Regensburg 2002 – wissenschaftliches Programm

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M: Metallphysik

M 22: Symposium on Structurally Complex Alloy Phases IV (SCAP IV)

M 22.2: Fachvortrag

Donnerstag, 14. März 2002, 16:15–16:30, H16

Atomic vacancies in the high-temperature intermetallic compound MoSi2 — •W. Sprengel1, X.Y. Zhang1,2, H. Inui3, and H.-E. Schaefer11Inst. f. Theoretische u. Angewandte Physik, Universität Stuttgart, 70550 Stuttgart — 2Yanshan University, College of Materials Science and Engineering, Qinhuangdao, P.R. China — 3Department of Materials Science and Engineering, Kyoto University, Kyoto, Japan

MoSi2 based complex intermetallic compounds are considered as prospective materials for high-temperature structural applications. Intensive studies have been carried out to characterize their mechanical properties. For a satisfactory understanding of these results data about the atomic defects in MoSi2 and MoSi2 based intermetallics are indispensable.

Atomic vacancies in MoSi2 single crystals were investigated by means of positron annihilation techniques. Analysis of the positron lifetime spectra of well annealed MoSi2 showed that no structural vacancies are present. The temperature dependence of thermal vacancy formation was studied in the range from 293 K to 1673 K employing positron lifetime spectroscopy. A value for the effective vacancy formation enthalpy of HVF = (1.6 ± 0.1) eV was determined. Furthermore, vacancies were selectively induced on the two sublattices of MoSi2 by low temperature electron irradiation in the energy range from 0.5 to 3 MeV. These vacancies then were specifically detected by coincident measurement of the Doppler broadening of the positron-electron annihilation photon. The results are discussed in relation to the mechanical properties of MoSi2.
(financially supported by DFG: Scha 428/17-3 and AvH: X.Y.Zhang)

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