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 A. 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 X 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 model to describe the Al85Ti15 crystal structure.