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4 Bulletin of the Polish Academy of Sciences. Chemistry

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Defect structure and its mobility in pure and chromium doped cobaltous oxide

Mrowec S., Grzesik Z.

Bulletin of the Polish Academy of Sciences. Chemistry

2003

Vol. 51, No. 1

45-57

Defect structure and the mobility of point defects in pure metal-deficient cobalt oxide (Co1-yO) and in Co1-yO-Cr(2)O(3) solid solutions have been studied as a function of temperature (1,223-1,573 K) and oxygen pressure (10-10(5)Pa) using microther-mograwimetric techniques. It has been shown that the predominant defects in pure and Cr-doped cobaltous oxide are singly ionized cation vacancies, and 3% at. of dopant is high enough to fix the concentration of predominant defects in such solid solutions on a constant level, being much higher than in pure Co(1-yO. The mobility of point defects in pure Co1-yO has been found to be concentration independent, strongly suggesting that in spite of rather high concentration no interactions and clustering of defects is to be expected. On the other hand, in Cr-doped cobaltous oxide, the defect structure is more complicated, although singly ionized cation vacancies seem to be still predominant defects.

Defect disorder of undoped and Sr-doped LaCoO3-delta

Nowotny J., Rękas M.

Bulletin of the Polish Academy of Sciences. Chemistry

2002

Vol. 50, No. 1

93-108

The paper considers defect disorder models of undoped lanthanum cobaltate, LaCoO(3)-delta, and Sr-doped LaCoO(3-delta, La(1-x)SrCoO(3-delta) (LSC), involving both random defect model and cluster defect model. The models are derived using the nonstoichiometry data reported in the literature. Doubly ionized oxygen vacancies are assumed to be the predominant ionic defects within the entire range of compositions. The effect of Sr content on defect disorder of LSC is discussed in terms of both defect models. Impact of segregationon surface composition of ionic solids in general and LSC materials in particular is briefly outlined. The effect of the interface layer on functional properties of LSC as electrode material is briefly discussed.

Surface electrical effects at the oxygen/zirconia interface during oxidation

Bąk T., Nowotny J., Rękas M., Sorrell C. C.

Bulletin of the Polish Academy of Sciences. Chemistry

2001

Vol. 49, No. 1

67-73

This paper describes application of a high temperature Kelvin probe (HTKP) for studies of the outermost surface layer of materials and related charge transfers (at or in this layer) at elevated temperatures in the gas phase of controlled composition. Specifically, the paper considers application of the HTKP for surface monitoring of yttria-stabilized zirconia (10Y—ZrO(2) during isothermal oxidation at 1073 and 1173 K. The obtained work function (WF) data are discussed in terms of oxygen reactivity with zirconia involving (i) oxygen chemisorption and (ii) oxygen incorporation into the outermost surface layer.

A model of Bi-functional zirconia

Bąk T., Nowotny J., Rękas M., Sorrell C. C.

Bulletin of the Polish Academy of Sciences. Chemistry

2001

Vol. 49, No. 1

57-65

The paper considers an effect of the gas/solid interface on performance of solid oxide fuel cells (SOFC's). Specifically, application of bi-functional zirconia, involving the functions of a solid electrolyte and electrodes, is outlined. A model, describing the effect of segregation on the formation of a bi-dimensional surface layer, is proposed. The model is considered in terms of the effect of the surface layer on the transfer of charge and matter at the oxygen/zirconia interface. Impact of surface processing of zirconia, involving incorporation of aliovalent ions into the surface layer, on the formation of the bi-functional zirconia is discussed. Application of the bi-functional zirconia for construction of a new generation of electrodeless electrochemical devices is discussed.