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 (Da) and along the c axis (Dc) of the close packed hexagonal structure are: Da=(4.51+0.55, 4.51–0.49) exp[−(72.27± 0.36)× 103/RT] cm2/sec,Dc=(3.71+0.87, 3.71–0.71) exp[−(72.05± 0.65)× 103/RT] cm2/sec.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 ωc/ωa=0.85 exp(+270/RT) where ωc and ωa are frequency out of the basal plane and frequency in the basal plane, respectively.