On the Kinetics and Mechanism of the Precipitation of Lithium from Germanium

Abstract

The kinetics of precipitation of lithium from germanium have been investigated and the following variables have been studied: (a) crystal source; (b) preannealing treatments prior to the introduction of lithium; (c) the effect of selective impurity additions, namely, oxygen and copper. The precipitation process can be described as following the law given below: $$\log {\mathrm{C/C}}_0=\exp {\mathrm{[-(t/\tau )}}^n]$$ . Upon saturation at elevated temperatures, (about 425°C), n is found to be $\frac{3}{2}$ for the first part of the process and 1 for the later part of the process. Upon saturation at low temperatures, however, n is found to be ½. It is suggested that this results from the nonuniform distribution of lithium in the crystal prior to precipitation. Nucleus number densities varying by orders of magnitude were obtained from different crystals. It was found that a preannealing treatment at 900°C was sufficient to increase the nuclei number densities for all crystals and the differences tend to disappear upon the preannealing treatment. Doping with oxygen tended to increase very markedly the number density of nuclei whereas doping with small amounts of copper (several orders of magnitude less than lithium present) decreased the number density of nuclei by about an order of magnitude. Interpretation of these results suggests that an impurity, consisting either of particles or oxygen‐vacancy pairs, is catalyzing the precipitation process.