Computer Simulation Investigation of Diffusion Mechanisms in the Alkali Metals

An interatomic potential for the alkali metals derived by Ho, based on pseudopotential theory but containing parameters adjusted to experimental data, has been used in a computer simulation study of point-defect configuration and migration in Li, Na, K, and Rb. The computed vacancy migration energies in all four cases are less than 0.1 eV, consistent with experimental results for vacancy formation and self-diffusion activation energies. A comparison of calculated activation energies, for both diffusion in the pure metal and homovalent impurity diffusion, with available experimental data has revealed satisfactory quantitative agreement and enabled us to suggest the operative mechanism of diffusion in a number of cases. In particular, the computational results considered in conjunction with those of experiment indicate that sodium may diffuse in potassium by some form of interstitial mechanism, and that in lithium both vacancy and interstitial self-diffusion mechanisms may occur.