Research On Preparation, Characterization And Valence Electron Structure Of LaGaO₃-based Electrolyte

Solid oxide fuel cells (SOFCs) possess low pollution and high efficiency, extensive application prospects. The key materials for SOFCs are solid electrolytes. In recent years, new type electrolyte materials based on LaGaO3 with high oxygen-ionic conductivity are attracting much attention. Currently the main problem to limit use of electrolyte materials is that it is difficult to synthesize the high-purity powders with low calcination temperature.In this dissertation, La0.8Sr0.2Ga0.85Mg0.15O2.825 (LSGM) materials was synthesized by means of EDTA combustion method and glycine combustion method, in order to find a highly-efficient method to obtain a high purity, particle size uniformity, high ionic conductivity and low cost of LaGaO3-based electrolyte materials with doping elements. In addition, the glycine combustion method was used to synthesize La0.8Sr0.2(Ga0.9Co0.1)0.85Mg0.05O2.825 (LSGMC) and the impact of Co on the ionic conductivity of electrolyte was also dealt with. Finally, the valence electron structure of LSGM with different contents were calculated by using the empirical electron theory (EET), in order to establish the relationship between the valence electron structure and ionic conductivity.Results show that, the LSGM powders prepared by glycine combustion were composed of the main phase without secondary phases when calcined at 1300℃, which is obviously lower than that of the solid-state reaction method(above 1500℃) and EDTA combustion method (1400℃). Results also show that, EDTA-derived powder particle size (average grain size 60 nm) is smaller than glycine-derived powder (about 700nm). The ionic conductivity of EDTA-derived is greater than that of glycine-derived electrolytes. According to the LSGMC synthesis experimental, the results reveal that doping with 8.5%(mole fraction) of transition metal Co is effective for improving the oxide ion conductivity. The ionic conductivity of materials of LSGM doping with Co were measured to be 6.529×10-2 S·cm-1 at 800℃, which is obviously higher than that of undoped LSGM materials.According to the calculation of valence electron structure, the relationship between compositions, valence electron structure and ionic conductivities were also dealt with. At last, the complex function "p" was put forward. LSGM with higher ionic conductivity can be forecast by using "p".