Phase transformations and vacancy formation energies of transition metals by positron annihilation |
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Authors: | H Matter J Winter W Triftshäuser |
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Institution: | (1) Hochschule der Bundeswehr München, Werner-Heisenberg-Weg 39, D-8014 Neubiberg, Fed. Rep. Germany |
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Abstract: | The technique of the coincidence count rate at the peak of the angular correlation curve (CCR) in positron annihilation has
been applied to the investigation of vacancy formation energies in thermal equilibrium in nickel, cobalt, and iron. The monovacancy
formation energyE
1v/F
has been determined to (1.55±0.05) eV and (1.34±0.07) eV for nickel and cobalt, and (1.60±0.10) eV for α-iron, and (1.40±0.15)
eV for γ-iron, respectively. The structural phase transformations in cobalt (693 K) and iron (1183 K, 1663 K) are exhibited
by discontinuities of the CCR. In the case of cobalt the CCR follows exactly the change of the thermal expansion at the transition
temperature. The temperature dependence of the CCR in the prevacancy region is found to be proportional to the thermal expansion
for all metals investigated. |
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Keywords: | 78 70 71 60 61 70 |
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