High-resolution positron-lifetime study in silver

The temperature dependence of positron annihilation in silver has been investigated between 20 and 950 °C by measurements of the positron lifetime. The lifetime spectrometer used has a resolution of 170 ps and a stability of ±1.5 ps over a period of four weeks. Data treatment in terms of the two-state trapping model shows a strong temperature dependence of the bulk lifetime ${\tau }_f^{\mathcal{’}}$ above 550 °C. The rapid increase of ${\tau }_f^{\mathcal{’}}$, as well as the fact that the vacancy-formation enthalpy calculated with the $I_2$/$I_1$ method is far too high, can be explained by the assumption of trapping during thermalization of the positrons. It should be pointed out that the evaluation of the vacancy-formation enthalpy by the $I_2$(${\lambda }_1$-${\lambda }_2$) and the τ¯ methods is only weakly influenced by such effects and gives $E_v^f$=1.18 and 1.16±0.05 eV, respectively.