YSZ-MgO composite electrolyte with adjusted thermal expansion coefficient to other SOFC components

YSZ-MgO composite electrolytes were prepared by mixing partially stabilized zirconia with various amounts of magnesium oxide and firing at 1400 °C for 5 h. From X-ray diffraction (XRD) and dilatometry it was observed that 15-20 mol% MgO was dissolved in the zirconia leading to composites composed of fully stabilized zirconia and magnesia. The thermal expansion increased with increasing MgO content and a thermal expansion coefficient (TEC) of 12.3 × 10^-6 K^-1 was obtained with 80 mol% MgO in the starting mixture. The thermal expansion fits very well with those of interconnect and electrode materials in a solid oxide fuel cell (SOFC) but the YSZ-MgO composite already contains high amounts of MgO, which percolatively inhibits the conductivity. Highest total conductivity at 800 °C of 0.015 S cm^-1 was measured on a composite with 20 mol% MgO in the starting mixture which is similar to values of fully yttria-stabilized zirconia (YSZ).