Hugo F. Franzen

XPS spectra of some transition metal and alkaline earth monochalcogenides

Abstract The first-row transition-metal monosulfides and alkaline-earth chalcogenides were studied by means of X-ray photoelectron spectroscopy. It is shown that the bonding in the alkaline earth compounds is relatively ionic with XPS evidence for significant charge separation. On the other hand, transition metal sulfides, with the exception of MnS, appear to be principally metallic with little or no charge separation. Values for the inner orbital binding energy shifts are reported for a large number of monochalcogenides.

Thermodynamic study of the zirconium-aluminum system

The heats of formation of the zirconium-aluminum intermetallic compounds ZrAl/sub 3/, ZrAl/sub 2/, Zr/sub 2/Al/sub 3/, ZrAl, Zr/sub 5/Al/sub 4/, Zr/sub 3/Al/sub 2/, Zr/sub 5/Al/sub 3/, and the solid solution of aluminum in bcc zirconium have been studied using a Knudsen cell mass spectrometric technique. The high temperature compound Zr/sub 5/Al/sub 4/ was identified in the residue of some of these experiments and this led to further heat treatment/X-ray diffraction experiments which indicated that Zr/sub 4/Al/sub 3/, previously reported to form from the melt, decomposes in the solid state at temperature in excess of 1050/sup 0/C. By measuring aluminum vapor pressures over the two-phase ranges of the system from 0 < X/sub Al/ < 0.75 the enthalpy changes for the decomposition reactions were determined by second- and third-law methods, and these were used along with the measured vapor pressure of aluminum over the solid solution of aluminum in bcc zirconium to derive the enthalpies of formation of the intermetallic phases (in kcal/mole): ZrAl/sub 3/, -38.96; ZrAl/sub 2/, -32.86; Zr/sub 2/Al/sub 3/, -56.12; ZrAl, -21.36; Zr/sub 5/Al/sub 4/, -93.76; Zr/sub 3/Al/sub 2/, -48.78; Zr/sub 5/Al/sub 3/, -74.57. 21 references, 4 figures, 4 tables.

New oxides of the filled-Ti2Ni type structure

Abstract The metal atom ordering and oxygen occupancy of four compounds of the filled-Ti2Ni type structure have been determined by single-crystal X-ray diffraction studies. Three additional phases have been identified and indexed from powder X-ray diffraction data. All the phases crystallize in space group Fd 3 m with the following compositions: Zr4Ni2O ( a = 12.1970(9) A ), ZΓ6Ni4Ti2O0.6 ( a = 12.0299(9) A ), Nb6Ni6O ( a = 11.2117(5) A ), and Nb6Ni4Ta2O2 ( a = 11.5813(3) A ). Phases identified using powder data are Nb4Ni2O ( a = 11.5933(3) A ), Zr4Cu2O ( a = 12.2659(7) A ), and Zr6Co4Ti2O ( a = 11.8649(9) A ). A comparison of the structures and oxygen occupancies is presented, as well as tentative explanations based on results of extended Huckel calculations. The role of interstitial oxygen as an electron acceptor and its effect on metal-metal bonding are considered.

The crystal structure of a new ternary metal-rich sulfide Ta6.08Nb4.92S4

The metal-rich sulfide Ta6.08Nb4.92S4 has been prepared by high temperature techniques and characterized by means of X-ray diffraction experiments. It crystallizes in the orthorhombic space group Pnma with four formula units in the cell: a = 3121.00 (54) pm, b = 335.07 (7) pm, and c = 959.18 (19) pm. Its structure is similar to that of niobium-rich sulfides, rather than to that of tantalum-rich sulfides. The metal coordinations are capped distorted cubic prisms and the coordinations of sulfur are capped trigonal prisms.

