An electron microscopic study of the polymorphic transformation in Ag₂Se II. The structure of α‐Ag₂Se

The structure of the high‐temperature phase, first proposed by Rahlfs, is revised on the basis of the interpretation of electron diffraction pattern from single crystals. In these patterns a diffuse intensity distribution is observed; it is explained in terms of a size displacement effect. The structure of the high‐temperature phase is described as a body‐centered cubic lattice of selenium atoms within which the silver atoms are associated with the 6e positions: (½ 0 0), (0 ½ 0), (0 0 ½), body‐centered. To a first approximation the distribution of four silver atoms among the six possible sites is at random; i.e. the silver atoms and the unoccupied 6e positions from a disordered atom‐vacancy system. Due to the disorder the silver atoms are displaced from their crystallographic positions, leading to diffuse scattering as observed on the diffraction patterns.