Ronald G. Cavell

University of Alberta, Edmonton, Alberta, Canada

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Publications (200)374.27 Total impact

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    ABSTRACT: The ability of molecular dynamics (MD) simulations to support the analysis of X-ray absorption fine-structure (XAFS) data for metals is evaluated. The low-order cumulants (ΔR, σ(2), C3) for XAFS scattering paths are calculated for the metals Cu, Ni, Fe, Ti and Au at 300 K using 28 interatomic potentials of the embedded-atom method type. The MD cumulant predictions were evaluated within a cumulant expansion XAFS fitting model, using global (path-independent) scaling factors. Direct simulations of the corresponding XAFS spectra, χ(R), are also performed using MD configurational data in combination with the FEFF ab initio code. The cumulant scaling parameters compensate for differences between the real and effective scattering path distributions, and for any errors that might exist in the MD predictions and in the experimental data. The fitted value of ΔR is susceptible to experimental errors and inadvertent lattice thermal expansion in the simulation crystallites. The unadjusted predictions of σ(2) vary in accuracy, but do not show a consistent bias for any metal except Au, for which all potentials overestimate σ(2). The unadjusted C3 predictions produced by different potentials display only order-of-magnitude consistency. The accuracy of direct simulations of χ(R) for a given metal varies among the different potentials. For each of the metals Cu, Ni, Fe and Ti, one or more of the tested potentials was found to provide a reasonable simulation of χ(R). However, none of the potentials tested for Au was sufficiently accurate for this purpose.
    Journal of Synchrotron Radiation 07/2013; 20(Pt 4):555-66. · 2.19 Impact Factor
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    ABSTRACT: Several 1:1 adducts of gallium trihalides with triarylphosphines, X(3) Ga(PR(3) ) (X=Cl, Br, and I; PR(3) =triarylphosphine ligand), were investigated by using solid-state (69/71) Ga and (31) P NMR spectroscopy at different magnetic-field strengths. The (69/71) Ga nuclear quadrupolar coupling parameters, as well as the gallium and phosphorus magnetic shielding tensors, were determined. The magnitude of the (71) Ga quadrupolar coupling constants (C(Q) ((71) Ga)) range from approximately 0.9 to 11.0 MHz. The spans of the gallium magnetic shielding tensors for these complexes, δ(11) -δ(33) , range from approximately 30 to 380 ppm; those determined for phosphorus range from 10 to 40 ppm. For any given phosphine ligand, the gallium nuclei are most shielded for X=I and least shielded for X=Cl, a trend previously observed for In(III) -phosphine complexes. This experimental trend, attributed to spin-orbit effects of the halogen ligands, is reproduced by DFT calculations. The signs of C(Q) ((69/71) Ga) for some of the adducts were determined from the analysis of the (31) P NMR spectra acquired with magic angle spinning (MAS). The (1) J((69/71) Ga,(31) P) and ΔJ((69/71) Ga, (31) P) values, as well as their signs, were also determined; values of (1) J((71) Ga,(31) P) range from approximately 380 to 1590 Hz. Values of (1) J((69/71) Ga,(31) P) and ΔJ((69/71) Ga,(31) P) calculated by using DFT have comparable magnitudes and generally reproduce experimental trends. Both the Fermi-contact and spin-dipolar Fermi-contact mechanisms make important contributions to the (1) J((69/71) Ga,(31) P) tensors. The (31) P NMR spectra of several adducts in solution, obtained as a function of temperature, are contrasted with those obtained in the solid state. Finally, to complement the analysis of NMR spectra for these adducts, single-crystal X-ray diffraction data for Br(3) Ga[P(p-Anis)(3) ] and I(3) Ga[P(p-Anis)(3) ] were obtained.
