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High Temperature Structural Behavior of SrRuO{sub 3}

Description: The unusual metal SrRuO{sub 3} is perhaps the only known 4d transition metal based ferromagnet (Tc = 162K) with a sizable moment. To complement low T polarized neutron diffraction measurements of the magnetization density, high T neutron diffraction measurements are reported here. Two structural phase transitions are observed. Between 10K and 800K SrRuO{sub 3} is orthorhombic and at 800K it appears to be tetragonal until 975K, where it becomes cubic. The temperature variation of the lattice parameters are reported along with a structural description of the tetragonal phase.
Date: July 15, 1997
Creator: Chakoumakos, B.C., Nagler, S.E., Misture, S.T., Christen, H.M.
Partner: UNT Libraries Government Documents Department

Role of C and P Sites on the Chemical Activity of Metal Carbide and Phosphides: From Clusters to Single-Crystal Surfaces

Description: Transition metal carbides and phosphides have shown tremendous potential as highly active catalysts. At a microscopic level, it is not well understood how these new catalysts work. Their high activity is usually attributed to ligand or/and ensemble effects. Here, we review recent studies that examine the chemical activity of metal carbide and phosphides as a function of size, from clusters to extended surfaces, and metal/carbon or metal/phosphorous ratio. These studies reveal that the C and P sites in these compounds cannot be considered as simple spectators. They moderate the reactivity of the metal centers and provide bonding sites for adsorbates.
Date: July 1, 2007
Creator: Rodriguez, J. A.; Vines, F.; Liu, P. & Illas, F.
Partner: UNT Libraries Government Documents Department

Preliminary studies on identification of inorganic species in complex mixtures by electrospray mass spectrometry in the counter ion mode

Description: Suppression of mass spectral peaks due to matrix problem is a major hurdle to overcome during identification work. So far, preliminary studies have been done in investigating solutions containing various percentages of nitric and hydrochloric acid. Since other anions would also be present in real samples, also needed to be examined is how the extent of suppression of metal complexes by Cl{sup {minus}} compares with suppression by other anions such as PO{sub 4}{sup 3{minus}} or SO{sub 4}{sup 2{minus}}. If suppression of other anions is as severe as that of the chloride ion, then it would be virtually impossible to analyze unknown samples containing large amount of such anions by direct infusion electrospray mass spectrometry. It seems like a separation step is needed to separate these matrix anions from the metal complexes prior to putting the solution through the electrospray. However, separation of inorganic complexes can be difficult and has not been studied thoroughly as LC separation of bioorganic compounds. Both zinc and copper chloro complexes have been observed to be more tolerant to higher amount of chloride ion present in a solution compared to the group I and II metal chloro complexes. Other transition metals including the lanthanide complexes need to be examined more intensively to see how they fare against other transition metal complexes. So far, only preliminary work has been done in identifying inorganic species in solutions using both ICP-MS and ES-MS. The solution contained a number of metals but only one major anion, NO{sub 3}{sup {minus}}. Therefore, complex solutions containing a number of anions and metals can be examined to see if identification is still feasible. This identification work can be continued on into investigating real samples.
Date: November 8, 1999
Creator: Mollah, Sahana
Partner: UNT Libraries Government Documents Department

A unified view of coherent and incoherent dihydrogen exchange in transition metal hydrides by nuclear resonance and inelastic neutron scattering

Description: In this paper a unified view of coherent and incoherent dihydrogen exchange in transition metal hydrides by nuclear magnetic resonance (NMR) and inelastic neutron scattering (INS) is presented. It is shown that both exchange processes coexist i.e. do not transform into each other although they may dominate the spectra in different temperature ranges. This superposition is the consequence of the incorporation of the tunnel frequency J of the coherent process into the nuclear two-spin hamiltonian of hydrogen pairs which allows to treat the problem using the well known density matrix theory of NMR line-shapes developed by Alexander and Binsch. It is shown that this theory can also be used to predict the line-shapes of the rotational tunneling transitions observed in the INS spectra of transition metal dihydrogen complexes and that both NMR and INS spectra depend on similar parameters.
Date: August 12, 1995
Creator: Limbach, H.H.; Ulrich, S.; Buntkowsky, G.; Sabo-Etienne, S.; Chaudret, B.; Kubas, G.J. et al.
Partner: UNT Libraries Government Documents Department

