Abstract
Single crystals of rutile in the form of slices were reduced in vacuum to investigate the diffusion of point defects. The reduction was performed in three kinds of vacuum atmospheres by using (A) a diffusion pump without traps, (B) a diffusion pump with liquid nitrogen traps and (C) an ion pump. The process of reduction is considered to represent the process of diffusion of point defects induced by reduction. The diffusion coefficients of point defects in the reduced rutile were determined by a theory of diffusion in a plane sheet with an equal surface concentration and a uniform initial distribution of solute in a sheet. These coefficients obtained in vacuum by a diffusion pump varied with the reduction time and this tendency was more remarkable in the case of (A). But the diffusion coefficients obtained in the case of (C) were nearly constant at any reduction temperature independent of the reduction time except for the beginning stage. It appears that the differences are due to the contamination introduced by the diffusion pump. By using the ion pump, the diffusion coefficient of point defects in the reduced rutile can be expressed as
D=91exp[−(2.42±0.33)(eV)⁄kT]cm2⁄sec.
This activation energy is very close in value to that of oxygen ions which diffuse in rutile by the vacancy mechanism.
