An ab-initio calculation study on the super ionic conductors α-AgI and Ag2X (X = S, Se) with BCC structure

The ionic conduction mechanisms of some super ionic conductors, α-AgI, β-Ag2S, and α-Ag2Se, have been investigated by means of ab-initio calculations using the VASP (Vienna Ab-initio Simulation Package) code. Each of these phases has a BCC (body-centered cubic) sub-lattice formed by the anions, while the cations, which partially occupy the 12d sites, migrate along pathways through the centers of the faces of the tetrahedra. The calculated band gaps of α-AgI, β-Ag2S, and α-Ag2Se are 0.88 eV, 0.06 eV, and 0 eV, respectively, which implies that α-AgI is only an ionic conductor, whereas β-Ag2S and α-Ag2Se are mixed electronic and ionic conductors.