Sm. Haile et al., Non-stoichiometry, grain boundary transport and chemical stability of proton conducting perovskites, J MATER SCI, 36(5), 2001, pp. 1149-1160
The interrelationship between defect chemistry, non-stoichiometry, grain bo
undary transport and chemical stability of proton conducting perovskites (d
oped alkaline earth cerates and zirconates) has been investigated. Non-stoi
chiometry, defined as the deviation of the A : M molar ratio in AMO(3) from
1 : 1, dramatically impacts conductivity, sinterability and chemical stabi
lity with respect to reaction with CO2. In particular, alkaline earth defic
iency encourages dopant incorporation onto the A-atom site, rather than the
intended M-atom site, reducing the concentration of oxygen vacancies. Tran
sport along grain boundaries is, in general, less favorable than transport
through the bulk, and thus only in fine-grained materials does microstructu
re impact the overall electrical properties. The chemical stability of high
conductivity cerates is enhanced by the introduction of Zr. The conductivi
ty of BaCe0.9-xZrxM0.1O3 perovskites monotonically decreases with increasin
g x (increasing Zr content), with the impact of Zr substitution increasing
in the order M = Yb --> Gd --> Nd. Furthermore, the magnitude of the conduc
tivity follows the same sequence for a given zirconium content. This result
is interpreted in terms of dopant ion incorporation onto the divalent ion
site. (C) 2001 Kluwer Academic Publishers.