Lithiated Oxides for Lithium-Ion Batteries

Description: Rechargeable lithium batteries that can be assembled in the discharged state with lithiated metal oxide cathodes and carbon anodes are being developed to minimize the safety hazards associated with batteries that use pure metallic lithium anodes. This paper highlights the progress that has been made to develop lithiated transition metal oxide cathodes that have a layered structure, Li{sub x}MoO{sub 2}, and those that have a spinel-type structure, Li{sub x}M{sub 2}O{sub 4}, (M = Co, Ni, Mn, V). Emphasis is placed on the structural properties of insertion electrodes that control their stability during electrochemical cycling. The use of lithiated spinel oxide instead of lithiated carbon (LiC{sub 6}) as the anode is briefly discussed.
Date: Autumn 1994
Creator: Thackeray, M. M.
Partner: UNT Libraries Government Documents Department

Magnetic and thermodynamic properties of the 3-D periodic anderson lattice hamiltonian

Description: Tight-binding models capture many of the qualitative features of interaction-induced effects in solids. For example, the simplest such model, the single-band Hubbard Hamiltonian, describes the Mott insulating phase which occurs in correlated systems, despite the fact that the one electron band is nominally only half-filled, as well as the tendency towards magnetic order. Both phenomena occur in the transition metal oxides. The Periodic Anderson Model (PAM) is a step towards incorporating more complex orbital structure. It contains a pair of orbitals on each site--a delocalized conduction band and a set of highly correlated, localized states. The PAM successfully describes conditions for transitions between antiferromagnetic order of the local moments and phases in which these moments are quenched into singlets paired with conduction electrons. These phenomena are central to heavy fermion systems. The pressure-induced volume collapse in Ce has also been attributed to Kondo-like quenching of the local f moments in this metal, as has been discussed in the context of the impurity Anderson Model. The authors describe Quantum Monte Carlo (QMC) calculations of the magnetic and thermodynamic properties of the PAM in three dimensions. Previous QMC studies have been reported in one and two dimensions. A focus of our attention will be on the density of states and the specific heat. The organization of this paper is as follows. They first introduce the PAM and outline some of its properties. Next, a brief presentation of the Quantum Monte Carlo, Maximum Entropy, and Hartree-Fock methods is given. They then show the equilibrium magnetic properties of the PAM, including the spin correlations between conduction and localized orbitals, and antiferromagnetic correlations in the localized band, before turning to the thermodynamics and the density of states. A concluding section describes connections of this work to the problem of the rare earth volume collapse transitions.
Date: September 10, 1998
Creator: Huscrot, C.; McMahan, A. K.; Pollock, E. I & Scalettar, R. T.
Partner: UNT Libraries Government Documents Department

New catalysts for coal processing: Metal carbides and nitrides. Final report, September 11, 1991--September 10, 1994

Description: The main objective of this project was to study transition metal carbides and nitrides as catalysts for hydroprocessing. In particular, the goals were to study the solid-state transformations that occur during synthesis of the compounds using a temperature-programmed method, and to investigate the catalytic properties of the materials for the upgrading of model coal liquids at realistic process conditions.
Date: June 8, 1994
Creator: Oyama, S.T.
Partner: UNT Libraries Government Documents Department

Electronic Structure and Geometries of Small Compound Metal Clusters

Description: During the tenure of the DOE grant DE-FG05-87EI145316 we have concentrated on equilibrium geometries, stability, and the electronic structure of transition metal-carbon clusters (met-cars), clusters designed to mimic the chemistry of atoms, and reactivity of homo-nuclear metal clusters and ions with various reactant molecules. It is difficult to describe all the research the authors have accomplished as they have published 38 papers. In this report, they outline briefly the salient features of their work on the following topics: (1) Designer Clusters: Building Blocks for a New Class of Solids; (2) Atomic Structure, Stability, and Electronic Properties of Metallo-Carbohedrenes; (3) Reactivity of Metal Clusters with H{sub 2} and NO; and (4) Anomalous Spectroscopy of Li{sub 4} Clusters.
Date: April 14, 1999
Partner: UNT Libraries Government Documents Department