    Chemistry 01/2013; 19:2826-2839. · 5.83 Impact Factor
  • M. A. Karolewski, R. G. Cavell
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    ABSTRACT: The primary ion directional effects observed in secondary electron yields induced by ion bombardment [5keV Ar+→Cu(100)] are simulated using a semi-empirical molecular dynamics model. The directional effects are presumed to arise from inelastic energy transfers that take place in close binary atomic encounters. The latter are estimated using the Oen-Robinson model, in combination with a critical apsidal distance (Rc). The connection between the measured kinetic electron emission (KEE) yields (γKEE) and the predicted inelastic energy loss in a binary atomic collision (ΔEi) is established through a semi-empirical fitting procedure involving Rc and other parameters in the following model: γe=γ0+γKEE=γ0+〈ΔEi(z)exp(−z/λ)〉, where z is the collision depth. The directional effects are best reproduced by fitting the model to Ar–Cu inelastic collisions for two azimuthal incident directions: Rc is estimated to be 0.47±0.03Å; the parameter, λ (an effective electron attenuation length), is estimated to be 18±2Å. The same model also describes the γKEE energy dependence for 5–10keV Ar+ normally incident on low-index Cu crystal targets [Phys. Rev. 129 (1963) 2409]. The spatial and temporal distributions of the hard collisions that initiate KEE are discussed on the basis of the model.
    Surface Science 10/2011; · 1.87 Impact Factor
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    ABSTRACT: Treatment of ThCl(4)(DME)(2) or UCl(4) with 1 equiv of dilithiumbis(iminophosphorano) methandiide, [Li(2)C(Ph(2)P═NSiMe(3))(2)] (1), afforded the chloro actinide carbene complexes [Cl(2)M(C(Ph(2)P═NSiMe(3))(2))] (2 (M = Th) and 3 (M = U)) in situ. Stable PCP metal-carbene complexes [Cp(2)Th(C(Ph(2)P═NSiMe(3))(2))] (4), [Cp(2)U(C(Ph(2)P═NSiMe(3))(2))] (5), [TpTh(C(Ph(2)P═NSiMe(3))(2))Cl] (6), and [TpU(C(Ph(2)P═NSiMe(3))(2))Cl] (7) were generated from 2 or 3 by further reaction with 2 equiv of thallium(I) cyclopentadienide (CpTl) in THF to yield 4 or 5 or with 1 equiv of potassium hydrotris(pyrazol-1-yl) borate (TpK) also in THF to give 6 or 7, respectively. The derivative complexes were isolated, and their crystal structures were determined by X-ray diffraction. All of these U (or Th)-carbene complexes (4-7) possess a very short M (Th or U)═carbene bond with evidence for multiple bond character. Gaussian 03 DFT calculations indicate that the M═C double bond is constructed by interaction of the 5f and 6d orbitals of the actinide metal with carbene 2p orbitals of both π and σ character. Complex 3 reacted with acetonitrile or benzonitrile to cyclo-add C≡N to the U═carbon double bond, thereby forming a new C-C bond in a new chelated quadridentate ligand in the bridged dimetallic complexes (9 and 10). A single carbon-U bond is retained. The newly coordinated uranium complex dimerizes with one equivalent of unconverted 3 using two chlorides and the newly formed imine derived from the nitrile as three connecting bridges. In addition, a new crystal structure of [CpUCl(3)(THF)(2)] (8) was determined by X-ray diffraction.
    Inorganic Chemistry 06/2011; 50(14):6500-8. · 4.59 Impact Factor
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    ABSTRACT: The title compounds are prepared from stoichiometric mixtures of the elements (900 °C, 7 d) and characterized by powder XRD, XPS, magnetic measurements, and TB-LMTO band structure calculations.
    ChemInform 05/2011; 42(19).
