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FZJ-2018-02773

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Untersuchung des Schwingungsverhaltens bestrahlungsinduzierter Zwischengitteratome in Al mit Hilfe der inelastischen, diffusen Neutronenstreuung

Urban, R. (Corresponding author)FZJ*

1987
Kernforschungsanlage Jülich, Verlag Jülich

Please use a persistent id in citations: http://hdl.handle.net/2128/18408

Report No.: Juel-2134

Abstract: Diffuse inelastic neutron scattering measurements have been performed for the first time to study the dynamics of self interstitial atoms (SIA). In order to produce a random distribution of individual SIA's the defects were produced by irradiation with 3 MeV electrons. Using a specially developed He-gas cooling circuit which supplies a cooling power of =200 Watt at 10 K large single crystals of Al (28g of Al) with the special shape of a hollow cylinder could be irradiated up to a defect concentrationof 480 ppm. The defect concentration could be monitored by in situ measurements of the change of the electrical resistivity at the bulk sample itself. After irradiation the samples were transferred, cold, to the IN3 spectrometer at the high flux reactor at Grenoble. Const-q-Scans were performed in energy loss at Q = (2, q, q) 2$\pi$/a with q = 0.4, 0.6, 0.8 over a frequency range from 0 to 2 THz. The measurements were made at 6 K on the sample before annealing and after annealing at 46 K (above stage I) and at = 300 K (after complete recovery). The irradiated sample showed a significant increase of the inelastic scattering intensity at transferred energies between 0.7 THz and 2 THz. By comparison with the results of computer calculations this broad frequency spectrum could be attributed to contributionsof different vibration modes of the interstitial atoms. Hence the most significant vibration modes of the self interstitial atom could be identified: the translation-mode A$_{2u}$ ($\nu$=0.75 THz) and the libration-mode E$_{g}$ ($\nu$=1.35 THz). In addition the B-modes of the SIA have been identified for the first time at frequencies around 2 THz. The observed frequency spectrum is in agreement with the experimental results for the migration energy (= 0.1 eV) and the elastic polarisibility of the SIA. The observed ordering of the lowest frequency modes is in contrast to the results of calculations with different potentials for copper, however it is in agreement with calculations using an Al-pseudo-potential and therefore we conclude this ordering to be specific for Al.

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Contributing Institute(s):

1. Publikationen vor 2000 (PRE-2000)

Research Program(s):

1. 899 - ohne Topic (POF3-899) (POF3-899)

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