Bulk nanocrystalline gamma magnesium hydride with low dehydrogenation temperature stabilized by plastic straining via high-pressure torsion

摘要

MgH2 with the alpha tetragonal structure was plastically strained using the high-pressure torsion (HPT) method and fully transformed to a nanonocrystalline gamma orthorhombic phase with increasing the strain. The formation of nano crystalline high-pressure gamma phase resulted in decreasing the dehydrogenation temperature by 80 K. First principles phonon calculations showed that both alpha and gamma phases are dynamically stable, but the gamma phase with the ionic binding has weaker hydrogen binding energy and accordingly lower dehydrogenation temperature. This study confirms the significance of crystal structure on thermal stability of hydrides for hydrogen storage applications. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.