On the temperature dependence of positron lifetimes in tin and the transition from theβ- to theα-phase

For the first time the positron lifetimes in polycrystalline tin have been measured as a function of temperature in the whole range from 80 K to the melting point. The temperature dependence of the mean lifetime could be divided into four regions which can be attributed to the depletion of shallow traps, normal thermal expansion, prevacancy effects, and trapping by vacancies, respectively. In one of the samples the phase transition fromβ- toα-Sn clearly could be detected at 230 K by a sharp increase in the mean lifetime.