Chemical Bond Properties Research Articles

Uranium nitride chloride UNCl: 30 K-class ferromagnet with layered structure

Uranium nitride chloride (UNCl) has an unique tetragonal crystal structure, in which the U/N/U trilayer is sandwiched by the chlorine (Cl) double layers. This structure is homologous to Hf(Zr)NCl, for which high- T C superconductivity ( T C = 25.5 K ) has been recently discovered to result from the lithium (Li) intercalation. Recent specific heat measurements on this compound have revealed the existence of a lambda-type phase transition around 32 K. In the present study, this anomaly was confirmed to be correspondent for a ferromagnetic transition in the uranium ions having a localized 4f 2(U 4+) character: Its saturation moment ( μ B(sat)) attains a value of ∼1.56 μ B at 2 K. Among varieties of actinide (An) compounds, UNCl and related systems, AnNX (X=halogens (Cl, Br, I)) may represent a novel class of layer mixed compounds with intriguing magnetic, electronic and chemical-bonding properties.

Protofilament and Hexagon: A Three-Dimensional Mechanical Model for the Junctional Complex in the Erythrocyte Membrane Skeleton

It is a long-standing mystery why erythrocyte actin filaments in the junctional complex (JC) are uniformly approximately 37 nm and the membrane skeleton consists of hexagons. We have previously proposed that a "molecular ruler" formed by E-tropomodulin and tropomyosin 5 or 5b functions to generate protofilaments of 12 G actin under mechanical stress. Here, we illustrate that intrinsic properties of actin filaments, e.g., turns, chemical bonds, and dimensions of the helix, also favor fragmentation into protofilaments under mechanical stress. We further construct a mechanical model in that a pair of G actin is wrapped around by a split alpha and beta spectrin, which may spin to two potential positions, and stabilize to one when the tail end is restricted. A reinforced protofilament may function as a mechanical axis to anchor three (top, middle, and bottom) pairs of Sp. Each Sp pair may wrap around the protofilament with a wide dihedral angle (approximately 166.2 degrees) and a minimal axial distance (2.75 nm). Such three Sp pairs may spiral down (right handed) the protofilament from the pointed end with a dihedral angle of approximately 55.4 degrees in between the Sp pairs. This first three-dimensional model of JC may explain the hexagonal geometry of the erythrocyte membrane skeleton.

Constituent chemical bonds and nonlinear optical coefficients of Na 2SeO 4·H 2SeO 3·H 2O molecular crystal

Constituent chemical bonds of Na 2SeO 4·H 2SeO 3·H 2O molecular crystal are studied by the chemical bond method. The valence state of constituent atoms, the chemical bond property of constituent chemical bonds, and the second-order nonlinear optical (NLO) coefficients of Na 2SeO 4·H 2SeO 3·H 2O crystal are quantitatively calculated. Contributions of all kinds of constituent chemical bonds to the total linear and NLO properties of this crystal at λ=871.6 nm have been determined. The hydrogen bonds play a very important role in contributing to the total optical properties of Na 2SeO 4·H 2SeO 3·H 2O crystal, however, the coordination environment of hydrogen bonds strongly affects their optical contributions.

The relationship between chemical bond properties and Stokes shift of Eu 2+ in some silicate host lattices

The covalency of each bond in divalent europium doped hosts CaSiO 3, SrSiO 3, BaSiO 3, Sr 2LiSiO 4F, Ba 5SiO 4Cl 6 and Ba 5SiO 4Br 6 were calculated by using the complicate crystal chemical bond theory. The relationship between the Stokes shift and the bond properties of Eu 2+ in these crystals was discussed. The result demonstrates that, in the isostructural crystals that being doped with Eu 2+, there is a more precise connection between the magnitude of Stokes shift and the mean covalency of the dopant site.

