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Infrared Spectra And Ab Initio Calculations For The F-−(Ch4)N (N = 1−8) Anion Clusters, Zoë M. Loh, R. L. Wilson, D. A. Wild, Evan J. Bieske, J. M. Lisy, Bosiljka Njegic, Mark S. Gordon Dec 2006

Infrared Spectra And Ab Initio Calculations For The F-−(Ch4)N (N = 1−8) Anion Clusters, Zoë M. Loh, R. L. Wilson, D. A. Wild, Evan J. Bieske, J. M. Lisy, Bosiljka Njegic, Mark S. Gordon

Chemistry Publications

Infrared spectra of mass-selected F-−(CH4)n (n = 1−8) clusters are recorded in the CH stretching region (2500−3100 cm-1). Spectra for the n = 1−3 clusters are interpreted with the aid of ab initio calculations at the MP2/6-311++G(2df 2p) level, which suggest that the CH4ligands bind to F- by equivalent, linear hydrogen bonds. Anharmonic frequencies for CH4 and F-−CH4 are determined using the vibrational self-consistent field method with second-order perturbation theory correction. The n = 1 complex is predicted to have a C3v structure with a single CH group hydrogen bonded to F- ...


An Amphiphilic Molecular Basket Sensitive To Both Solvent Changes And Uv Irradiation, Eui-Hyun Ryu, Yan Zhao Nov 2006

An Amphiphilic Molecular Basket Sensitive To Both Solvent Changes And Uv Irradiation, Eui-Hyun Ryu, Yan Zhao

Chemistry Publications

A molecular basket was obtained by linking four cholate units to a cone-shaped calix[4]arene scaffold through azobenzene spacers. The molecule turns its polar faces inward in nonpolar solvents to bind polar molecules such as sugar derivatives. In polar solvents, the nonpolar faces turn inward, allowing the binding of hydrophobic guests such as pyrene. The molecule can also respond to UV irradiation by transcis isomerization of the azobenzene spacers. Response toward both solvents and UV light is fully reversible.


Effect Of Surface Functionalization Of Mcm-41-Type Mesoporous Silica Nanoparticles On The Endocytosis By Human Cancer Cells, Igor I. Slowing, Brian G. Trewyn, Victor S.-Y. Lin Nov 2006

Effect Of Surface Functionalization Of Mcm-41-Type Mesoporous Silica Nanoparticles On The Endocytosis By Human Cancer Cells, Igor I. Slowing, Brian G. Trewyn, Victor S.-Y. Lin

Chemistry Publications

We have synthesized a series of MCM-41-type mesoporous silica nanoparticles (MSN). The surface of the MSNs are functionalized with 3-aminopropyl (AP), 3-guanidinopropyl (GP), 3-[N-(2-guanidinoethyl)guanidino]propyl (GEGP), and N-folate-3-aminopropyl (FAP). In contrast to the ζ-potential of −18.4 mV for FITC-MSN, the values of ζ-potential for AP-, GP-, GEGP-, and FAP-functionalized FITC-MSNs in 100 mM PBS buffer (pH 7.4) increased positively from −11.3, −10.6, −4.0, to +4.9 mV, respectively. The uptake efficiency, endocytosis mechanism, and biocompatibility of these organically functionalized MSNs were investigated with human cervical cancer cells (HeLa). Flow cytometry results ...


Use Of Allylic Strain To Enforce Stereochemistry. Direct Syntheses Of 7,8-Dihydroxycalamenene And Mansonone C, George A. Kraus, Insik Jeon Oct 2006

Use Of Allylic Strain To Enforce Stereochemistry. Direct Syntheses Of 7,8-Dihydroxycalamenene And Mansonone C, George A. Kraus, Insik Jeon

Chemistry Publications

Direct syntheses of 7,8-dihydroxycalamenene and mansonone C were achieved. The cis-stereochemistry required for the synthesis of 7,8-dihydroxycalamenene was introduced by an intramolecular cyclization directed by allylic strain.