The ideal strength and mechanical hardness of solids

Description: Relationships between intrinsic mechanical hardness and atomic-scale properties are reviewed, Hardness scales closely and linearly with shear modulus for a given class of material (covalent, ionic or metallic). A two-parameter fit and a Peierls-stress model produce a more universal scaling relationship, but no model can explain differences in hardness between the transition metal carbides and nitrides. Calculations of ''ideal strength'' (defined by the limit of elastic stability of a perfect crystal) are proposed. The ideal shear strengths of fcc aluminum and copper are calculated using ab initio techniques and allowing for structural relaxation of all five strain components other than the imposed strain. The strengths of Al and Cu are similar (8-9% of the shear modulus), but the geometry of the relaxations in Al and Cu is very different. The relaxations are consistent with experimentally measured third-order elastic constants. The general thermodynamic conditions of elastic stability that set the upper limits of mechanical strength are derived. The conditions of stability are shown for cubic (hydrostatic), tetragonal (tensile) and monoclinic (shear) distortions of a cubic crystal. The implications of this stability analysis to first-principles calculations of ideal strength are discussed, and a method to detect instabilities orthogonal to the direction of the applied stress is identified. The relaxed ideal shear and tensile strengths of bcc tungsten are also calculated using ab initio techniques and are favorably compared to recent nano-indentation measurements. The {l_brace}100{r_brace} tensile strength (29.5 GPa) is governed by the Bain instability. The shear strengths in the weak directions on {l_brace}110{r_brace}, {l_brace}112{r_brace}, and {l_brace}123{r_brace} planes are very nearly equal ({approx} 18 GPa) and occur at approximately the same strain (17-18%). This isotropy is a function of the linear elastic isotropy for shear in directions containing {l_angle}111{r_angle} in bcc and of the atomic configurations of energetic saddle points reached during shear. ...
Date: April 1, 2000
Creator: Krenn, Christopher
Partner: UNT Libraries Government Documents Department


Description: Recent developments in hard x-ray resonant inelastic x-ray scattering as a probe of strongly correlated systems are reviewed. Particular attention is paid to studies of Nd{sub 2}CuO{sub 4}. A charge transfer excitation is observed when the incident photon energy is tuned in the vicinity of the copper K-edge. It is shown that the presence of resonant enhancements is controlled by the polarization dependence of the excitation process and by the overlap between a given intermediate state and the particular excitation being studied. This latter observation has shed light on the non-local effects present in certain intermediate states.
Date: August 23, 1999
Creator: HILL,J.P.
Partner: UNT Libraries Government Documents Department

Reaction synthesis of heat-resistant materials

Description: Exothermicity associated with the synthesis of aluminides can be utilized to obtain aluminides of transition metals. Combustion synthesis, extrusion, and hot pressing were utilized to obtain dense intermetallics and their composites. Composites were analyzed by X- ray diffraction and microscopy techniques, and tensile properties were measured on button-head and sheet specimens of intermetallics and their composites. Mechanical properties of intermetallics obtained by reaction synthesis and densification compare well with conventionally processed materials. Reaction-synthesis principles were also extended to weld overlays. Possible approaches to obtaining dense products by reaction synthesis and densification are summarized in a schematic illustration. 19 refs., 14 figs., 3 tabs.
Date: December 31, 1995
Creator: Deevi, S.C. & Sikka, V.K.
Partner: UNT Libraries Government Documents Department

Mesoscale Charge-Ordering in Transition Metal Oxides: Formation and Signatures

Description: The authors briefly outline the value of an inhomogeneous (unrestricted) Hartree-Fock plus Random Phase approach for understanding the types and properties of mesoscopic patterns of localized small polarons in transition metal oxides. Using a multiband Peierls-Hubbard model for a hole-doped CuO{sub 2} layer as an illustrative example, they demonstrate the appearance of correlated high-energy (electronic) and low-energy (localized phonon and spin-wave) signatures of various vertical, diagonal, metal-centered, and oxygen-centered mesoscopic stripe patterns of localized holes (small polarons).
Date: June 1, 1998
Creator: Bishop, A.R. & Yu, Z.G.
Partner: UNT Libraries Government Documents Department

Chemical Activation of Molecules by Metals: Experimental Studies of Electron Distributions and Bonding

Description: This research program is directed at obtaining detailed experimental information on the electronic interactions between metals and organic molecules. These interactions provide low energy pathways for many important chemical and catalytic processes. A major feature of the program is the continued development and application of our special high-resolution valence photoelectron spectroscopy (UPS), and high-precision X-ray core photoelectron spectroscopy (XPS) instrumentation for study of organometallic molecules in the gas phase. The study involves a systematic approach towards understanding the interactions and activation of bound carbonyls, C-H bonds, methylenes, vinylidenes, acetylides, alkenes, alkynes, carbenes, carbynes, alkylidenes, alkylidynes, and others with various monometal, dimetal, and cluster metal species. Supporting ligands include -aryls, alkoxides, oxides, and phosphines. We are expanding our studies of both early and late transition metal species and electron-rich and electron-poor environments in order to more completely understand the electronic factors that serve to stabilize particular organic fragments and intermediates on metals. Additional new directions for this program are being taken in ultra-high vacuum surface UPS, XPS, scanning tunneling microscopy (STM) and atomic force microscopy (AFM) experiments on both physisorbed and chemisorbed organometallic thin films. The combination of these methods provides additional electronic structure information on surface-molecule and molecule-molecule interactions. A very important general result emerging from this program is the identification of a close relationship between the ionization energies of the species and the thermodynamics of the chemical and catalytic reactions of these systems.
Date: March 26, 2002
Creator: Lichtenberger, Dennis L.
Partner: UNT Libraries Government Documents Department

