Hydrogen absorption-desorption and crystallographic characteristics of RCo3−xGax(R ≡ Y, Gd; x = 0.6–1.2) intermetallics

Abstract

Abstract The replacement of cobalt by gallium in RCo3 intermetallics (R ≡ Y, Gd) leads to a decrease in the hydrogen absorption capacity from H/RCo3 = 3.7 to 2.0–2.5 atoms of H per formula unit (at.H/f.u.) in the case of RCo2.4Ga0.6 compounds. The increase of Ga content in the intermetallics (Y, Gd)Co3−xGax from x = 0.6 to 1.2 is accompanied by a gradual fall in their hydrogen capacity and by a noticeable complication of their activation behaviour, and leads to a decrease in the hydrogen sorption rate. Hydride phases (Y, Gd)Co3−xGaxHy contain 1.5–2.5 at.H/f.u. Their formation proceeds by means of an isotropic expansion of the original lattice of the CeNi3-type structures (Δa/ao = 2.1–3.5%, Δc/co = 2.6–5.1%, ΔV/V = 7.2–12.6%). The increase in the gallium content is accompanied by a rise in the thermal stability of the hydride and by a considerable fall in hydrogen capacity during sorption-desorption cycling.