Bond Ionicity Research Articles

Synthesis and photoluminescent properties of Y1 − x La x PO4:Eu3+ nanophosphor

In this paper, Y1 − x La x PO4:Eu3+ (x = 0.5, 0.7, and 0.3) nanophosphors were synthesized by a rather simple method. The products present different morphologies. For Y1 − x La x PO4:Eu3+, they have similar phase composition of a mixture of monoclinic LaPO4 and tetragonal YPO4. Furthermore, the luminescence behavior of Eu3+ has been investigated in this type of matrices. In Y1 − x La x PO4:Eu3+, the 5D0-7F1 magnetic dipole transition is dominant, indicating that the Eu3+ site is inversion symmetry. The difference in the Eu-O charge transfer (CT) band with La3+ ion concentration suggests the difference in the ionicity of the Eu-O bond. Among those products, the red to orange intensity ratio (R/O) of 5D0-7F2 to 5D0-7F1 value of Eu3+ is different, furthermore, for La3+ x = 0.3, the R/O value of Eu3+ is the biggest on the contrary, indicating that the inversion symmetry Eu3+ is lowest.

Thermal and structural interactions in transition elements containing silicate–phosphate glasses

The DSC, XRD and 31P MAS NMR methods were applied to study the interactions between the transition elements (Zn, Cu, Mn, Mo) and structural components of glasses from the P2O5K2OCaOMgOTE (Zn/Cu/Mn/Mo) system. In order to determine the structure of domains being the result of interactions in transition elements containing silicate–phosphate glasses, the course of thermally induced crystallization of glasses was considered. To explain the different local chemical affinity of the studied transition elements to the POTE bridging bonds formation, the crystallochemical analysis based on the ionicity of the chemical bonds was used.

A new method of calculation of the melting temperatures of crystals of Group 1A metal halides and francium metal

A new method of calculation of melting temperatures of binary ionic crystals has been suggested. The method is based on finding a matrix relation between the ionic radii (the lattice energy U) and melting temperature of ionic crystals of the MX type, where M is a Group 1A metal, and X is a halogen. From the equation for the lattice energy U, a new equation has been derived for calculation of the melting temperature of ionic crystals with the use of only the ionic radii and the degree of bond ionicity ɛ: Tm = f(U, ɛ). The average error of determination of Tm for alkali-metal halides is 2.80%. The melting temperatures of francium halides and alkali-metal astatides (including FrAt) have been calculated. It has been shown that the accuracy of calculation of the melting temperature of ionic crystals depends on the degree of bond ionicity: the error increases with an increase in the covalent contribution. On the basis of the melting temperatures of metal halide crystals, a method has been developed for the calculation of the melting temperatures of corresponding metals. The melting temperature of francium has been calculated to be 24.861 ± 0.517°C.

Correlation Between Hydroxide ion Dynamics and Transport Properties of Hydroxide/Chloride Melts According to Raman Spectroscopy Data

