Hydrogen absorption in RE2T2In compounds

• Hydrogenation on selected RE2T2X was performed.
• Nd2Ni2In is unique among “221” compounds, exhibiting a very high H absorption.
• The behavior found in RE2Ni2In changes when replacing Ni for Pd.
• The amorphization of La2Pd2In allows to go up to 4.6 H/f.u.
• RE2Pd2In with heavy RE can absorb 2 H/f.u. without structure distortion.

RE2T2In compounds (RE = rare earth, T is a late transition metal) were found, depending on the composition, absorbing different amounts of H. Several types of reaction of crystal structure have been found. Mere volume expansion, analogous to U2T2X compounds, was found e.g. in Tb2Pd2In, allowing to accommodate up to 2 H atoms/f.u. (one formula unit comprises 2 RE atoms). More dramatic structure modifications are required, to keep the H–H spacing higher than 2.1 Å, for higher H absorption. One type of reaction is amorphization, observed in La2Pd2In. Other type was observed in Nd2Ni2In, undergoing an orthorhombic distortion and forming four different H sites. The volume expansion exceeds 23%.