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    ABSTRACT: Reaction of tetrafluoro- or tetrachloro-p-benzoquinone with silylated phosphoranimines R2R′P=NSiMe3 (R = Ph, Me) yields very highly colored monosubstituted derivatives of the p-quinone that act as two-electron acceptors showing clean, reversible CV traces. The molar absorptivity values are typical of dyes. These ligands also form chelate complexes with Rh(I) precursors using the quinone oxygen and the imine nitrogen donor sites. One of the quinone derivatives, 3,5,6-trichloro-2-(triphenylphosphinimino)-p-benzoquinone, has been structurally characterized. The iminated quinone shows a normal P=N bond length (1.597(2) Å) and P-N-C angle (P-N-C(3) 132.7(2)°). The N—C(3) bond, 1.327(3) Å, is a little shorter as is expected for the establishment of a conjugated structure between the phosphinimine substituent and the quinone ring. Some steric crowding pushes the Cl and N substituents on the quinone ring out of the plane of the ring. Key words: quinones, phosphinimines, fluorine, chlorine, rhodium.
    Canadian Journal of Chemistry 02/2011; 74(11):2378-2385. · 0.96 Impact Factor
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    ABSTRACT: X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES) have been applied to examine the electronic structures of lanthanum copper oxychalcogenides LaCuOCh (Ch=S, Se, Te), whose structure has been conventionally viewed as consisting of nominally isolated [LaO] and [CuCh] layers. However, there is evidence for weak La–Ch interactions between these layers, as seen in small changes in the satellite intensity of the La 3d XPS spectra as the chalcogen is changed and as supported by band structure calculations. The O 1s and Cu 2p XPS spectra are insensitive to chalcogen substitution. Lineshapes in the Cu 2p XPS spectra and fine-structure in the Cu L- and M-edge XANES spectra support the presence of Cu+ species. The Ch XPS spectra show negative BE shifts relative to the elemental chalcogen, indicative of anionic species; these shifts correlate well with greater difference in electronegativity between the Cu and Ch atoms, provided that an intermediate electronegativity is chosen for Se.
    Journal of Solid State Chemistry 01/2011; 184(7):1649-1654. · 2.04 Impact Factor
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    ABSTRACT: The quaternary rare-earth phosphides RECuZnP2 (RE=Pr, Nd, Gd-Tm, Lu) have been prepared by reaction of the elements at 900 °C, completing this versatile series which forms for nearly all RE metals. They adopt the trigonal CaAl2Si2-type structure (Pearson symbol hP5, space group P3¯m1, Z=1), as confirmed by single-crystal X-ray diffraction analysis on ErCuZnP2 and powder X-ray diffraction analysis on the remaining members. The Cu and Zn atoms are assumed to be disordered over the single transition-metal site. Band structure calculations on a hypothetically ordered YCuZnP2 model suggest a semimetal, with a zero band gap between the valence and conduction bands. This electronic structure is supported by XPS valence band spectra for RECuZnP2 (RE=Gd-Er), in which the intensity drops off smoothly at the Fermi edge. The absence of a band gap permits the electron count to deviate from the precise value of 16 e- per formula unit, as demonstrated by the formation of a solid solution in GdCuxZn2-xP2 (1.0
    Journal of Solid State Chemistry 01/2011; 184:97-103. · 2.04 Impact Factor
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    ABSTRACT: We present an X-ray absorption spectroscopic study of the optical and electronic properties of freestanding, alkyl-functionalized silicon nanocrystals (Si-NCs). These materials were derived from thermal processing of hydrogen silsesquioxane, subsequently etched with hydrofluoric acid and functionalized via photochemical hydrosilylation with alkenes. These materials are of interest for their size-dependent photoluminescence (PL), that spans the visible and near-IR regions. Using near-edge X-ray absorption fine structure spectroscopy and X-ray excited optical luminescence, we have investigated the impact of quantum confinement effects and surface species on the Si-NC PL. These materials exhibit PL found to be consistent with the quantum confinement model; however, ambient oxidation was proposed to strongly influence the results.
    The Journal of Physical Chemistry C. 12/2010; 114(51).
  • Peter E. R. Blanchard, Ronald G. Cavell, Arthur Mar
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    ABSTRACT: ZrAs2 is established to be a true binary phase that is strictly stoichiometric.
    ChemInform 10/2010; 41(42).
