A journey through the defects structure in (Nd,Tm)-doped ceria electrolytes using x-rays absorption and μ-Raman spectroscopies at cryogenic temperatures

Doping ceria with trivalent rare earth (RE) ions gives rise to systems characterized by a high ionic conductivity in the intermediate temperature range (773–973 K), making these oxides possible solid electrolytes for solid oxide cells. A combined X-ray absorption and low temperature µ-Raman spectroscopy study was performed on Ce1-x(Nd0.74Tm0.26)xO2-x/2 with x ranging between 0.05 and 0.60, to investigate the local structural properties of the system and to correlate them with the average ones. The origin of an extra mode occurring close to the most intense signal in the Raman spectrum of samples with x ≤ 0.30 was explained and attributed to the effect of local collapses in the Ce-O interatomic distances, induced by the creation of vacancies. Moreover, a strong deformation of the ceria structure was observed starting from x = 0.20, causing a shrinkage of the Ce/RE-O and Ce/RE-Ce/RE distances within the first two coordination shells. The so obtained local scale information is of help in providing a comprehensive overview of the structural properties of rare earth doped ceria.