High-pressure phases of NaAIH_4 from first principles

摘要

High-pressure phases of NaAlH_4 are predicted using the ab initio evolutionary algorithm. our first-principles calculations reveal that the low-pressure I4_1/a phase containing A1H_4 tetrahedra transforms into the monoclinic P2_1/c phase at 3.8 GPa and then into the orthorhombic Ima2 phase at 20.5 GPa. The predicted two structures contain A1H_6 octahedra and A1H_7 decahedra, respectively. Coexistence of P2_1/c and Ima2 phases can explain better the measured x-ray diffraction patterns, transition pressure, and volume contraction. Our results provide a comprehensive understanding for the experimental findings.