Structural Transitions Of Lialh₄Under High Pressure:a Density Functional Theory Study

Complex light-metal hydrides with the general formula MAH4(M=Li, Na; A=B, A1) have received considerable attention due to their high hydrogen content. One of the potential candidates is LiA1H4, which releases hydrogen10.6wt%, and in some cases, may reversibly take up and release hydrogen under controlled thermodynamic conditions.In this work, we carried out a first principles calculation on the properties of LiA1H4under high pressure based on the density functional theory. The results shows that the materials undergoes a pressure-induced structural transition of from a-LiA1H4(space group P21/c) to β-LiA1H4(space group12/b) at2.0GPa. It suggests, the phase transition is associated with significant decreases in volume of17%. The volume collapses are associated with the electronic transition from Al-s to p state. There is no pressure-induced phonon softening behavior from our calculated phonon dispersion curves near the phase transition. Based on the Mulliken population analysis, though the phase transition from a-LiA1Ht to β-LiAlH4crystal structure with volume contraction, the activation energy of β-LiAlH4structure is higher than that of the a-LiAlH4structure The β-LiAlH4structure is expected to be more promising candidate for hydrogen storage.