Electromigration in polycrystalline and single crystal magnesium

The electromigration of magnesium single and polycrystal samples was measured under the influence of a d.c. current density of approximately $\text{6×10}{}^3\text{A}\text{cm}{}^2$ using the vacancy flux technique. The single crystal data were taken on samples with the c-axis of the metal making angles of 22° and 63° respectively with the cylindrical axis of the specimen. Accurate measurements of the longitudinal and transverse motion were made over a period of several weeks and used to calculate a value for the atom drift velocity, V_a. The atom drift velocity is used to calculate Z¹, the effective eiectromigration charge on the ion. All of the observed motion was directed toward the anode. The polycrystal runs yielded an average value of $\text{Z}{}^1\text{?}\text{= ?2.03 ±0.33}$. The single crystal runs resulted in an anisotropic drift velocity ratio of $\text{V}{}_{\mathrm{a\perp }}\text{V}{}_{\mathrm{a\parallel }}\text{= 1.4}$. However, the product of diffusivity times resistivity is anisotropic by the same ratio as the atom drift velocity and the correlation factor f is nearly isotropic for magnesium. As a result Z¹ is isotropic and turns out to be ?1.6.