UDC 541.454;543.42;535.375.5 Using data obtained in analysis of the band contour for the totally symmetric stretching vibration of the OH - anion in Raman spectra of hydroxide/chloride ionic melts, a correlation has been established between the orientational relaxation time and effective moment of inertia of the hydroxide ion and the transport properties of the electrolyte. Study of the structure of ionic compounds and its controlling infl uence on physical and chemical properties is one of the fundamental scientifi c problems in physical chemistry. Today the appearance of new and improvement of conventional experimental methods for studying the structure of matter and also creation of high-tech device components has permitted considerable expansion of the range of systems that can be studied, including high-temperature ionic melts. Development of methodological approaches has led to a signifi cant increase in the amount of information that can be extracted and an increase in the reliability of this information. Raman spectroscopy is a physical method for investigation of matter which, based on recorded vibrational spectra of the analyte system, allows us to carry out structural analysis, to determine the vibrational frequencies, and to calculate force constants and the moment of inertia of a molecule and the rates of relaxation processes. In contrast to x-ray diffraction and neutron diffraction methods, determining the structure of materials (the symmetry type, the interatomic distances, the coordination numbers), the Raman spectroscopy method allows us to obtain a much greater amount of information: the recorded vibrational frequencies correspond to the position of the vibrational levels in the molecule, the width of the vibrational bands contain information about its rotational motion, and the intensity of the Raman spectra directly determines the bond ionicity or covalency (1, 2). Today a methodological approach has been developed that allows us, from analysis of the contour of the vibrational bands and the width of their isotropic and anisotropic components, to obtain important information about the dynamics of the particles in the picosecond time range (1-4). It has been shown (4) that information about relaxation processes can be obtained by calculating the temporal correlation functions, the vibrational and orientational relaxation times for the structural units. Unique information on estimation of the moments of inertia of particles, which is practically inaccessible by other methods for studying the condensed state of matter and which can be obtained only using high-resolution rotational spectra of gas molecules, can be extracted by analyzing the shape of the contour of vibrational bands using the spectral moments method (4). According to this method, the moment of inertia can be calculated from the equation (3): I = 6kT/4π 2 c 2 Mor(2),

DFT simulations of water adsorption and activation on low-index α-Ga2O3 surfaces.

Density functional theory (DFT) calculations are used to explore water adsorption and activation on different α-Ga2O3 surfaces, namely (001), (100), (110), and (012). The geometries and binding energies of molecular and dissociative adsorption are studied as a function of coverage. The simulations reveal that dissociative water adsorption on all the studied low-index surfaces are thermodynamically favorable. Analysis of surface energies suggests that the most preferentially exposed surface is (012). The contribution of surface relaxation to the respective surface energies is significant. Calculations of electron local density of states indicate that the electron-energy band gaps for the four investigated surfaces appears to be less related to the difference in coordinative unsaturation of the surface atoms, but rather to changes in the ionicity of the surface chemical bonds. The electrochemical computation is used to investigate the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) on α-Ga2O3 surfaces. Our results indicate that the (100) and (110) surfaces, which have low stability, are the most favorable ones for HER and OER, respectively.

Structural properties, phase stability and theoretical hardness of Cr23−xMxC6 (M = Mo, W; x = 0–3)

The stability of Cr23−xMxC6 (M=Mo, W; x=0–3) increases when Mo/W replaces Cr at 8c site, and decreases when replacing at 4a site. The bonds of Cr23−xMxC6 (M=Mo, W; x=0–3) are complex mixtures of metallic, covalent and ionic characters. The replacement of Mo and W at 4a site increases the metallicity of M23C6, while the ionicity of the chemical bond is less affected in the Cr23−xMxC6 (M=Mo, W; x=1–3). The C–M bonds between the metal atoms (Cr/Mo/W) at 4a (8c) sites and C atoms are not found in the M23C6 type crystal. Mo/W replacing 4a site Cr will decrease the hardness of M23C6, while Mo/W replacing 8c site Cr enhances the hardness of M23C6. The Debye temperature (θD) of Cr23C6 is 666K, and that of Cr23−xMxC6 (M=Mo, W; x=0–3) decreases with the increase of the Mo/W content.

DFT study of chlorine adsorption on bimetallic surfaces - Case study of Pd3M and Pt3M alloy surfaces

Chlorine adsorption on Pd3M and Pt3M alloy surfaces (M=Fe, Co, Ni, Rh, Pd, Pt) with ideal bulk surface composition and Pt and Pd-skin type surfaces was analyzed by means of spin-polarized periodic Density Functional Theory calculations. The Pd-based surfaces tended to adsorb chlorine more strongly than the Pt-based surfaces. On bimetallic surfaces, Cl preferred to adsorb on the high-coordination sites. The ratio of surface stabilities, that is the preference of non-segregated surfaces or the skin-type ones, can be inverted under chlorine chemisorption conditions. The relative surface stability was linked to catalytic activity of Pt3Ni surfaces towards the oxygen reduction reaction in chloride-containing solutions. The charge transfer from metallic substrate to the Cl adatom was found to become more pronounced when the position of the solute M in the Periodic Table of Elements moved upward and left. However, the degree of bond ionicity did not exceed 20% in any case. In order to contribute to the comprehension of the adsorption trends, the Cl adsorption energy was correlated to the charge transfer parameters and to the electronic structure of the investigated bimetallic surfaces.

A first-principles investigation of oxygen reduction reaction catalysis capabilities of As decorated defect graphene.

Single and multiple As adatom adsorptions on double vacancy (DV) defect graphene sheets are extensively analyzed using dispersive force corrected density functional theory (DFT). Defect pentagonal and heptagonal bridge sites and the immediate neighborhood of the defect center are found to be most favorable for this purpose. Quantitative analysis of electronic structures revealed the As-C bonding to be mostly ionic in nature with some covalency arising from the overlap of As p states and C p states. For multiple As adatoms adsorption in close vicinity, ionicity of the As-C bonds are found to decrease to support As-As cohesion; the net result of which is manifested as better binding of dioxygen molecule with them and additional weakening of the O-O bond in the adsorbed state. Free energy profile of oxygen reduction reaction (ORR) cycle using multiple As atom adsorbed DV graphene as electrocatalyst predicts high affinity towards four electron process and forbids the formation of H2O2via two electron process. Other traits, such as no intermediate O-O-H formation and high stability of the catalytic system throughout the reaction process indicate As adatoms adsorbed on DV graphene system to be efficient and highly stable as an alternate Pt free ORR electrocatalyst.

Effect of the type of chemical bonding on surface autosegregation processes

Experimental studies of thermally stimulated surface autosegregation (TSAS) processes on single crystals of binary and ternary (oxide) compounds and analysis of our and others’ results are used to assess the effect of the type of chemical bonding on surface segregation processes in chemical compounds. Parameters are proposed that relate the segregation tendency to characteristics of segregation processes. The surface segregation tendency is shown to become less pronounced with increasing bond ionicity.

First-principles calculations of the structural, elastic and electronic properties of MNxC1−x (M = Ti, Zr, Hf; 0 ≤ x ≤ 1) carbonitrides at ambient and elevated hydrostatic pressure

The structural, electronic, and elastic properties of three mixed transition metal carbonitrides TiNxC1−x, ZrNxC1−x, and HfNxC1−x (0 ≤ x ≤ 1) with the rock-salt structure were calculated at ambient and elevated up to 50 GPa hydrostatic pressures in the framework of the density functional theory methods. The lattice constants, densities, and bulk moduli of the considered compounds were shown to behave as linear functions of the nitrogen concentration x. The obtained linear dependencies of all these parameters allow for getting their estimates at any value of x in the range from 0 to 1. Gradual enhancement of the ionicity of the chemical bonds with gradual replacement of carbon by nitrogen was demonstrated by calculating the bond orders and electron density difference distributions.

Equibiaxial strain: tunable electronic structure and optical properties of bulk and monolayer MoSe2

Using ab initio calculations based on density functional theory, we have studied the equibiaxial strain effect on the electronic and optical properties of bulk and monolayer MoSe2. Very low value of the elastic constants of monolayer MoSe2 compared to bulk MoSe2 suggests that the tailoring of the electronic structure and optical properties of monolayer MoSe2 may easily be achieved by strain. We find that the band gap (Eg) of MoSe2 undergoes a transition from indirect to direct upon reducing the thickness of the monolayer which is associated with an enhancement of Eg and is further tunable by strain engineering. We noticed that the splitting of the bands that generally determines the luminescence property of MoSe2 can be modified by strain. Strain effect on bond ionicity, dielectric property (real and imaginary component) of bulk and monolayer MoSe2 has also been briefly discussed. We noticed that the plasma oscillation, found in bulk MoSe2, is absent in MoSe2 monolayer.

