Enhanced ionic conductivity in an otherwise poorly conducting Ce(0.90)Ca(0.10)O(2-delta) system

Abstract

A poorly conducting ionic material Ce(0.90)Ca(0.10)O(2-delta) was converted to a highly conducting composition by a codoping strategy with Sm3+ and Gd3+. A 50 precent replacement of Ca with either Sm or Gd has increased the conductivity at 550 degrees C of Ce(0.90)Ca(0.10)O(2-delta) from 0.0040 to 0.0169 S/cm for the Ce(0.90)Ca(0.05)Sm(0.05)O(2-delta) composition and to 0.0184 S/cm for the Ce(0.90)Ca(0.05)Gd(0.05)O(2-delta) composition. The enhancement in the oxide ion conductivity of these codoped samples has been related to the low ionic radii mismatch and the elastic strain. The extended X-ray absorption fine structure measurements on these systems confirmed that Gd, when coupled with Ca, introduced more disorder in the system, leading to lower activation energy and higher conductivity. In addition, a reduction in the Ce-O bond distance and coordination number has also been observed with codoping.