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.