Ionicity Of Chemical Bonds Research Articles

Effect of chemical bond polarity on wafer and cleavage surface oxidation for GaAs, GaSb, InAs and InSb single crystals

Rapid development of III–V semiconductor device technologies and broadening of device applications are hindered by the high density of surface states produced in those materials by intrinsic complex oxides and surface contaminations. Surface oxides acting as non-radiating recombination centers produce a number of surface levels in the band gap. Oxidation mechanisms depend on the chemical composition of a specific III–V semiconductor compound because surface reactivities differ between materials. The effect of chemical bond polarity on surface oxidation processes in single crystal III–V semiconductor wafers is currently an important research topic. In this work, surface-sensitive XPS method has been used for studying oxidation regularities in GaAs, InAs, GaSb and InSb single crystals undergoing natural atmospheric oxidation and subjected chemical-mechanical polishing. A method of assessing oxidation levels based on chemical shifts of XPS spectral features has been developed. Oxidation level has been shown to depend on chemical bond ionicity degree, the latter being evaluated using the Sanderson and Phillips models. A decrease in surface oxidation level with an increase in bond ionicity degree has been observed for (110) single crystal wafer cleavage surfaces and for (100) single crystal wafer surfaces after single crystal slicing and chemical-mechanical polishing. We show that surface oxidation level increases in the InAs–GaAs–InSb–GaSb sequence, from arsenides to antimonides.

First-principles definition of ionicity and covalency in molecules and solids.

The notions of ionicity and covalency of chemical bonds, effective atomic charges, and decomposition of the cohesive energy into ionic and covalent terms are fundamental yet elusive. For example, different approaches give different values of atomic charges. Pursuing the goal of formulating a universal approach based on firm physical grounds (first-principles or non-empirical), we develop a formalism based on Wannier functions with atomic orbital symmetry and capable of defining these notions and giving numerically robust results that are in excellent agreement with traditional chemical thinking. Unexpectedly, in diamond-like boron phosphide (BP), we find charges of +0.68 on phosphorus and -0.68 on boron atoms, and this anomaly is explained by the Zintl-Klemm nature of this compound. We present a simple model that includes energies of the highest occupied cationic and lowest unoccupied anionic atomic orbitals, coordination numbers, and strength of interatomic orbital overlap. This model captures the essential physics of bonding and accurately reproduces all our results, including anomalous BP.

Dispersion properties of (La0.06Ga0.94)2O3:Eu thin films

The dispersion of the refractive index of (La0.06Ga0.94)2O3:Eu thin films obtained by radio-frequency ion-plasma sputtering has been studied. It was found that the films have a polycrystalline structure corresponding to the monoclinic structure of β- Ga2O3. It is shown that the freshly deposited films are characterised by an abnormal dispersion, and after annealing in argon, a normal dispersion of the refractive index is observed. It was found that at normal dispersion, the spectral dependence of the refractive index in the visible region of the spectrum is mainly determined by electronic transitions from the 2p-state oxygen band, which form the upper filled level of the valence band to the bottom of the conduction band formed by hybridised 2p-states of oxygen and 4s-states of gallium. Two single-oscillator approximation models were analysed and compared for the films annealed in argon, and the approximation parameters, dispersion energy, degree of chemical bond ionicity, coordination number, and static refractive index were determined.

Breaking Through the Luminescence Stability Bottleneck of Oxyfluoride Phosphor for Sun‐Like Led Lighting

AbstractSunlight like optical source is the primary objective of healthy lighting. In contrast, achieving full spectrum lighting with high stability remains challenging, mostly due to the scarcity of purple chip‐pumped cyan‐green phosphors and their inherent emission instability. In this study, a novel strategy is presented that realizes simultaneous enhancements in both humidity stability (increased by 2.9 times) and luminescence quantum efficiency (enhanced by 1.5 times) for cyan‐emitting Sr3AlO4F:Ce3+ phosphor by employing Si/N doping. Theoretical modelling shows that these improvements are attributed to the regulation of energy bands and structural rigidity as well as modulation of the ionicity of chemical bonds. Furthermore, blending the other violet chip‐pumped phosphors, sun‐like LEDs that accurately replicate solar spectra in different times of the day with an optimal color rendering index of 99 is successfully engineered. Moreover, the universality of this strategy on other oxyfluoride phosphors has also been validated. This groundbreaking outcome offers a practical solution to overcome the inherent luminescence stability limitations in oxyfluoride phosphors, thus catalyzing the application of these cyan‐green candidates in sun‐like LED lighting.

