Activation Volume and Chemical Environment of Atomic Vacancies in Inter metallic Compounds

摘要

Positron annihilation spectroscopy was used to investigate the temperature, time and pressure dependence of the equilibration of the thermal vacancy concentration in B2-Fe_(61)Al_(39) after fast temperature changes at elevated temperatures. A two stage equilibration process was observed with a migration enthalpy of H~1_(v~M) = (0.8 +- 0.2) eV and H~2_(v~M) = (1.7+- 0.3) eV for a faster, initial process and a long-term, main process, respectively. For the main process a formation volume of F_(v~F) = (1.5 +- 0.3) Ω and a migration volume of V_(v~F) = (4.6 +- 1.1) Ω for thermal vacancies were determined. By employing coincident Doppler broadening studies it could be demonstrated for the first time for the model case of FeAl that thermal vacancies are formed on the transition metal sublattice.