Hydrogen in RE6Fe13XHy intermetallic compounds

Abstract. The tetragonal ternary intermetallics RE6Fe13X.RE D Pr;NdIX D Ag, Au, Si, Ge, Sn, Pb), which all crystallize in the Nd6Fe13Si structure, are found to absorb approximately 12– 18 hydrogen atoms/formula unit in a largely irreversible reaction at 390 K under a gas pressure of 1 bar. The unit cell volume expands by 10–15 % without any change in the crystal symmetry and structure type, corresponding to an increase of volume per hydrogen atom of 2:910−3 nm3. Lattice expansion is highly anisotropic, being an order of magnitude greater along c than along a. The anisotropic lattice expansion and hydrogenation characteristics are explained in a model where the hydrogen atoms enter the 0:7 nm rare-earth slabs in an amount controlled by the element X. The 0:5 nm iron slabs expand little. Magnetization and Mössbauer measurements on the parent compounds show them to be essentially antiferromagnetic with a net moment of 0–1 B=formula unit but on hydrogenation there is ferromagnetic behaviour with a moment of 23–27 B=formula unit at room temperature. 1