Revealing the concentration quenching mechanism of oxygen ion conduction in Sm3+-doped CeO2 via photoluminescence

Abstract

Probing local lattice distortions in acceptor-doped CeO₂ oxygen ion conductors is important to understanding ionic conduction mechanism and improving performance. Dense Ce_1-xSm_xO_2-δ (SDC) oxygen ion conductors were synthesized. AC impedance shows that x = 0.10 yields the highest bulk conductivity (8 mS/cm at 500 °C), surpassing reported values. Raman results indicate a monotonic increase in defect association between oxygen vacancies and Sm³⁺ with doping. We propose a spectral probe strategy using Sm³⁺ photoluminescence to detect local lattice distortions in SDC. Photoluminescence shows local lattice distortion decreases then increases with Sm³⁺ content, with x = 0.05 lowest, explaining the activation energy of bulk conduction trend, then revealing the structural origin of bulk conductivity quenching. Furthermore, photoluminescence analysis shows that higher Sm³⁺ levels also increase disorder around Ce⁴⁺ and Sm³⁺. This photoluminescence strategy offers a sensitive tool for probing local lattice distortions and can be extended to other materials with Sm³⁺-doping available.