Bond, vibration and microwave dielectric properties of LiYMo2O8 ceramics with low sintering temperature

This study presents the synthesis of LiYMo2O8 ceramic through a solid-state reaction. XRD analysis reveals a tetragonal structure (I41/a space group) for the LiYMo2O8 phase. The sample sintered at 800 °C achieved a maximum relative density of 95.8 % and exhibited excellent microwave properties: εr = 15.7, Q × f = 24380 GHz, and τf = 147.6 ppm/ °C. The results demonstrate a positive correlation between the relative density and both εr and Q × f, while Q × f and τf are found to be associated with packing fraction and Mo-O bond valence, respectively. The microwave dielectric properties are predominantly influenced by the Mo-O bond, as supported by the P-V-L theory and Raman spectroscopy analysis. Furthermore, the study reveals a correlation between εr and the ionicity of chemical bonds, a significant impact of lattice energy on Q × f, and a relationship between τf and bond energy and thermal expansion coefficient.

Crystal structures, chemical bond features, and Raman vibrations of Li2Co2Mo3O12 microwave dielectric ceramics with low sintering temperature

AbstractLi2Co2Mo3O12 (LCMO) ceramics were synthesized using the solid‐state reaction method. X‐ray diffraction analysis results indicated that the sole crystalline phase present in the ceramics was LCMO, which belongs to the orthorhombic structure of the Pnma space group. The sample, which was sintered at 850°C, demonstrated outstanding microwave dielectric properties, with an εr value of 8.95, a Q × f value of 43 200 GHz, and a τf value of –71.3 ppm/°C. It was found that while the main factor influencing εr was ionic polarizability, sintering density had a lesser effect on it. Furthermore, Q × f was primarily affected by relative density, and there was no significant relationship between packing fraction and this property. The higher the degree of distortion of the [Li/CoO6] octahedron is, the poorer the τf value of LCMO ceramics. Additionally, the microwave dielectric properties of LCMO ceramics were intrinsically linked to ionicity, lattice energy, bond energy, and thermal expansion coefficient of chemical bonds, with Mo–O bonds being the primary factor affecting these properties, as supported by analysis using chemical bonding theories. Mo–O bond vibration dominated the Raman spectra. Good chemical compatibility between silver and LCMO ceramics was demonstrated through our co‐firing experiment.

Crystal structure, Raman spectra, bond characteristics, and microwave dielectric properties of MnMoO4 ceramics

MnMoO4 ceramic was prepared using solid-state reaction method. XRD and Rietveld refinement results confirmed the formation of a single phase of MnMoO4 with monoclinic structure of C2/m space group. Excellent microwave dielectric properties, including εr = 9.32, Q × f = 56,230 GHz, and τf = −62.32 ppm/°C, were achieved for the resulting MnMoO4 ceramic at 925 °C, which had a relative density of 97%. The dielectric polarization and packing fraction were closely related to the dielectric constant and quality factor of MnMoO4 ceramics, respectively. Furthermore, our P–V-L analysis demonstrated that the ionicity, lattice energy, and bond energy of chemical bonds were all dominated by the Mo–O bond, which had a greater influence on microwave dielectric properties than the Mn–O bond. This finding was confirmed using Raman spectroscopy, which revealed that [MoO4] tetrahedron vibrations predominated Raman vibrations, supporting the P–V-L theory. Additionally, the chemical compatibility of the MnMoO4 ceramic with Ag co-firing was explored to investigate potential technological applications.

Mechanochemistry and the Evolution of Ionic Bonds in Dense Silver Iodide.

External mechanical stress alters the nature of chemical bonds and triggers novel reactions, providing interesting synthetic protocols to supplement traditional solvent- or thermo-based chemical approaches. The mechanisms of mechanochemistry have been well studied in organic materials made of a carbon-centered polymeric framework and covalence force field. They convert stress into anisotropic strain which will engineer the length and strength of targeted chemical bonds. Here, we show that by compressing silver iodide in a diamond anvil cell, the external mechanical stress weakens the Ag-I ionic bonds and activate the global diffusion of super-ions. In contrast to conventional mechanochemistry, mechanical stress imposes unbiased influence on the ionicity of chemical bonds in this archetypal inorganic salt. Our combined synchrotron X-ray diffraction experiment and first-principles calculation demonstrate that upon the critical point of ionicity, the strong ionic Ag-I bonds break down, leading to the recovery of elemental solids from a decomposition reaction. Instead of densification, our results reveal the mechanism of an unexpected decomposition reaction through hydrostatic compression and suggest the sophisticated chemistry of simple inorganic compounds under extreme conditions.

