The Preparation Of Apatite-type Nitrogen Doping Lathanum Silicate Solid Electrolye And Its Electric Conduction Performance Study

Apatite-type La_9.33（SiO₄）₆O₂（LSO） is a new solid state electrolytes and has a goodpotential for application in the field of fuel cell as the new energy and clean energy.Currently, there are still much problems exist in the materials such as the preparationmethod is inconvenient and energy-intensive, the studies of Multi-bit doping are notsystem and so on.Using appropriate doping means and preparation process can improvethe oxygen ion conductivity performance of the LSO, promote its commercial use inSOFCs. In this thesis, the nitrogen-doped apatite-type lanthanum silicate solid electrolyte（hereinafter referred to as LSON） was successfully prepared by optimized urea gel-combustion method and supplemented N₂/H₂microwave plasma enhanced. Moreover,the LSON powders and sintered bodies were characterized and testing. On this basis, themain contents and results of the research as follows:（1） The elements composition and valence state of LSON was researched by usingthe characterization methods of Electron microprobe and XPS. The results showed that:the chemical formula of LSON should be La_9.33（SiO₄）6O₂-1.5xNx, wherein, N substitutedthe channel O which the position is the63direction of c-aixs. Coulomb force is formedbetween La （II） and N. This is La （II）–N bond. At the same time, the Coulomb force of[N…O] is produced.（2） The nitrogen-doped structural unit of the LSON was researched by FT-IR andRaman spectra. The results showed that: The vibration mode of the apatite type crystalstructure will be affected by nitrogen doping.That the triple degeneracy of ν1and ν3at[SiO4] tetrahedral will be split by nitrogen doping. The division of symmetric stretchingvibration can be up to20cm^-1.（3） The Raman intensity of La （II）–N bond and the Coulomb force of [N…O]respectively at315cm^-1and355cm^-1was analyzed. The amount of nitrogen-doped inLSON at different plasma process conditions was researched. The results showed that: inthe conditions of microwave power300W and effect time15min, the amount ofnitrogen-doped can be up to0.26wt%. （4） Using TG-DSC and SEM characterization means, combined with the linearshrinkage test of the sintered body, the thermal stability and sintering properties of LSONwas researched. The results showed that: The nitrogen exists in the lattice structure ofapatite-type LSON will be released from the lattice structure if the sintering temperature ishigher than1200℃.LSON’s optimum sintering conditions is sintered at1200℃for6h,sintering density can be up to95%.（5） The electrical properties of the LSON sintered body was studied by usingimpedance spectroscopy. The results showed that: The nitrogen doping the lanthanumsilicate by microwave plasma can improve the O^2-ion conductivity. In the experimentalconditions under300W/10min, the highest conductivity can be1.28×10^-2S·cm^-1at800℃.（6） The conductivity enhancement mechanism of LSON was researched. The resultsshowed that: When the defect structure of the electrolyte has the similar environment, theconductivity and is proportional to the cell parameters and the O^2-vacancy concentrationwith nitrogen-doped. It could be definite as “space conductance” enhancement effect.