Temperature dependence of the Doppler-broadened spectra in Ag obtained by positron annihilation

Abstract

Doppler-broadened spectra have been measured in well-annealed high-purity polycrystalline silver as a function of temperature between 9 and 1098 K by a two-detector Doppler-broadening positron-annihilation technique. Those positrons which annihilate with high-momentum core electrons exhibit a larger fractional change in intensity than those which annihilate with the low-momentum electrons when positron trapping at vacancies occurs. The probability of annihilation with the high-momentum core electrons remains constant as a function of temperature before positron trapping at vacancies is detected. The vacancy-formation enthalpy obtained by applying the two-state trapping model to the high-momentum spectra is 1.11 ± 0.05 eV. The importance of utilizing high-momentum spectra for extracting vacancy-formation enthalpies is discussed, and a new structure is observed in the curves of the ratio between the high- and low-temperature momentum spectra.