On the effect of thermal treatment and hydrogen vibrational dynamics in sodium alanates: An inelastic neutron scattering study

Highlights: ► High resolution INS spectra of thermally treated NaAlH4 and Na3AlH6. ► Detailed spectral features assignments based on high quality DFT(GGA) calculations. ► Treated materials spectra are described as sum of the corresponding reactants and products. ► The existence of AlH3 and AlH52− species is not observed in the bulk, under equilibrium. - Abstract: We have measured inelastic neutron scattering (INS) spectra from Ti-doped polycrystalline alanates (NaAlH4 and Na3AlH6), at low temperature, in the energy transfer range 3–500 meV, both for thermally treated and untreated samples. From the spectral range corresponding to the fundamental vibrational bands of these aluminohydrides, accurate one-phonon spectra and hydrogen-projected densities of phonon states have been extracted and analyzed using ab initio lattice dynamics calculations. Satisfactory agreement has been found for the untreated samples. In the case of thermally treated samples, due to thermal decomposition, different ionic species are present and the sample composition could be quantitatively evaluated. No evidence for the existence of intermediate species such as AlH3 or AlH52− has been found.