First-Principles Studies Of Cathode Material Sr_n+1Ti_nO_3n+1(n=1,2,3,∞) For Solid Oxide Fuel Cell

Based on the density functional theory (DFT), the first-principles PAW pseudopotential method within the generalized gradient approximation (GGA) is employed to investigate the following two problems:1:The geometry and electronic structure of the bulk cathode material Sr_n+1Ti_nO_3n+1(n = 1,2,3,∞) have been studied by first principles calculations. The crystal structure, density of states and the band decomposed charge density has been analyzed. On one hand, we have obtained the theoretical lattice constant and electronic structure; on the other hand, the PAW+GGA method will be justifed by comparing with results attained by other theoretical or experimental methods. It is found that the results obtained by our calculations are in good agreement with other theoretical results and experimental data.2:O diffused in the SrTiO₃ and Sr₂TiO₄ are studied through first principles based on the density functional theory (DFT) calculation for the first time. The energy barriers for O diffusion are calculated with nudged elastic band (NEB) method. The results show that oxygen vacancy formation energy is very high, indicating that oxygen vacancies are difficult to be formed in the SrTiO₃ and Sr₂TiO₄ lattices. The energy barriers for O diffusion are also very high. All these data show that the structure of SrTiO₃ and Sr₂TiO₄ are stable and the oxygen ionic conductivity is low.