Bond Stretching Force Constant Research Articles

Computational study of lattice dynamics and mechanical properties of AlxIn1-xPySbzAs1-y-z/InP under the effect of composition

For the first time, the composition dependence of pentanary AlInPSbAs alloy is described. The effect of composition on the polarity (∝p), mechanical parameters have been calculated for the AlxIn1-xPySbzAs1-y-z alloy. The impact of composition on the internal strain parameter (ζ), bond-bending force constant (α), bond-stretching force constant (β), and sound velocity (v) has been reported. Results from experiments and the investigated properties of the new alloy show a high degree of agreement. In this work, the density function theory (DFT) and the empirical pseudo-potential approach (EPM) with the virtual crystal approximation (VCA) have been used. The outcomes are expected to be used in optoelectronic applications and in understanding the mechanical properties of AlxIn1-xPySbzAs1-y-z alloy.

Atomic scale structure and bond stretching force constants in stoichiometric and off-stoichiometric kesterites.

The deviation from stoichiometry and the understanding of its consequences are key factors for the application of kesterites as solar cell absorbers. Therefore, this study investigates the local atomic structure of off-stoichiometric Cu2ZnSnS4 (CZTS), Cu2ZnSnSe4 (CZTSe) and Cu2ZnGeSe4 (CZGSe) by means of Extended X-ray Absorption Fine Structure Spectroscopy. Temperature dependent measurements yield the bond stretching force constants of all cation-anion bonds in stoichiometric CZTS and CZTSe and nearly stoichiometric CZGSe. Low temperature measurements allow high precision analysis of the influence of off-stoichiometry on the element specific average bond lengths and their variances. The overall comparison between the materials is in excellent agreement with measures like ionic/atomic radii and bond ionicities. Furthermore, the small uncertainties allow the identification of systematic trends in the Cu-Se and Zn-Se bond lengths of CZTSe and CZGSe. These trends are discussed in context of the types and concentrations of certain point defects, which gives insight into the possible local configurations and their influence on the average structural parameters. The findings complement the understanding of the effect of off-stoichiometry on the local structure of kesterites, which affects their electronic properties and thus their application for solar cells.

Novel Bis-1,3,4-Thiadiazoles Derivatives: Synthesis, Spectroscopic Characterization, DFT Calculations and Evaluation of their Antimicrobial and Antioxidant Activities

Two new, bis-1,3,4-thiadiazoles derivatives (I and II), were prepared by cyclization reaction of oxalic acid with N-alkyl/allyl thiosemicarbazides and phosphorous oxychloride (POCl3). Then the newly prepared products screened for their antimicrobial and antioxidant activities. The biological activity results shown that tested compounds exhibited effective antibacterial activity against six different bacteria. However, the compound II demonstrated greater ABTS˙+ scavenging ability. The characterization of the synthesized molecules was done by FT-IR, 1H NMR, 13C NMR spectroscopic methods and elemental analysis. Moreover, the experimental FT-IR and NMR spectra of the molecules were compared with the results calculated at the cc-pvtz, 6-311g(2d,2p), and 6-311++g(2d,2p) levels of theory. The effect of substituted groups on the spectral and electronic properties of the compounds was investigated. NCI and QTAIM analyses were performed to examine the effects of allyl group and intramolecular interactions on σ and π bonds. How the N-H bonds of the substituted groups affect the bond degrees was investigated using Fuzzy, Laplacian and Mayer approaches, and the relationship of the data with the antioxidant properties of the compounds was examined. In addition, the relationship between bond stretching force constant and intrinsic bond strength index, electron density, and delocalization index for some bonds was revealed.

