The self-diffusivity of O in TiO2-x was determined for x-values of between 0.0005 and 0.0084 by using gas/solid isotope exchange between 16O and 18O, and microgravimetric techniques. It was found that the diffusivity increased with increasing non-stoichiometry (table 135). It was concluded that O vacancies contributed about 20% to the non-stoichiometry at x = 0.0084. It was further suggested that both singly and doubly ionized vacancies were present in the approximate ratio of 1:2. The results indicated that a complete description of the defect structure should include interstitial Ti ions with 3 positive effective charges. These were the major defect in the more reduced oxide, while interstitial Ti ions with 4 effective charges became important in the almost stoichiometric material.

F.Millot, C.Picard: Solid State Ionics, 1988, 28-30, 1344-8

 

 

 

Table 135

Diffusion of O in TiO2-x at 1373K

 

PO2 (atm)

x

D (m2/s)

3.31 x 10-10

5 x 10-4

1.45 x 10-16

3.80 x 10-11

7 x 10-4

1.87 x 10-16

3.39 x 10-12

1.1 x 10-3

2.70 x 10-16

3.80 x 10-13

1.7 x 10-3

2.95 x 10-16

3.38 x 10-14

2.8 x 10-3

4.09 x 10-16

5.37 x 10-15

4.1 x 10-3

5.01 x 10-16

1.35 x 10-15

5.6 x 10-3

6.85 x 10-16

4.17 x 10-16

7.0 x 10-3

7.58 x 10-16

1.70 x 10-16

8.4 x 10-3

9.20 x 10-16