Conductivity Increase As a Result of the Disappearance of Short-Range Ordering in a Scandia-Zirconia Electrolyte

Abstract

Solid oxide cell electrolytes and structures have been greatly optimised to offer high performance and good durability for commercial implementation. This has highlighted an underlying issue where the slow, long-term conductivity degradation in the generally used fluorite structured oxide-ion conducting doped zirconias known to be related to reorganisation of their defect short-range structures. Among the doped zirconia systems, scandia stabilised zirconia (SSZ) gives the highest ionic conductivity due to the smallest mismatch between the dopant and host cations. However, owing to these similar and small sizes, the system is more prone to defect short-range ordering. This leads to a complex phase diagram of the Sc2O3-ZrO2 system and, depending on the composition, its ionic conductivity ages more significantly than other zirconia systems on high temperature annealing. Here, we report a magnesia and india co-doped scandia stabilised zirconia (IMSSZ) composition that offers high ionic conductivity, 0.14 at 850 ℃ and 0.4 at 1000 ℃, improved phase stability in both macro- and micro scales, and long-term conductivity stability. The conductivity after annealing the sample at 850 ℃, for different times, 0 (as-sintered), 167 and 426 hours, is correlated to the microdomain structural evolution. We show the initial of conductivity increase over time as a result of eliminating the defect short-range ordering using electron diffraction and powder neutron diffraction, resulting in a long-term stable disordered structure with improved conductivity. We will discuss here the thermodynamic driving forces for the breakdown of defect short-range ordering, and how right co-dopant sizes may play a role. Figure 1