Nuclear magnetic resonance study of self-diffusion in solid selenium.

The self-diffusion in crystalline selenium is investigated by means of nuclear spin relaxation under selective spin excitation between 350 K and the melting point (492 K). Diffussion coefficients down to 10-19 qcm sec-1 have been observed. The diffusion process is attributed to a monovacancy mechanism, but the temperature dependence of the measured diffusion coefficients indicates also a small additional contribution to the monovacancy process near the melting point (T bigger than 460 K). For temperatures below 400 K, pipe diffusion along dislocations occurs. Generally, the observed diffusion coefficients are about a factor of 20 smaller than the tracer diffusion coefficients as measured by Braetter and Gobrecht.