Mechanical and lattice vibrational investigations of nanostructured AlxIn1-xPySbzAs1-y-z alloys

The compositional dependence of the polarities, elastic constants, elastic moduli, Poisson's ratio, and linear compressibility has been computed for zinc blende AlxIn1-xPySbzAs1-y-z alloys with composition y ranging from 0 to 1. Also, the compositional influence of the bond-stretching force constant, bond-bending force constant, internal strain parameter, Cauchy ratio, effective charge, the Born ratio, anisotropy factor, and sound velocity has been determined. The experimental data and the studied properties for the novel studied alloy lattice matched to the InP substrate show a good level of agreement. The empirical pseudo-potential approach and the virtual crystal approximation have been employed in this work. The obtained results are predicted to help understand the elastic characteristics of AlxIn1-xPySbzAs1-y-z and for applications in optoelectronics.

Effect of hydrostatic compression on physical properties of Li2TmSi3 (Tm = Ir, Pt, Rh, Os) with ground-state optical features

Using density functional theory (DFT) the first-principles calculations are employed to systematically investigate the effect of hydrostatic compression on the structural, elastic, electronic, thermal and thermodynamic properties of ternary silicides Li2TmSi3 (Tm = Ir, Pt, Rh, Os) with the ground-state optical features. The gradual decrease of bond length, unit cell volume and a smooth change of c/a with pressure deny the possibility of pressure induced phase transition up to 50 GPa. All the compounds studied here are mechanically stable within the considered pressure range. The constants C11, C12, C13 and C33 exhibit an almost linear increase trend with increase of pressure, while C44 shows anomalous behavior. The bond-stretching and bond-bending force constants are calculated based on the data of elastic constants and their pressure dependent behavior are discussed. Hydrostatic pressure enhances the inherent elastic anisotropy of Li2TmSi3. The ternary silicides studied here cannot be easily compressed under uniaxial stress. The atomic bonds between the nearest neighbors along [001] direction are stronger than those along [100] direction in the whole range of pressure. All ternary silicides except Li2PtSi3 are brittle in nature at ambient pressure. Under elevated pressure all studied compounds show brittle to ductile transition except Li2PtSi3 that exhibits brittle nature under 10 GPa. The shear modulus of Li2OsSi3 shows anomalous change under pressure, which may be attributed from its anomalous change of θD. The higher melting point of all silicides implies that they might have possible uses in harsh environments. The TDOS at EF in Li2TmSi3 decreases almost linearly with pressure. Pressure and temperature dependent thermodynamic properties and ground-state optical functions are described with implications, which may be supportive for further investigation of these compounds through experiments and theories.

Theoretical investigation of thermal disorder in CuCo alloys

In this work, we investigate thermal disorder in intermetallic CuCo alloys by extending the anharmonic correlated Einstein model in extended X-ray absorption fine structure (EXAFS) theory. The expressions of bond-stretching force constants, Einstein frequency and temperature, the atomic mean-square relative displacement characterizing the EXAFS Debye–Waller factor have been derived in terms of Morse potential parameters. We perform numerical calculations for CuCo alloys up to temperature 800 K to study the temperature effects on these thermodynamic quantities. Our research shows that Co–Co bonds are stiffer than Cu–Cu bonds. This leads to the atomic mean-square relative displacement curve of CuCo alloys is lower than the one of Cu metal, but higher than the one of bulk Co. The increasing of Co concentration in CuCo alloys will make the increasing of thermal disorder in the alloy system. Moreover, the dynamic disorder caused by thermal lattice vibrations gives significant contribution to the EXAFS Debye–Waller factor at high temperature.

Bond-stretching force constants and vibrational frequencies in ternary zinc-blende alloys: A systematic comparison of (In,Ga)P, (In,Ga)As and Zn(Se,Te)

We present element-specific effective bond-stretching force constants and Einstein frequencies of (In,Ga)P ternary alloys determined by temperature-dependent extended x-ray absorption fine structure spectroscopy. The bond-stretching force constants of both bond species show a nearly linear composition dependence between the values of GaP and InP. In contrast, the corresponding Einstein frequencies are different for the two bond species over the whole compositional range. Furthermore, we demonstrate that the composition dependence of bond-stretching force constants and Einstein frequencies for (In,Ga)P, (In,Ga)As, and Zn(Se,Te) is mostly caused by the associated bond length changes. Remaining deviations may be explained by coupling effects between different bond species within the alloy.

