Abstract The microstructure of LiAlD 4 has been studied during the decomposition process using powder X-ray diffraction (PXD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Selected area diffraction (SAD) confirmed the existence of all the decomposed phases presented in the X-ray powder diffraction data. High-resolution transmission electron microscopy confirmed the presence of the LiAlD 4 phase before decomposition. After the first decomposition reaction, the electron diffraction patterns were dominated by metallic Al, but significant amounts of Li 3AlD 6 were also present. Inhomogeneous distribution of the phases was confirmed by scanning electron microscopy. Most of the Al was present in discrete particles on the surface of the decomposed alanate. For the LiAlD 4 sample heated to 275 °C under dynamical vacuum, many of the interplanar distances for Al and LiD phase overlap. Some of the Li 3AlH 6 phase was found to remain in the material and two characteristic spacings were identified in both the electron and X-ray diffraction data. Fine scale variation in composition was observed in the backscattered scanning electron image.