Structural properties of the nanoscopic Al85Ti15 solid solution observed in the hydrogen-cycled NaAlH4 + 0.1TiCl3 system

The twice-hydrogen-cycled NaAlH4 + xTiCl3 (x < 0.15) system has been studied by high-resolution X-ray synchrotron diffraction and transmission electron microscopy. Intense low d-spacing shoulders are formed on Al reflections, indicating the formation of a face-centred cubic Al85Ti15 solid solution of unit cell dimension 4.0356 Å. The Al85Ti15 solid solution is found as isolated 4–25 nm nanocrystallites on the NaAlH4 surface. The Al85Ti15 phase is highly 〈1 1 0〉{1 1 1} edge dislocated to ∼6 × 1016 m−2. Local energy-dispersive spectroscopy shows an Al:Ti ratio consistent with an Al85Ti15 composition, confirming an extended solubility of Ti in Al. Structural analysis indicates a quenched L12 superlattice obtained by Al and Ti sublattice swapping, yielding an equivalent A1 Fm3¯m model to describe the Al85Ti15 crystal structure.