In Situ Measure of Intrinsic Bond Strength in Crystalline Structures: Local Vibrational Mode Theory for Periodic Systems.

The local vibrational mode analysis developed by Konkoli and Cremer has been successfully applied to characterize the intrinsic bond strength via local bond stretching force constants in molecular systems. A wealth of new insights into covalent bonding and weak chemical interactions ranging from hydrogen, halogen, pnicogen, and chalcogen to tetrel bonding has been obtained. In this work we extend the local vibrational mode analysis to periodic systems, i.e. crystals, allowing for the first time a quantitative in situ measure of bond strength in the extended systems of one, two, and three dimensions. We present the study of one-dimensional polyacetylene and hydrogen fluoride chains and two-dimensional layers of graphene, water, and melamine-cyanurate as well as three-dimensional ice I h and crystalline acetone. Besides serving as a new powerful tool for the analysis of bonding in crystals, a systematic comparison of the intrinsic bond strength in periodic systems and that in isolated molecules becomes possible, providing new details into structure and bonding changes upon crystallization. The potential application for the analysis of solid-state vibrational spectra will be discussed.

Anharmonic correlated Debye model for thermal disorder in iron-rich B2-FeAl intermetallic alloy

The anharmonic correlated Debye model has been developed to investigate the thermal disorder in B2-type FeAl intermetallic alloy. We derive analytical expressions of the bond-stretching force constants, the Debye temperature and frequency, the atomic mean-square displacement and the first three extended X-ray absorption fine structure (EXAFS) cumulants. Numerical calculations of these thermodynamic quantities have been performed for B2-type Fe-40 at.%Al up to temperature 1300 K using the Morse potential whose parameters were derived within the Möbius lattice inversion scheme. Our research shows that the anharmonicity contributions of thermal lattice vibrations are important to the EXAFS cumulants at high temperature. The theoretical predictions are compared with available experimental data when possible to verify the developed anharmonic correlated Debye model.

Bond-strength inversion in (In,Ga)As semiconductor alloys

The atomic-scale structure and vibrational properties of semiconductor alloys are determined by the energy required for stretching and bending the individual bonds. Using temperature-dependent extended x-ray absorption fine-structure spectroscopy, we have determined the element-specific In-As and Ga-As effective bond-stretching force constants in (In,Ga)As as a function of the alloy composition. The results reveal a striking inversion of the bond strength where the originally stiffer bond in the parent materials becomes the softer bond in the alloy and vice versa. Our findings clearly demonstrate that changes of both the individual bond length and the surrounding matrix affect the bond-stretching force constants. We thus show that the previously used common assumptions about the element-specific force constants in semiconductor alloys do not reproduce the composition dependence determined experimentally for (In,Ga)As.

Influence of composition, temperature and pressure on the optoelectronic and mechanical properties of InPxSb1-x alloys

A detailed study of the effect of composition, temperature and pressure on the mechanical and optoelectronic properties of InPxSb1-x alloys has been reported. The calculations have been done using pseudo-potential method (EPM) within the improved virtual crystal approximation (VCA), where the compositional disorder effect is taken into account. Our results for the elastic constants, elastic moduli, Poisson's ratio, bond stretching force constant, bond bending force constant, internal strain parameter, linear compressibility, Cauchy ratio, and anisotropy factor are successfully calculated and compared with the available published data.