Infrared reflectivity spectra, complex chemical bond and microwave dielectric properties of Ce2[Zr1–x(Al1/2Sb1/2)x]3(MoO4)9 (0.02≤x≤0.10) ceramics

Ce2[Zr1–x(Al1/2Sb1/2)x]3(MoO4)9 (CZ1–x(AS)xM) (0.02 ≤ x ≤ 0.10) ceramics were prepared via a solid-state reaction route, and their microstructure was investigated using scanning electron microscopy. A single phase, belonging to the space group of R3‾c, was confirmed by X-ray diffraction patterns. On the basis of the Rietveld refinement results, the chemical bond ionicity, lattice energy and bond valence were calculated. The intrinsic dielectric constants and losses were evaluated by Far-infrared reflectivity spectroscopy. Optimal microwave dielectric properties: εr = 10.12, Q×f = 82,382 GHz and τf = −14.01 ppm/°C were obtained for Ce2[Zr0.98(Al1/2Sb1/2)0.02]3(MoO4)9 ceramics sintered at 850 °C for 4 h.

Characterization of structure, chemical bond and microwave dielectric properties in Ca0.61Nd0.26TiO3 ceramic substituted by chromium for titanium

Abstract We studied the phase constitutions, microstructure, chemical bond and microwave dielectric properties for Ca0.61Nd0.26Ti1-xCrxO3 (0 ≤ x ≤ 0.03) ceramics synthesized by solid-state reaction using SEM, X-ray diffractometer, Raman spectroscopy, microwave measuring system, etc. Although the second phase TiO2 appeared when x ≥ 0.015 as presented in XRD patterns, TiO2 was confirmed to have no effects on the tendency of microwave dielectric properties as a function of x value. The SEM images showed that the grain size decreased as Cr content increased, which could be explained by that doping Cr increased the grain boundary energy or decreased surface energy for Ca0.61Nd0.26TiO3 ceramic. The SRO effects enhanced with increase of Cr substitution, which was verified by Raman spectra. The dielectric constant and τf value were concerned with the average ionicity of chemical bond and the ionic polarizability for Ca0.61Nd0.26Ti1-xCrxO3 ceramics. The SEM images suggested that the optimized sintering temperatures was 1400 °C for samples with x = 0.01. The XPS spectra and the trend of Q × f value indicated that the balanced amount of Cr substitution could restrain the generation of Ti3+. Hence, the Q × f value of Ca0.61Nd0.26Ti1-xCrxO3 ceramics reached the maximum of 16,078 GHz at x = 0.01 compared with that of 11,425 GHz in pure Ca0.61Nd0.26TiO3 ceramic.

Relationships among optical and structural characteristics of ABSO4 crystals

We systematize the data for refractive indices and optical birefringences of ABSO4 crystals (A, B = Li, Na, K, NH4, Rb, Cs) and analyze their interrelations with structural and energy-band parameters. Besides of a number of empirical relationships that reveal low correlation coefficients and cannot be used for predictions, we find nearly functional links of the average refractive index n with the average lattice-cell parameter and the ionic radius of alkali cation for most of the ABSO4 crystals. The refractive index n correlates perfectly with the combinations of crystal density and average atomic mass that follow from Gladstone–Dale, Lorentz and Lorentz–Lorenz formulae. Moreover, we obtain a fair correlation of n with the unit-cell volume per one sulphur atom, which is associated with chemical-bond ionicity. We discuss also the links of the refractive index and the birefringence with the bandgap and its anisotropy, which follow from the Moss and Ravindra–Gupta formulae. Resources for ascertaining the birefringence size and availability of a zero-birefringence point in the ABSO4 crystals are poorer, when compared with the case of refractive indices. Our results suggest some physical and practical means for predicting basic optical properties of new materials.