Chemical bond properties and Mössbauer spectroscopy in REBa 2Cu 3O 7 (RE=Eu, Y)

By using the chemical bond theory of complex crystals, the chemical bond properties of REBa 2Cu 3O 7 (RE=Eu, Y) were calculated. The calculated covalencies for Cu(1)–O and Cu(2)–O bond in REBa 2Cu 3O 7 compounds are 0.41 and 0.28 respectively. Mössbauer isomer shifts of 57 Fe doped, and 119 Sn doped in REBa 2Cu 3O 7− x were calculated by using the chemical environmental factor, h e, defined by covalency and electronic polarizability. Four valence state tin ion and iron ion sites were identified in 57 Fe and 119 Sn doped REBa 2Cu 3O 7− x superconductors.

High-pressure densification of fluoride, GeS 2 and silicate glasses

Densification of glasses having different chemical-bond properties and also different structures have been examined by treating ionic ZrF 4-based fluoride glasses, mixed ionic and covalent SiO 2-based oxide glasses, and a covalent GeS 2 sulfide glass at temperatures of about three-quarters of their respective glass-transition temperatures under pressures up to 9 GPa. The densities of GeS 2 glass and silicate glasses of SiO 2 contents >50 mol% increased with increasing applied pressure. In ZrF 4-based glasses and silicate glasses with SiO 2 contents <50 mol%, on the other hand, the densities increased until an applied pressure around 3 GPa, the maximum densities were measured at pressures around 3 GPa, and then decreased with increasing pressure. The pressure dependences of permanent densification observed in the latter glasses are a permanent densification that has not been reported to our knowledge.

Magnetic Susceptibility and Peculiarities of Chemical Bond in the AgGa(S1-xSex)2 Solid Solutions

The measurements of magnetic susceptibility of the AgGa(S1-xSex)2solid solutions with the chalcopyrite structure have been performed and the lattice susceptibility separated into the Langevin diamagnetic and the Van Vleck paramagnetic terms. The obtained data were used to evaluate the character of chemical bond in these alloys. The correlations between the parameters of chemical bond and other physical properties are discussed. It is shown that the investigated solid solutions have preferably ionic character of chemical bond. The Ga-S(Se) (B-C) bonds are found to be stronger than the Ag-S(Se) (A-C) bonds.

Magnetic Susceptibility and Peculiarities of Chemical Bond in the AgGa(S1-xSex)2 Solid Solutions

The measurements of magnetic susceptibility of the AgGa(S1-xSex)2solid solutions with the chalcopyrite structure have been performed and the lattice susceptibility separated into the Langevin diamagnetic and the Van Vleck paramagnetic terms. The obtained data were used to evaluate the character of chemical bond in these alloys. The correlations between the parameters of chemical bond and other physical properties are discussed. It is shown that the investigated solid solutions have preferably ionic character of chemical bond. The Ga-S(Se) (B-C) bonds are found to be stronger than the Ag-S(Se) (A-C) bonds.

Study on the extraction of trivalent lanthanide ions with N,N′-dimethyl-N,N′-diphenyl-malonamide and diglycolamide

The extraction of trivalent lanthanide (Ln(III) ions with two diamides: (1) N,N′-dimethyl-N,N′-diphenyl-malonamide (MA) and (2) N,N′-dimethyl-N,N′-diphenyl-diglycolamide (DGA) from nitric acid solution was studied. Chemical bond properties of extracted complexes were investigated by UV-VIS and FT-IR spectroscopies. The chemical bond strength between Ln(III) ions and the ligands in extracted complexes was closely related with the magnitude of the distribution ratios of Ln(III) ions: the extracted complex having a stronger bond between Ln(III) ion and the ligand showed a higher magnitude of the distribution ratio of Ln(III) ion.

Ion Beam Processing of Carbon Nitride Thin Films

AbstractAmorphous carbon nitride films have been deposited by two different methods: (1) direct ion beam deposition from a gas mixture of CH4/N2; and (2) nitrogen ion beam sputtering of a graphite target. The chemical composition, deposition rate, chemical bond and optical properties of the as-deposited films were studied as a function of the process parameters. In the first technique, ions (CH3+, N2+, N+, NH4+, NH3+, NH2+, HCN+, CN+ and N2H2+) were directly impacted onto the substrate surface. The effects of RF power, CH4/N2 gas ratio, total gas flow, pressure, and ion energy on the film properties and deposition rates were studied. In the second technique, a flux of energetic nitrogen ions (N2+, N+), generated by N2 and N2/Ar plasmas, were used to directly sputter a graphite target. In this case, the effects of RF power, gas mixture (N2, N2/Ar), and ion energy on the film characteristics and deposition rates were determined. The properties of the films generated by the two alternative techniques were also compared.

