha-2 = 95.27 (2)-degrees. The modulation wavevector is q2 = a11*. The subsystem superspace group is [GRAPHICS] (alpha-1, 0, 0). The relation between the two unit cells is defined by the common (a-nu-2*, a-nu-3*) plane. The symmetry of the complete system is described by the single superspace group G(s) = [GRAPHICS] (alpha, 0, 0). Reciprocal lattice parameters for this superspace embedding are a1* = a11*, a2* = a12*, a3* = a13* and a4* = a21*. Refinements on 1449 main reflections, with I > 2.5-sigma(I), converged smoothly to R(F2) = 0.064 (R(F) = 0.069). The final structure model included displacive modulation parameters up to second harmonics for Pb and first harmonics for the other atoms. The largest modulation amplitudes are on both atoms of the PbS subsystem. They mainly desribe displacements parallel to the layers, along the commensurate direction a-nu-2. A detailed analysis is given of the coordination of the Pb (nu = 2) and S (nu = 1) atoms by plotting interatomic distances as a function of the fourth superspace coordinate.

On the nature of a new phase transition in α-MnS

Abstract Magnetic-susceptibility and X-ray-diffraction data of polycrystalline and oriented single crystal α-MnS reveal a new phase transition at T tr = 131 K below the Neel temperature T N = 148 K. The phase transition is characterized by an abrupt inversion of the rhombohedral distortion of the f.c.c. lattice along [111]. At T tr there is a discontinuous change in the susceptibility of single crystals.