First-principles study of point defect diffusion in CoMn2O4 crystal

The conductivity of spinel coating on metallic interconnects is of great significance for solid oxide fuel cells. Here, we develop a thorough theoretical study on the point defect diffusion based on first-principles calculations that reveals the conduction mechanism of a CoMn2O4 spinel crystal. Defect models that use three types of vacancies and five types of interstitial atoms of Co, Mn, and O, are proposed and optimized. The energy barriers for diffusion of the vacancies, interstitial atoms and cascade reactions are calculated and analyzed. The diffusion pathways across the entire crystal are established. From the calculation of the corresponding diffusion coefficients, it is found that the mobility of O atomic defect is higher than that of Co defect, and that of the Mn defect is the lowest. Our results reveal that the conductivity of a CoMn2O4 crystal may mainly depend on diffusion of interstitial O atoms and O vacancies. Therefore, our study suggests that the conductivity of CoMn2O4 spinel crystal may be improved by increasing the concentration of O atomic defects. The obtained activation energies and diffusion coefficients can provide theoretical support to the related experiments.