AbstractAn exhaustive microstructural characterization is reported for the LiBH4–MgH2 reactive hydride composite (RHC) system with and without titanium isopropoxide additive. X-ray diffraction with Rietveld analysis, transmission electron microscopy coupled to energy dispersive X-ray analysis, selected-area electron diffraction and electron energy loss spectroscopy are presented in this paper for the first time for this system for all sorption steps. New data are reported regarding average crystallite and grain size, microstrain, phase formation and morphology; these results contribute to the understanding of the reaction mechanism and the influence of the additives on the kinetics. Microstructural effects, related to the high dispersion of titanium-based additives, result in a distinct grain refinement of MgB2 and an increase in the number of reaction sites, causing acceleration of desorption and absorption reactions. Considerations on the stability of phases under electron beam irradiation have also been reported.