Feature article formation of vacancies in noble metals and alloys

Abstract

In 1975, Hehenkamp and his group began to develop an apparatus to allow the precise determination of the absolute concentration of thermally generated vacancies in both noble metals and alloys. After a period of development of a few years the research group was able to measure absolute vacancy concentrations with an accuracy of about a few 10⁻⁵ according to the differential dilatometric technique. The results of several measurements in copper and different copper and silver alloys will be described. In alloys, vacancy-impurity interactions will be determined in terms of the complex model. In addition, positron annihilation spectroscopy was established in Hehenkamp's group. The attractive interaction between positrons and vacancies makes this technique a probe sensitive to the formation of vacancies. Due to the combination of both the differential dilatometric technique and the positron lifetime spectroscopy vacancies have become detectable now over a temperature range of about 500 K corresponding to concentrations of more than three orders of magnitude. For the first time, the concentration of divacancies in copper and their binding values have been estimated by means of a combination of both measurements.