Characterizing the ZrBe₂H<i>_x</i> Phase Diagram via Neutron Scattering Methods

Abstract

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, ZrBe2H1.5, 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 ZrBe2D1.5). It is desirable from both fundamental and technological viewpoints to have a more complete understanding of the ZrBe2Hx phase diagram. In the present study, both neutron powder diffraction and neutron vibrational spectroscopy measurements of ZrBe2Hx at lower hydrogen contents (x x values of 1 and 0.67. Compared to ZrBe2H1.5, 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 ZrBe2H1.5.

Keywords

• ZrBe₂
• intermetallic hydrides
• hydrogen storage materials
• neutron diffraction
• neutron vibrational spectroscopy
• density functional theory