Oxygen Non-Stoichiometry and Thermal–Chemical Expansion of Ce0.8Y0.2O1.9−δ Electrolytes by Neutron Diffraction

A dense tubular solid electrolyte with the composition Ce_0.8Y_0.2O_1.9?δ (CY20) was prepared. In situ time-of-flight neutron powder diffraction (TOF-ND) was performed at 900°C in the oxygen partial pressure p O₂ range from 10^?1–10^?18 atm, and TOF-ND data were analyzed by the Rietveld method. Diffraction data showed that the lattice parameter moderately increased with decreasing p O₂ in the range of p O₂>10^?14 atm, while a dramatic expansion (～0.6%) of the fluorite structure occurred at a p O₂ of 10^?18 atm. By refining all reasonable structural parameters, an approximately linear relationship between lattice parameter and oxygen vacancy δ was observed, resulting in ?_c/δ=0.08 and corresponding to δ=0.10 at a p O₂ of 10^?18 atm, all in agreement with the data published in the literature. The relative change in lattice parameter Δ a / a followed a ?1/4 power relation with p O₂ in a low- p O₂ regime. As several (often strongly correlated) structural parameters can affect the intensities in ND profiles, care was taken to select refinement variables. It was found that O atom thermal factors for CY20 increased as the oxygen vacancy concentration and lattice expansion increased.