Characterizing the ZrBe 2 H x Phase Diagram via Neutron Scattering Methods.

Since the initial assessment four decades ago of zirconium diberyllide, ZrBe₂, as a potential hydride-forming intermetallic for hydrogen-storage applications, structural and dynamical studies to date have been chiefly limited to the hydride composition, ZrBe₂H_1.5, which exists as a single-phase disordered hydride with hexagonal P6/mmm symmetry that undergoes hydrogen sublattice ordering below ~200 K (~235–250 K for ZrBe₂D_1.5). It is desirable from both fundamental and technological viewpoints to have a more complete understanding of the ZrBe₂H_x phase diagram. In the present study, both neutron powder diffraction and neutron vibrational spectroscopy measurements of ZrBe₂H_x at lower hydrogen contents (x < 1.5) indicate that at least two other ordered phases exist at low temperatures, coinciding with respective nominal x values of 1 and 0.67. Compared to ZrBe₂H_1.5, these more-hydrogen-dilute phases possess different structural symmetries (orthorhombic) with different H-sublattice orderings and undergo much-higher-temperature order-disorder transitions at ≈ 460 K (x = 1) and ≈ 490 K (x = 0.67) to the characteristic H-disordered hexagonal P6/mmm structure associated with ZrBe₂H_1.5. [ABSTRACT FROM AUTHOR]