First-principles study of the structural, electronic, dynamical, and thermodynamic properties of Li₅AlO₄

Pentalithium aluminate, Li₅AlO₄, has attracted increasing attention for its high lithium density and potential uses in tritium breeding materials and thermal batteries. In this work, the structural, electronic, lattice dynamical, and thermodynamic properties of α- and β-phase Li₅AlO₄ were investigated using first-principles density functional theory. The optimized structural parameters were consistent with the experimental values, with the absolute deviation being less than 2.5%. The indirect band gaps of α- and β-Li₅AlO₄ were 4.82 and 5.16 eV, respectively, showing that they are insulators. In addition, the vibrational properties of α- and β-Li₅AlO₄ were computed using density functional perturbation theory. By adding Born effective charges into the phonon calculations, the longitudinal optical–transverse optical (LO-TO) splittings were calculated. The optical modes at the Γ point were categorized as Raman- and IR-active modes. Our results show that β-Li₅AlO₄ is more polar and anisotropic than α-Li₅AlO₄. Furthermore, their thermodynamic functions were determined using the calculated phonon density of states. The results were in good agreement with those of previous theoretical studies. The data presented in this work will help in the further characterization of Li₅AlO₄, which may be valuable for future experimental studies. - Highlights: • Thermodynamic properties of α- and β-Li₅AlO₄ are determined using DFT. • Calculated and experimental structural parameters are in good agreement. • Indirect band gaps of α- and β-Li₅AlO₄ are 4.82 and 5.16 eV, respectively. • Data presented in this work provide a further characterization of Li₅AlO₄.