AN ABSTRACT OF THE THESIS OF James Morrow, for the Master of Science degree in Mechanical Engineering, presented on November 3, 2017, at Southern Illinois University Carbondale. TITLE: INVESTIGATION OF THE MATERIAL PROPERTIES OF CERIUM OXIDE WITH DOPANTS FOR AN OXYGEN TRANSPORT MEMBRANE MAJOR PROFESSOR: Dr. Kanchan Mondal Many physical properties of cerium oxide both undoped and doped have been studied herein. These properties include electrical conductivity, hardness, sintered density, and microstructure. These will be used to help determine a cerium oxide compound to use as an oxygen transport membrane in a combustion system. These compounds have been readily studied beforehand with exception to compounds with multiple dopants. Along with single doped cerium oxide, dual doped was investigated as well. The samples to be tested were created using co-precipitation and the subsequent powders were sintered at 1500°C to generate solid pellets. Once the pellets were formed the physical properties were tested. It was found that hardness and sintered density had little to no effect on electrical conductivity and the microstructures of the samples were shown to be favorable. As far as single or dual dopants were concerned, it was found that by including a second dopant along with zirconium that the electrical conductivity was reduced. Except for in the case where iron was doped along with zirconium, where the conductivity was increased. It was suggested to use samarium as the second dopant along with zirconium for the membrane.