Divalent oxygen, content

From this it is evident that the diffusivity of La2Ni04+d was competitive with current mixed conducting perovskites with diffusion coefficients of the order of 10 ernes. Evidently the identification of a new mixed conducting ceramic warranted further optimization and hence substitution of both A and B sites was investigated [4,5,7,8,14,18]. Introducing a divalent cation to either the A or B site was expected to reduce the hyperstoichiometry and it was therefore unsurprising to find that the presence of Sr lowered the oxygen content and, as the excess oxide species were viewed as the mobile species, the diffusivity [7]. The effects of a number of dopants are illustrated in Table 1. Most notably the incorporation of cobalt was shown to enhance the low temperature diffusivity of these materials [5, 18] and these materials may prove to be attractive candidates for lower temperature cathode materials (<750 °C). 

In addition to the exclusion of carbon dioxide, it is necessary to exclude oxygen from reactions where cations of the metal hydroxide layer are easily oxidized under basic conditions. LDHs of this type include manganese, cobalt (131) and iron in the divalent oxidation state, and vanadium in the trivalent state. Reactions involving these metal ions have formed LDHs with, for instance, Co " /Co and Fe " /Fe metal content, with the latter, known as green rust, being discussed earlier in Section II.J. 

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