Synthesis And Natural Distribution Of Anti-Inflammatory Alkamides From Echinacea, George A. Kraus, Jaehoon Bae, Lankun Wu, Evve S. Wurtele Oct 2006

Synthesis And Natural Distribution Of Anti-Inflammatory Alkamides From Echinacea, George A. Kraus, Jaehoon Bae, Lankun Wu, Evve S. Wurtele

Chemistry Publications

The synthesis of the alkamides 2Z,4E-undeca-2,4-dien-8,10-diynoic acid isobutyl amide (1) and 2Z,4E-undeca-2,4-dien-8,10-diynoic acid isobutyl amide (5) was accomplished by organometallic coupling followed by introduction of the doubly unsaturated amide moiety. The distribution of these two amides in accessions of the nine species of Echinacea was determined.


Crystal-Melt Interfacial Free Energies Of Hard-Dumbbell Systems, Yan Mu, Xueyu Song Sep 2006

Crystal-Melt Interfacial Free Energies Of Hard-Dumbbell Systems, Yan Mu, Xueyu Song

Chemistry Publications

The crystal-melt interfacial free energies of different crystal orientations and crystal forms for the hard-dumbbell systems have been calculated directly using a multistep thermodynamic perturbation method via nonequilibrium work measurements with a cleaving procedure. We found that for the plastic crystal phase, the interfacial free energies decrease as the reduced bond length L∗ increases and the anisotropy is very weak as in isotropic systems. On the other hand, for the orientationally ordered crystal phase, the interfacial free energies become more than three times larger and the anisotropy is about 13%. These results may have significant implications for our understanding on ...


Detection Of Hg2+ In Aqueous Solutions With A Foldamer-Based Fluorescent Sensor Modulated By Surfactant Micelles, Yan Zhao, Zhenqi Zhong Sep 2006

Detection Of Hg2+ In Aqueous Solutions With A Foldamer-Based Fluorescent Sensor Modulated By Surfactant Micelles, Yan Zhao, Zhenqi Zhong

Chemistry Publications

A hybrid foldamer constructed from six cholate units and two methionines was labeled with a DANSYL (DNS) group. The foldamer was solubilized by surfactant micelles to allow its usage as a fluorescent sensor for mercury ions present in the micromolar range in aqueous solutions. Its sensitivity was largely independent of the concentration of nonionic surfactants but was strongly influenced by both the nature and the concentration of ionic surfactants.


Incremental Solvation Of Nonionized And Zwitterionic Glycine, Christine Marie Aikens, Mark S. Gordon Sep 2006

Incremental Solvation Of Nonionized And Zwitterionic Glycine, Christine Marie Aikens, Mark S. Gordon

Chemistry Publications

Microsolvation and combined microsolvation−continuum approaches are employed in order to examine the structures and relative energies of nonionized (N) and zwitterionic (Z) glycine clusters. Bridging structures are predicted to be the global minima after 3−5 discrete water molecules are included in the calculations. Calculations incorporating electron correlation stabilize the zwitterionic structures by about 7−9 kcal/mol relative to the N structures regardless of the number of discrete water molecules considered. Continuum calculations stabilize the Z structures relative to N structures; this effect decreases as the number of discrete water molecules is increased. Eight water molecules do not ...


Assessing The Roles Of The Constituents Of Ionic Liquids In Dynamic Solvation:  Comparison Of An Ionic Liquid In Micellar And Bulk Form, Prasun Mukherjee, Jeffrey Aaron Crank, Mintu Halder, Daniel W. Armstrong, Jacob W. Petrich Aug 2006

Assessing The Roles Of The Constituents Of Ionic Liquids In Dynamic Solvation:  Comparison Of An Ionic Liquid In Micellar And Bulk Form, Prasun Mukherjee, Jeffrey Aaron Crank, Mintu Halder, Daniel W. Armstrong, Jacob W. Petrich

Chemistry Publications

Dynamic solvation of the dye, coumarin 153, is compared in an ionic liquid that forms micelles in water against the bulk solvent. This provides the unprecedented opportunity of investigating the behavior of the ionic liquid in two globally different configurations. It is proposed that the imidazolium moiety is in both cases responsible for the majority of the solvation, which manifests itself in the first 100 ps. Exploiting the use of ionic liquids capable of accommodating specific structures thus provides a deeper insight into how solutes interact with these fascinating and interesting solvents (at least those that are imidazolium based) that ...


