Abstract
In this study, 5Y-PSZ-based ceramics with 15 mol.% of manganese oxide were obtained from PSZ + MnO2 powders mixtures by pressing and direct firing. The resulting materials show a stable cubic fluorite structure with only minor traces of segregated manganese oxides and relative density from 90% to 98%. The linear thermal expansion coefficient is in the order of 10−5 K−1 at 500 K and increases gradually with temperature, due to the onset of a contribution of chemical expansion, reaching about 13 × 10−6 K−1 at 1100 K. These results are suitable for prospective applicability as buffer layers to minimize degradation and delamination of electrolyte/oxygen electrode interfaces in solid electrolyte cells. The electrical conductivity remains close to 1 S/m at 973 K and close to 7 S/m at 1273 K, suggesting mixed conductivity with a prospective contribution to electrode processes occurring at electrode/electrolyte interfaces. Guidelines for further improvement were also established by a detailed analysis of the impact of heating/cooling rate, firing temperature, and time on those properties, based on Taguchi planning.
Highlights
Additions of manganese oxide to ZrO2 -based materials have attracted significant interest for catalytic applications [1,2] and in solid-state electrochemical cells
Mn is a key component in oxygen electrode materials and its incorporation in zirconia-based buffer layers may minimize electrode/electrolyte reactivity and delamination [3]
The firing schedules determine structural, microstructural, and redox changes in zirconia-based materials with relatively high additions of manganese oxide, and may have important effects on relevant properties, if one considers the design of buffer layer materials to minimize degradation and delamination at oxygen electrode–electrolyte interfaces
Summary
Additions of manganese oxide to ZrO2 -based materials have attracted significant interest for catalytic applications [1,2] and in solid-state electrochemical cells. Possible explanations for the contribution of Mn2+ to stabilize the cubic phase may rely on the ratio of ionic radii rMn2+ : rO2− = 0.69, which is close to the ideal cation:anion ratio rc : ra = 0.732 for close packing with coordination 8, whereas the corresponding ratio rZr4+ : rO2− = 0.59 is significantly lower. This cannot explain a decrease in lattice parameter of cubic zirconia with increasing additions of manganese [6], if one considers only differences in cationic radii (rMn2+ > rZr4+ ).
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