Ab initio study of La10_xSrx(Si,Ge)6O27_0.5x apatite for SOFC electrolyte

International audienceApatite structure materials have outstanding performances as electrolytes for SOFC. Among them,La10_xSrx(Si,Ge)6O27_0.5x (LSO) series have attracted more attention for a higher ionic conductivity. Twodoping positions have been investigated, Sr dopant at La position and Ge dopant at Si position. DopedLSO conductivity was studied using first principle density functional theory (DFT) calculations. Withthe increase of Sr-doped ratio, the DOS (density of states) peaks above Fermi level shift to a higher energylevel. Furthermore, the electron energy gap broadening reduces the electron migration, while ion migrationwas limited. However, few changes of DOS with Ge substitution can be observed. The activationenergies of these two dopants are simulated by the energy barriers of the migration channel. We haveobserved that the two dopant positions affect the apatite ionic conductivities with different mechanisms.Indeed, La doped position change the electron energy level and activation energy. However, the Siposition can affect the density of electrons since it is surrounded by the oxygen and away from themigration channel. The calculation results of ionic conductivity are also consistent with those obtainedby experiments