Chemical Bond Properties Research Articles

Chemical bond properties and charge transfer bands of O(2-)-Eu(3+), O(2-)-Mo(6+) and O(2-)-W(6+) in Eu(3+)-doped garnet hosts Ln3M5O12 and ABO4 molybdate and tungstate phosphors.

Charge transfer (CT) energy from the ligand to the central ions is an important factor in luminescence properties for rare earth doped inorganic phosphors. The dielectric theory of complex crystals was used to calculate chemical bond properties. Combining the photoluminescence and the dielectric theory of complex crystals, the CT bands of O(2-)-Eu(3+), O(2-)-Mo(6+) and O(2-)-W(6+) for Eu(3+)-doped inorganic phosphors have been investigated experimentally and theoretically. Taking Eu(3+)-doped Ln3M5O12 (Ln = Y, Lu and M = Al, Ga), Gd3Ga5O12, MMoO4 (M = Ca, Sr, Ba) and MWO4 (M = Ca, Sr, Ba) as typical phosphors, we investigated the effects of the cation size on the CT bands and chemical bond properties including the bond length (d), the covalency (fc), the bond polarizability (αb) and the environmental factor (he) of O(2-)-Eu(3+), O(2-)-Mo(6+) and O(2-)-W(6+), respectively. For systematic isostructural Ln3M5O12 (Ln = Y, Lu and M = Al, Ga) phosphors, with the increasing M ion radius, the bond length of Ln-O decreases, but fc and αb increase, which is the main reason that the environmental factor increased. For the isostructural MMoO4:Eu, with the increasing M ion radius, the Mo-O bond length increases, but fc and αb decrease, and thus he decreases. However, in the compound system MWO4:Eu (M = Ca, Ba) with the increasing M ion radius, the O-W bond length increases, but fc and αb increase, and thus he increases and the O-W CT energy decreases. Their O(2-)-Eu(3+), O(2-)-Mo(6+) and O(2-)-W(6+) CT bands as well as their full width at half maximum (FWHM) were directly influenced by he. And with the increasing he, CT bands of O-Eu or O-Mo or O-W decrease and their FWHM increases. These results indicate a promising approach for changing the material properties, searching for new Eu(3+) doped molybdate, tungstate or other oxide phosphors and analyzing the experimental result.

Effects of Bias on Optical and Chemical Bonding Properties of Germanium Carbon Films

Amorphous hydrogenated Ge1-xCx films are prepared by radio frequency (RF) magnetron cosputtering using Ge/graphite composite target and their composition, optical and chemical bonding properties as a function of bias have been investigated. The results show a decrease in the deposition rate with increasing bias, and the optical gap nearly keep constant due to effects of both composition and chemical bonding. Through the analysis of X-ray photoelectron spectroscopy, we find that the content of Ge-C bonds first increases and then decreases as increasing bias while the Ge-O bond decreases monotonically.

Topological Properties of Chemical Bonds from Static and Dynamic Electron Densities

Dynamic and static electron densities (EDs) based on the independent spherical atom model (IAM) and multipole (MP) models of crambin were successfully computed, holding no series-termination effects. The densities are compared to EDs of small biological molecules at diverse temperatures. It is outlined that proteins exhibit an intrinsic flexibility, present as frozen disorder at 100 K, in contrast to small molecules. The flexibility of the proteins is reflected by atomic displacement parameters (B-factors), which are considerably larger than for small molecules at 298 K. Thus, an optimal deconvolution of deformation density and thermal motion is not guaranteed, which prevents a free refinement of MP parameters but allows an application of transferable, fixed MP parameters. The analysis of the topological properties, such as the density at bond critical points (BCPs) and the Laplacian, reveals systematic differences between static and dynamic EDs. Zero-point-vibrations, yet present in dynamic EDs at low temperature, affect but marginally the EDs of small molecules. The zero-point-vibrations cause a smearing of the ED, which becomes more pronounced with increasing temperature. Topological properties, primarily the Laplacian, of covalent bonds appear to be more sensitive to effects by temperature and the polarity of the bonds. However, dynamic EDs at ca. 20 K based on MP models provide a good characterization of chemical bonding. Both the density at BCPs and the Laplacian of hydrogen bonds constitute similar values from static and dynamic EDs for all studied temperatures. Deformation densities demonstrate the necessity of the employment of MP parameters in order to comprise the nature of covalent bonds. The character of hydrogen bonds can be roughly pictured by IAM, whereas MP parameters are recommended for a classification of hydrogen bonds beyond a solely interpretation of topological properties.

