TbMgNi4-xCox–(H,D)2 System. I: Synthesis, Hydrogenation Properties, and Crystal and Electronic Structures

Abstract

A series of cubic TbMgNi4-xCox (x = 0–4) pseudo-binary compounds have been synthesized by either a solid-state reaction or mechanical alloying with further annealing treatment. Their hydrogenation properties have been studied by pressure–composition–temperature (PCT) measurements, showing the formation of α-, β-, and γ-hydrides. The Co for Ni substitution yields a lowering of the equilibrium pressure and an increase of the hydrogen capacity. An improvement of the kinetics of hydrogen absorption was observed with an increasing Co content. β-TbMgNi4-xCoxH∼4 (x = 0–3) hydrides show an orthorhombic distortion (Pmn21 space group), whereas the β-TbMgCo4H3.3 hydride crystallizes in a monoclinic structure (Pm space group) derived from the orthorhombic structure. Sensitivity of the formation of the β-TbMgCo4H3.3 hydride to temperature has been observed in PCT curves to exist below 50 °C. γ-TbMgNi4-xCoxHy (x = 2–4, y > 5) hydrides preserve the parent cubic structure (F43m space group) with a hydrogen-induced volum...