  • Peter E.R. Blanchard, Ronald G. Cavell, Arthur Mar
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    ABSTRACT: Zirconium diarsenide, ZrAs2, has been established to be a genuine binary phase that is strictly stoichiometric. At 900 °C, it supports extensive solubility of Ge to form the ternary extension Zr(GexAs1−x)As (0 ≤ x ≤ 0.4). The crystal structures of ZrAs2 and Zr(Ge0.33(6)As0.67)As were determined by single-crystal X-ray diffraction (orthorhombic PbCl2-type, space group Pnma, Z = 4), with one of the two possible anion sites being preferentially occupied by the Ge atoms. X-ray photoelectron spectra and band structure calculations confirmed that the Ge and As atoms are anionic in character and that the substitution of Ge for As is driven by a depopulation of anion–anion antibonding states. ZrGe0.3As1.7 exhibits metallic behaviour and temperature-independent Pauli paramagnetism.
    Journal of Alloys and Compounds 08/2010; 505(1):17–22. · 2.73 Impact Factor
  • Peter E.R. Blanchard, Ronald G. Cavell, Arthur Mar
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    ABSTRACT: X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES) have been applied to examine the electronic structure of the rare-earth transition-metal oxyarsenides REFeAsO (RE=Ce, Pr, Nd, Sm, Gd) and CeNiAsO. Within the metal-arsenic layer [MAs], the bonding character is predominantly covalent and the As atoms are anionic, as implied by the small energy shifts in the M 2p and As 3d XPS spectra. Within the rare-earth-oxygen layer [REO], the bonding character is predominantly ionic, as implied by the similarity of the O 1s binding energies to those in highly ionic oxides. Substitution with a smaller RE element increases the O 1s binding energy, a result of an enhanced Madelung potential. The Ce 3d XPS and Ce L{sub 3}-edge XANES spectra have lineshapes and energies that confirm the presence of trivalent cerium in CeFeAsO and CeNiAsO. A population analysis of the valence band spectrum of CeNiAsO supports the formal charge assignment [Ce{sup 3+}O{sup 2-}][Ni{sup 2+}As{sup 3-}].
    Journal of Solid State Chemistry 08/2010; 183(7):1477-1483. · 2.04 Impact Factor
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    Guibin Ma, Michael J Ferguson, Ronald G Cavell
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    ABSTRACT: A geminal dithallated bis(iminodiphenylphosphorano)methine carbon complex was prepared and isolated as a solid dimer, stable in an inert atmosphere. It has been fully characterized in both solution and solid states. Bonding has been assessed with the aid of DFT calculations. All data demonstrate that the dimer contains a single carbon center sigma bound to two Tl((I)) atoms (Tl((I))-C-Tl((I))). Two geminal monomers associate via Tl((I))-Tl((I)) interactions to form the dimer.
    Chemical Communications 08/2010; 46(29):5370-2. · 6.38 Impact Factor
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    ABSTRACT: We report the influence of processing atmosphere on the evolution of oxide-embedded germanium nanocrystals (Ge-NCs) formed by the thermal processing of (CHGeO{sub 1.5}){sub n} sol-gel polymers. In an inert processing atmosphere (100% Ar), the generation of elemental Ge from thermally induced disproportionation of the germanium rich oxide (GRO) leads to GeO-embedded Ge-NCs whose size is independent of peak processing temperature and time. Processing in a slightly reducing atmosphere (5% H/95% Ar) activates a second Ge-NC formation and growth pathway, involving the reduction of Ge oxide species. Here, we report that the processing atmosphere governs the distribution of Ge species. By modifying the contributions from redistribution and reduction reactions within the GRO, diffusion of Ge atoms throughout the oxide matrix and formation and growth of Ge-NCs are impacted.
