Density functional study of thermodynamic properties, thermal expansion and lattice thermal conductivity of Fe$_{2}$VAl at high temperature region

Here, we present the phonon calculations for thermodynamic properties, thermal expansion and lattice thermal conductivity of Fe$_{2}$VAl in the temperature range of $300-800$ K and compared with existing experiment. Phonon dispersion is computed using finite displacement method and supercell approach. The positive frequencies of all the phonon modes indicate the mechanical stability of the compound. The specific heat at constant volume and Helmholtz free energy are calculated under harmonic approximation, while calculation of thermal expansion is done under quasi-harmonic approximation. Lattice thermal conductivity ($κ_{L}$) is calculated using first-principle anharmonic lattice dynamics calculations. The zero-point energy and Debye temperature are computed as $\sim$21 kJ/mol and 638 K, respectively. The calculated thermal expansions are found to be $\sim$6.3 $\times$ 10$^{-6}$ K$^{-1}$ and $\sim$7.2 $\times$ 10$^{-6}$ K$^{-1}$ at 300 and 800 K, respectively. A significant deviation between calculated ($\sim$48.6 W/m-K) and experimental ($\sim$22.8 W/m-K) values of $κ_{L}$ are observed at 300 K. But, as the temperature increases, the calculated and experimental $κ_{L}$ come closer with the corresponding values of $\sim$18.2 W/m-K and $\sim$11.0 W/m-K at 800. The possible reasons for the deviation of $κ_{L}$ are addressed. The temperature dependent of phonon lifetime is computed in order to understand the feature of $κ_{L}$. Present study suggests that DFT based phononic calculations provide reasonably good explanations of available experimental phonon related properties of Fe$_{2}$VAl in the high temperature range of $300-800$ K.

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