The temperature dependence of positron annihilation in α-Hf

Doppler-broadening of the positron annihilation photopeak has been measured for α-Hf (6.8 at% Zr) in the interval 298-1945 K. The data, in terms of peak (S) and wing (W) line-shape parameters, show three regions of behaviour. Region I, 298-750 K, shows a complex temperature response of W and S: it is associated with positron interactions with impurity-related defects. Region II, 750-1750 K, shows a linear temperature dependence of S and W: it is associated with thermal expansion effects. Region III, 1750-1945 K, shows an increasing temperature dependence of both S and W: this is indicative of positron-interactions with equilibrium vacancies. The vacancy formation energy deduced from the data is 2.5 eV. (author). 15 refs., 2 figs