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).