Atomic Motions in LiBH4 by NMR

1 H, 7 Li, and 11 B NMR measurements were used to understand atomic translational motions in both the low- and high-temperature phases (LT, HT) of LiBH 4 . In the HT phase 7 Li spectra, spin−echo T 2, and T 1 all indicate very rapid lithium ion diffusion. Just above the phase transition, the hydrogen resonance is broad, about 22 kHz fwhm (full width at half of maximum), showing that H translations remain slow. From 120 to 170 °C, a rapidly decreasing T 1D (relaxation time of dipolar spin-order) shows that the hydrogens diffuse increasingly rapidly. This motion eventually results in marked hydrogen line-narrowing centered near 190 °C; the hydrogen diffusion is likely relevant to the kinetics of dehydriding. The extent of 11 B line-narrowing demonstrates that the boron atoms also diffuse rapidly at temperatures above 200 °C. In the LT phase, the hydrogen T 1D decreases rapidly with increasing temperature, here due to 7 Li diffusion which is too slow for line-narrowing.