Characterization of microwave dielectric materials NiZrNb2O8 based on the chemical bond theory

Wolframite structure NiZrNb2O8 ceramics were prepared by the solid state reaction method. Sintering characteristics and microwave dielectric properties were investigated under various sintering temperatures ranging from 1100 to 1300 °C. The micro-structure, crystal structure and phase composition were studied by the scanning electron microscopy techniques, X-ray diffraction and energy disperse spectroscopy, respectively. Refinement was used to analyze the crystal structure. Based on the cell parameters, the chemical bond theory was used to calculate the lattice energy, bond ionicity and the coefficient of thermal expansion for the characterization of correlations between properties and structures of NiZrNb2O8 ceramics. The microwave dielectric properties of NiZrNb2O8 were strongly dependent on the chemical bond ionicity, lattice energy and coefficient of thermal expansion. The er values could be strongly dependent on the bond ionicity of the Nb–O bonds. The Q·f values were affected by the lattice energy of Nb–O bonds. As for the τf values, it could be mainly affected by the coefficient of thermal expansion of Ni–O bonds. At the sintering temperature of 1250 °C, NiZrNb2O8 ceramics exhibited the excellent microwave properties of er = 18.84, Q·f = 18, 142 GHz and τf = −35.43 ppm/°C.

Dispersion Properties of (Y0.06GA0.94)2O3 Thin Films

We have studied the refractive index dispersion in (Y0.06Ga0.94)2O3 thin films obtained by high-frequency ion plasma sputtering. We show that the films are formed with mixed orientation, and the maxima of the diffraction patterns correspond to the monoclinic crystal structure of β-Ga2O3. We have established that as for β-Ga2O3 films, we observe anomalous dispersion in the near UV region for (Y0.06Ga0.94)2O3 films annealed in hydrogen, while we observe normal dispersion for films annealed in oxygen or argon. For the studied films with normal dispersion, we compare two single-oscillator approximation models, and we fi nd the parameters of the approximation, the dispersion energy, the chemical bond ionicity, the coordination number, the static refractive index, the characteristic wavelength for UV absorption, and the average oscillator absorption energy. We established that the static refractive index in the studied films increases as the number of oxygen vacancies increases, and that it is inversely proportional to the average oscillator absorption energy.

Characterization of low loss microwave dielectric materials Li3Mg2NbO6 based on the chemical bond theory

The low loss microwave dielectric materials Li3Mg2NbO6 with orthorhombic structure were prepared by the conventional solid-state method. The microwave dielectric properties of Li3Mg2NbO6 ceramics exhibited significant dependence on the sintering conditions, microstructure and compositions. Single phase of Li3Mg2NbO6 could be obtained throughout the range of sintering temperatures. The saturated samples sinterted at 1225 °C for 4 h showed excellent microwave properties of εr value of 14.94, Q·ƒ value of 100,965 GHz and τf value of −21.96 ppm/°C. The chemical bond theory was used to calculate the lattice energy, ionicity energy and the coefficient of thermal expansion for the characterization of correlations between properties and structures of Li3Mg2NbO6 ceramics. The microwave dielectric properties of Li3Mg2NbO6 were strongly dependent on the chemical bond ionicity, lattice energy and coefficient of thermal expansion.

Characterization of crystal structure and microwave dielectric properties of AZrNb2O8 (A=Zn, Co, Mg, Mn) ceramics based on complex bond theory

Single phase AZrNb2O8 (A=Zn,Co,Mg,Mn) ceramics with monoclinic wolframite structure were prepared and characterized by crystalline structure refinement for the investigation on the correlations between crystal structure and microwave dielectric properties. A semiempirical method based on the complex bond theory was used to calculate the bond ionicity, lattice energy, and coefficient of thermal expansion of AZrNb2O8 ceramics. The crystal structure changed with the variation of A site ions and affected the Nb–O octahedral correspondingly. Due to the variation of crystal structure, the observed bond ionicity was helpful to understand the electric polarization. The variation of the Q·ƒ and τƒ values could be attributed to the lattice energy and coefficient of thermal expansion respectively. The microwave properties of AZrNb2O8 ceramics were strongly dependent on the chemical bond ionicity, lattice energy and coefficient of thermal expansion.

Band structures of atomic chains of group IV, III–V, and II–VI elements

The relativistic band structures of AN and ANB8–N chains have been calculated by the linear augmented-cylindrical-wave method, which is an extension of the augmented-plane-wave method for cylindrical polyatomic systems. The band structures of covalent monatomic chains of Group IV elements are characterized by σ(s), π+, and π–, and σ(pz)* bands. The C, Si, Ge, and Sn chains are metallic. There is a considerable difference between the relativistic and nonrelativistic band structures. Because of the cylindrical symmetry of chains in the nonrelativistic model, the π bands crossing the Fermi level are orbitally doubly degenerate (i.e., the π+ and π– band energies are exactly the same). The spin and orbital motion of electrons are coupled in the chains to split π bands, but each π+ and π- band is doubly spin-degenerate. The spin–orbit splitting energy for C and Sn chains varies from 1.7 meV to 0.67 eV. The mass–velocity correction reduces all valence band levels: the level shifts are 2–5 meV for C and up to 2.2 eV for Sn. The Darwin corrections are several-fold lower than the mass–velocity contributions. A sharp change in the band structure is observed in going from covalent to partially ionic chains. The carbon chain has a metallic band structure with a zero gap in the center of the Brillouin zone, and a boron nitride chain is an insulator with an optical gap of 8 eV and optical transitions between the occupied π and vacant π* states at the edge of the Brillouin zone (this is explained by the existence of the antisymmetric component of the electron potential in the BN wire, which mixes even bonding and odd antibonding π states). Going from the BN chain to the AlP, GaAs, and InSb chains is accompanied by a decrease in the chemical bond ionicity, which leads to a gradual decrease in the π–π* gaps.

