Elastic properties and spectroscopic studies of lithium lead borate glasses

Elastic properties of xLi₂O — 20PbO — (80-x)B₂O₃ glasses have been measured at a frequency of 10 MHz using X-cut and Y-cut quartz transducers. The trends in the variation of elastic moduli, Poisson’s ratio and Debye temperature have been studied. The elastic moduli namely longitudinal and young’s modulus show strong linear dependence while bulk and shear modulus vary marginally as a function of Li₂O concentration. The Poisson’s ratio is found to be almost constant and Debye temperature increases with the increase of Li₂O concentration. IR, MAS-NMR and glass transition temperature studies have been also carried out. Glass transition temperature is found to increase with increase of Li₂O concentration. IR and MAS-NMR spectra show characteristic features of borate network and systematic change as a function of Li₂O concentration. The variation in the elastic properties and structural features of IR and MAS-NMR indicate that Pb²⁺ ions are likely to occupy network forming positions in this glass system. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

Relation of Poisson’s ratio on average with Young’s modulus. Auxetics on average

A linear relation between the Poisson’s ratio averaged along the transverse directions and Young’s modulus of the tensed cubic crystal is established. It is found that the coefficients of the linear relation in the dimensionless form depend on two dimensionless elastic parameters combined from three compliance coefficients. By virtue of this fact, the form of angular regions of the crystal orientation with negative Poisson’s ratio on average varies as the magnitude of one dimensionless coefficient and the sign of the other one. We find the critical value of the dimensionless parameter at which there is the topological change in the structure of the angular regions occurs is established.     

Elastic properties of graphene: The Keating model

The elastic properties of graphene have been described in terms of the Keating model. It has been shown that the two-dimensional structure of graphene is described by two independent elastic constants, like an isotropic solid. The Young’s modulus and the Poisson’s ratio have been determined. The results are compared with the experimental data obtained for graphite.     

Elastic constants of lead-bismuth alloys

A study of ultrasonic velocities and internal friction has been carried out in Pb-Bi alloys in the concentration range of 0 to 49.5 atomic % Bi using the composite oscillator technique. From the velocity and density data a set of elastic constants namely, Young’s modulus, rigidity modulus, bulk modulus and Poisson’s ratio are estimated. The results are interpreted in terms of the phase changes occurring in the alloy system. Internal friction is found to be more sensitive than the elastic constants to the phase changes.     

Concentration dependences of the elastic constants of the two-dimensional graphene-silicene system

The concentration dependences of the elastic constants of the two-dimensional Si _x C_{1 − x} system have been investigated with the use of the Harrison bonding-orbital method and the Keating model. The central and non-central force constants and the Grüneisen parameter have been considered by means of the bonding-orbital method. All quantities under consideration have been shown to exhibit a nonlinear behavior during the transition from graphene to silicene. A nontrivial role of the short-range repulsion has been discussed. The second-order and third-order elastic constants, the pressure dependences of the second-order elastic constants, as well as the Poisson’s ratio and Young’s modulus have been investigated in the Keating model. It has been found that the elastic constants and Young’s modulus change almost linearly upon the transition from graphene to silicene, whereas the other quantities under consideration exhibit nonlinearity.     

Relation between the Grüneisen ratio and the pressure dependence of Poisson's ratio for metals

The Grüneisen ratio of crystalline solids is shown to be dependent on a parameter n whose values are characteristic of each solid, and can be determined by two independent ways: from experimental shock data and from the pressure derivative of Poisson's ratio. The determinations are made for several metals, using data on the pressure derivatives of polycrystalline elastic moduli or of the second order elastic constants measured on single crystals, and giving the pressure derivatives of Poisson's ratio by means of the Voigt-Reuss-Hill averaging procedure. The values of the parameter n deduced from shock data are found to be in good agreement with those deduced from the pressure derivatives of Poisson's ratio. Positive and negative values of parameter n correspond respectively to increasing and decreasing Poisson's ratio with increasing pressure. Discussion of the results is made using the linear and the quadratic relationships between shock velocity and particle velocity. It is shown that shock wave data cannot yield directly an accurate estimation of the derivative of the initial slope of the Hugoniot.     

Effect of rare earth (Pr2O3, Nd2O3, Sm2O3, Eu2O3, Gd2O3 and Er2O3 ) on the acoustic properties of glass belonging to bismuth-borate system

Bismuth-borate glasses doped with some rare earth ions were studied with respect to the density, molar volume and the elastic moduli, Poisson’s ratio, Debye temperature, microhardness, softening temperature, acoustic impedance, diffusion constant and latent heat of melting. Ultrasonic velocities were measured by the pulse echo overlap technique at a frequency of 10 MHz and at room temperature. From these velocities and density values, various elastic moduli were calculated. The correlation of elastic stiffness, the cross link density, and the fractal bond connectivity of these glasses are discussed. The derived experimental values of shear modulus, bulk modulus, Young’s modulus, and Poisson’s ratio for our glasses are compared with the theoretically calculated values in terms of the bond compression model and Makishima-Mackenize theory.     

