RbAlH4, a member of the complex metal aluminum hydride family, can be synthesized phase pure by different synthesis routes. Synthesis from the metals by a mechanochemical reaction requires the presence of a catalyst, but also emphasizes the reversibility of hydrogenation. The structure refinement of neutron diffraction data confirms that RbAlD4 is isostructural to KAlD4. The decomposition proceeds via two distinct processes at temperatures above 275 °C. However, the structures formed during decomposition seem to be different from the compounds formed during hydrogen release of early alkali metal aluminum hydrides.