Measurements of the vacancy formation enthalpy in aluminum using positron annihilation spectroscopy

Abstract

The temperature dependence of positron annihilation in aluminum has been investigated over the range 20-435°C by simultaneous measurements of positron lifetime and Doppler broadening of the annihilation spectrum. The analyses of lifetime data are critically examined, especially with respect to the effects of instrumental resolution-function uncertainties. The lifetime and Doppler-broadening data have been analyzed in terms of the two-state trapping model. Application of this model to the measurement of the vacancy-formation enthalpy $E_{\mathrm{v}}^F$ in aluminum is discussed in light of the observation of a strong temperature dependence of the apparent positron lifetime in the bulk or lattice state above 370°C. The monovacancy formation enthalpy in aluminum, $E_{1\mathrm{v}}^F=0.66\mathrm{}\pm 0.02$ eV, was determined for temperatures below 372°C. This is compared with values previously reported.