Orientation relationships at structural transformation of monoclinic and cubic phases in silver sulfide

The orientation relationships between the low-temperature monoclinic semiconductor acanthite $\alpha$-Ag$_2$S and the high-temperature body-centered argentite $\beta$-Ag$_2$S are determined based on high-temperature X-ray diffraction and high-resolution transmission electron microscopy (HRTEM) data on silver sulfide. It is found that, in contrast to acanthite, the possible distances between silver atoms in cubic argentite are too small to allow Ag atoms to occupy metal sublattice sites with a probability of 1. It is shown that the (010) and (001) atomic planes of acanthite are parallel to the (1$\bar1$0) and (221) planes of argentite, respectively. The found orientation relationships between acanthite and argentite are important for understanding the physical operation of the Ag$_2$S/Ag heteronanostructure, which is considered as a potential basis for designing resistive switches and nonvolatile memory devices.