Atomistic simulation techniques were used to examine the defect chemistry of this perovskite-structured material. In practice, dopants were added in order to obtain a high electrical conductivity and rapid gas adsorption/desorption. Thus, a wide range of dopants, substituted at both Nd and Co sites, was examined here. Charge compensation for aliovalent dopants was predicted to occur via the formation of oxide-ion vacancies. These were thought to be key sites with respect to catalytic and sensor activity. The low activation energies calculated for oxide-ion migration were consistent with the high O mobilities measured experimentally. Here, Sr and Ca - which occupied Nd sites in the lattice - were found to be the most soluble of the alkaline earth metals, in agreement with experiment. These dopant ions also had the weakest binding energies for dopant-vacancy cluster formation. Mechanisms of electronic defect formation, critical to the overall transport properties of the material, were also considered. The results suggested that disproportionation of the Co ion to form small polaron species was the most favorable intrinsic defect process. In doped compounds, formation of electronic holes via uptake of O at vacant sites was found to be a low energy process.

Disproportionation, Dopant Incorporation and Defect Clustering in Perovskite-Structured NdCoO3. C.Tealdi, L.Malavasi, C.A.Fisher, M.S.Islam: Journal of Physical Chemistry B, 2006, 110[11], 5395-402