Effect of sintering atmosphere on densification, redox chemistry and conduction behavior of nanocrystalline Gd-doped CeO2 electrolytes

Nanocrystalline 10 mol% gadolinia doped ceria (GDC) was processed and sintered in air and oxygen to study the role of sintering atmosphere on densification and the redox reaction (Ce4+↔Ce3+) and its effect on the conduction behavior. The density of the air-sintered sample was higher than the oxygen-sintered sample. X-ray photoelectron spectroscopy (XPS) confirmed the presence of higher fraction of Ce3+ and Raman spectroscopy revealed higher concentration of oxygen vacancies in GDC sintered in air indicating higher degree of reduction in air compared to oxygen atmosphere. Impedance spectroscopy studies revealed breaks in the slope of the Arrhenius plot of bulk conductivity indicating presence of different conduction mechanisms which can be related to the redox and defect chemistry. GDC sintered in oxygen atmosphere showed higher ionic conductivity and lower activation energy than the air sintered sample in lower temperatures whereas it showed higher activation energy in the higher temperature range owing to a change in the redox and defect chemistry.