Troisiéme Conférence Européenne sur les Matériaux et les Procédés Avancés
J. Phys. IV France 03 (1993) C7-1987-C7-1992
Search for positron localization near transition-metal solutes of negative effective charge in Ni and CuD.M. HUNTER1, R.I. GRYNSZPAN1 and A.S. ARROTT2
1 Equipe de Spectroscopie des Leptons, Laboratoire de Microstructure et Mécanique des Matériaux, URA 1219 du CNRS, Ecole Nationale Supérieure d'Arts et Métiers, 151 Bd. de l'Hôpital, 75013 Paris, France
2 Dept. of Physics, Simon Fraser University, Burnaby B.C., V5A 1S6, Canada
Results of an early (1973) angular correlation (ACAR) study of dilute (0.5 at.%) Cu based alloys by a Japanese group were interpreted in terms of an attraction of e+ by transition metal solutes of effective negative charge. Doppler Broadening (DB) measurements reveal no such an effect for Cu(Mn) and Cu(Ni) solid solutions as well as for Ni alloys with 3d, 4d and 5d transition metal solutes (0.1 to 1.5 at.%) i.e. no evidence of e+ localization near these impurities is seen. Our results strongly suggest that the ACAR results are due to the metallurgical state of the samples. In contrast, significant DB lineshape parameter variations, observed for our Ni(Zr) alloys, are attributed to positron trapping in and near Ni5Zr precipitates. Our DB results for a series of Ni(Au) alloys are understood in terms of a combination of the effect of an overall lattice expansion and a positron preference for clusters of Au atoms. The above comparison between DB and ACAR results is supported by our 'spin polarized' DB results for a (001) Ni single crystal which resemble those obtained by other groups using a 'spin polarized' 2D-ACAR technique.
© EDP Sciences 1993