Porous ceramics based on yttrium and scandium-cerium doped ZrO₂ with fluorite structure: Impact of chromium on conductivity

The total conductivity of the compositions containing Zr_0.89Sс_0.1Ce_0.01О₂ or Zr_0.92Y_0.08О₂ powders and Cr₂O₃ was studied to evaluate a potential impact of the chromium deposition on the surface of electrolyte grains in the porous composite cathode. The compositions were fabricated in the corresponding ratios: (100-х) mol% Zr_0.89Sс_0.1Ce_0.01О₂ - х mol% CrO_1.5 (10Sc1CeSZ-Cr) and (100-х) mol% Zr_0.92Y_0.08О₂ - х mol% CrO_1.5 (8YSZ-Cr) with х = 0.25, 0.5, 1, and 2. Porous ceramic Zr_0.89Sс_0.1Ce_0.01О₂ with 49% relative density exhibits higher conductivity than Zr_0.92Y_0.08О₂. In general, a small addition of chromium decreases the conductivity of Zr_0.89Sс_0.1Ce_0.01О₂ and Zr_0.92Y_0.08О₂, although the values of the conductivity change in a non-linear way, reaching minimum for 10Sc1CeSZ-Cr1 and 8YSZ-Cr0.25 compositions. This is accompanied by the decrease in the activation energy of the conductivity from 1.35 eV to 1.19 eV in the 10Sc1CeSZ-Cr series and from 1.28 eV to 1.19 eV in the 8YSZ-Cr series with the rise in the chromium content. Evolution of the conductivity values is associated with the interstitial incorporation of chromium into the fluorite structure as well as with its segregation on the surface of grains and grain boundaries. Chromium coexists in the multivalent states (Cr³⁺ and Cr⁶⁺) on the surface of grains. Considering a long-term operation of the SOFC system, one could suggest that Zr_0.89Sс_0.1Ce_0.01О₂ will show more promising transport characteristics in the presence of the chromium containing interconnects.