Electronic Conductivity of ZrO2-CeO2-YO1.5 Solid Solutions

ZrO2-CeO2-YO1.5 (ZCY) solid solutions have higher surface catalytic activity for oxygen exchange reaction than ZrO2-YO1.5(YSZ) and CeO2-YO1.5 (YDC) electrolytes. The high catalytic activity is strongly related to the physical properties such as electronic conductivity in ionic or mixed electric/ionic conductors. On the other hand, ZCYs have lower oxide ion conductivity than YSZ, which is not preferable when the material is used as electrode materials for SOFCs. The improvement of the conductivity of CeO2-ZrO2 based solid solutions should be achieved by changing the dopant from YO1.5 to ScO1.5 because the oxide ion conductivity of a scandia stabilized zirconia (ScSZ) electrolytes is a couple of times higher than YSZ. In this study, the electronic conductivity of [(ZrO2)1-x(CeO2)x]0.8(ScO1.5)0.2 (ZCS20, x = 0, 0.1, 0.2) was directly measured by a DC polarization method with a modified Hebb-Wagner’s type ion blocking cell. ZCS20 solid solutions were prepared by a conventional solid state reaction method. Appropriate amounts of ZrO2(TOSOH, TZ-0), CeO2(WAKO, 99.9%) and Sc2O3 (Daiichi Kigenso Kagaku Kogyo, 99.9%) powders were weighed and mixed by ball-milling method. The mixture was shaped into disks, pressed by CIP at 390 MPa, and sintered at 1773 K in air for 5 h. The obtained pellets were ground and polished. The thickness and diameter of the pellet was about 1 mm and 17 mm, respectively. Porous platinum electrodes with platinum current collectors and leads were attached on the centers of both surfaces of the pellet. The setting of our ion blocking cell was drown in our previous paper. The oxygen partial pressure around the blocking cell was usually fixed at 1 kPa during the measurement. A constant voltage was applied between the reversible and the blocking electrode as the oxygen was transferred from the blocking to the reversible electrodes in order to avoid a gas leakage from the glass seal due to the increase of pressure around the blocking electrode. When the voltage(Eapp) is applied to the sample, the current changes until an ionic current is fully blocked. In the steady state, the measured current is electronic current(Ie). The electronic conductivity (σe) was determined by the equation as follows,