Studies On Ion Migration In Solid Electrolye Using Micro Raman Spectroscopy

Diffusion in solids plays an essential role in the conduction behavior of electrolyte,the determination of interface reaction.The detection of ion migration is benefit for understanding the conduction behavior in electrolyte materials and control the process of interface diffusion.Moreover,it is important to establish the relationship between the material properties with their micro structure.In the present thesis,we have put forward new methods for the determination of ion diffusivity and mobility in solid electrolytes based on different experimental design using a laser confocal micro Raman spectrometer.Ceria based electrolyte as the representative,the diffusion coefficient of oxygen ions and the migration of ceria cation during fabrication of multi-layer electrolyte has been investigated.A series of ceria based electrolyte with various dopant concentration Ce_1-xLa_xO_2-x/2（x=0.05～0.35）has been synthesized successfully.Raman spectroscopy has been measured for all compositions.The intensity ratio of peak for oxygen vacancy to the total intensity(A₅₇₀/A_Total)increases linearly with the dopant concentration.The distribution of oxygen vacancies has been obtained by measuring the Raman spectroscopy point by point along sample surface.The concentration of oxygen vacancies exhibits linear distribution under electric field and the concentration gradient increase with the electric field.The diffusion coefficient of oxygen ions has been acquired through analyzing the distribution of oxygen vacancies under electric field.An electric field was applied on the electrolyte to induce the inhomogeneity of oxygen vacancies.Then the electric field was removed and the distribution of oxygen vacancies at different time was recorded using Raman spectroscopy.The concentration of oxygen vacancies near electrode part changed obviously while the side away from electrode changed slowly.The concentration change of oxygen vacancies with test positions and measured time was derived.The diffusion coefficient of oxygen ions was acquired by fitting with the experiment data using Matlab.An electric field which change the direction periodically was applied on the electrolyte.The change of oxygen vacancies at test position was recorded by Raman spectroscopy.The time interval between two steady state of oxygen vacancies was measured and it was inversely proportional to the value of applied electric field.A possible migration process of oxygen ions in solid electrolyte under strong electric field was put forward based on the experiment discovery.The mobility of oxygen ions was acquired with a physical model.Yttria stabilized zirconia（YSZ）/samarium and neodymium co-doped ceria（SNDC）bilayer electrolyte was fabricated successfully.The conductivity of composite electrolyte is between pure YSZ and SNDC.The diffusi on region can be observed visually using Raman mapping.The diffusion thickness at interface region can be measured using Raman intensity ratio of characteristic peaks of YSZ and SNDC(I₄₆₅/I₆₃₀).The diffusion thickness acquired using Rman spectroscopy is consistant with the one measured by EDS.The thickness of diffusion region increase with the sintering temperature and holding time.The migration of Ce cations follow Fick’s law.