Lattice vibrations from 20 K to room temperature in lithium alanates LiAlH 4 and Li 3AlH 6, which decompose to release hydrogen over 423 K, were investigated by neutron spectroscopy. For both alanates, the overall spectra already start to broaden at 100-150 K with increasing temperature. The spectral lines assigned to the librational (rotational) modes of the polyhedral Al hydrido complexes, [AlH 4] - and [AlH 6] 3-, exhibit not only broadening but also softening at around 250-300 K. These results suggest that the decomposition stems from low-temperature bulk lattice instability/ anharmonicity, in particular, due to the weakening of binding between the complexes and their surroundings.
ASJC Scopus subject areas
- Physics and Astronomy (miscellaneous)