Effects of strontium content on microstructure and ionic conductivity of samarium-doped ceria

Abstract

Samarium doped ceria is a material which can achieve a high oxygen ion conductivity making it a promising electrolyte material for applications such as solid oxide fuel cells. Co-doping ceria with strontium alongside another dopant such as samarium has been the subject of a number of studies. Most suggest that strontium co-doping will improve the ionic conductivity compared to singly doped materials. However, there are a number of apparent inconsistencies in the literature due to the range of preparation methods employed. This meant that the true effects of Strontium co-doping were difficult to ascertain. To address this, two different compositional series of strontium and samarium co-doped ceria were studied. The first compositional series, Ce_0.8-xSm_0.2Sr_xO_1.9-x-δ, partially replaced Ce with Sr and was designed to be comparable to existing materials. The second series, Ce_0.8+xSm_0.2-2xSr_xO_1.9-δ, was designed to have a constant oxygen vacancy concentration in order to study the intrinsic effects on conductivity. In order to control for impurities and microstructural effects a high purity synthesis method was used and microstructural studies of all the materials were performed.

The individual effects of strontium co-doping on conductivity were separated out allowing explanations of the contradictions in the existing literature. None of the codoped materials studied showed increases in conductivity compared to the singly doped materials at a typical fuel cell operating temperature. It was concluded that strontium co-doping of ceria can mitigate the deleterious effects on conductivity of silicon impurities or poor microstructure, but not improve the conductivity beyond that of the best singly doped ceria electrolytes.

Date of Award	30 Nov 2016
Original language	English
Awarding Institution	University of St Andrews
Supervisor	Richard Baker (Supervisor)