Abnormal lattice behavior of MgH2 in isotope labeled LiBD4-MgH2 composites at the melting of LiBD4

Abstract We found abnormal lattice behavior of MgH2 in LiBD4-MgH2 composites at the melting of LiBD4 using high resolution x-ray diffraction measurements. At the LiBD4 melting point, the tetragonal MgH2 unit cell contracted isotropically which is attributed to D atoms diffused from neighboring LiBD4; these D atoms can occupy interstitals or lattice points of MgH2. Endothermic behavior of LiBD4 during melting might also have contriubuted to the contraction of MgH2. In addition, the intensity of MgH(D)2 Bragg peaks measured in in situ neutron diffraction experiment confirms that H/D exchange between the two hydrides starts below the LiBD4 melting temperature.