Ab initio study of diffusion of hydrogen, silver and lithium in PbS and Ag2S

Abstract

Lead and silver sulfides are materials with diverse technological applications, such as photovoltaic dispositives, electrodes and catalysts. More recent applications in the formation of quantum dots and catalysts synthesis for hydrogen evolution reactions involves these sulfides and some similar compounds. It is well known that defects, and consequently the diffusion process, can change some properties and performances of such materials. Herein, a study of defect formation and ionic diffusion process were performed in PbS and Ag2S lattice structure. The activation energies for diffusion of Ag+, Li+, and H+ in PbS and Ag2S lattices were calculated at the DFT level and diffusion coefficients were estimated within the Arrhenius approximation. Pb-doped Ag2S exhibited a very small activation energy and an anomalous high diffusion coefficient for Ag+ diffusion, which is in good agreement with experimental data. Less evident is the fact that Li+ present lower diffusion coefficients than Ag+. For H+ diffusion in PbS lattice, the process is completely different. The hydrogen moves over the lattice from a sulfur site to the other, apparently cleaving and forming H-S bonds. The present work can provide more understanding of the features of defect formation and solid state ionic diffusion mechanism in sulfides from an atomic perspective. Hopefully, this results can help experimentalists in the development of more efficient materials for some important technological applications.