Co-doping Effect of Divalent (Mg(superscript 2+), Ca(superscript 2+), Sr(superscript 2+)) and Trivalent (Y(superscript 3+)) Cations with Different Ionic Radii on Ionic Conductivity of Zirconia Electrolytes

Abstract

The purpose of this study is to develop a novel co-doping zirconia electrolyte with high ionic conductivity for application in solid oxide fuel cell (SOFC). The effect of ionic radius, lattice binding energies and doped concentration on ionic conductivities of divalent (Mg(superscript 2+), Ca(superscript 2+), Sr(superscript 2+)) and trivalent (Y(superscript 2+)) cations co-doped zirconia (Zr0.92Y(subscript 0.16-x)M(subscript x) O(subscript 2.08-0.5x), wherein M=Mg(superscript 2+), Ca(superscript 2+), Sr(superscript 2+) and x=0, 0.005, 0.01, 0.015 and 0.02) electrolytes were investigated by using X-ray diffractometer, scanning electron microscopy and AC impedance analysis in this work. Experimental results show the best ionic conductivity (0.022 S/cm) in Zr0.92Y0.155M0.005O2.0775 specimen which is 46% higher than that of (ZrO2)0.92(Y2O3)0.08 (0.015 S/cm). Hard sphere model is used to measure the average radius of oxygen vacancies. The tendency of ionic conductivity of co-doping zirconia system decreases with increase of the ionic radius of divalent cation and the order of ionic conductivity is σ(subscript MgYSZ)＞σ(subscript CaYSZ) ＞σ(subscript SrYSZ), similar to that of oxygen vacancy radius r(subscript Vo)(MgYSZ)＞r(subscript Vo)(CaYSZ)＞r(subscript Vo)(CaYSZ), implying that the hard-sphere model is a useful tool to measure the average radius of oxygen vacancies and to estimate the ionic conductivity of zirconia electrolyte.