An in-depth study of the defects architecture in co-doped ceria electrolytes for solid oxides cells

Doped ceria systems, crystallizing with a fluorite-type structure, form a family of widely studied electrolytes for IT-SOCs (Solid Oxides Cells working at Intermediate Temperatures). In particular, in Ce1-xRExO2-x/2 compounds (RE= trivalent Rare Earth), the partial substitution of Ce4+ by RE leads to the formation of not-associated oxygen vacancies, allowing the conduction of O2- ions through the structure, thanks to a vacancy-hopping mechanism. However, the factors ruling the ionic conductivity in such compounds are quite complex and strictly related to the structure of the electrolyte (in particular, to the different families of defects occurring in it). In the last years, our research group extensively explored the structural and micro-structural properties of RE-doped ceria through different techniques, both at ambient and non-ambient conditions, thus giving a deep knowledge on the structure of such compounds. Moreover, we recently undertook a study on the defects architecture in co-doped ceria systems, in which two RE doping ions with different dimensions are simultaneously used; as a result, the overall ionic conductivity is generally higher with respect to singly doped ones. X-ray absorption spectroscopy and pair distribution function studies were recently performed on Ce1-x(Nd0.74Tm0.26)xO2-x/2 samples at the ESRF synchrotron (respectively at ID22 and LISA beamlines), to deepen the knowledge on the local structure in such compounds. The analysis of the collected data should provide information on the deformations taking place with the increasing dopants amount, also laying the foundations for future in-operando measurements. With the present contribution, an overview on the recently acquired data and their implications will be given.