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 (table 20) 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

Figure 3

Diffusion of H2O in Ba4Ca2Nb2O11