P. Lucasson

Point-defect production in the h.c.p. heavy-rare-earth metals Gd, Tb, Dy, Ho, Er, Tm and Lu during electron irradiation at low temperatures

Abstract Defect production in the h.c.p. heavy lanthanides Gd, Tb, Dy, Ho, Er, Tm and Lu has been investigated by electron irradiation in the energy range 0.7–1.7 MeV, at liquid-helium temperatures. Fitting with displacement cross-sections yielded minimum threshold energies for displacement, T d1 = 14.0 to 17.3 eV, which exhibit the same dependence on the atomic number Z as the reduced reciprocal interatomic distance (c/a)l1.633r 1. A correlation with the sizes of the interatomic ‘lenses’ via the replacement-collision mechanism is suggested. The electrical resistivity increase due to a Frenkel pair is shown to depend both on the phonon resistivity and on the magnetic resistivity of the metal, in the form ρ F ∼ 270ρ ph + 100ρmag at room temperature, implying the introduction of additional spin disorder around a defect.

Defect annealing in the hexagonal close packed heavy rare earth metals Gd, Tb, Dy, Ho, Er, Tm and Lu after electron irradiation at low temperatures

Abstract The recovery spectra of the heavy rare earths Gd, Tb, Dy, Ho, Er and Tm were determined after irradiation with electrons at low temperatures. In the cases of Er and Tm, strong thermal cycling phenomena were observed and attributed to hydrogen atoms changing configurations and interacting with the magnetic structure of the metal. After elimination of these effects in Er and Tm, all the spectra—together with those of the earlier treated Lu—had rather similar form: several close-pair peaks followed by a broad complex substage resembling the stage I D in f.c.c metals and attributed to long-range interstitial migration. A correlation is found between the temperature of the maximum of this substage (normalized to the melting temperature) and the c/a-ratio of the metals.

Free migration of interstitials in electron irradiated pure Ag and Ag Cu and Ag Ni dilute alloys

Abstract The interaction of self interstitials with impurity atoms in a silver matrix, has been investigated by resistivity measurements for the two dilute alloys: AgCu and AgNi. The free migration of self interstitials in pure silver, and their interaction with the solute impurities in the alloys, have been studied by means of a kinetics analysis (based on diffusion theory) of stage I recovery. With p F = 2 μωcm/at. %, the capture radii of self interstitials by the impurities, measured in terms of rV (capture radius by the vacancy), are found: Rt Ag (Cu) = 0.2 + 0.05 and RAg (Ni) = 0.05 + 0.1. The influence upon Rl of the various parameters entering the analysis is discussed.

Low-temperature electron radiation damage in scandium

Abstract Electron irradiation of hcp scandium at T ⪅ 12 K allowed to determine the energy threshold for Frenkel-pair creation, T d = 13.8 ± 0.5 eV, and the defect resistivity, ϱ F ≈ 5 × 10 −3 Ω cm/F.P . The annealing spectrum exhibits four substages between 20 and 70 K, a broad substage centered at 105 K attributed to interstitial long-range migration, and a stage III between 240 and 300 K.

Low temperature electron irradiation damage in europium

Abstract Electron irradiation of the divalent b.c.c. rare earth metal Eu has permitted determination of its displacement threshold energy, T d1 (Eu) = 7.5±0.5 eV, after fitting with a three-step displacement probability function. The Frenkel pair resistivity is composed of a phononic and of a spin-disorder term; a tentative value of ρf ≳ 100 × 10−4 Ohm cm/F.P. is proposed. The low-temperature recovery spectrum after irradiation at 10 K contains stages between 12 and 22 K, a main annealing region with two peaks at 67 and 77 K, and a small stage at 110 K; more than 90% of the damage has recovered at 160 K.

On the resistivity anomaly in quenched and irradiated TmH solid solutions

Abstract TmHx solid solutions with ∼0.005⩽x⩽0.105 have been studied in the range of the resistivity anomaly around 160 K. The effect of a quench from room temperature and of an electron irradiation at low temperature was investigated. As both effects recover in the region of the anomaly, an explanation of the processes occurring in this region is proposed in the framework of the H-pair model.

The effect of hydrogen in solid solution on the magnetic transitions in thulium

Abstract The influence of hydrogen on the magnetic structures in thulium was determined by measuring the temperature dependence of the electrical resistivity up to 75 K. The H acts by lowering the Neel temperature and the spin-disorder resistivity, by smearing out the manifestation of the Curie temperature, and by revealing additional magnetic transitions below T C . This behaviour and the observation of an energy gap in the spin-wave spectrum are commented within the framework of the RKKY-model.

On the self interstitial atom interactions in metals and their study

Abstract The determination of self-interstitial atomic defect interaction radii Ri from recovery experiments after electron irradiation is re-examined in the light of the recent results obtained in Julich, with particular attention paid to interstitial-defect interactions. The possible sources of errors are mainly neglect of impurity effects, of electrical size effect and casually adapted treatment of the data. The latter point is emphasized. It comes to light that in simple processes with a unique mobile species—as in Al—the possible error on Ri may not affect estimates of Rr , the impurity interstitial trapping radius. Such is not the case if the process is complex as in Cu. Moreover, the analytical expressions given allow easy quantitative estimates of Ri and Rr from experiments on very pure metals and very dilute alloys. It is shown that in the metals studied so far, namely Al, Cu and Pt, the interaction radii to form a di-interstitial atom are about equal in units of annihilation radii. The extreme i...

Point defect creation in electron irradiated praseodymium and neodymium

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.

Temperature dependence of the hydrogen resistivity in HCP lutetium: Observation of the Manninen-Jena effect

Abstract We have measured the temperature dependence of the electrical resistivity between 4.4 and 170 K in α-Lu(H, D) x , with 0 ⩽ x ⩽ 0.2, in order to test the predictions of Manninen and Jena. The latter are confirmed as concerns the temperature dependence of the hydrogen resistivity and the isotope effect. In addition, we have obserced an H-concentration dependent turning-in temperature for excitation to higher excited states, which can be related to a varying binding energy of the H-H pairs prevailing in this temperature range in our system.