The self-diffusion of O in undoped alumina monocrystals was investigated by using the gas-solid isotope exchange technique. After diffusion annealing, the profiles of 18O were determined by means of secondary ion mass spectrometry. This revealed 2 parts, in which the behavior close to the initial surface was attributed to bulk self-diffusion while the diffusion tails were attributed to migration in dislocation walls. At temperatures ranging from 1500 to 1720C (table 10), the bulk self-diffusivity of O could be described by:

D(cm2/s) = 206 exp[-636(kJ/mol)/RT]

Possible diffusion mechanisms were proposed in terms of an extrinsic behavior that was associated with Si contamination. Within the same temperature range, the O diffusivity in sub-boundaries (table 11) could be described by:

D(cm2/s) = 3.1 x 1014exp[-896(kJ/mol)/RT]

The high activation enthalpy was attributed to segregation effects at sub-boundaries.

D.Prot, C.Monty: Philosophical Magazine A, 1996, 73[4], 899-917

 

 

 

Table 10

Bulk Diffusivity of O in Undoped -Al2O3

 

Temperature (C)

D (cm2/s)

1500

4.6 x 10-17

1520

5.1 x 10-17

1550

1.0 x 10-16

1570

2.9 x 10-16

1577

2.0 x 10-16

1600

3.5 x 10-16

1630

7.0 x 10-16

1660

1.2 x 10-15

1685

3.1 x 10-15

1720

4.2 x 10-15

 

 

 

 

Table 11

Sub-Boundary Diffusivity of O in Undoped -Al2O3

 

Temperature (C)

D (cm3/s)

D (cm2/s)

1500

2.6 x 10-20

8.3 x 10-13

1520

9.1 x 10-20

2.9 x 10-12

1550

2.3 x 10-19

7.3 x 10-12

1570

8.1 x 10-19

2.6 x 10-11

1577

3.2 x 10-19

1.0 x 10-11

1600

2.0 x 10-18

6.4 x 10-11

1630

2.9 x 10-18

9.1 x 10-11

1650

5.0 x 10-18

1.6 x 10-10

1660

6.4 x 10-18

2.0 x 10-10

1675

3.2 x 10-18

1.0 x 10-10

1685

1.1 x 10-17

3.5 x 10-10

1707

2.3 x 10-17

7.3 x 10-10

1720

2.9 x 10-17

9.2 x 10-10

1751

1.5 x 10-17

4.8 x 10-9