Density functional theory study of the structural, mechanical and thermal conductivity of uranium dialuminide (UAl2)

Abstract

In this work, we present a systematic study on the structural, mechanical, and thermal conductivity of uranium dialuminide (UAl2) using the ab initio calculation, based on the density functional theory (DFT). The structural and mechanical properties such as the volume expansion, thermal expansion coefficient, density variation and the bulk modulus of UAl2 as a function of temperature (between 300 K and 1500 K) are evaluated within quasiharmonic approximation (QHA). The total thermal conductivity (κTot) of UAl2 as a function of temperature were predicted considering both the lattice thermal conductivity (κph) and the electronic contribution (κe). The κph was estimated by solving the Boltzmann Transport Equation (BTE) using the harmonic and anharmonic interatomic force constants. Whereas, the κe was evaluated using the Wiedemann-Franz law. The absolute value of electrical conductivity (σ) required for the Wiedemann-Franz law was evaluated employing the BoltzTraP code and the Electron-Phonon Wannier (EPW) code. In addition to the total thermal conductivity κTot=κe+κph, the mode-dependent phonon scattering rates and the group velocities, as well as their impacts on the lattice thermal conductivity, are discussed in detail. The results obtained demonstrated that κTot of UAl2 decreased with increasing temperature up to 600 K and then remained nearly invariant at ∼5.9 Wm−1K−1 up to 1500 K. Moreover, a large optical mode contribution (31% at 300 K) to the κph was predicted for UAl2.