Ab initio calculation of the electronic structure,Fermi surface,and elastic properties of the new 7.5-K superconductor Nb<Subscript>2</Subscript>InC

Ab initio calculations were performed to investigate electronic and elastic properties of the newly discovered 7.5 K superconductor: layered Nb₂InC. As a result, electronic bands, total and site-projected l—decomposed density of states at the Fermi level, shape of the Fermi surface for Nb₂InC were obtained for the first time. Besides, independent elastic constants, bulk modulus, compressibility, shear modulus, Young’s modulus, Poisson’s ratio together with the elastic anisotropy parameters and indicator of brittle/ductile behavior of Nb₂InC were evaluated and analyzed in comparison with the available data.     

Poisson ratio and plasticity of glasses

Analysis of experimental data reveals a regular relation between Poisson’s ratio and plastic characteristics of inorganic glasses.     

Calculated structural, electronic and elastic properties of M2GeC (M=Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W)

Using ab initio calculations, we have studied the structural, electronic and elastic properties of M₂GeC, with M=Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W. Geometrical optimizations of the unit cell are in agreement with the available experimental data. The band structures show that all studied materials are electrical conductors. The analysis of the site and momentum projected densities shows that bonding is due to M d-C p and M d-Ge p hybridizations. The elastic constants are calculated using the static finite strain technique. The shear modulus C ₄₄, which is directly related to the hardness, reaches its maximum when the valence electron concentration is in the range 8.41–8.50. We derived the bulk and shear moduli, Young’s moduli and Poisson’s ratio for ideal polycrystalline M₂GeC aggregates. We estimated the Debye temperature of M₂GeC from the average sound velocity. This is the first quantitative theoretical prediction of the elastic constants of Ti₂GeC, V₂GeC, Cr₂GeC, Zr₂GeC, Nb₂GeC, Mo₂GeC, Hf₂GeC, Ta₂GeC and W₂GeC compounds, and it still awaits experimental confirmation.     

Hydrostatic pressure and thermal loading induced long-term optical effects in tightly jacketed double-coated optical fibers

By the viscoelastic theory, the hydrostatic pressure and thermal loading simultaneously induced optical effects in tightly jacketed double-coated optical fibers in the long term are analyzed. Using the Laplace transformation method, close-form solutions for the microbending loss and refractive index changes are obtained in the transform domain. The results of the microbending loss are initially identical to those obtained by the elastic analysis, and then decrease gradually as time progresses. The microbending loss and refractive index changes of the glass fiber are functions of material properties of the coating layers and jacket. To minimize the microbending loss and refractive index changes in the long term, the viscosity ratio η₃/η₁, Young’s modulus ratio E₂/E₁ and E₃/E₁, and ratio of Poisson’s ratio ν₃/ν₁ should be increased. Nevertheless, the ratio of Poisson’s ratio ν₂/ν₁ should be decreased. PACS 42.79.Wc; 61.20.Lc; 68.65.Ac     

Elastic moduli of nc-TiN/a-Si3N4 nanocomposites: Compressible, yet superhard

Earlier measurements of elastic moduli of nc-TiN/a-Si₃N₄ nanocomposites of different composition and hardness by means of vibrating reed and surface Brillouing scattering, that yield Young’s and shear modulus, as well as the Poisson’s ratio, have been confirmed by high-pressure X-ray diffraction measurements, that yield bulk modulus. It is found that elastic moduli of all measured samples are essentially the same within relatively small error of measurements, and only slightly lower than that of pure TiN. The nanocomposites are superhard thanks to their unique nanostructure with strengthened SiN_x interface.     

Structural, electronic and elastic properties of Ti2TlC, Zr2TlC and Hf2TlC

Using First-principle calculations, we have studied the structural, electronic and elastic properties of M₂TlC, with M = Ti, Zr and Hf. Geometrical optimization of the unit cell is in good agreement with the available experimental data. The effect of high pressures, up to 20 GPa, on the lattice constants shows that the contractions are higher along the c-axis than along the a axis. We have observed a quadratic dependence of the lattice parameters versus the applied pressure. The band structures show that all three materials are electrical conductors. The analysis of the site and momentum projected densities shows that bonding is due to M d-C p and M d-Tl p hybridizations. The M d-C p bonds are lower in energy and stiffer than M d-Tl p bonds. The elastic constants are calculated using the static finite strain technique. We derived the bulk and shear moduli, Young’s modulus and Poisson’s ratio for ideal polycrystalline M₂TlC aggregates. We estimated the Debye temperature of M₂TlC from the average sound velocity. This is the first quantitative theoretical prediction of the elastic properties of Ti₂TlC, Zr₂TlC, and Hf₂TlC compounds that requires experimental confirmation.      

