Anisotropic Self-Diffusion in Erbium Single Crystals

The rate of self‐diffusion in single crystals of erbium has been studied over the temperature range from 1202 to 1412°C using a radioactive tracer (¹⁶⁹Er)‐sectioning (grinding) technique. The diffusion coefficients along the a axis (D_a) and along the c axis (D_c) of the close packed hexagonal structure are: $$\begin{array}{c}{D}_a\text{=(4.51+0.55,\hspace{0.17em}4.51–0.49)\hspace{0.17em}}\exp {\text{[−(72.27± 0.36)× 10}}^3\mathrm{/RT]\hspace{0.17em}}{\mathrm{cm}}^2/\sec ,\\ D_c\text{=(3.71+0.87,\hspace{0.17em}3.71–0.71)\hspace{0.17em}}\exp {\text{[−(72.05± 0.65)× 10}}^3\mathrm{/RT]\hspace{0.17em}}{\mathrm{cm}}^2/\sec .\end{array}$$ By making use of Mullen's table for the diffusion of hcp metals by the vacancy mechanism, the ratio of jump frequencies is determined to be ${\omega }_c{\mathrm{/\omega }}_a\text{=0.85\hspace{0.17em}}\exp \text{(+270/RT)}$ where ω_c and ω_a are frequency out of the basal plane and frequency in the basal plane, respectively.