Solvent-Induced Amphiphilic Molecular Baskets: Unimolecular Reversed Micelles With Different Size, Shape, And Flexibility, Eui-Hyun Ryu, Jie Yan, Zhenqi Zhong, Yan Zhao Aug 2006

Solvent-Induced Amphiphilic Molecular Baskets: Unimolecular Reversed Micelles With Different Size, Shape, And Flexibility, Eui-Hyun Ryu, Jie Yan, Zhenqi Zhong, Yan Zhao

Chemistry Publications

Amphiphilic molecular baskets were obtained by attaching facially amphiphilic cholate groups to a covalent scaffold (calix[4]arene or 1,3,5-2,4,6-hexasubstituted benzene). In a solvent mixture consisting of mostly a nonpolar solvent (i.e., CCl4) and a polar solvent (i.e., DMSO), the hydrophilic faces of cholates turned inward to form a reversed-micelle-like conformer whose stability was strongly influenced by the number of the cholates and the topology of the scaffold. Preferential solvation of the hydrophilic faces of cholates within the molecule by the polar solvent was cooperative and gave the fundamental driving force to the conformational ...


Methanol−Water Mixtures:  A Microsolvation Study Using The Effective Fragment Potential Method, Ivana Adamovic, Mark S. Gordon Aug 2006

Methanol−Water Mixtures:  A Microsolvation Study Using The Effective Fragment Potential Method, Ivana Adamovic, Mark S. Gordon

Chemistry Publications

The formation process of methanol−water mixtures, (MeOH/H2O)n, n = 2, 3,..., 8 is studied at the molecular level using the general effective fragment potential (EFP2) method and second-order perturbation theory (MP2). Extensive Monte Carlo/simulated annealing global optimizations were used to locate global minimum structures for each n, for both homo and hetero clusters. Mixing at the microscopic level was investigated, and some general conclusions about the microsolvation behavior of these mixtures are presented. For all of these clusters, incomplete mixing is observed at the molecular level. Low-energy (MeOH/H2O)n clusters retain much of their initial structure ...


Dynamic Solvation In Imidazolium-Based Ionic Liquids On Short Time Scales, Lindsay Elizabeth Sanders Headley, Prasun Mukherjee, Jared L. Anderson, Rongfang Ding, Mintu Halder, Daniel W. Armstrong, Xueyu Song, Jacob W. Petrich Jul 2006

Dynamic Solvation In Imidazolium-Based Ionic Liquids On Short Time Scales, Lindsay Elizabeth Sanders Headley, Prasun Mukherjee, Jared L. Anderson, Rongfang Ding, Mintu Halder, Daniel W. Armstrong, Xueyu Song, Jacob W. Petrich

Chemistry Publications

Steady-state and time-resolved Stokes shift data for the probe coumarin 153 in two imidazoles, six imidazolium-based ionic liquids, and several other solvents are presented. These results are consistent with our original suggestion (J. Phys. Chem. B 2004, 108, 10245−10255) that initial solvation is dominated by the organic moiety of the ionic liquid, and they show that for the imidazole-based liquids initial solvation is in all cases very rapid. Solvation by methylimidazole and butylimidazole is complete in 100 ps, and all of the imidazolium ionic liquids demonstrate similarly rapid initial solvation. Owing to the importance of determining the amount of ...


Tuning The Sensitivity Of A Foldamer-Based Mercury Sensor By Its Folding Energy, Yan Zhao, Zhenqi Zhong Jul 2006

Tuning The Sensitivity Of A Foldamer-Based Mercury Sensor By Its Folding Energy, Yan Zhao, Zhenqi Zhong

Chemistry Publications

A fluorescent sensor for Hg2+ was obtained by incorporation of two methionine units into a cholate hexamer and by attaching a Dansyl group at the chain end. Folding could be made highly favorable or unfavorable in different solvents. Because folding was required to bring the sulfur groups together to chelate the mercury ion, binding affinity of the foldamer and, thus, its sensitivity as a sensor, could be tuned over broad ranges (at least 5 orders of magnitude) by solvent changes.


