Hyperstoichiometric material

The method of heterogeneous isotopic exchange was used to determine the self-diffusion coefficient of oxygen in Pr70j2 (iota phase) as a function of temperature and pressure. The results indicated that there are two types of hyperstoichiometric material depending on the degree of oxygen excess. When the compound is close to stoichiometry, the diffusion coefficient can be written... 

Diffusion coefficient and surface exchange coefficient measurements have been reported for the K2MF4 type oxide materials by a number of authors [4-8, 13-19] and have been complemented by electrochemical permeation measurements [20-27] all of which demonstrate the fast oxide ion conduction of hyperstoichiometric K2NiF4 type oxides. Early reports also demonstrate the relatively poor oxide ion mobility in those materials found to be hypostoichiometric [28,29]. Initial reports of the fast oxide ion conduction in La2Ni04+s [4, 6-8] have generated a number of further studies [13-19] regarding the optimization of composition and determination of the effects of anisotropy on the conduction properties of these materials. Each of these features will be discussed in more detail below. 

To construct a Brouwer diagram to depict the relative concentration of these defects with P02, it is necessary to define a series of approximations to the full neutrality condition. The first of these corresponds to a region (R I) where 6 > 0 and where the material is hyperstoichiometric. 

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