Detailed measurements of the temperature dependence of the tracer diffusivity of substitutional Na ions (table 11) indicated that the activation energy for the formation of a Frenkel pair was temperature-dependent. However, the decreases in defect formation enthalpy at high temperatures, as deduced from these diffusion experiments, were somewhat smaller than those obtained from conductivity data. The activation enthalpy for the jumping of a Na ion into a neighboring vacancy was found to be almost twice that for the motion of a free vacancy. The higher migration barrier was assumed to result from the absence of covalent interactions in the case of the Na ion.

A Study of the High-Temperature Transport Anomaly in AgBr, by Diffusion of Sodium Tracer. A.P.Batra, L.M.Slifkin: Journal of Physics and Chemistry of Solids, 1977, 38[7], 687-92

 

Table 11

Diffusivity of Na in AgBr

 

Temperature (C)

D (cm2/s)

419.0

1.10 x 10-6

401.2

5.31 x 10-7

375.1

1.70 x 10-7

349.8

5.78 x 10-8

324.8

1.92 x 10-8

300.6

6.39 x 10-9

277.2

2.06 x 10-9

250.7

5.49 x 10-10

224.7

1.31 x 10-10

201.2

3.02 x 10-11

200.3

2.77 x 10-11

181.3

8.34 x 10-12

181.1

7.93 x 10-12

160.8

1.96 x 10-12

160.5

1.90 x 10-12

 

Figure 1

Diffusivity of Nd3+ in AgBr