Experimental And Theoretical Investigations Of Solvation Dynamics Of Ionic Fluids:  Appropriateness Of Dielectric Theory And The Role Of Dc Conductivity, Mintu Halder, Lindsay Elizabeth Sanders Headley, Prasun Mukherjee, Xueyu Song, Jacob W. Petrich Jun 2006

Experimental And Theoretical Investigations Of Solvation Dynamics Of Ionic Fluids:  Appropriateness Of Dielectric Theory And The Role Of Dc Conductivity, Mintu Halder, Lindsay Elizabeth Sanders Headley, Prasun Mukherjee, Xueyu Song, Jacob W. Petrich

Chemistry Publications

An analysis is provided of the subnanosecond dynamic solvation of ionic liquids in particular and ionic solutions in general. It is our hypothesis that solvation relaxation in ionic fluids, in the nonglassy and nonsupercooled regimes, can be understood rather simply in terms of the dielectric spectra of the solvent. This idea is suggested by the comparison of imidazolium ionic liquids with their pure organic counterpart, butylimidazole (J. Phys. Chem. B 2004, 108, 10245−10255). It is borne out by a calculation of the solvation correlation time from frequency dependent dielectric data for the ionic liquid, ethylammonium nitrate, and for the ...


Kinetics, Mechanism, And Computational Studies Of Rhenium-Catalyzed Desulfurization Reactions Of Thiiranes (Thioepoxides), Abdellatif Ibdah, William S. Jenks, James H. Espenson Jun 2006

Kinetics, Mechanism, And Computational Studies Of Rhenium-Catalyzed Desulfurization Reactions Of Thiiranes (Thioepoxides), Abdellatif Ibdah, William S. Jenks, James H. Espenson

Chemistry Publications

The oxorhenium(V) dimer {MeReO(edt)}2 (1; where edt = 1,2-ethanedithiolate) catalyzes S atom transfer from thiiranes to triarylphosphines and triarylarsines. Despite the fact that phosphines are more nucleophilic than arsines, phosphines are less effective because they rapidly convert the dimer catalyst to the much less reactive catalyst [MeReO(edt)(PAr3)] (2). With AsAr3, which does not yield the monomer, the rate law is given by v = k[thiirane][1], independent of the arsine concentration. The values of k at 25.0 °C in CDCl3 are 5.58 ± 0.08 L mol-1 s-1 for cyclohexene sulfide and ca. 2 ...


Electronic Structure Studies Of Tetrazolium-Based Ionic Liquids, Deborah D. Zorn, Jerry A. Boatz, Mark S. Gordon May 2006

Electronic Structure Studies Of Tetrazolium-Based Ionic Liquids, Deborah D. Zorn, Jerry A. Boatz, Mark S. Gordon

Chemistry Publications

New energetic ionic liquids are investigated as potential high energy density materials. Ionic liquids are composed of large, charge-diffuse cations, coupled with various (usually oxygen containing) anions. In this work, calculations have been performed on the tetrazolium cation with a variety of substituents. Density functional theory (DFT) with the B3LYP functional, using the 6-311G(d,p) basis set was used to optimize geometries. Improved treatment of dynamic electron correlation was obtained using second-order perturbation theory (MP2). Heats of formation of the cation with different substituent groups were calculated using isodesmic reactions and Gaussian-2 calculations on the reactants. The cation was ...


Tribological Properties Of Quasicrystals: Effect Of Aperiodic Versus Periodic Surface Order, Jeong Young Park, D. F. Ogletree, M. Salmeron, R. A. Ribeiro, Paul C. Canfield, Cynthia J. Jenks, Patricia A. Thiel Jan 2006

Tribological Properties Of Quasicrystals: Effect Of Aperiodic Versus Periodic Surface Order, Jeong Young Park, D. F. Ogletree, M. Salmeron, R. A. Ribeiro, Paul C. Canfield, Cynthia J. Jenks, Patricia A. Thiel

Chemistry Publications

We investigated the nanoscale tribological properties of a decagonal quasicrystal using a combination of atomic force microscopy and scanning tunneling microscopy in ultrahigh vacuum. This combination permitted a variety of in situ measurements, including atomic-scale structure, friction and adhesion force, tip-sample current, and topography. We found that thiol-passivated tips can be used for reproducible studies of the tip-quasicrystal contact while nonpassivated probes adhere irreversibly to the clean quasicrystalline surface causing permanent modifications. The most remarkable results were obtained on the twofold surface of the Al-Ni-Co decagonal quasicrystal where atoms are arranged periodically along the tenfold axis and aperiodically in the ...


