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

Abstract

A dense tubular solid electrolyte with the composition Ce0.8Y0.2O1.9−δ (CY20) was prepared. In situ time‐of‐flight neutron powder diffraction (TOF‐ND) was performed at 900°C in the oxygen partial pressure pO2 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 pO2 in the range of pO2>10−14 atm, while a dramatic expansion (∼0.6%) of the fluorite structure occurred at a pO2 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 ɛc/δ=0.08 and corresponding to δ=0.10 at a pO2 of 10−18 atm, all in agreement with the data published in the literature. The relative change in lattice parameter Δa/a followed a −1/4 power relation with pO2 in a low‐pO2 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.