Elastic properties of FeSi

Measurements of the sound velocities in a single crystal of FeSi were performed in the temperature range 4-300 K. Elastic constants $C_{12}$ and $C_{44}$ deviate from a quasiharmonic behavior at high temperature; whereas, $C_{12}$ increases anomalously in the entire range of temperature, indicating a change in the electron structure of this materia

Detailed electronic structure studies on superconducting MgB2_2 and related compounds

In order to understand the unexpected superconducting behavior of MgB$_2$ compound we have made electronic structure calculations for MgB$_2$ and closely related systems. Our calculated Debye temperature from the elastic properties indicate that the average phonon frequency is very large in MgB$_2$ compared with other superconducting intermetallics and the exceptionally high $T_c$ in this material can be explained through BCS mechanism only if phonon softening occurs or the phonon modes are highly anisotropic. We identified a doubly-degenerate quasi-two dimensional key-energy band in the vicinity of $E_{F}$ along $\Gamma$-A direction of BZ which play an important role in deciding the superconducting behavior of this material. Based on this result, we have searched for similar kinds of electronic feature in a series of isoelectronic compounds such as BeB$_2$, CaB$_2$, SrB$_2$, LiBC and MgB$_2$C$_2$ and found that MgB$_2$C$_2$ is one potential material from the superconductivity point of view. There are contradictory experimental results regarding the anisotropy in the elastic properties of MgB$_2$ ranging from isotropic, moderately anisotropic to highly anisotropic. In order to settle this issue we have calculated the single crystal elastic constants for MgB$_2$ by the accurate full-potential method and derived the directional dependent linear compressibility, Young's modulus, shear modulus and relevant elastic properties. We have observed large anisotropy in the elastic properties. Our calculated polarized optical dielectric tensor shows highly anisotropic behavior even though it possesses isotropic transport property. MgB$_2$ possesses a mixed bonding character and this has been verified from density of states, charge density and crystal orbital Hamiltonian population analyses

Equation of state and elastic properties of face-centered-cubic FeMg alloy at ultrahigh pressures from first-principles

We have calculated the equation of state and elastic properties of face-centered cubic Fe and Fe-rich FeMg alloy at ultrahigh pressures from first principles using the Exact Muffin-Tin Orbitals method. The results show that adding Mg into Fe influences strongly the equation of state, and cause a large degree of softening of the elastic constants, even at concentrations as small as 1-2 at. %. Moreover, the elastic anisotropy increases, and the effect is higher at higher pressures.Comment: 6 figure

CONFIGURATION-INDEPENDENT ELASTIC INTERACTIONS IN METAL HYDROGEN SOLUTIONS

The authors demonstrate quantitative methods for estimating that part of the elastic interaction energy between defects in solids which does not depend on the precise spatial arrangement of the defects. This energy involves both the total volume change per defect in the finite solid and the purely shear part of the volume change. Several different continuum and atomistic modelling methods are used to calculate these volume changes for H in Pd, V, Nb and Ta. An estimate of the configuration-independent elastic interaction energy is made for the Pd-H system as a function of the H concentration, and is given in a form suitable for comparison with statistical models