Phase Transition in Ag2S and the Relative Position of Atomic Planes of the α-Ag2S and β-Ag2S Phases

The relative position of atomic planes of low-temperature monoclinic acanthite α-Ag2S and high-temperature bcc argentite β-Ag2S has been determined from X-ray and electron microscopy data. A reversible β‑Ag2S–α-Ag2S phase transition is due to the distortion of the bcc S sublattice in the structure of argentite β-Ag2S to the monoclinic sublattice of acanthite α-Ag2S. Distances between Ag atoms in cubic argentite are too small for the sites of the metal sublattice to be completely filled with Ag atoms. For this reason, the filling probabilities of sites of the metal sublattice is less than 0.1. Silver atoms in acanthite are at fairly large distances from each other because of monoclinic distortion and fill their positions with a probability close to 1. The relative orientations of the atomic planes of acanthite and argentite have been determined taking into account the displacements S and Ag atoms.