We have applied density-functional theory based ab initio molecular dynamics to examine Li4 BN3 H10 at temperatures both above and below the experimental melting point. We examine the structure of the liquid, diffusivity, vibrational spectra and compare to both experimental data and analogous properties from solid-state calculations. We find the following: (1) the liquid state, like the solid state, is primarily a mixture of Li+, BH4-, and NH 2- with ionic interactions between the BH 4- and NH 2- anions and the Li+ cations. (2) We observe the reaction of two amide anions exchanging hydrogen to form ammonia and an imide anion: 2 NH2- → NH3- + NH2-. (3) The liquid demonstrates wide bond-angle distributions in the BH 4- and NH 2- units and thus these anionic units are not simply rigid complexes. (4) The Li+ sublattice disorders before the anionic sublattices and the liquid exhibits very fast Li+ diffusion. We calculate the activation energy and pre-exponential factor for Li+ diffusivity in the liquid to be ∼20 kJ/mol and 15× 10-4 cm2/s, respectively. (5) Finally, we find that the liquid contains the same generic types of vibrational modes as the solid, however the lower-frequency anionic vibration and rotation modes become more prominent with increasing temperature.
|Original language||English (US)|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - Dec 10 2009|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics