The self-diffusion of Na ions was studied in the face-centered cubic, body-centered cubic and hexagonal high-temperature phases of (Li,Na)2SO4. It was found that the activation energy (table 25) was close to 0.4eV for compositions with 25, 50 or 75mol%Na; that is, for all 3 phases. A comparison was made with the self-diffusion of Li ions, and with conductivity data (table 26). It was noted that the solid solutions exhibited a higher conductivity than did the pure salt in the case of face-centered cubic Li2SO4 as well as hexagonal Na2SO4. The effect was particularly marked in the latter case. Both the Li+ and Na+ ions were very mobile in hexagonal solid solutions. It was suggested that this was because the Li+ ions entered interstitial positions of (½,0,0) type, while vacancies were created in the Na+ lattice.
A.Lunden, L.Nilsson, R.Tärneberg: Solid State Phenomena, 1994, 39-40, 199-202
Table 25
Diffusivity of Li and Na at 873K in Li2SO4-Na2SO4 Solid Solutions
Na(%) |
Li(%) |
Diffusant |
D(cm2/s) |
Q(eV)
|
0 |
100 |
Na |
1.8 x 10-5 |
0.34 |
25 | 75 | Na | 1.8 x 10-5 | 0.41 |
50 | 50 | Na | 1.6 x 10-5 | 0.42 |
75 | 25 | Na | 4.0 x 10-6 | 0.40 |
0 | 100 | Li | 2.1 x 10-5 | 0.33 |
50 | 50 | Li | 1.8 x 10-5 | 0.68
|
Table 26
Conductivity of Li2SO4-Na2SO4 Solid Solutions
Na(%) |
Li(%) |
873K(S/cm) |
QT(eV)
|
0 |
100 |
1.07 |
0.44 |
25 | 75 | 1.22 | 0.40 |
50 | 50 | 1.25 | 0.45 |
75 | 25 | 0.29 | 0.68 |
100 | 0 | 0.002 | 1.70 |