Scalable Implementation Of Analytic Gradients For Second-Order Z-Averaged Perturbation Theory Using The Distributed Data Interface, Christine Marie Aikens, Graham D. Fletcher, Michael Schmidt, Mark S. Gordon Jan 2006

Scalable Implementation Of Analytic Gradients For Second-Order Z-Averaged Perturbation Theory Using The Distributed Data Interface, Christine Marie Aikens, Graham D. Fletcher, Michael Schmidt, Mark S. Gordon

Chemistry Publications

The analytic gradient expression for second-order Z-averaged perturbation theory is revised and its parallel implementation is described in detail. The distributed data interface is used to access molecular-orbital integral arrays stored in distributed memory. The algorithm is designed to maximize the use of local data and reduce communication costs. The iterative solution and the preconditioner used to induce the convergence of the coupled-perturbed Hartree-Fock equations are presented. Several illustrative timing examples are discussed.


Dissociation Potential Curves Of Low-Lying States In Transition Metal Hydrides. 3. Hydrides Of Groups 6 And 7, Shiro Koseki, Takeshi Matsushita, Mark S. Gordon Jan 2006

Dissociation Potential Curves Of Low-Lying States In Transition Metal Hydrides. 3. Hydrides Of Groups 6 And 7, Shiro Koseki, Takeshi Matsushita, Mark S. Gordon

Chemistry Publications

The dissociation curves of low-lying spin-mixed states in monohydrides of groups 6 and 7 were calculated by using an effective core potential (ECP) approach. This approach is based on the multiconfiguration self-consistent field (MCSCF) method, followed by first-order configuration interaction (FOCI) calculations, in which the method employs an ECP basis set proposed by Stevens and co-workers (SBKJC) augmented by a set of polarization functions. Spin−orbit coupling (SOC) effects are estimated within the one-electron approximation by using effective nuclear charges, since SOC splittings obtained with the full Breit−Pauli Hamitonian are underestimated when ECP basis sets are used. The ground ...


Gradients Of The Polarization Energy In The Effective Fragment Potential Method, Hui Li, Heather Marie Netzloff, Mark S. Gordon Jan 2006

Gradients Of The Polarization Energy In The Effective Fragment Potential Method, Hui Li, Heather Marie Netzloff, Mark S. Gordon

Chemistry Publications

The effective fragment potential (EFP) method is an ab initio based polarizable classical method in which the intermolecular interaction parameters are obtained from preparative ab initiocalculations on isolated molecules. The polarization energy in the EFP method is modeled with asymmetric anisotropic dipole polarizabilitytensors located at the centroids of localized bond and lone pair orbitals of the molecules. Analytic expressions for the translational and rotational gradients (forces and torques) of the EFP polarization energy have been derived and implemented. Periodic boundary conditions (the minimum image convention) and switching functions have also been implemented for the polarization energy, as well as ...


Exploring The Effect Of Anharmonicity Of Molecular Vibrations On Thermodynamic Properties, Bosiljka Njegic, Mark S. Gordon Jan 2006

Exploring The Effect Of Anharmonicity Of Molecular Vibrations On Thermodynamic Properties, Bosiljka Njegic, Mark S. Gordon

Chemistry Publications

Thermodynamic properties of selected small and medium size molecules were calculated using harmonic and anharmonic vibrational frequencies. Harmonic vibrational frequencies were obtained by normal mode analysis, whereas anharmonic ones were calculated using the vibrational self-consistent field (VSCF) method. The calculated and available experimental thermodynamic data for zero point energy, enthalpy,entropy, and heat capacity are compared. It is found that the anharmonicity and coupling of molecular vibrations can play a significant role in predicting accurate thermodynamic quantities. Limitations of the current VSCF method for low frequency modes have been partially removed by following normal mode displacements in internal, rather than ...


Charge Transfer Interaction In The Effective Fragment Potential Method, Hui Li, Mark S. Gordon, Jan H. Jensen Jan 2006

Charge Transfer Interaction In The Effective Fragment Potential Method, Hui Li, Mark S. Gordon, Jan H. Jensen

Chemistry Publications

An approximate formula is derived and implemented in the general effective fragment potential (EFP2) method to model the intermolecular charge transferinteraction. This formula is based on second order intermolecular perturbation theory and utilizes canonical molecular orbitals and Fock matrices obtained with preparative self-consistent field calculations. It predicts charge transferenergies that are in reasonable agreement with the reduced variational space energy decomposition analysis. The formulas for the charge transfer gradients with respect to EFP translational and rotational displacements are also derived and implemented.