Correlations of crystal structure, bond energy and microwave dielectric properties of AZrNb2O8 (A = Zn, Co, Mg, Mn) ceramics

The monoclinical structure AZrNb2O8 (A = Zn, Co, Mg, Mn) ceramics were prepared by the conventional solid-state method. The microwave dielectric properties of AZrNb2O8 (A = Zn, Co, Mg, Mn) ceramics exhibited significant dependence on the sintering conditions, microstructure and compositions. The crystalline structure refinement, chemical bond ionicity, lattice energy were carried out to investigate the correlations between the crystalline structure and microwave dielectric properties for AZrNb2O8 (A = Zn, Co, Mg, Mn) ceramics based on the complex bond theory. The effects of A-site cations (Mn, Zn, Mg and Co) at AZrNb2O8 compounds on structural parameters such as packing fraction and B-site octahedral distortion were studied based on Rietveld refinement. Variations in the dielectric constant (εr) were explained by the ionic polarizability of the compositions. The quality factor (Q·ƒ) and temperature coefficient of resonant frequency (τf) were correlated with the packing fraction and B-site octahedral distortions (δ) in these compositions, respectively. Correlations between the microwave dielectric properties and crystal structure, the chemical bond energy were also discussed based on the variation of A-site ions.

The relationship between bond ionicity, lattice energy, coefficient of thermal expansion and microwave dielectric properties of Nd(Nb(1-x)Sb(x))O4 ceramics.

The crystalline structure refinement, chemical bond ionicity, lattice energy and coefficient of thermal expansion were carried out for Nd(Nb(1-x)Sb(x))O4 ceramics with a monoclinic fergusonite structure to investigate the correlations between the crystalline structure, phase stability, bond ionicity, lattice energy, coefficient of thermal expansion, and microwave dielectric properties. The bond ionicity, lattice energy, and coefficient of thermal expansion of Nd(Nb(1-x)Sb(x))O4 ceramics were calculated using a semiempirical method based on the complex bond theory. The phase structure stability varied with the lattice energy which was resulted by the substitution constant of Sb(5+). With the increasing of the Sb(5+) contents, the decrease of Nb/Sb-O bond ionicity was observed, which could be contributed to the electric polarization. The ε(r) had a close relationship with the Nb/Sb-O bond ionicity. The increase of the Q×f and |τ(f)| values could be attributed to the lattice energy and the coefficient of thermal expansion. The microwave dielectric properties of Nd(Nb(1-x)Sb(x))O4 ceramics with the monoclinic fergusonite structure were strongly dependent on the chemical bond ionicity, lattice energy and coefficient of thermal expansion.

The correlations among bond ionicity, lattice energy and microwave dielectric properties of (Nd(1-x)La(x))NbO4 ceramics.

(Nd1-xLax)NbO4 ceramics were prepared via a conventional solid-state reaction route and the correlations among bond ionicity, lattice energy, phase stability and microwave dielectric properties were investigated. The diffraction patterns showed that the (Nd1-xLax)NbO4 ceramics possessed a monoclinic fergusonite structure. The chemical bond ionicity, bond covalency and lattice energy were calculated using the empirical method. The phase structure stability varied with the lattice energy which resulted due to the substitution content of La(3+) ions. With the increase of La(3+) ion contents, the decrease of Nd/La-O bond ionicity was observed, which could be attributed to the electric polarization. εr has a close relationship with the Nd/La-O bond covalency. The increase of the Q × f values and τf values could be attributed to the change in the lattice energy. The microwave dielectric properties of (Nd1-xLax)NbO4 ceramics with a monoclinic fergusonite structure were strongly dependent on the chemical bond ionicity, bond covalency and lattice energy.

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 $$\mathrm{H}_{2}$$ .