    Chemistry of Materials 04/2010; 22:2653-2661. · 8.24 Impact Factor
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    ABSTRACT: Solid-state (115)In and (31)P NMR spectroscopy, relativistic density functional theory (DFT) calculations, and single-crystal X-ray diffraction were used to investigate a series of triarylphosphine indium(III) trihalide adducts, X(3)In(PR(3)) and X(3)In(PR(3))(2) (X = Cl, Br or I; PR(3) = triarylphosphine ligand). The electric field gradient tensors at indium as well as the indium and phosphorus magnetic shielding tensors and the direct and indirect (115)In-(31)P spin-spin coupling were characterized; for complexes possessing a C(3) symmetry axis, the anisotropy in the indirect spin-spin coupling, DeltaJ((115)In,(31)P), was also determined. The (115)In quadrupolar coupling constants, C(Q)((115)In), range from +/-1.25 +/- 0.10 to -166.0 +/- 2.0 MHz. For any given phosphine ligand, the indium nuclei are most shielded for X = I and least shielded for X = Cl, a trend also observed for other group-13 nuclei in M(III) complexes. This experimental trend, attributed to spin-orbit effects of the halogen ligands, is reproduced by the DFT calculations. The spans of the indium magnetic shielding tensors for these complexes, delta(11)-delta(33), range from 40 +/- 7 to 710 +/- 60 ppm; those determined for phosphorus range from 28 +/- 1.5 to 50 +/- 3 ppm. Values of (1)J((115)In,(31)P) range from 550 +/- 20 to 2500 +/- 20 Hz. For any given halide, the (1)J((115)In,(31)P) values generally increase with increasing basicity of the PR(3) ligand. Calculated values of (1)J((115)In,(31)P) and DeltaJ((115)In,(31)P) duplicate experimental trends and indicate that both the Fermi-contact and spin-dipolar Fermi-contact mechanisms make important contributions to the (1)J((115)In,(31)P) tensors.
    Journal of the American Chemical Society 03/2010; 132(15):5479-93. · 10.68 Impact Factor
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    ABSTRACT: An X-ray absorption spectroscopic investigation into the electronic and optical properties of silicon nanocrystals (Si-NCs) derived from the thermal processing of hydrogen silsesquioxane (HSQ) is presented. Hydrofluoric (HF) acid etching and subsequent photochemical hydrosilylation with styrene liberates the as-synthesized oxide-embedded Si-NCs from their matrix and renders them solution dispersible through the formation of surface Si–C bonds. The impact of this process on the photoluminescence behavior exhibited by these materials has been studied through near edge X-ray absorption fine structure (NEXAFS) and X-ray excited optical luminescence (XEOL) spectroscopies.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 02/2010; 268(s 3–4):246–250. · 1.19 Impact Factor
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    ABSTRACT: Isothiocyanates react with Me2P-N(SiMe3)2 with elimination of (Me3Si)2S to give new structurally characterized heterocyclic diazaphosphole derivatives, and in one case the intermediate zwitterionic compound was isolated and structurally characterized. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:196–202, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20595
    Heteroatom Chemistry 01/2010; 21(3):196-202. · 1.58 Impact Factor
  • C. M. ANGELOV, R. G. CAVELL, R. SCHMUTZLER
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 01/2010; 26(17).
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    ABSTRACT: The electronic structures of the quaternary oxyarsenides LaMAsO (M = Fe, Co, Ni) were examined with X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES). Interpretation of the metal 2p3/2 and arsenic 3d5/2 binding energies, as well as a satellite feature in the Co 2p XPS spectrum, suggests charges that are much less extreme than expected (i.e., not M2+ and As3−) because of the strong covalent character within the M–As bonds. As M is varied, the differing degrees of charge transfer from M to As atoms within these bonds are manifested by shifts in the As 3d5/2 binding energies and changes in the As K-edge intensities. This charge transfer is isolated within the [MAs] layer and does not influence the O 1s and La 3d XPS spectra. Fitting the experimental valence band spectra of these oxyarsenides LaMAsO yielded electron populations of states that support the formal charge assignment [La3+O2−][M2+As3−]. The mixed-metal series LaFe1−xM′xAsO (M′ = Co, Ni) was examined by XANES; analysis of the metal K- and L-edges, as well as of the Co 2p XPS satellite feature, revealed that no metal–metal charge transfer takes place.
    Solid State Sciences. 01/2010; 12(1):50–58.
  • ChemInform 01/2010; 41(35).