Regensburg 2002 – wissenschaftliches Programm
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M: Metallphysik
M 15: Intermetallische Phasen II
M 15.3: Fachvortrag
Mittwoch, 13. März 2002, 17:15–17:30, H16
Switching of 111In impurity sites in the HfAl2 lattice — •Agnieszka Kulińska1,2, PawełWodniecki1,2, Barbara Wodniecka1, Michael Uhrmacher2, and Klaus-Peter Lieb2 — 1The Henryk Niewodniczański Institute of Nuclear Physics, PL 31-342 Kraków, Poland — 2II. Physikalisches Institut, Universität Göttingen, D 37073 Göttingen, Germany
The lattice locations of impurity atoms in metals are governed by arguments of size, relative valency and electronegativity. Oversized impurity atoms introduced via ion implantation may reach substitutional sites, either if strong binding prevails or if sufficient free volume is created by lattice expansion, trapping of vacancy-type defects at the impurity, or other means. The hyperfine interaction of radioactive impurity tracers are particularly sensitive to their local environment(s) and in this way to the implantation sites. Here we report on the unexpected behavior of 111In hyperfine probes in the HfAl2 Laves phase, occupying either Hf or Al sites at different temperatures. To our knowledge, up to now it has never been observed that impurity atoms alternatively substitute both constituents of a binary alloy. Below 370 K the 111In impurities are located at the unique hafnium site. Above 400 K they occupy the two aluminum sites, however with a clear prefernece of the 2(a) site. This process, which is fully reversible when heating and cooling the sample, is attributed to atomic size effects.
This work was founded by the Polish State Committee for Scientific Research (grant No. 2 P03B 066 18), the Deutche Forschungsgemeinschaft and the WTZ program (grant POL 215-96).