The formation energy of vacancies is measured under conditions of very low vacancy concentrations for ultrahigh purity aluminium, after quenching down to 4 K. A value of (0.69 & 0.03) eV is found. Similar experiments made using pure magnesium yield a formation energy of (0.79 f 0.03) eV. It is shown that in magnesium vacancies are mobile well below room temperature. L'6nergie de formation des lacunes a 6th mesuree dans I'aluminium au moyen de trempes jusqu'8 4 K, en travaillant 8. de trAs faibles concentrations de lacunes et avec un metal ultra-pur. La valeur trouv6e est (0,69 0,03) eV. Des experiences similaires effectuees sur du magnesium de haute puret6 ont conduit it une 6nergie de formation de (0,79 f & 0,03) eV. Elles ont Bgalement montr6 que, dans ce metal, les lacunes presentaient une mobilite importante au-dessous de la temperature ambiante. 85X,

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Fe/Ti metallic multilayers with an average Fe3?Ti6, composition have been studied by x-ray diffraction, Mossbauer spectroscopy and electrical resistivity as a function of period. For small periods. broad diffraction peaks characteristic of a disordered, amorphous-like structure are observed, although composition modulation still exists along the growth direction. Beyond A = 4 nm, crystalline Ti appears with a BCC structure. It then reverts to its stable Hcpform for A = 6 nm. with its c axis along the growth direction. At aperiod of 8 nm. the iron-rich layer in turn crystallises. This correlates to a sudden decrease of the electrical resistivity. The appearance of this Fe-rich RCC phase, corresponding to the onset of magnetic ordering in the Mossbauer spectra, induces a change in the texture of the titanium layer, the c axis now lying preferentially in the plane. Anomalies in both the lattice parameters and size of the crystallitesoccur from this period up to about 12 nm. whereas a plateau is observed for the electrical resistivity. For larger periods, the Ti content of the Fe-rich BCC phase decreases, corresponding to the further decrease of the electrical resistivity and increase of both hyperfine field and magnetic contribution in the Mossbauer spectra.

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1984) Single and multiple trapping of radiation-induced defects in AgZn alloys, Radiation Effects, 82:1-2, 141-153, Experimental results on the recovery spectra of low temperature electron irradiated pure Ag and AgZn alloys in the concentration range 0.018 to 30 at.% of zinc are presented. Their comparison leads to consider two distinct concentration domains. In the low concentration domain the classical model of Corbett, Smith and Walker applies with some modifications. The resistivity recovery is governed by the combinations and annihilations of point defects. It must be noted that even in dilute alloys, new kinds of point defects (such as mixed interstitials) arise from the presence of solute atoms. In the high concentration domain, the resistivity recovery is dominated by the setting in of short-range order as a result of the point defect migration: interstitial migration in stage I1 and, mainly, vacancy migration in stage 111. The defect migration, free in the pure metal, is influenced, in the concentrated alloys, by the local environment. The proposed model consistently allows the interpretation of the existing results, particularly from electron microscopy.Nous presentons des spectres d'evolution de la resistivite electrique obtenus lors de recuits apres irradiation electronique a basse temperature, dans I'argent pur et dans des alliages AgZn dont la concentration varie de 0,018 a 30% at. de zinc. La comparaison des resultats amkne a considerer deux domaines de concentration. Dans le domaine des faibles concentrations, le modele classique de Corbett, Smith et Walker avec quelques modifications explique bien ces spectres. Le recuit de la resistivitk est regi par les combinaisons et annihilations des defauts ponctuels. II importe de ne pas perdre de vue que la presence d'impuretts m&me en faible concentration peut induire de nouvelles expkces de defauts (interstitiels mixtes, par exemple). Aux concentrations plus elevies, le recuit de la resistivite est domine par la mise en ordre a courte distance qui resulte de la migration des defauts; interstitiels dans I'etape I1 et, surtout, lacunes dans I'etape 111. La migration des defauts, libre dans le mCtal pur ou les alliages dilues, est influencCe par I'environnement local dans le cas des alliages concentrks. Le modele propose permet une interpretation cohCrente des rtsultats existants, en particulier de microscopie electronique. ?Permanent address : Ecole Nationale Superieure de Ceramique Industrielle, 47, rue Albert Thomas, F-87100 Limoges, France. 141 Downloaded by [Michigan State University] at 00:21 05 February 2015 142 F. M A U R Y el tit. I INTRODUCTIONUsing a strain relaxation method Halbwachs and Hillairet have shown that in the electron irradiated alloy Ag-30 at. % Zn, the vacancies are more mobile than the interstitial defects in a wide temperature range around and above room temperature.','! By high voltage electron microscopy, Halbwachs and Yoshida3 reached a similar conclusion in the more dilute Ag-9 at.% Zn provided the temperature was lower than ...