Application Of Rare Earth Luminescent Structure Probe And Study Of Grain Boundary Scavenging Effect In Oxygen Ion Conductor

As the electrolyte material of Solid Oxide Fuel Cell?SOFC?,the grain and grain boundary conductivity of the polycrystalline oxygen ion conductor have important influence on the overall electrical properties of the material.In this paper,the doped CeO₂-and doped Bi₂O₃-based oxygen ion conductors are taken as the research object.The rare earth luminescence spectrum is used as the probe to detect the change of local crystal structure.The influence of doping and preparation conditions on the local crystal structure of oxygen ion conductors is studied.By adjusting the sintering temperature of ceramic materials and combining with in-depth electrochemical impedance data analysis,the internal mechanism of impurity cleaning effect at grain boundary which significantly affects the conductivity of the material at grain boundary was studied.The details are as follows:Firstly,Using Eu³⁺ion photoluminescence as structural probe and Raman spectrum,the structure regulation of Sr doping on GDC oxygen ion conductor was studied,so as to further understand the regulation mechanism of cationic doping on grain conduction of GDC oxygen ion conductor.When two Gd³⁺are replaced by one Ce⁴⁺and one Sr²⁺,the new oxygen vacancy introduced by Sr²⁺will always exist in the nearest position of Sr²⁺,which will lead to a slight increase of E_?^bulk.At the same time,the original oxygen vacancy beside Gd³⁺/Eu³⁺will move from the neighboring coordination position of Gd³⁺/Eu³⁺to the coordination position of Ce⁴⁺ions,which will lead to the decrease of E_?^bulk.In this chapter,the structure change results obtained based on photoluminescence spectrum and Raman spectrum are in good agreement with the results of electrical properties,indicating that this strategy has an important application prospect in exploring the structure change of oxygen ion conductor induced by doping and the corresponding conduction mechanism of oxygen ion.It is of great significance to improve the electrical properties of oxygen ion conductors by optimizing the type of cation doping.Secondly,by Dy³⁺ion optical spectrum as structure probe,preliminarily explores the Dy/W doped Bi₂O₃ oxygen ion conductor with high electrical conductivity and at the same time reducing atmosphere with high structural stability of structure under origin,found that the oxygen ion conductor is likely to have natural core-shell structure,W dopant is located in the outer layer can improve the chemical stability,Dy dopant is located in the inner layer increased oxygen ionic conductivity.Thirdly,based on the control of appropriate experimental conditions and in-depth analysis of the conductivity data at grain boundaries,the specific mechanism of impurity cleaning effect at grain boundaries,which has been widely reported in the literature but has a wide range of differences,was expounded in Sr doped GDC,a representative oxygen ion conductor.It was found that when the impurity sweeper Sr was added into the grain boundary,only when the sintering temperature was higher than the eutectic temperature of the impurity Sr and Si at the grain boundary could the impurity sweeper effect lead to the increase of the electrical conductivity at the grain boundary be observed.However,when the sintering temperature is lower than the eutectic temperature of the impurity at grain boundary such as Sr and Si,Sr²⁺will not clean the impurity at grain boundary but will increase the impurity coverage ratio at grain boundary and reduce the conductivity at grain boundary.At the same time,the introduction of Sr²⁺will reduce the number of grain boundaries and the size of space charge potential,which will lead to the increase of the overall grain boundary conductivity of the electrolyte.The introduction of Sr²⁺can also reduce the conductivity of grain boundary to some extent by reducing the impurity dilution effect.The results of this study are of great significance for further understanding the mechanism of influence of various grain boundary sweepers on the conductivity of grain boundary,especially the mechanism of impurity scavenging effect at grain boundary.