Chemical bond properties of rare earth ions in crystals

By using the dielectric description theory of ionicity of solids, chemical bond properties of rare earth ions with various ligands are studied. Calculated results show that chemical bond properties of the same rare earth ion and the same ligand in different crystals depend on the crystal structures. In a series of compounds, chemical bond properties of crystals containing different rare earth ions are similar. The magnitude of covalency of chemical bonds of trivalent rare earth ions and various ligands has an order like F<Cl<Br<As<Sb.

Structure–Property Relationships in Li1−xHxIO3Type Complex Crystals

Chemical bond parameters and the linear and nonlinear optical (NLO) properties of all constituent chemical bonds in Li1−xHxIOx[x(the amount of hydrogen)=0.0, 0.28, and 0.34] (LHIO) type complex crystals have been investigated from the chemical bond viewpoint. At the same time, the relationship between the crystal structure and its optical properties has been obtained, based on the calculated results of LiIO3, Li0.72H0.28IO3, and Li0.66H0.34IO3. The nonlinear optical properties of LHIO single crystals are found to be particularly sensitive to the H+impurity concentration.

Interpretation of Raman intensities: effective induced bond charges from atomic polarizability tensors

A method for interpreting Raman intensities is proposed. Free from rotational contributions atomic polarizability tensors are transformed into quantities termed effective induced bond charges σ k . The new quantity is expected to be associated with polarizability properties of chemical bonds. The formulation developed is applied in analyzing atomic polarizability tensors obtained from HF/6-311 + G∗∗ ab initio MO calculations for a series of 17 molecules: CH 4, NH 3, H 2O, HF, SiH 4, PH 3, H 2S, HCl, CH 3CH 3, CH 3NH 2, CH 3OH, CH 3F, CH 2CH 2, CH 2NH, CH 2O, CH 2S and s trans-butadiene. The trends of changes of σ k are discussed.

Stability, Chemical Bonding and Vibrational Properties of Amorphous Carbon at Different Mass Density

ABSTRACTWe describe correlations between the atomic-scale structure and the global electronic and vibrational properties in amorphous carbon versus mass density. The model structures have been generated by applying different annealing regimes using a density-functional based molecular-dynamics (DF-MD) method. The stability of the amorphous modifications and the calculated vibrational density of states (VDOS) are strongly affected by the density and the annealing sequences, altering the chemical composition, the sp/sp2/sp3-clustering, the structure and related physical properties. A mass density of 3.0 g/cm3 is confirmed as a magic density favoring the formation of most stable a-C modifications having lowest defect densities and maximum band gap. In analyzing the vibrational spectra and the localization of modes in comparison with crystalline diamond and graphite, we identify the spectral signatures for chemically different bonded species and defects, that may be used for comparison with related Neutron-, Raman- and IR- work.

Characterization of aluminum surface layers produced by ion implantation.

The surface properties such as depth profile, chemical bond, and structure, and electrical properties of oxide and nitride layers in aluminum produced by high dose implantation of oxygen and nitrogen ions were investigated. High dose of oxygen (4×10 18 ions/cm 2 ) and nitrogen (2×10 18 ions/cm 2 ) molecule ions were implanted into polycrystalline and single crystal aluminium sheets. The implanted layers were characterized by means of AES, XPS, X-ray and transmission electron diffraction, transmission electron microscopy, and IR spectroscopy. The electrical resistivity and breakdown electric field strength of oxide and nitride layers were measured by current-voltage characteristics

A chemical model of Frenkel defects in fluorite

A technique based on the empirical properties of chemical bonds is used to model Frenkel defects in fluorite. It can identify likely positions for the interstitial F ion and, by predicting the ideal defect geometry from the resulting chemical bond network, it predicts a relaxed defect geometry which agrees with both neutron scattering measurements and the geometries predicted by other methods.

