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Abstract
Irradiation of Pr and of Nd specimens at 10 K with electrons of 0.4 to 1.7 MeV energy yielded threshold energies for atomic displacement: Td (Pr) = (10.0±0.2) eV and Td (Nd) = (9.3+0.5 −0.3) eV. The result Td (Pr) ⩾ Td (Nd) is attributed to a higher bond energy due to a smaller fraction of “band” 4f-electrons in Pr, following a model by Gschneidner. The electrical resistivity of a Frenkel pair, which contains also a magnetic spin-disorder term, is estimated to p F = (100 to 170) Ω10−4 ωcm/FP. A subsequent annealing study revealed a big complex recovery stage centered in Pr at Tann = 57 K and in Nd Near Tann = 70 K attributed to interstitial long-range migration. Both the smaller threshold energies for displacement and the higher migration temperatures for an interstitial than expected from empirical relations derived for hep rare earths are imputed to a lower symmetry of the dhcp unit cell of the two metals.