| Abstract
| - NaAlH4 samples with Ti additives (TiCl3, TiF3, and Ti(OBu)4) have been investigated by synchrotron X-raydiffraction in order to unveil the nature of Ti. No crystalline Ti-containing phases were observed after ballmilling of NaAlH4 with the additives, neither as a solid solution in NaAlH4 nor as secondary phases. However,after cycling, a high-angle shoulder of Al is observed in the same position with 10% TiCl3 as that with 2%Ti(OBu)4, but with considerably higher intensity, indicating that the shoulder is caused by Ti. After prolongedreabsorption, there is only a small fraction of free Al phase left to react with Na3AlH6, whereas the shouldercaused by Al1-yTiy is dominating. The Ti-containing phase causing the shoulder therefore contains less Tithan Al3Ti, and the aluminum in this phase is too strongly bound to react with Na3AlH6 to form NaAlH4. Thecomposition of the Al1-yTiy phase is estimated from quantitative phase analysis of powder X-ray diffractiondata to be Al0.85Ti0.15. Formation of this phase may explain the reduction of capacity beyond the theoreticalreduction from the dead weight of the additive and the reaction between the additive and NaAlH4.
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