A study of the inhibition of pitting of aluminum by chromate

Description: The location of chromate activity during the pitting corrosion of aluminum has been studied. Scanning vibrating probe technique monitored the current densities above cathodic and anodic sites and SIMS was used to determine the location of chromium reduction products. Products deposited preferentially on cathodes but chromates dramatically inhibited the anodic pitting processes. 8 refs., 3 figs.
Date: January 1, 1991
Creator: Hawkins, J.; Thompson, G.E.; Wood, G.C. (University of Manchester Inst. of Science and Technology (UK). Corrosion and Protection Centre) & Isaacs, H.S. (Brookhaven National Lab., Upton, NY (USA))
Partner: UNT Libraries Government Documents Department

X-ray diffraction patterns of metal aurocyanides

Description: Aurocyanides of the following metal cations have been prepared: Ag, Hg(II), Ga, Fe(III), Tl(I), Bi, Pb, Mn(II), Ni, Zn, Cu(II), Cd, In, and Co(II). Most of the aurocyanides are of the type M(Au(CN)/sub 2/)/sub x/ where M is the metal cation and x its valence. However, under some conditions mixed aurocyanides containing K may be formed, such as KCo(Au(CN)/sub 2/)/sub 3/. Only Ag and Hg(II) form aurocyanides which are sufficiently insoluble for the potentiometric determination of the aurocyanide anion. The diffraction patterns of the various aurocyanides are reported. 12 refs., 16 tabs.
Date: June 1, 1989
Creator: Selig, W.S.; Smith, G.S.; Harding, K.K. & Summers, L.J.
Partner: UNT Libraries Government Documents Department

Study of ZrCl by self-consistent band calculation

Description: A nonrelativistic self-consistent electronic band structure calculation has been performed on zirconium monochloride using the KKR method. The exchange potential was approximated by the X..cap alpha.. method. The compound contains homoatomic layers in the sequence Cl--Zr--Zr--Cl and has the characteristics of a graphite-like two-dimensional metal. A substantial charge transfer is found toward the metallic layers and away from the loosely bonded halogen layer. There is also significant admixture of Zr-d character within the filled Cl-3p bands. The total density of states is in good agreement with the valence band photoemission results.
Date: July 1, 1979
Creator: Marchiando, J.F.
Partner: UNT Libraries Government Documents Department

SEM analysis of rock varnish chemistry: A geomorphic age discriminator

Description: Rock varnish, a manganese- and iron-rich coating commonly found on rock surfaces in arid and semiarid regions, has long been of interest as a potential age indicator. Rock varnish has been shown to be an effective medium for dating of geomorphic surfaces over a time range of several thousand to over a million years, utilizing a ratio among minor cations ((K + Ca)/Ti) for the total volume of rock varnish. We have recently, developed a technique using the scanning electron microscope (SEM) equipped with an energy dispersive x-ray analyzer (EDAX) to analyze the chemistry of rock varnish. This technique has several advantages over the earlier cation ratio technique.
Date: July 1, 1989
Creator: Harrington, C.D. & Raymond, R. Jr.
Partner: UNT Libraries Government Documents Department

Rotational spin-glass properties of Tb sub 0. 3 Y sub 0. 7 Ag

Description: This cubic pseudobinary compound with antiferromagnetic order and spin-glass properties below T{sub g} (36 K) was studied by magnetization-vector measurements on a field-cooled (fc) polycrystalline sample disk rotated in various fixed fields ({rvec H}). At 4.2 K, the fc-induced anisotropy field {rvec H}{sub K} is seen to turn rigidly with the sample for all rotational magnetization follows {rvec H}{sub K} very closely, it is deduced that H{sub K} > 100 kOe. At 20 K, {rvec H}{sub K} turns rigidly but only below a threshold field, above which {rvec H}{sub K} rotates up to some critical angle relative to {rvec H}, where it remains as the sample continues to turn. Thus, {rvec H}{sub K} rotates frictionally relative to the sample. Nevertheless, it is found that its magnitude continues to exceed 100 kOe. 7 refs., 3 figs.
Date: January 1, 1989
Creator: Said, M.R.; Kouvel, J.S.; Brun, T.O. (Illinois Univ., Chicago, IL (USA). Dept. of Physics & Argonne National Lab., IL (USA))
Partner: UNT Libraries Government Documents Department

