Ca7Ge-type hydride Mg6VNaxHy (0 ≤ x ≤ 1): High pressure synthesis, synchrotron X-ray analysis and hydrogen storage properties

► Mg6VNaxHy hydride was synthesized under high pressure H2 (8 GPa). ► Synchrotron X-ray diffraction and Rietveld crystallographic structure analysis. ► Mg6VNaxHy hydride has the Ca7Ge-type cubic structure. ► Reversible reaction with H2 was observed. ► Comparison with related hydride Mg7TiNaxHy.