Estimation Of Elastic Constants Research Articles

High Pressure-Temperature study on thermodynamics, half-metallicity, transport, elastic and structural properties of Co-based Heusler alloys: A first-principles study

Employing first-principles based on density functional theory, we have investigated thermodynamics, half-metallicity, transport, elastic and structural properties of Co2ScSb and Co2TiSb full-Heuslers at high temperature and pressure. The existence of perfect band structure and density of states through the modified version of Becke Johnson (mBJ) system delivers more precise and accurate results rather than GGA and GGA ​+ ​U for both these Heuslers. Structural optimizations support the stability in AlCu2Mn-prototype with space symmetry of Fm3−m (#225) space group in both these alloys. The density of states and band occupation describes the semiconducting nature. Co2ScSb and Co2TiSb possess an indirect band-gap of 1.08 ​eV and 1.32 ​eV respectively. The estimation of elastic constants and its other associated mechanical constituents exhibits ductile behavior along with high melting temperature. The thermoelectric coefficients are used to check the applicability of the material for waste heat recovery systems and technological purposes. Thermodynamic potentials which include heat capacity, thermal expansion and Grüneisen parameter have been keenly predicted by employing quasi harmonic Debye model to exhibit its stability at high temperature and pressure varying conditions. Hence, the overall theme of this current study creates an application stand in spintronics, power generation as well as green energy sources for future technologies.

Ab-initio DFT based investigation of double perovskite oxide Ba2CdOsO6 with cubic structure

Electronic structure, magnetic, mechanical and thermodynamic properties of perovskites oxide Ba2CdOsO6 have been calculated within well know density functional theory via full potential linearized augmented plane wave (FP-LAPW) method. The structural study discloses ferromagnetic phase stability with a magnetic moment equal to integer value of 2 μB. The spin polarized band structure and density of states present half-metallic nature for the compound. The mechanical stability has also been determined by the estimation of elastic constants. From the calculated elastic constants mechanical properties like Shear modulus (G), Youngs modulus (Y) Poisson ratio (ν), anisotropic factor (A) etc have been estimated. The calculated Pugh's ratio and Cauchy pressure both characterize this material as ductile. The effect of pressure and temperature on thermodynamic properties like heat capacity, thermal expansion, Grüneisen parameter and Debye temperature have been analyzed via quasi harmonic Debye model.

On the Relationship between Structural-Elastic Properties of Co-Zn Ferrites at 300 K

The structural - elastic properties correlations have been studied for polycrystalline spinel ferrite system, ZnxCo1-xFe2O4, x = 0.0-0.6, at 300 K. The cation distribution formulae determined from X-ray diffraction line intensity calculations are used to calculate bulk modulus (Ko) in particular and Young′s modulus (E0), rigidity modulus (G0), longitudinal modulus (L0) and Lame′s constant (λL0) in general. The longitudinal wave velocity (Vl0) and transverse wave velocity (Vso) computed from empirical relation based on X-ray density and mean atomic weight is used to calculate L0 and G0 respectively. The applicability of the heterogeneous metal mixture rule for theoretical estimation of elastic constants has been tested. The results are compared with elastic moduli determined from conventional ultrasonic pulse transmission technique and causes for the observed difference between the two have been discussed.

Estimation of Elastic Constants of Restoration Mortars, Used on Historic Masonries Restoration Interventions, VIA Ultrasonic Technique and Correlation to their Mechanical and Microstructure Parameters

ABSTRACTEight syntheses of mortars used for restoration interventions in historic masonry were produced using the traditional materials of aerial lime and artificial pozzolanic additives. The mortars were aged over a 15-month period and then tested for properties related to chemical and mechanical stabilization using the following four analytical techniques: ultrasonic velocity propagation and the mortars' dynamic modulus of elasticity (Ed), mercury intrusion porosimetry for evaluation of microstructural characteristics (percentage open porosity, bulk density, average pore radius, total cumulative volume, and specific surface area), water capillary rise tests for the determination of total cumulative volume accessible to water and capillary rise coefficients of the mortars, and conventional mechanical tests for the determination of the mortars' flexural and compressive strength. Performance is correlated to the mortars' chemical composition, microstructural characteristics (as measure by average pore radius) and mechanical characteristics as measured by dynamic modulus of elasticity (Ed) and flexural and compressive strength (Fc).