The Quantum Mechanics of Materials

In the past 25 years, new quantum-mechanical methods have been developed for predicting the configuration of the valence electrons in an atom or an aggregate of many atoms, within the range of energy excitations in which the atoms form interatomic bonds. A theory specifying the configuration of the valence electrons has much to say about the bulk properties of matter that depends on the nature of the interatomic bonds. The new method regards the core electrons and the atomic nucleus as if they constituted a single particle without internal structure. The method is called the pseudopotential theory. A general quantum-mechanical prediction of the properties of a substance in terms of the additive properties of separate chemical bonds is not yet feasible for molecules. However, there is one realm where prediction is now practical: crystalline solids. The regularity of the lattice into which the atoms are organized in a crystal makes it possible to calculate the properties of a macroscopic solid. In other words, many properties of an elemental solid such as lead or a simple binary solid such as gallium arsenide can not be deduced from energy considerations alone. (SC)

Chemical bond and related properties of SiO2

With the help of a high-intensity X-ray generator with rotating anode diffraction measurements are performed on commercial SiO powder and vapour deposited SiOx samples obtained from the commercial SiO. From an extensive analysis of corresponding radial distribution functions the atomic distances within the short-range order, the average chemical composition x, and the bonding statistics of SiOx are determined. Different statistical and fitted models for the chemical disorder of SiOx are tested. It is shown that a statistical model in which network defects are simulated by OO bond sleads to an excellent reproduction of the experimental data. The random-bonding character of vapour deposited SiOx and other structural and chemical differences between differently prepared types of SiOx are shown. Mit Hilfe eines Hochleistungsrontgengenerators mit rotierender Anode werden Beugungsmessungen an kommerziellem SiO-Pulver sowie an SiOx-Proben, die durch Verdampfung des kommerziellen SiO erhalten wurden, durchgefuhrt. Aus einer ausfuhrlichen Analyse entsprechender radialer Verteilungsfunktionen werden der Atomabstand in der Nahordnung, die mittlere chemische Zu- sammensetzung x und die Bindungsstatistik von SiOx bestimmt. Unterschiedliche statistische und angepaste Modelle fur die chemische Unordnung des SiOx werden getestet. Es wird gezeigt, das ein statistisches Modell, in dem Netzwerkdefekte durch OO-Bindungen simuliert werden, eine ausgezeichnete Reproduktion der experimentellen Daten ermoglicht. Der random-bonding- Charakter des aus der Dampfphase niedergeschlagenen SiOx und andere strukturelle und chemische Unterschiede zwischen unterschiedlich praparierten SiOfx-Typen werden nachgewiesen.

Chemical bond and related properties of SiO2. VII. Structure and electronic properties of the SiOx region of Si–SiO2 interfaces