Crystal structure and electronic structure of NbxTa2-xS (x≃0.95) : a new layered compound in ternary Ta-Nb-S system

Abstract During the continuing study of the metal-rich region of the ternary Ta-Nb-S system a new layered compound, Nb x Ta 2− x S ( x ≈0.95), was found using the arc-melting method and characterized by means of X-ray diffraction experiments. The compound crystallizes in the tetragonal space group P 4/ nmm with unit cell dimensions α =333.04(7) pm and c =909.28(94) pm. The tetragonal cell contains two formula units. The structure contains homoatomic layers sequenced S-M2-M1-M1-M2-S (M is a Nb, Ta mixture) generating six-layer sheets stacked along [001] and is closely related to b.c.c. Weak S-S interactions at 319 pm between sheets contrast with the M-M binding within and between the sheets, the former presumably being responsible for the observed graphitic slippage of the samples. Based upon extended Huckel band calculations metallic properties can be expected for this compound. The relative preference of the metal sites for the two metal elements (Ta, Nb) is explained by band calculations.

Infrared Spectra and Structure of Matrix Isolated Thallous Halides

The infrared absorption spectra of the vapor species over thallous fluoride, chloride, bromide, and iodide have been observed in the frequency range 33–4000 cm−1 using the matrix isolation technique. In addition to the absorption frequencies of the TlX monomers, the spectra of the Tl2F2 and Tl2Cl2 dimers have been observed. The absorption bands assigned to the dimer species are consistent with a proposed X–Tl–Tl–X dimer structure. A comparison of the observed to the calculated entropy of Tl2F2 and Tl2Cl2 lends support to the spectral assignments. A qualitative discussion of the bonding for the dimer species is included, to show that the proposed linear symmetrical structure for the Tl2X2 molecules is in agreement with several predictions based upon the qualitative bonding theory.

Synthesis and characterization of Pt-Ti4O7 microelectrode arrays

The synthesis of Pt-Ti4O7 microelectrode arrays is achieved from mixtures of TiO2 and Ti2O3 powders plus Pt particles by a thermal procedure commonly used in solid-state chemistry. Data obtained for the Pt-Ti4O7 materials by X-ray diffractometry and scanning electron microscopy are consistent with the existence of heterogeneous mixtures of Pt particles imbedded within the conductive Ti4O7 matrices. Rotated disc electrodes (RDEs) constructed from pure Pt and from the Pt-Ti4O7 materials are compared on the basis of their voltammetric and amperometric response for I− and H2O2 in 0.10m H2SO4. The observed enhancement of current densities for the Pt-Ti4O7 RDEs is rationalized on the basis of the behaviour expected for microelectrode arrays.

The X-ray photoelectron spectra of MnS, MnSe, and MnTe

Abstract The core level binding energies and valence band spectra of MnS, MnSe, and MnTe have been examined by X-ray photoelectron spectroscopy. The results demonstrate that the compounds are substantially more ionic in character than related transition metal compounds, and that the compounds lack significant metalmetal interactions, accounting for the nontypical nature of the compounds as transition metal chalcides.

Second‐Order Phase Transition in the VS One‐Phase Region

The lattice parameters and the densities of vanadium monosulfide samples have been determined by Guinier x‐ray powder diffraction and pycnometry, respectively. The samples spanned the homogeneity range of vanadium monosulfide. The data obtained are consistent with sulfur vacancies in samples for which S / V   1. The lattice parameters were found to vary continuously through the transition from the NiAs structure type to the MnP structure type, indicating that the transition is second order.

High‐Temperature Mass Spectrometry, Vaporization, and Thermodynamics of Titanium Monosulfide

A high temperature mass spectrometric investigation of the congruent vaporization of vanadium monosulfide, VS(s), from 1700 to 2000°K has shown that the two principal vaporization reactions produce VS(g) and V(g) + S(g) with a minor contribution from the reaction to produce VS2(g) + V(g). Thermodynamic results were obtained from three investigations of the congruent vaporization of the stoichiometric monosulfide. The second law enthalpy changes for the vaporization reactions at absolute zero were calculated from the experimental data and by use of a measured low temperature heat capacity for VS(s), estimated heat capacities for the solid above room temperature and for the vapor molecules, and literature values for the heat capacities of the atomic species. The Δ H0° values obtained and the estimated uncertainties are: 143±3 kcal for the reaction to form VS(g), 259±5 kcal for the reaction to form V(g) + S(g), and 144±5 kcal for the reaction to form ½ VS2(g) + ½ V(g). Ionic fragmentation of VS+ is considere...