New Polar Intermetallic Phases RE2Zn5Tt (RE = La–Nd; Tt = Sn and Pb): Synthesis, Structure, Chemical Bonding, and Magnetic Properties

Reported are the synthesis, crystal structure, electronic structure, and magnetic properties of a series of zinc-rich ternary phases with formulas RE2Zn5Tt (RE = La-Nd; Tt = Sn and Pb). The structures of these compounds have been established by single-crystal and powder X-ray diffraction. They crystallize in the orthorhombic space group Cmcm (No. 63, LaRhSn2 structure type, Pearson symbol oC32). The most prominent structural feature is the trigonal-planar coordination of the Sn(Pb) atoms; the latter interconnect layers of Zn atoms to comprise a complex [Zn5Tt] polyanionic framework. The structural relationships between the structure of the title compounds and the EuIn4, La3Al11, and YIrGe2 structure types are highlighted. Temperature-dependent DC magnetization measurements indicate Pauli-like paramagnetism for La2Zn5Sn, while Ce2Zn5Sn, Pr2Zn5Sn, and Nd2Zn5Sn display Curie-Weiss behavior in the high-temperature regime. At cryogenic temperatures, the magnetic responses of Ce2Zn5Sn, Pr2Zn5Sn, and Nd2Zn5Sn appear to deviate from the Curie-Weiss law; however, no magnetic orderings could be observed down to 5 K. Theoretical considerations of the electronic structure on the basis of the tight-binding linear muffin-tin orbital (TB-LMTO-ASA) method are also presented and discussed.

First Principle Study of Electronic Structure, Chemical Bonding and Optical Properties of 5-azido-1H-tetrazole

First Principle Study of Electronic Structure, Chemical Bonding and Optical Properties of 5-azido-1H-tetrazole

First-Principles Calculations on Electronic, Chemical Bonding and Optical Properties of Cubic Hf3N4

Electronic, chemical bonding and optical properties of cubic Hf3N4(c-Hf3N4) are calculated using the first-principles based on the density functional theory (DFT). The optimized lattice parameter is in good agreement with the available experimental and calculational values. Band structure shows that c-Hf3N4 has direct band gap. Densities of states (DOS) and charge densities indicate that the bonding between Hf and N is ionic. The optical properties including complex dielectric function, refractive index, extinction coefficient, absorption coefficient, and reflectivity are predicted. From the theory of crystal-field and molecular-orbital bonding, the optical transitions of c-Hf3N4 affected by the electronic structure and molecular orbital are studied. It is found that the absorptive transitions of c-Hf3N4 compound are predominantly composed of the transitions from N T22p valence bands to Hf T2 (dxy, dxz, dyz) conduction bands.

S114045 ATR-IR法による金属表面上の油性剤吸着層の化学物性測定([S114-04]トライボロジーの基礎と応用(4))

S114045 ATR-IR法による金属表面上の油性剤吸着層の化学物性測定([S114-04]トライボロジーの基礎と応用(4))

Characterization of Cr Doped Diamond-Like Carbon Films and Research on Mechanical Properties

Diamond-like carbon (DLC) films have been extensively studied for more than a decade due to their unique combination of properties. The internal compressive stress affects their adhesion and preventing wide usage of these films. Metal-containing DLC films are expected to relax internal stress. The present work focused on the synthesis, chemical bond and mechanical property characterization of Cr-containing DLC films. The films thickness, internal stress and composition were characterized by scanning electron microscopy, optical interferometry and X-ray photoelectron spectroscopy respectively. Incorporation of Cr into DLC causes an initial internal stress reduction and subsequent stabilization around 0.5 GPa. The hardness behavior was found to depend on Cr content. Films with less than 7.36 at.% Cr (no formation of C-Cr bond) showed a dramatically hardness reduction compared to pure DLC films. Above 7.36 at.% Cr (C-Cr bond formed) the hardness increases above 12 GPa.

Electronic Structure, Optical Properties, Chemical Bonding and Elastic Properties of Ca2LiC3H by First Principles Investigation

Electronic Structure, Optical Properties, Chemical Bonding and Elastic Properties of Ca₂LiC₃H by First Principles Investigation

Discriminating Chemical Bonds

An atomic force microscope equipped with a functionalized tip can map out the electronic and structural properties of individual chemical bonds.