It is shown that some SiOx forms (electron-beam evaporated SiOx and SiOx regions at the interface between Si and its thermally grown oxide) must be described by a random-bonding statistics, whereas others (CVD films and SiOx at elevated temperatures) can be considered as a simple mixture of Si and SiO2. The microscopic coexistence of Si-Si and Si-O bonds and of their properties in SiOx is discussed. The total electronic properties of SiOx reveal in dependence on x an ensemble behaviour with a threshold at x ≈ 1.25. This threshold can be explained in terms of percolation theory or with the help of more general considerations. The strongest variation of electronic properties of SiOx takes place within the range from x = 0 to x ≈ 1.25. From the fact that the electronic properties of SiO2 are almost completely reached already at x ≈ 1.5 follows that the thickness of gradual SiOx regions of Si-SiO2 interfaces is greater than commonly deduced from their electronic properties. The number of broken Si-O bonds is calculated in dependence on thermodynamic parameters. In agreement with recent predictions it is 1019 cm−3 for SiO2. Es wird gezeigt, das einige SiOx-Formen (elektronenstrahlverdampftes SiOx und SiOx-Regionen an der Interface zwischen Si und seinem thermischen Oxid) durch eine Random-Bonding-Statistik beschrieben werden mussen, wohingegen andere (CVD-Filme und SiOx bei erhohten Temperaturen) als ein einfaches Gemisch aus Si und SiO2 betrachtet werden konnen. Die mikroskopische Ko-existenz von Si-Si- und Si-O-Bindungen und ihren Eigenschaften in SiOx wird diskutiert. Elektronische Gesamteigenschaften von SiOx zeigen in Abhangigkeit von x ein Ensembleverhalten mit einer Schwelle bei x ≈ 1,25. Diese Schwelle kann durch die Perkolationstheorie oder mit Hilfe allgemeinerer Betrachtungen erklart werden. Die starkste Variation elektronischer Eigenschaften von SiOx findet im Bereich von x = 0 bis x ≈ 1,25 statt. Aus der Tatsache, das die elektronischen Eigenschaften von SiO2 bereits bei x ≈ 1,5 fast vollstandig-erreicht werden, folgt, das die Dicke von graduellen SiOx-Regionen von Si-SiO2-Interfaces groser ist als allgemein aus ihren elektronischen Eigenschaften geschlusfolgert wird. Die Anzahl abgerissener Si-O-Bindungen wird in Abhangigkeit von thermodynamischen Parametern berechnet. In Ubereinstimmung mit kurzlich getroffenen Voraussagen betragt sie fur SiO2 1019 cm−3.

Chemical bond and related properties of SiO2 VI. electronic structure of SiOx

Real-space distributions of the pseudopotential and of the corresponding valence charge density are investigated in dependence on the chemical composition of SiOx with the help of three different crystal models, that means with a mixed-crystal model, with a model in which five Si-(SiyO4–y) crystals (y = 0 to 4) are compared, and a random-bonding model for which a statistical distribution of the five possible bonding tetrahedra Si-(SiyO4–y) within SiOx is considered. The superiority of the random-bonding model to the mixture model, in which a simple mixture of Si and SiO2 is assumed, is demonstrated. Furthermore, it is shown that the composition rate of SiOx, at which the electronic properties of SiO2 begin to dominate, is x = 1.5 or even smaller, and that therefore the SiOx transition regions at the Si/SiO2 interfaces are somewhat thicker than commonly deduced from electronic SiOx properties. Selected problems concerning oxygen impurities in Si crystals and interactions between Si-O and Si-Si bonds in SiOx are discussed. The electronic dielectric function of SiOx is calculated. Ortsraumverteilungen des Pseudopotentials und der entsprechenden Valenzladungsdichte werden in Abhängigkeit von der chemischen Zusammensetzung von SiOx mit Hilfe dreier unterschiedlicher Kristallmodelle untersucht, d. h. mit einem Mischkristallmodell, mit einem Modell, in dem fünf Si-(SiyO4–y)-Kristalle (y = 0 bis 4) verglichen werden, und mit einem random-bonding-Modell, für das eine statistische Verteilung der fünf möglichen Bindungstetraeder Si-(SiyO4–y) innerhalb des SiOx betrachtet wird. Die Überlegenheit des random-bonding-Modells gegenüber dem mixture-Modell, in dem eine einfache Mischung von Si und SiO2 angenommen wird, wird demonstriert. Außerdem wird gezeigt, daß der Zusammensetzungsfaktor von SiOx, bei dem die elektronischen Eigenschaften von SiO2 zu dominieren beginnen, x = 1,5 oder sogar kleiner ist, und daß folglich die SiOx-Übergangsgebiete an Si/SiO2-Interfaces etwas dicker sind als überlicherweise aus elektronischen SiOx-Eigenschaften geschlossen wird. Ausgewählte Probleme bezüglich Sauerstoffverunreinigungen in Si-Kristallen und der Wechselwirkungen zwischen Si-O- und Si-Si-Bindungen in SiOx werden diskutiert. Die elektronische dielektrische Funktion von SiOx wird berechnet.