Application Of Sm³⁺ Photoluminescence In The Study Of Electrical Properties Of La³⁺/Bi³⁺/Gd³⁺ Co-doped SDC Oxygen Ion Conductor

Adjusting the local environment of oxygen vacancies by doping or co-doping is the most common and effective strategy to improve the ionic conductivity of oxygen ion conductors.In this paper,the most potential CeO₂based electrolyte materials of intermediate temperature solid oxide fuel cell will be selected to obtain the local structure information around Ce⁴⁺and various doped ions,including the acceptor doped cations such as Sm³⁺,La³⁺,Gd³⁺and Bi³⁺.The photoluminescence spectrum of Sm³⁺ion is used as the structure probe and then combined with Raman spectrum,the effect of different kinds of cation doping on the electrical properties of CeO₂based electrolyte materials is finally revealed by considering the effects of local lattice distortion,defect association and cation electronegativity.The specific results are shown as follows:1.For La³⁺and Sm³⁺co-doped systems,when Sm³⁺ions are replaced by La³⁺ions,the oxygen vacancy introduced by La³⁺ion substitution moves from the adjacent coordination site of La³⁺ions to the coordination lattice of Sm³⁺and Ce⁴⁺ions.The crucial factor of grain conductivity is not the defect association and the local lattice distortion on the oxygen vacancy migration path in the lattice,but the cationic electronegativity on the oxygen vacancy migration path.2.For Gd³⁺and Sm³⁺co-doped systems,when Sm³⁺ions are replaced by Gd³⁺ions,the oxygen vacancies introduced by Gd³⁺substitution are mainly located around Ce⁴⁺.The dominating factors of grain conductivity are defect association and the cationic electronegativity on the oxygen vacancy migration path,rather than the local lattice distortion on the oxygen vacancy migration path,which further proves the importance of cationic electronegativity on oxygen ion conduction.3.For Bi³⁺/Sm³⁺co-doped system,with Bi³⁺replacing Sm³⁺,the oxygen vacancy at Bi _Smlattice will be inclined to migrate around the remaining Bi³⁺,and the attraction of Bi³⁺to oxygen vacancy is stronger than that of Sm³⁺.It is the defect association but not the electronegativity of doped ions that regulates the conductivity of Bi³⁺doped CeO₂based electrolyte materials,which is different from the doping of rare earth ions such as Sm³⁺,La³⁺and Gd³⁺.In conclusion,the strategy of revealing the relationship between doping and local structure through photoluminescence proposed in this work is helpful to understand the changes of oxygen vacancy coordination environment caused by different dopants,to obtain the mechanism of different dopants regulating the electrical properties of materials,so as to select appropriate dopants to optimize the electrical properties of various oxygen ion conductors.