Comparative studies of structure, spectroscopic properties and intensity parameters of tetragonal rare earth vanadate nanophosphors doped with Eu(III)

Hydrothermal method was applied in order to synthesize nanocrystalline YVO4, LaVO4 and GdVO4 materials doped with Eu3+ ions. The conditions of synthesis were chosen to allow control of the process based on precipitation reaction in an autoclave, at elevated temperature and pressure. The prepared materials crystallized as single phase spherical-like nanocrystals of the tetragonal I41/amd structure. The average size of the particles was in the range of 7–10 nm in the YVO4- and GdVO4-based products and about 32 nm when LaVO4 was the host compound. The excitation spectra of the materials prepared revealed a broad and intense band in the UV region. The band resulted from charge transfer phenomena: excitation of the VO43+ groups was followed by the energy transfer to Eu3+ ions. Intense, red emission of the samples was a result of electronic transitions in Eu3+ dopant ions. The theoretical Judd-Ofelt intensity parameters Ωλ, obtained using the novel approach to the calculation of Eu-O bond stretching force constant and subsequently charge factors, were compared to the experimental Ωλ. Forced electric dipole part of Ωλ was calculated from scratch (using Eu3+ coordination geometry in REVO4 from DFT calculations), while a single parameter in the dynamic coupling part was fitted to the experimental data. The issues related to the force constant calculation are discussed. Crucial influence of crystal lattice distortions on Ωλ and Eu3+ emission intensities of the materials was shown.

Preparation, structural characterization and biological studies of some new levofloxacin metal complexes

A new series of metal complexes of Ti(IV), V(IV), Y(III), Zr(IV), Ce(IV) and U(VI) with levofloxacin (Levo) were synthesized and characterized by elemental analysis, molar conductivity, magnetic moment measurements, UV–Vis, FT-IR and 1H NMR, XRD as well as TG-DTG techniques. The data indicated that levofloxacin reacts as a bidentate ligand chelate to the metal ion through the pyridone oxygen and one carboxylato oxygen. The thermal dehydration and decomposition of the complexes were studied kinetically using Coats–Redfern and Horowitz–Metzger methods, and the thermodynamic data reflected the thermal stability for all complexes. The calculated bond length and the bond stretching force constant, F(U=O), values for UO2 bond are 1.86 A and 690.67 N m−1. The biological activities of the levofloxacin, meta-salts and their metal complexes were assayed against different bacterial and fungal species as well as their effect on degradation of calf thymus DNA.

On Estimating the G-peak shift in graphene Raman spectra

The frequency shift of the Raman G peak of epitaxial graphene due to the interaction with a substrate described by effective bond force constant k is investigated using the model of two coupled oscillators. The relative G-peak shift is shown to be Δω(G)/ω(G) ∝ k/k0g, where k0g is the bond-stretching force constant of single-layer graphene. Assuming k ∝ P and k ∝–T, where P and T are the pressure and temperature, and the k variation to be dominant, we qualitatively explain the experimental dependences of Δω(G) on P and T. The effect of the substrate on the G-peak broadening in epitaxial graphene is discussed.

New insights from the relation between lattice energy and bond stretching force constant in simple ionic compounds

Lattice energy and bond stretching force constant are two quantities considered in many fields of chemistry and physics. Both quantities can be used to describe the stability or reactivity of a simple system. In the present study, by inspecting the correlation between lattice energies and bond stretching force constants for some sets of simple ionic molecules having similar bonding type, we present simple and useful equations to estimate the bond stretching force constants of simple ionic compounds. In order to determine lattice energies taken into account in this study, Born–Haber–Fajans (BHF) thermochemical cycle and lattice energy equations proposed by Jenkins and Kaya were used. It is shown that bond force constant of a simple ionic compound can be easily calculated in agreement with its spectroscopic counterpart through its lattice energy value. Percentage deviation values determined considering calculated and observed bond stretching force constants for the tested ionic compounds are pretty small except of some molecules like cesium halides (CsF, CsCl, CsBr). Such small values of percentage deviation probe the reliability and validity of the correlation between lattice energy and bond stretching force constant.

Inter atomic force constants of binary and ternary tetrahedral semiconductors

In this paper, we present the expressions relating the inter atomic force constants like as bond-stretching force constant (α in N/m) and bond-bending force constant (β in N/m) for the binary (zinc blende structure) and ternary (chalcopyrite structure) semiconductors with the product of ionic charges (PIC) and crystal ionicity (fi). Interatomic force constants of these compounds exhibit a linear relationship; when plot a graph between Interatomic force constants and the nearest neighbor distance d (A) with crystal ionicity (fi), but fall on different straight lines according to the product of ionic charges of these compounds. A fairly good agreement has been found between the observed and calculated values of the α and β for binary and ternary tetrahedral semiconductors.

