Temperature dependence of the Doppler-broadened lineshape of positron annihilation in α-Ti

Doppler-broadened lineshapes of positron annihilation in pure alpha -Ti were measured in the temperature range between 293 and 1143K. The peak parameter S indicated significant effects from positron interactions with equilibrium vacancies above 970K. A vacancy formation enthalpy of 1.27+or-0.05 eV was obtained from the temperature where the curve of S against temperature deviates from the linear increase due to thermal expansion. A long exposure of the specimen to high temperatures, however, yielded a predominantly linear increase of S with temperature, as reported by Hood et al. (1976, 1978, 1979), and effects due to thermally created vacancies were smeared.