Investigation of conductivity of (Ce_xY_0.2−x)Sc_0.6Zr_3.2O8−δ (0 < x < 0.2) system and its dependence upon oxygen partial pressure

The system Y2O3-Sc2O3-ZrO2 has been extensively studied in the last decade, with the purpose of using it as an electrolyte for solid oxide fuel cells (SOFCs). Scandia stabilized zirconia (SSZ) materials have good ionic conductivity, and yttria, when introduced, stabilizes the SSZ against phase transformation. As cerium is a large ion, it is expected to stabilize the cubic fluorite phase and enhance the conductivity of the scandia zirconia system. The electrical properties of system (CexY0.2-xSc0.6)Zr3.2O8-delta were studied, observing how conductivity changes when cerium is introduced and the amount of yttrium is decreased. Compositions were produced by an innovative sol-gel combustion method in an attempt to obtain a compositionally homogeneous, dense material. This material has the potential to be used as an electrolyte, at intermediate temperatures, for SOFCs. Conductivity in the system (CexY0.2-xSC0.6)Zr3.2O8-delta, has been investigated as a function of partial pressure of oxygen down to 10(-24) bars, at 700 degrees C. Samples with Ceria content have better conductivity at higher pO(2) values. When they are subjected to lower partial pressures of oxygen, there is a clear drop in the conductivity. This drop in the conductivity could be a consequence of the clustering of vacancies, resulting in a decrease of ionic conductivity, as the number of vacancies increases with ceria content. For the samples tested in this system, there is no evidence of significant electronic conductivity. The temperature dependence of conductivity was determined at ambient pressure from 300 to 800 degrees C. From the Arrhenius plot a phase transition is observed to occur between 550 and 600 degrees C. Composition does not have a very significant effect on conductivity values for each temperature. At low temperatures, the dominant contribution to conductivity is due to the poor grain boundary conductivity. (C) 2010 Elsevier B.V. All rights reserved.