Measuring enthalpies of formation using thick multilayer foils and differential scanning calorimetry

Description: The ability to measure formation enthalpies of compounds at relatively low temperatures using thick multilayer foils and differential scanning calorimetry is demonstrated. Cu/Zr and Al/Zr multilayers were deposited onto Si and glass substrates using a planetary, magnetron source sputtering system. The as-deposited foils were removed from their substrates and heated from 50 to 725C in a differential scanning calorimeter (DSC). The Cu/Zr samples, which are all Cu-rich, showed three distinct, reproducible, and exothermic solid state reactions. The heats from the first two reactions were summed and analyzed to measure 14.3{plus_minus}0.3 kJ/mol for Cu{sub 51}Zr{sub 14}`s enthalpy of formation. This quantity agrees with the single value of {Delta}H{sub f} = 14.07{plus_minus}1.07kJ/mol reported for this compound. The composition of the Al/Zr multilayers ranged from 8 at% Zr to 64 at% Zr. These samples showed a variety of distinct, reproducible, and exothermic solid state reactions. The total heats from these reactions were summed and analyzed to measure enthalpies of formation for five different Al-Zr alloys. The results compare favorably with literature values of {Delta}H{sub f}. Advantages of measuring enthalpies of formation using thick multilayer foil samples and low temperature DSC calorimetry are discussed.
Date: April 14, 1995
Creator: Weihs, T.P.; Barbee, T.W. Jr. & Wall, M.A.
Partner: UNT Libraries Government Documents Department

Universal Bronsted-Evans-Polanyi Relations for C-C, C-O, C-N, N-O, N-N, and O-O Dissociation Reactions

Description: It is shown that for all the essential bond forming and bond breaking reactions on metal surfaces, the reactivity of the metal surface correlates linearly with the reaction energy in a single universal relation. Such correlations provide an easy way of establishing trends in reactivity among the different transition metals.
Date: October 27, 2010
Creator: Wang, Shengguang
Partner: UNT Libraries Government Documents Department

Geometry of some metal halides

Description: Thesis. Two polarizable ion models are developed to describe the gas phase of metal dihalide molecules. Both models use electrostatic and repulsive interactions to predict molecular geometries and molecular constants. The first model is applied to the dihalides of the alkaline earths, group II-b metals, transition metals, group IV-a metals, and europium. In addition to the molecular geometry, bending frequencies are derived for most of these molecules. The second or linear'' model is applied to the alkaline eanth dihalides; equilibrium internuclear bond lengths, stretching force constants, and stretching frequencies are determined. (LK)
Date: July 1, 1973
Creator: Yarnell, P.A.
Partner: UNT Libraries Government Documents Department

Energy savings through use of an improved reduction-cell cathode. Interim technical report, October 1, 1978-December 31, 1978

Description: This report summarizes the development work during the fifth quarter of the cost sharing contract between the Department of Energy and Kaiser Aluminum and Chemical Corporation. The project purpose is to develop a wettable and drained Hall cell cathode which will reduce the specific energy consumption of commercial cells by 20 to 25%. During this quarter the material characterization work has continued. In the last half of this period the decision was made to restart the 15KA piloe cell for a testing campaign of TiB/sub 2/ parts. The latter were ordered and partial shipments were received at the end of the quarter.
Date: January 1, 1978
Creator: Goodnow, W. H.
Partner: UNT Libraries Government Documents Department

Magnetic field dependence of the specific heat of heavy-fermion YbCu sub 4. 5

Description: The specific heat of a polycrystalline sample of YbCu{sub 4.5} has been measured between 0.3 and 20K in magnetic fields to 7T. At zero field a minimum in C/T is observed near 11K. Below that temperature C/T increases and below 0.5K exhibits an upturn ascribed to a hyperfine contribution. The increase in C/T below 11K is reduced by a factor 1.5 for H = 7T, whereas the hyperfine term is enhanced due to the contribution of the {sup 63}Cu and {sup 65}Cu and nuclei. 5 refs., 3 figs.
Date: March 1, 1990
Creator: Amato, A.; Fisher, R.A.; Phillips, N.E. (Lawrence Berkeley Lab., CA (USA)); Jaccard, D. & Walker, E. (Geneva Univ. (Switzerland). Dept. de Physique de la Matiere Condensee)
Partner: UNT Libraries Government Documents Department