Growing Multiconfigurational Potential Energy Surfaces With Applications To X+H2 (X=C,N,O) Reactions, Heather Marie Netzloff, Michael A. Collins, Mark S. Gordon Jan 2006

Growing Multiconfigurational Potential Energy Surfaces With Applications To X+H2 (X=C,N,O) Reactions, Heather Marie Netzloff, Michael A. Collins, Mark S. Gordon

Chemistry Publications

A previously developed method, based on a Shepard interpolation procedure to automatically construct a quantum mechanical potential energy surface (PES), is extended to the construction of multiple potential energy surfaces using multiconfigurational wave functions. These calculations are accomplished with the interface of the PES-building program, GROW, and the GAMESS suite of electronic structure programs. The efficient computation of multiconfigurational self-consistent field surfaces is illustrated with the C+H2, N+H2, and O+H2reactions.


The Structure Of The Si9h12 Cluster: A Coupled Cluster And Multi-Reference Perturbation Theory Study, Ryan M. Olson, Mark S. Gordon Jan 2006

The Structure Of The Si9h12 Cluster: A Coupled Cluster And Multi-Reference Perturbation Theory Study, Ryan M. Olson, Mark S. Gordon

Chemistry Publications

Full geometry optimizations using both singles and doubles coupled clustertheory with perturbative triple excitations, CCSD(T), and second order multi-reference perturbation theory, MRMP2, have been employed to predict the structure of Si9H12, a cluster commonly used in calculations to represent the Si(100) surface. Both levels of theory predict the structure of this cluster to be symmetric (not buckled), and no evidence for a buckled (asymmetric) structure is found at either level of theory.


A Systematic Multireference Perturbation-Theory Study Of The Low-Lying States Of Sic3, Jamie Marie Rintelman, Mark S. Gordon, Graham D. Fletcher, Joseph Ivanic Jan 2006

A Systematic Multireference Perturbation-Theory Study Of The Low-Lying States Of Sic3, Jamie Marie Rintelman, Mark S. Gordon, Graham D. Fletcher, Joseph Ivanic

Chemistry Publications

The three known lowest-energy isomers of SiC3, two cyclic singlets (2s and 3s) and a linear triplet (1t), have been reinvestigated using multireference second-order perturbation theory (MRPT2). The dependence of the relative energies of the isomers upon the quality of the basis sets and the sizes of the reference active spaces is explored. When using a complete-active-space self-consistent-field reference wave function with 12 electrons in 11 orbitals [CASSCF (12, 11)] together with basis sets that increase in size up to the correlation-consistent polarized core-valence quadruple zeta basis set (cc-pCVQZ), the MRPT2 method consistently predicts the linear triplet to be the ...


The 1/1 And 2/1 Approximants In The Sc – Mg – Zn Quasicrystal System. Triacontahedral Clusters As Fundamental Building Blocks, Qisheng Lin, John D. Corbett Jan 2006

The 1/1 And 2/1 Approximants In The Sc – Mg – Zn Quasicrystal System. Triacontahedral Clusters As Fundamental Building Blocks, Qisheng Lin, John D. Corbett

Chemistry Publications

Single-crystal structures are reported for Sc3Mg0.18(1)Zn17.73(3), the 1/1 approximant crystal (AC), and Sc11.18(9)Mg2.5(1)Zn73.6(2), the 2/1 AC, in the corresponding icosahedral quasicrystal (i-QC) system. The 1/1 AC crystallizes in space group Im3̄, a = 13.863(2) Å, Z = 8, and the 2/1 AC, in Pa3̄, a = 22.412 (2) Å, Z = 8. The latter, which is valuable in pointing the way to the QC structure, is the best ordered and refined 2/1 example to date. The fundamental building blocks in both ...


