Novel High Pressure Phases of β-AlH₃: A Density-Functional Study

Using total energy calculations within the generalized-gradient approximation the high pressure phases, optimized geometry, and electronic structure of AlH 3 are established. Among the 58 structural arrangements considered for the structural optimization calculations, the experimentally known β modification becomes the ground-state structure. Application of pressure makes the sequence of phase transitions from β → α′ → α → hp1 ( P 63/ m ) → hp2 ( P m 3̅ n ) modification and the estimated transition pressures are 2.4, 4.3, 64, and 104 GPa, respectively. The coordination of Al has been changed from six to nine in the newly identified high pressure hp1 and to twelve in hp2 polymorph. The electronic structures reveal that α, α′, β, and γ polymorphs are nonmetals with calculated band gap varying between 1.99 and 3.65 eV, whereas the hp1 and hp2 phases possess semiconducting and metallic behavior, respectively.