Single crystal slices of rutile were reduced in vacuum in order to investigate the diffusion of point defects. The reduction was performed under three kinds of vacuum atmospheres by using a diffusion pump without traps (A), a diffusion pump with liquid nitrogen traps (B) or an ion pump (C). The reduction process was 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 applying the theory of diffusion in a plane sheet having an equal surface concentration and a uniform initial distribution of solute in the sheet. The coefficients obtained under diffusion pump vacuum varied with the reduction time, and this tendency was more marked in case A. The diffusion coefficients obtained in case C were nearly constant at all reduction temperatures, independent of the reduction time; except in the initial stage. It appeared that the differences were due to contamination introduced by the diffusion pump. When using an ion pump, the diffusion coefficients (figure 6) of point defects in the reduced rutile could be described by:

D (cm2/s) = 9.1 x 101exp[-2.42(eV)/kT]

This activation energy was very close to that of oxygen ions, which diffused in rutile via the vacancy mechanism.

Influence of Contamination on Diffusion of Point Defects in Rutile Reduced in Vacuum. Iguchi, E., Yajima, K.: Transactions of the Japan Institute of Metals, 1972, 13[1], 45-9

Figure 6

Point defect diffusivity in rutile