Rare-earth dihydride compounds: Lattice thermal expansion and investigation of the thermal dissociation

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Abstract
The lattice parameters of seven rare‐earth (La, Nd, Gd, Dy, Er, Tm, Lu) dihydrides are determined between room temperature and a temperature ranging from 500 to 800 °C. The parameter‐vs‐temperature curves, presenting a ’’knee’’ at temperatures which vary with the rare‐earth compound, are fitted by a least‐squares method in two separate regions. In the first region, the crystalline properties of dihydrides are compared to those of the parent rare earths. In the second region where a thermal dissociation occurs, we have calculated the formation energy Ef of a point defect. Ef increases with the rare‐earth atomic number from 0.25 to 0.7 eV. A law of corresponding states between these rare‐earth dihydride compounds is established. The participation of the rare‐earth sublattice in the process of hydrogen diffusion and thermal dissociation is predicted.

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