On phases and interference of local communications in molecules

The role of phases in local Communication Theory of the Chemical Bond is investigated. Probability amplitudes of such molecular (fine-grained) information systems originate from the superposition principle of quantum mechanics involving the projection onto the bond system defined by the subspace of the state occupied Molecular Orbitals. They are explicitly phase-dependent, thus being capable of interference effects. The phase factors of the local direct and indirect (bridge, cascade) channels are examined and the associated amplitude/probability sum rules are established. The entropic descriptors of the local channels, providing the system “covalent” (communication-noise) and “ionic” (information-flow) components, are investigated using prototype one-electron systems. The competition between these information-theoretic measures of the chemical bond covalency (electron delocalization) and ionicity (electron localization) is illustrated in $$\mathrm{H}_{2}^{+}$$ and $$\mathrm{H}_{2}$$ .

Theoretical study of the adsorption of 3d- and 4d-metals on a WC(0001) surface

The interaction of 3d- and 4d-metals with a WC(0001) surface has been studied theoretically by density-functional theory methods depending on surface termination and adsorbate position. The most stable sites of metal adsorption on the surface have been determined. The binding energy of d-metals with the surface is shown to be higher in the case of carbon terminated surface. This is explained by the predominant ionic-covalent contribution to the chemical bond at the interface, with the bond ionicity being determined by charge transfer from the metals to the electronegative carbon. Analysis of the electronic and structural characteristics has revealed the factors affecting the bonding energetics at the metal-carbide interface depending on the metal d-shell filling with electrons.

Dispersion and edge absorption of Y2O3 thin films obtained by different methods

In the visible and near UV regions of the spectrum, we have measured optical dispersion in Y2O3 thin films obtained by stepwise vaporization and high-frequency RF ion plasma sputtering. We studied the edge absorption spectrum. We have determined the parameters of the single-oscillator approximation and determined the dispersion energy, the bond ionicity, and the coordination number. We compare the results obtained with the structural perfection of the Y2O3 films.

Effects of bifunctional metal sulfide interlayers on photovoltaic properties of organic–inorganic hybrid solar cells

Bilayer organic–inorganic hybrid solar cells have been fabricated with chemical-bath deposited In2S3, SnS, and Sb2S3 interlayers between the organic P3HT hole-conducting and inorganic TiO2 electron-conducting layers. Sb has the highest electronegativity among the elements investigated, and the ionicity of the metal–sulfur bond decreases in the order In2S3 (15%) > SnS (9%) > Sb2S3 (7%). Thus, with a larger covalent character of the Sb–S bond, Sb may bond to S atoms on P3HT relatively easily compared to In or Sn. Such chemical bonding between Sb2S3 and P3HT may then reduce the overall incompatibility between the TiO2 and P3HT layers, making Sb2S3-based devices more efficient compared to In2S3- and SnS-based devices. Along with strong photon absorption, the presence of the metal–sulfur bond promotes improved wetting between the TiO2 sand P3HT layers, resulting in dual functionality for the metal sulfide interlayers. However, along with differences in metal–sulfur bond ionicity, the efficiency improvements seen with Sb2S3 can further be attributed to factors like differences in crystal structure, morphology, photon absorption, charge carrier recombination rates, and the manner in which the sulfide layer interacts with TiO2. While further studies are required to elucidate the exact reason behind the behavior of Sb2S3, the findings discussed herein can provide guidelines for identifying novel absorber layers for developing efficient and cost-effective organic–inorganic hybrid photovoltaics.

Refractometric studies of chalcogenide glasses in Ag–As–S system

Compositional behavior of refractometric parameters and refractive index dispersion for (Ag2S)x(As2S3)100−x glassy alloys in Ag–As–S system were studied. Nonlinear compositional dependences of density and refractive index were revealed. Chemical bond ionicity as well as average coordination number and molar refraction versus silver content variation in the glassy alloys were estimated.

