Dresden 2003 – wissenschaftliches Programm
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M: Metallphysik
M 31: Intermetallische Phasen I
M 31.2: Vortrag
Mittwoch, 26. März 2003, 15:00–15:15, IFW B
High-temperature atomic processes in MoSi2 — •W. Sprengel1, X.Y. Zhang1,2, H. Inui3, and H.-E. Schaefer1 — 1Inst. f. Theor. u. Angew. Physik, Universität Stuttgart, 70550 Stuttgart — 2Coll. of Mater. Sci. Eng., Yanshan University, 066004 Qinhuangdao, China — 3Dept. Mater. Sci. Eng., Kyoto University, Kyoto, Japan
Atomic vacancies in MoSi2 single crystals were investigated
by means of positron annihilation spectroscopy. For well-annealed
MoSi2 a positron lifetime τ =117 ps was determined
which characterizes the delocalized positron state and shows that
no structural or remnant thermal vacancies are present at 300 K.
An increase of the mean positron lifetime τ with
temperature in the range from 300 to 1343 K shows the formation
of thermal vacancies. From the temperature dependence of
τ the vacancy formation enthalpy
HVF =(1.6 ± 0.1) eV was determined. For the
vacancy migration enthalpy a value of
HVM < (1.1 ± 0.1) eV was estimated from the
temperature dependence of the equilibration time of the thermal
vacancy concentration after fast temperature changes. The ratio
of HVM / HVF < 1 indicates a high
mobility of thermal vacancies in MoSi2. By employing
coincident measurements of the Doppler broadening of the
positron-electron annihilation radiation at high temperatures,
the thermally formed vacancies were found to be surrounded by
Mo atoms. This demonstrates that the thermal vacancies in
MoSi2 are formed on the Si sublattice.
The work was supported by AvH (X.Y.Z.) and DFG
(Scha428/17-3).