First-principles investigations of aluminum hydrides: M{sub 3}AlH{sub 6} (M=Na,K)

Journal Article · Tue Mar 01 04:00:00 EST 2005 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PhysRevB.71.092103· OSTI ID:20666278

Vajeeston, P; Ravindran, P; Kjekshus, A; Fjellvaag, H ^[1]

---

1. Department of Chemistry, University of Oslo, Box 10339, Blindern N-0315, Oslo (Norway)

The structural stability of Na{sub 3}AlH{sub 6} and K{sub 3}AlH{sub 6} has been systematically investigated using accurate density-functional total-energy calculations. The experimentally known crystal structure of {alpha}-Na{sub 3}AlH{sub 6} is reproduced and {alpha}-K{sub 3}AlH{sub 6} is predicted to be isostructural ({alpha}-Na{sub 3}AlF{sub 6} type; space group P2{sub 1}/n). This structure contains a pseudo-face-centered-cubic Al sublattice and each Al atom is surrounded by distorted octahedra of hydrogen atoms with the long octahedral axis tilted from the [001] direction toward <111>. We predict that the {alpha} modifications will not be stable at higher pressures. On application of pressure to Na{sub 3}AlH{sub 6}, the {alpha} phase transforms into a Cs{sub 3}NdCl{sub 6}-type structure at 19.8 GPa. Similarly {alpha}-K{sub 3}AlH{sub 6} transforms into two high-pressure forms: (1) {alpha} transforms to {beta} with Rb{sub 3}TlF{sub 6}-type structure at 53.4 GPa and (2) {beta} transforms to {gamma} with U{sub 3}ScS{sub 6}-type structure at 60.2 GPa.

• OSTI ID: 20666278
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Journal Name: Physical Review. B, Condensed Matter and Materials Physics Journal Issue: 9 Vol. 71; ISSN 1098-0121
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ALUMINIUM FLUORIDES
ALUMINIUM HYDRIDES
DENSITY FUNCTIONAL METHOD
FCC LATTICES
HYDROGEN
MONOCLINIC LATTICES
PHASE TRANSFORMATIONS
POTASSIUM COMPOUNDS
PRESSURE RANGE GIGA PA
SODIUM FLUORIDES
SPACE GROUPS