An Insight into Slag Structure from Sulphide Capacities

The molar sulphide capacities \( C_{\text{S}}^{'} \) = (mol pct S) (\( P_{{{\text{O}}_{2} }} /P_{{{\text{S}}_{2} }} \))1/2 on four binary systems, MgO-SiO2, CaO-SiO2, MnO-SiO2 and FeO-SiO2 are elucidated so as to compare the magnitudes of the basicities of four metallic oxides and to estimate the temperature dependencies of the basicities of metallic oxides. The enthalpy changes of the reaction 2O− = O + O2−, viz. the silicate polymerization reaction (denoted as \( \Updelta H_{(8)}^{^\circ } \)) have been calculated from the slopes of the log \( C_{\text{S}}^{'} \)vs 1/T curves for four binary silicates. The \( \Updelta H_{(8)}^{^\circ } \) value is considered in the present work to be an index of the basicity of silicate melts. The basicities obtained on the basis of the \( \Updelta H_{(8)}^{^\circ } \) values are in the order MgO < CaO < MnO < FeO, which are determined by two effects; (i) ionicity of chemical bonds between metallic and oxygen ions and (ii) clustering of metallic oxides in silicates. It is also found that the basicity of the FeO-SiO2 system is larger at higher temperatures.

Conversion of covalent to ionic character of V2O5–CeO2–PbO–B2O3 glasses for solid state ionic devices

Abstract x V 2 O 5 – x CeO 2 –(30− x )PbO–(70− x ) B 2 O 3 glasses are synthesized by using the melt quench technique. The number of studies such as XRD, density, molar volume, optical band gap, refractive index and FTIR spectroscopy are employed to characterize the glasses. The band gap decreases from 2.20 to 1.78 eV and density increases from 3.49 to 4.25 g/cm 3 . FTIR spectroscopy reveals that incorporation of V 2 O 5 in glass network helps to convert the structural units of [BO 3 ] into [BO 4 ]. At higher concentration of vanadium, VO vibration of [VO 5 ] structural units and V–O–V vibration are present. The bond ionicity of glasses increases with incorporation of V 2 O 5 contents.

Relationship Between Bond Ionicity, Lattice Energy, and Microwave Dielectric Properties of Zn(Ta1−xNbx)2O6 Ceramics

The crystalline structure refinement, chemical bond ionicity, and lattice energy were carried out for Zn(Ta1−xNbx)2O6 ceramics with tri‐α‐PbO2 structure to investigate the correlations between the crystalline structure, phase stability, bond ionicity, and microwave dielectric properties. The chemical bond ionicity and lattice energy of the ZnTa2O6 system were calculated and evaluated using a semiempirical method based on the dielectric description theory proposed by Phillips, Van Vechten, and Levine (P–V–L theory). The crystalline structure stability varied with the content of Nb5+ ion resulted in the lattice energy decrease. The increase of Ta/Nb–O bond ionicity was observed in the crystalline structure, which should be main contribution to electric polarization. The dielectric properties of the Zn(Ta1−xNbx)2O6 ceramics were strongly dependent on the chemical bond ionicity of Ta/Nb–O bond with tri‐α‐PbO2 structure.

Transparent conductivity of fluorine-doped anatase TiO2 epitaxial thin films

Transparent conductive anatase TiO2−xFx(F:TiO2) epitaxial thin films were fabricated by reactive pulsed laser deposition with a solid fluorine source. F-doping as high as 1.6 × 1021 cm−3 (TiO1.95F0.05) was achieved under optimal growth conditions, and the obtained anatase TiO1.95F0.05 film had a low resistivity of 1.6 × 10−3 Ωcm and a high internal transmittance of &amp;gt;95%. Furthermore, the refractive index of a TiO1.95F0.05 film was &amp;gt;0.2 less than that of undoped TiO2. By comparing the refractive indices of F:TiO2 and Nb:TiO2, we concluded that the decreased refractive index in F:TiO2 can be attributed to a reduced electronic polarizability due to increased bond ionicity as well as doped electrons.