posted on 2024-08-02, 06:13authored byJavier Zamudio-García, Jose M. Porras-Vázquez, Aurelio Cabeza, Jesús Canales-Vázquez, Enrique R. Losilla, David Marrero-López
Rare-earth doped CeO2 materials
find extensive
application
in high-temperature energy conversion devices such as solid oxide
fuel cells and electrolyzers. However, understanding the complex relationship
between structural and electrical properties, particularly concerning
rare-earth ionic size and content, remains a subject of ongoing debate,
with conflicting published results. In this study, we have conducted
comprehensive long-range and local order structural characterization
of Ce1–xLnxO2–x/2 samples (x ≤ 0.6; Ln = La, Nd, Sm, Gd, and Yb) using X-ray
and neutron powder diffraction, Raman spectroscopy, and electron diffraction.
The increase in the rare-earth dopant content leads to a progressive
phase transformation from a disordered fluorite structure to a C-type
ordered superstructure, accompanied by reduced ionic conductivity.
Samples with low dopant content (x = 0.2) exhibit
higher ionic conductivity in Gd3+ and Sm3+ series
due to lower lattice cell distortion. Conversely, highly doped samples
(x = 0.6) exhibit superior conductivity for larger
rare-earth dopant cations. Thermogravimetric analysis confirms increased
water uptake and proton conductivity with increasing dopant concentration,
while the electronic conductivity remains relatively unaffected, resulting
in reduced ionic transport numbers. These findings offer insights
into the relationship between transport properties and defect-induced
local distortions in rare-earth doped CeO2, suggesting
the potential for developing new functional materials with mixed ionic
oxide, proton, and electronic conductivity for high-temperature energy
systems.