A novel method for the calculation of bond stretching force constants of diatomic molecules

Chemical hardness is one of the chemical reactivity descriptors of chemical species and this concept has widely benefited from the development of Density Functional Theory (DFT). In the present report, chemical hardness values for approximately fifty diatomic molecules have been calculated using a new molecular hardness (ηM) equation derived by us in recent times. Then, correlation between force constant (k) and chemical hardness for the above mentioned diatomic molecules that situate hydrides, halides, oxides and sulfides among them has been investigated. Consequently, a relation that can be presented by a simple equation between chemical hardness with bond stretching force constants has been found.

Synthesis, Spectral, Characterization, DFT and Biological Studies of New 3-[(3-Chlorophenyl)-hydrazono]-pentane-2,4-dione Metal Complexes

A new series of metal complexes of V(IV), Pd(II), Pt(IV), Ce(IV) and U(VI) with 3-[(3-chlorophenyl)-hydrazono]-pentane-2,4-dione (Cphpd) were synthesized and characterized by elemental analysis, molar conductivity, magnetic moment measurements, UV-vis, FT-IR and <TEX>$^1H$</TEX> NMR as well as TG-DTG techniques. The data indicated that the Cphpd acts as a bidentate ligand through the hydrazono nitrogen and one keto oxygen. The kinetic parameters have been evaluated by using Coats Redfern (CR) and Horowitz-Metzeger (HM) methods. The thermodynamic data reflected the thermal stability for all complexes. The calculated bond length and the bond stretching force constant, F(U=O), values for <TEX>$UO_2$</TEX> bond are <TEX>$0.775{\AA}$</TEX> and <TEX>$286.95Nm^{-1}$</TEX>. The bond lengths, bond angles, dipole moment and the lowest energy model structure of the complexes have been determined with DFT calculations. The antimicrobial activity of the synthesized ligand and its complexes were screened.

Preparation and characterization of new tetradentate Schiff base metal complexes and biological activity evaluation

A new Schiff base (N,N′-ethylene (bis 1-cyclopropyl-6-fluoro-4-oxo-7-(piperazine-1-yl)-quinoline-3-carboxylic acid) and its Zn(II), Zr(IV), Ce(IV) and U(VI) complexes were synthesized and characterized by elemental analysis, molar conductance, IR, UV–Vis, 1H NMR spectra, magnetic moment, thermal analysis as well as mass spectra. The IR results demonstrate that the tetradentate binding mode of the ligand involving azomethine nitrogen and carboxylato oxygen atoms. The calculated bond length and the bond stretching force constant, F(UO), values for UO2 bond are 1.744Å and 654.49Nm−1. The antimicrobial activity of the synthesized ligand and its complexes were screened and the results showed that the metal complexes were found to be more active than free ligand.

Structural properties of binary semiconductors

Using the plasma oscillations theory of solids, 2 empirical relations have been proposed for the calculation of the structural properties such as bond-stretching central force constant (α) and bond-bending non-central force constant (β) for II-VI and III-V group binary semiconductors. We find that α =D (N›ωp) 2 and β = S (N›ωp) 2, where D and S are constants. The numerical values of D and S are respectively, 0.151 and 0.016 for II-VI and 0.177 and 0.031 for III-V group binary semiconductors. The structural properties of binary semiconductors exhibit a linear relationship when plotted on a log-log scale against the plasmon energy N›ωp (in eV), which lies on the straight lines. We have applied the proposed empirical relations on these binary semiconductors and found a better agreement with the experimental data as compared to the values evaluated by earlier researchers. Key words: Plasmon energy, structural properties, III-V and II-VI Semiconductors.