It was recalled that vacancy concentrations were determined by using differential dilatometry to measure simultaneously, and in a single specimen, the relative change in length (by using a laser/optical slit technique) and changes in lattice parameter (by using Debye-Scherrer techniques). The accuracy had been improved to a few ppm. Precautions against the selective evaporation of constituents had now made such measurements feasible in alloys at temperatures of up to 1150C. The temperature range within which vacancy formation could be reliably observed could also be extended to lower temperatures by adding the results of positron lifetime measurements. These furnished absolute vacancy concentrations only if the trapping rate of vacancies for positrons was known. As the differential dilatometry measurements, and those which used positron annihilation, exhibited regions of overlap, the trapping rate could be determined by combining both techniques. The results were analyzed in terms of mono/di-vacancy formation for pure metals (Cu, Ag, Al) and for some Cu and Ag alloys, from which reliable data on the enthalpy and entropy of binding could be deduced.

T.Hehenkamp: Journal of the Physics and Chemistry of Solids, 1994, 55[10], 907-15