Effect of Pressure on the Interstitial Diffusion of Lithium in Germanium to 45 kbar

We have measured the diffusion of lithium in germanium to pressures of up to 45 kbar using the $p-n$-junction-depth method for temperatures between 300 and 550 °C and by the ion-pairing method near room temperature. The data were analyzed assuming a single effective mechanism of diffusion with a temperature- and pressure-dependent activation energy and pre-exponential factor. The activation energy and volume at room temperature and atmospheric pressure are, respectively, $\Delta H=10.8\mathrm{}\pm 0.3$ kcal/mole and $\frac{\Delta V}{V_0}=0.05\mathrm{}\pm 0.03$. The pressure and temperature coefficients of the activation volume are, respectively, $V_0^{-1\mathrm{}}\frac{\partial \Delta V}{\partial P}=-(2.1\mathrm{}\pm 0.9)\times {10}^{-3\mathrm{}}$ ${\mathrm{kbar}}^{-1\mathrm{}}$ and $V_0^{-1\mathrm{}}\frac{\partial \Delta V}{\partial T}=(2.0\mathrm{}\pm 0.3)\times {10}^{-4\mathrm{}}$ °${\mathrm{K}}^{-1\mathrm{}}$. A small but nonzero specific heat of activation was found ($\frac{\Delta C_p}{R}=0.9\mathrm{}\pm 0.3$) suggesting an increase of about one degree of freedom as the impurity moves from its equilibrium position to the saddle point. The small activation energy in comparison to that for self-diffusion, along with the near-zero activation volume, is indicative of pure interstitial diffusion.