Ionic Character Of Chemical Bond Research Articles

Ab initio calculations of surface electronic states in indium oxide

A slab approach in the framework of ab initio calculations was applied to study surface electronic states in In2O3 crystal. Density functional theory (DFT) calculations were carried out employing the WIEN 2k code and using the full potential method with Augmented Plane Waves + local orbitals (APW+lo) formalism. Total and partial DOS (Density of States) were calculated for In and O atoms in two upper (110) surface layers. Comparison of total and partial DOS allowed determining a contribution of electronic states of different In and O surface atoms into formation of surface electronic spectra and corresponding chemical bonds. A dominant ionic character of chemical bonds in In2O3 is found. Calculations were performed for three slab models with different geometry parameters. It was shown that an optimal ratio between the whole vertical size of a supercell and the vertical size of atomic cluster has to be chosen. The size of vacuum region in the slab model influences significantly on the reliability of calculated characteristics of the surface electronic structure. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Photoacoustic investigations of beryllium containing wide gap II–VI mixed crystals

Mixed crystals of II–VI binary compounds with Be chalcogenides make it possible to tune band gap energies and lattice constants of these materials by adjusting Be content in the alloy. The reduced ionic character of chemical bonds in Zn1−xBexSe leads to increased lattice rigidity. For this reason, beryllium containing II–VI semiconducting compounds may offer the possibility of achieving a significant impact on the defect propagation and therefore increasing the laser structure lifetime.The photoacoustic technique was used to investigate the properties of ZnxBe1−xSe mixed crystals as a function of composition. The Jackson–Amer model and Blonskij et al. method for piezoelectric detection were used to estimate the values of energy gaps and thermal diffusivities. An attempt to measure thermal diffusivity in liquid nitrogen temperature was made.

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.

Mössbauer study on the chemical state of iron in binary oxide glasses based on Fe 2O 3

Iron-containing binary oxide glasses in the systems of Fe 2 O 3 -P 2 O 5 , -TeO 2 , -SrO, -BaO, -PbO and -Bi 2 O 3 were prepared by using a twin-roller quenching method, and 57 Fe Mossbauer effect measurements were carried out on these glasses in order to determine the chemical state of iron ions. All the iron ions existed as Fe 3+ ions in all the glasses except Fe 2 O 3 -P 2 O 5 ones in which Fe 2+ ions coexisted. Fe 3+ ions in Fe 2 O 3 -P 2 O 5 and -TeO 2 glasses were laid on octahedral sites while they occupied tetrahedral sites in Fe 2 O 3 -SrO, -BaO, -PbO and -Bi 2 O 3 glasses. The covalency of Fe-O chemical bond was directly estimated from the isomer shift. The covalency was large in Fe 2 O 3 -SrO, -BaO, -PbO and Bi 2 O 3 glasses, while it was small in Fe 2 O 3 -P 2 O 5 and -TeO 2 glasses. This large dependence of the chemical state of iron ion on the kind of other cations coexisting with iron ions was explained based on the ionic character of chemical bonds between other cations and oxygen ions. Furthermore, the effect of covalency of Fe-O bonds on the magnetic properties of the glasses was discussed qualitatively.

Ionic Character and the Dipole Moment of Chemical Bonds. Calculations of the Dipole Moment of HCl

The method of assigning the ionic character of chemical bonds by the use of the dipole moment is examined for the case of hydrogen chloride. Using both the atomic orbital and the LCAO molecular orbital approximation, the ionic character of HCl is calculated. Not only do the values so calculated seem unreasonable from energy considerations, but the calculated rate of change of dipole moment with respect to internuclear distance does not agree with the experimentally observed infra-red intensity. This discrepancy is due to the large dipole moment associated with the covalent bond. Although the results for a purely covalent compound are in agreement both with the dipole moment, and the infra-red intensity, if the dipole is assumed to have the orientation Cl+H−, this assumption is discredited by the fact that one would have to assume more ionic character for HBr than HCl. If we make the assumption that s—p hybridization occurs, these difficulties are removed. It is shown that the dipole moment of the purely covalent molecule is a very sensitive function of the amount of hybridization, and the covalent molecule can have almost any reasonable dipole moment. Thus it is shown that there are difficulties which must be surmounted before one can use dipole moments to obtain ionic character.