Atomic Force Pulling: Probing the Local Elasticity of the Cell Membrane

A novel approach based on atomic force microscopy (AFM) for exploring the elastic properties of the membrane-skeleton complex in living cells is presented. Three major elements constitute the basis for the proposed method: (a) Pulling the cell membrane by increasing the adhesion of the tip to the cell surface provided by the appropriate tip modification; (b) Measuring force-distance curves with the emphasis on the selection of the appropriate withdraw regions for analysis; and (c) Fitting of the theoretical model based on the bending deformation of an elastic plate to the experimental curve in the withdraw region, prior to the detachment point of the tip from the cell membrane. This approach, applied to human erythrocytes, suggests a complementary technique to the commonly used indentation method. The presented method enables us to avoid certain important problems relating to the measurements of elastic characteristics of biological objects by the indentation technique. Firstly, in the range of the pulling technique, it is not necessary to define a “point of contact”. A spurious definition of this point can produce significant errors in the estimation of elastic constants. Secondly, the problem of interference with the substrate is eliminated in the AFM pulling technique. The last feature is important when probing the elastic properties of thin soft samples like a thin flat cells or protein layers.

Estimation of Elastic Constants from Surface Acoustic Wave Velocity by Inverse Analysis using the Downhill Simplex Method

The measurement of surface acoustic wave (SAW) velocity is used to estimate the surface properties because the velocity depends on the elastic properties near the surface. To estimate the elastic constants, we developed a new inverse method combining the Monte Carlo method and the downhill simplex method. The initial values are determined using many random numbers, instead of an arbitrarily chosen several sets of values, in order to reduce the risk of trapping by the local pseudo minima. We confirm that the estimated elastic constants agree well with the reported elastic constants of Si and the experimental SAW velocity is quite well reproduced. We estimate the elastic constants of quartz for application purposes.

Local volume potentials for actinide metals

We have generated preliminary local volume potentials with a self-looping fitting procedure for the actinide metals thorium and plutonium based on the available experimental data of their cohesions and lattice constants and estimates of elastic constants and vacancy energies. This effort is an attempt to model the mechanical and transport properties and the stability of phases of these actinide metals under various pressures and temperatures. The successes and deficiencies will be discussed.

Estimation of Elastic Constants, Mass Density and Thickness of Thin Films from SAW Velocity Dispersion

The paper describes a method of estimating the elastic constants, mass density and thickness of a thin film fabricated on a substrate. The method is substantially based on fitting simplified theoretical SAW velocity dispersion to experimental dispersion data by non-linear least squares. The result has shown that when the film thickness is large, or when the film thickness or the longitudinal wave velocity is known, other material constants can be estimated without much difficulty.

Lattice dynamics and inelastic neutron scattering from forsterite, Mg2SiO4: Phonon dispersion relation, density of states and specific heat

Magnesium-rich olivine (Mg0.9Fe0.1)2SiO4 is considered to be a major constituent of the Earth's upper mantle. Because of its major geophysical importance, the temperature and pressure dependence of its crystal structure, elastic and dielectric constants, long-wavelength phonon modes and specific heat have been measured using a variety of experimental techniques. Theoretical study of lattice dynamics provides a means of analyzing and understanding a host of such experimental data in a unified manner. A detailed study of the lattice dynamics of forsterite, Mg2SiO4, has been made using a crystal potential function consisting of Coulombic and short-range terms. Quasiharmonic lattice dynamical calculations based on a rigid molecular-ion model have provided theoretical estimates of elastic constants, long-wavelength modes, phonon dispersion relation for external modes along the three high symmetry directions in the Brillouin zone, total and partial density of states and inelastic neutron scattering cross-sections. The neutron cross-sections were used as guides for the coherent inelastic neutron scattering experiment on a large single crystal using a triple axis spectrometer in the constant Q mode. The observed and predicted phonon dispersion relation show excellent agreement. The inelastically scattered neutron spectra from a powder sample have been analyzed on the basis of a phonon density of states calculated from a rigid-ion model, which includes both external and internal modes. The experimental data from a powder sample show good agreement with the calculated spectra, which include a multiphonon contribution in the incoherent approximation. The computed phonon densities of states are used to calculate the specific heat as a function of temperature using both the rigid molecular-ion and rigid ion models. These results are in very good agreement with the calorimetric measurement of the specific heat. The interatomic potential developed here can be used with some confidence to study physical properties of forsterite as a function of pressure and temperature.