Development of zirconia–magnesia/zirconia–yttria composite solid electrolytes

Composite solid electrolytes were prepared by thoroughly mixing ZrO2:8 mol% MgO (Z8Mg) and ZrO2:3 mol% Y2O3 (Z3Y) ceramic powders followed by pressing and sintering at 1500 °C/1 h. The properties of the sintered pellets were studied by X-ray diffraction for evaluation of the structural phases by the Rietveld method, by high-temperature dilatometry for analysis of the thermal shrinkage/expansion behavior, and by impedance spectroscopy for determination of the oxide ion conductivity. The x(Z8Mg) + (1 − x)(Z3Y) specimens, x = 0.2, 0.4, 0.5, 0.6, 0.8 and 1.0, are partially stabilized (monoclinic, cubic and tetragonal phases) with density > 94% of the theoretical density and show thermal shock resistance and electrical conductivity values suitable for high-temperature oxygen gas detection. One-end closed tube samples of the composite solid electrolytes were assembled in Pt/Z8Mg + Z3Y/Cr + Cr2O3/Pt electrochemical cells for exposure to different levels of oxygen in the 1–850 ppm range. The total electrical conductivity increases for increasing the relative Z3Y content. Addition of Z3Y to Z8Mg (80 wt.%–20 wt.%) suppresses the electronic contribution to the electrical conductivity at 620 °C.