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

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 (κ_Tot) of UAl₂ as a function of temperature were predicted considering both the lattice thermal conductivity (κ_ph) and the electronic contribution (κ_e). The κ_ph was estimated by solving the Boltzmann Transport Equation (BTE) using the harmonic and anharmonic interatomic force constants. Whereas, the κ_e 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 κ_Tot=κ_e+κ_ph, 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 κ_Tot 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 κ_ph was predicted for UAl₂.