Ab Initio Study of the Thermodynamics of Intrinsic Point Defects in Thermoelectric Oxychalcogenide BiCuSeO

We report on the results of an ab initio study of thethermodynamics of intrinsic point defects in the thermoelectric oxy-chalcogenide BiCuSeO. By using phase boundary mapping, we build athermodynamic stability diagram that enables identification of severalthermodynamic conditions that could be targeted experimentally in orderto control the concentration of defects by tuning the chemical potential of theelements. In these conditions, the formation energies of selected intrinsicdefects in their different possible charged states have been calculated. It showsthat if the copper vacancy dominates the other defects over the whole energyband gap,VBivacancy as well asCuSesubstitution can also play a role incertain thermodynamic limits. Last, calculations of the equilibrium Fermienergy and defect concentrations show that native copper vacancies areresponsible for the p-type conductivity in pristine BiCuSeO. They also givepossible directions to achieve n-type conductivity in this system and tooptimize the carrier concentrations in the p-type regime.