First Principles Investigation of Electronic Structure, Chemical Bonding, Elastic and Optical Properties of Novel Rhenium Nitrides

we investigate the electronic structure, chemical bonding, optical and elastic properties of the novel rhenium nitrides, hexagonal phase re3n and re2n by using density-functional theory (dft) within generalized gradient approximation (gga). the calculated equilibrium lattice constants of both re3n and re2n are in reasonable agreement with the experimental results. the band structure along the higher symmetry axes in the Brillouin zone, the density of states (dos) and the partial density of states (pdos) are presented. the calculated energy band structures and dos show that re3n and re2n are metal compounds. The dos and pdos show that the dos at the fermi level (ef) is located at the bottom of a valley and originate mainly from the 5d electrons of re. population analyses suggest that the chemical bonding in re3n and re2n has predominantly covalent character with mixed covalent and ionic characteristics. the dielectric function, reflectivity, absorption coefficient, refractive index, electron energy-loss function and optical conductivity are presented in an energy range for discussing the optical properties of re3n and re2n. basic mechanical properties, such as elastic constants cij, bulk modulus b and shear modulus g are calculated. The young’s modulus e, poisson's ratio ν and bh/gh are also predicted. results conclude that the hexagonal phase re3n and re2n are mechanical stable and behaves in a ductile manner. polycrystalline elastic anisotropy is also derived from polycrystalline bulk modulus b and shear modulus g.

Electronic Structure and Thermoelectric Property of Misfit Layered Cobaltite and Doped Series

The relations between electronic structure, chemical bond and thermoelectric property of misfit layered cobaltite of Ca3Co4O9 and 3d transitional metal (Ti, Cr, Mn, Fe and Cu) doped series are studied using density function and discrete variation method (DFT-DVM). Ca3Co4O9 consists of two layers of CoO2 and Ca2CoO3. The highest valence band (HVB) and the lowest conduction band (LCB) near Fermi level are only mainly from O 2p and Co 3d in Ca2CoO3 layer. Therefore, the semiconductor, or thermoelectric property of Ca3Co4O9 should be mainly from Ca2CoO3 layer, but it seems to have no direct relation to the CoO2 layer, which is consistent with that binary oxides hardly have thermoelectric property, but trinary oxide compounds have quite good thermoelectric property. The variation of electronic structure, chemical bond strength and thermoelectric property of doping series is discussed. The improvement of thermoelectric property of Cu-doped Ca3Co4O9 is the most obvious.

Classification Prediction of Photochemical Ractions Based on MOLMAP

In this article, MOLMAP (molecular maps of atom-level properties) descriptors of reactants, products and reactions were derived from the structures of reactants and products which were represented by physicochemical properties and topological properties of chemical bonds of the compounds. The MOLMAP descriptors above-mentioned were applied to a data set composed of seven classes of photochemical reactions, and three kinds of models were constructed by random forest: (1) The model to predict the type of reaction the reactants produce; (2) the model to predict the type of reaction from which the product can be synthesized; (3) the model to predict the type of the whole reactions. Because the specification of the bonds involved in the reactions was not required in data sets, the MOLMAP descriptors can be used widely. The results obtained in this article were better than those results in our previous researches for the same data set. Therefore, the modification of bond description is helpful for improving the prediction ability of MOLMAP descriptors.

Investigation of optical and chemical bond properties of hydrogenated amorphous silicon nitride for optoelectronics applications

The aim of this work is to determine optimal deposition parameters of silicon nitride for optical applications. The authors present the investigation of hydrogenated amorphous silicon nitride SiN x :H deposited by the low temperature PECVD method in high frequency reactors. The study of hydrogen bonds in the SiN x :H thin films were detailed. The impact of NH 3, SiH 4 and N 2 flow ratio and radio frequency power on optical coefficients in relation to chemical composition and roughness of the film is studied. The correlation between chemical bonds (N–H, Si–H) and refractive index and extinction coefficients is systematically verified. The experimental results show that the films with high refractive indexes superior to 2.05 and low roughness of about 0.35 nm can be achieved for optoelectronics applications by tuning the flow ratio or decreasing the RF power. A variety of processes have been suggested as compatible with low thermal budget (under 350 °C) in order to integrate optical waveguides with lower loss. In particular, the incorporation of N 2 as dilution gas is suited to the fabrication of SiN x :H films optical waveguide requiring low N–H bonds, low concentration of hydrogen [H] and high refractive index.

