A new behaviour of the interstitial element H or D in solution in rare-earth metal

The study of the resistivity of the Lu-(H or D) system makes clear certain characteristics of the α phase and indicates a change for the interstitial element in the transition range 170–400°C. On both sides of this domain an appreciable difference is observed in the properties of the solid solution. The α1 phase of the domain below 170°C has a higher resistivity and a maximum hydrogen concentration independent of the temperature. For the phase α of the domain above 400°C, the expansions both with the concentration growth and with the rise in temperature are isotropic contrary to the α1 phase.The resistivity and X-ray diffraction studies, taking into account the lattice symmetry, allow us to conclude that a change may occur in the type of interstices filled by the hydrogen atoms, tetrahedral for the α phase and octahedral with H atoms associating in pairs for the α1 phase. Among the lanthanide metals, we find that only lutetium and thulium, in uniting with H or D, have the low temperature α1 phase.