Ultrasonic measurement of the elastic properties of benzoyl glycine single crystals

Certain organic crystals are found to possess high non-linear optical coefficients, often one to two orders of magnitude higher than those of the well-known inorganic non-linear optical materials. Benzoyl glycine is one such crystal whose optical second-harmonic generation efficiency is much higher than that of potassium dihydrogen phosphate. Single crystals of benzoyl glycine are grown by solvent evaporation technique usingN, N-dimethyl formamide as the solvent. All the nine second-order elastic stiffness constants of this orthorhombic crystal are determined from ultrasonic wave velocity measurements employing the pulse echo overlap technique. The anisotropy of elastic wave propagation in this crystal is demonstrated by plotting the phase velocity, slowness, Young’s modulus and linear compressibility surfaces along symmetry planes. The volume compressibility, bulk modulus and relevant Poisson’s ratios are also determined. Variation of the diagonal elastic stiffness constants with temperature over a limited range are measured and reported.     

DSC and elastic moduli studies on tellurite-vanadate glasses containing antimony oxide

xSb₂O₃-40TeO₂-(60 − x) V₂O₅ glasses with 0 ≤ x ≤ 10 (in mol%) have been prepared by rapid- melt quenching method. DSC curves of these ternary glasses have been investigated. The glass transition properties that have been measured and reported in this paper, include the glass transition temperature (T _g ), glass transition width (ΔT _g ), heat capacity change at glass transition (ΔC _P ) and fragility (F). Thermal stability, Poisson’s ratio, fragility and glass forming tendency of these glasses have been estimated, to determine relationship between chemical composition and the thermal stability or to interpret the structure of glass. In addition, Makishima and Makenzie’s theory was applied for determination of Young’s modulus, bulk modulus and shear modulus, indicating a strong relation between elastic properties and structure of glass. Generally, results of this work show that glass with x = 0 has the highest shear, bulk and Young’s moduli which make it as suitable candidate for the manufacture of strong glass fibers in technological applications; but it should be mentioned that glass with x = 8 has higher handling temperature and super resistance against thermal attack.     

Eigenmodes of a cylindrical cavity in a solid body

We determine the characteristics (eigenfrequencies and radiation Q-factors) of elastic oscillations existing at the boundary of a cylindrical cavity in a solid body. These oscillations become Rayleigh waves with increasing cavity radius. It is shown that such oscillations in bodies with moderate Poisson’s ratios (about 0.2–0.3) can exist in the case of sufficiently large cavity diameters exceeding 100 Rayleigh wave lengths. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 12, pp. 1051–1055, December 2006.     

Band parameters of α-LiBeN semiconductor from density functional calculations

The structural, elastic, electronic, optical and thermal properties of α phase in LiBeN semiconductor have been studied using pseudo-potential plane wave method based on the density functional theory. The computed lattice parameter agrees well with previous theoretical work. The elastic constants and their pressure dependence are predicted using the static finite strain technique. A set of isotropic elastic parameters and related properties, namely bulk and shear moduli, Young’s modulus, Poisson’s ratio, average sound velocity and Debye temperature are numerically estimated in the frame work of the Voigt–Reuss–Hill approximation for α-LiBeN polycrystalline aggregate. The assignments of the structures in the optical spectra and band structure transitions have been examined and discussed. The thermal effect on heat capacities is investigated by the quasi-harmonic Debye model. To the best of our knowledge, most of the studied properties of the material of interest are reported for the first time.     

Elastic properties of mono- and poly-crystalline PbO-type FeSe1−xTex (x = 0–1.0): A first-principles study

The structural parameters of the alloys are obtained as non-magnetic cases for which justification is provided. The elastic coefficients and various moduli of the monocrystalline FeSe_1−xTe_x system as a function of doping are predicted for the first time using density functional method. The bulk moduli, shear moduli, Young’s moduli, Poisson’s ratios, velocities of sound and Debye temperature of the corresponding poly-crystalline aggregates have been calculated and the results discussed.     

Sound transmission across orthotropic laminates with a 3D model

This investigation examines the propagation of elastic waves in orthotropic materials to explain the sound insulation of FRP (Fiber Reinforced Plastics). The mechanical characteristics of an orthotropic material generally require nine independent parameters: three Young’s moduli, three shear moduli and three Poisson’s ratios. Three-dimensional analysis is performed with the elastic wave equations of an orthotropic material. The transfer matrix method which expresses the relationship between stress and velocity is adopted to calculate the sound transmission loss across an orthotropic material. Further, the transfer matrix method can only be calculated under the continuous boundary condition in the interface of each FRP layer. The boundary conditions which are indicated above are velocity and stress. The numerical results are compared with the experimental results. Additionally, along with varying material properties such as Young’s modulus, the acoustical properties of the orthotropic material are explained and discussed later.     

Empirical modeling of longitudinal tension and compression of graphene nanoparticles and nanoribbons

Longitudinal tension and compression of graphene nanoparticles and nanoribbons have been studied using an empirical model. The pseudo-Young’s modulus of graphene nanoparticles and nanoribbons has been calculated. The size effect, i.e., the dependence of the elastic modulus on linear parameters of graphene objects, has been studied. An increase in pseudo-Young’s modulus discontinues as the length increases during the nanoparticle-to-nanoribbon transition. For the same perimeter, the graphene ribbon edges are characterized by smaller pseudo-Young’s moduli in comparison with uniaxial carbon nanotubes. Elastic deformation of graphene nanoparticles and nanoribbons has been observed in the relative length variation range of 0.93–1.12.