ChemInform Abstract: Synthesis, Structure, and Theoretical Investigations of an Alkaline Earth Vanadate Oxide Compound (Ca4V4O14): Electronic, Optical, and Chemical Bond Properties

AbstractThe title compound is hydrothermally synthesized from an aqueous mixture of V2O5 and Ca(NO3)2 (autoclave, 250 °C, 7 d, 20% yield).

Effects of quantum confinement and shape on band gap of core/shell quantum dots and nanowires

A quantum confinement model for nanocrystals developed is extended to study for the optical gap shifts in core/shell quantum dots and nanowires. The chemical bond properties and gap shifts in the InP/ZnS, CdSe/CdS, CdSe/ZnS, and CdTe/ZnS core/shell quantum dots are calculated in detail. The calculated band gaps are in excellent agreement with experimental values. The effects of structural taping and twinning on quantum confinement of InP and Si nanowires are elucidated. It is found theoretically that a competition between the positive Kubo energy-gap shift and the negative surface energy shift plays the crucial role in the optical gaps of these nanosystems.

Hardness and Bonding of Silicate Garnets

The chemical bond properties of the andradite garnet Ca3Fe2Si3O12, grossular garnet Ca3Al2Si3O12, and pyrope garnet Mg3Al2Si3O12 have been investigated using a chemical bond theory of complex crystals. The calculated hardness, isomer shifts of these garnets are in good agreement with the available experimental data. Predictions are made for those cases where no experimental data have been reported. The chemical bond properties, hardness and isomer shifts of the andradite garnet Ca3Fe2Si3O12, grossular garnet Ca3Al2Si3O12, and pyrope garnet Mg3Al2Si3O12 have been investigated using a chemical bond theory of complex crystals.

Synthesis, Structure, and Theoretical Investigations of an Alkaline Earth Vanadate Oxide Compound (Ca4V4O14): Electronic, Optical, and Chemical Bond Properties

One novel purely inorganic d0 polyoxovanadate compound Ca4V4O14 (1) was obtained and characterized structurally. The chain-like [V4O14]8– anion, built up from distorted VO5 trigonal bipyramids and VO4 tetrahedras is rarely observed. The reason for structural distortions is ascribed to the second-order Jahn-Teller effect. The band structure, the density of states, linear optical response functions, the dielectric constants of the static case ϵ(0), and refractive indexes were calculated by the density functional theory method. The nature of the V–O and Ca–O bonds, and of the electronic absorption peak are discussed in detail.

Theoretical Investigations on the Chemical Bonding, Electronic Structure, And Optical Properties of the Metal−Organic Framework MOF-5

The chemical bonding, electronic structure, and optical properties of metal-organic framework-5 (MOF-5) were systematically investigated using ab initio density functional calculations. The unit cell volume and atomic positions were optimized with the Perdew-Burke-Ernzerhof (PBE) functional leading to a good agreement between the experimental and the theoretical equilibrium structural parameters. The calculated bulk modulus indicates that MOF-5 is a soft material. The estimated band gap from a density of state (DOS) calculation for MOF-5 is about 3.4 eV, indicating a nonmetallic character. As MOFs are considered as potential materials for photocatalysts, active components in hybrid solar cells, and electroluminescence cells, the optical properties of this material were investigated. The detailed analysis of chemical bonding in MOF-5 reveals the nature of the Zn-O, O-C, H-C, and C-C bonds, that is, Zn-O having mainly ionic interaction whereas O-C, H-C, and C-C exhibit mainly covalent interactions. The findings in this paper may contribute to a comprehensive understanding about this kind of material and shed insight into the synthesis and application of novel and stable MOFs.

GGA+U method investigating structural and chemical bond properties of CeB 6 and EuB 6

The structural and chemical bond properties of CeB 6 and EuB 6 have been calculated by means of an all-electron full-potential linearized augmented plane wave (FPLAPW) and so-called GGA+U method, which are implemented within the EXCITING code. The calculated results indicate that concerning both CeB 6 and EuB 6, the optimized lattice constant, fitted bulk modulus, calculated spin magnetic moment and correlation energy parameter are in good agreement with experimental data. In addition, although the number of 4f electrons in Ce atom is different from that in Eu atom, the CeCe and EuEu bonds are mainly ionic bond, Ce (Eu)−B bonding includes ionic and covalent bond characteristics while the bonding between the nearest-neighbor B atoms (B1 and B2, B3 and B4) has a stronger covalent character than that of the next-nearest B bonds (B2 and B3).