It was recalled that complex perovskite-type oxides of the form, A3Nb2-xCa1-xO9, became excellent protonic conductors (if x was greater than zero) when they were exposed to water vapor. By using X-ray diffraction and transmission electron microscopy, it was shown that the 1:2 ordering of stoichiometric samples was gradually replaced by 1:1 ordering plus random order. The variously ordered regions appeared as nano-scale fluctuations. A study of the protonic conductivity (tables 11 and 12) revealed that a rapid increase in the effective mobility of protons accompanied the structural changes. This could be explained in terms of percolation in a composite.

D.Yang, A.S.Nowick: Journal of the American Ceramic Society, 1995, 78[11], 3033-9

 

 

 

Table 11

Proton Conductivity of Ba3Nb2-xCa1-xO9

 

 

x/3

 

[H] (%)

 

400C (S/cm)

 

 

0.02

 

1.0

 

0.00013

0.03

1.7

0.00074

0.06

6.4

0.00272

0.08

8.7

0.00394

0.12

13.1

0.00648

 

 

 

 

Table 12

Proton Conductivity of Sr3Nb2-xCa1-xO9

 

 

x/3

 

[H] (%)

 

400C (S/cm)

 

 

0.02

 

1.4

 

0.00013

0.03

2.5

0.00026

0.05

4.1

0.00046

0.06

5.3

0.00089

0.07

6.1

0.0028

0.08

8.0

0.0034

0.10

9.9

0.0040