Zn13sb10:  A Structural And Landau Theoretical Analysis Of Its Phase Transitions, Yurij Mozharivskyj, Yuri Janssen, Joel L. Harringa, Alfred Kracher, Alexandra O. Tsokol, Gordon J. Miller Jan 2006

Zn13sb10:  A Structural And Landau Theoretical Analysis Of Its Phase Transitions, Yurij Mozharivskyj, Yuri Janssen, Joel L. Harringa, Alfred Kracher, Alexandra O. Tsokol, Gordon J. Miller

Chemistry Publications

Composition, crystal structures, polymorphic transformations, and stability of the thermoelectric material known in the literature as “Zn4Sb3” have been studied on a polycrystalline sample and Bi-flux-grown single crystals using X-ray diffraction techniques, resistance, and Seebeck coefficient measurements at various temperatures ranging from 4 to 773 K. Microprobe analysis yields the composition of the flux-grown crystals to be close to Zn13Sb10, with minor Bi doping. High-temperature X-ray and Seebeck coefficient studies show that the phase is unstable at high temperatures in a vacuum because of Zn losses. Both X-ray diffraction and resistivity measurements indicate the ...


Structural Variations In Gd5si4-Xsnx: Size Vs. Electronic Effects, Yurij Mozharivskyj, Alexandra O. Tsokol, Gordon J. Miller Jan 2006

Structural Variations In Gd5si4-Xsnx: Size Vs. Electronic Effects, Yurij Mozharivskyj, Alexandra O. Tsokol, Gordon J. Miller

Chemistry Publications

B12 icosahedra cluster-containing rare earth borosilicides REB44Si2 (RE = Tb, Dy, Ho, Er, Tm, Yb) were grown by the floating zone method and their physical properties were investigated. REB44Si2 compounds are isostructural to REB50 and they are unique among the newly discovered boron-rich phases in that it is possible to grow large crystals with dimensions exceeding 10 mm. The rare earth atoms form a coupled chain structure like a ladder along the c-axis which is also the axis along which there is a B12 icosahedral chain. Magnetic properties, resistivity, and specific ...


Intergrowth Compounds In The Zn-Rich Zn−Pd System:  Toward 1d Quasicrystal Approximants, Olivier Gourdon, Gordon J. Miller Jan 2006

Intergrowth Compounds In The Zn-Rich Zn−Pd System:  Toward 1d Quasicrystal Approximants, Olivier Gourdon, Gordon J. Miller

Chemistry Publications

A series of γ-brass related structures in the Zn-rich portion of the Zn−Pd phase diagram (ca. 80 at % Zn) is investigated using single-crystal diffraction and tight-binding electronic-structure calculations. Earlier research identified regular arrays of inversion antiphase domains (IAPDs) over a narrow composition range but did not report any characteristic superstructure(s) over the same range. Single-crystal X-ray diffraction allowed for the identification of lattice constants for six “phases” in Zn1-xPdx (0.15 < x < 0.25), and refinements of two crystal structures indicate two important potential building blocks for the intermediate compositions, one of these being the cubic γ-brass structure. A Farey tree construction is described that accounts for the observed long-period superlattice and provides a possible algorithm for targeting one-dimensional, quasiperiodic phases in this and related systems. Tight-binding electronic-structure calculations on the two limiting structures for this region of the Zn−Pd phase diagram suggest a relationship between structure and bonding in these complex intermetallic systems.


Superstructure In Re2-Xfe4si14-Y (Re = Y, Gd−Lu) Characterized By Diffraction, Electron Microscopy, And Mössbauer Spectroscopy, Mi-Kyung Han, Ya-Qiao Wu, Matthew Kramer, Benjamin Vatovez, Fernande Grandjean, Gary J. Long, Gordon J. Miller Jan 2006

Superstructure In Re2-Xfe4si14-Y (Re = Y, Gd−Lu) Characterized By Diffraction, Electron Microscopy, And Mössbauer Spectroscopy, Mi-Kyung Han, Ya-Qiao Wu, Matthew Kramer, Benjamin Vatovez, Fernande Grandjean, Gary J. Long, Gordon J. Miller

Chemistry Publications

Ternary rare-earth iron silicides RE2-xFe4Si14-y (RE = Y, Gd−Lu; x ≈ 0.8; y ≈ 4.1) crystallize in the hexagonal system with a ≈ 3.9 Å, c ≈ 15.3 Å, Pearson symbol hP20−4.9. Their structures involve rare-earth silicide planes with approximate compositions of “RE1.2Si1.9” alternating with β-FeSi2-derived slabs and are part of a growing class of rare-earth/transition-metal/main-group compounds based on rare-earth/main-group element planes interspersed with (distorted) fluorite-type transition-metal/main-group element layers. The rare-earth silicide planes in the crystallographic unit cells ...