The high-temperature superionic behaviour of Ag₂S

Abstract

Powder neutron diffraction and molecular dynamics (MD) simulations have been used to investigate the structural behaviour of silver sulfide, Ag2S, at elevated temperatures. Above ~450 K Ag2S adopts the β phase in which the S2- possess a body-centred cubic arrangement. Analysis of the neutron diffraction is in good agreement with the previously proposed structural model in which the Ag+ predominantly reside within the tetrahedral interstices. At ~865 K Ag2S transforms to the α phase in which the anion sublattice adopts a face-centred cubic arrangement. Structural refinements of this phase indicate that the cations are distributed predominantly in the tetrahedral cavities but with a significant fraction in the octahedral holes. MD simulations, using established potentials for this compound, confirm the stability of the two high-temperature superionic phases and show good agreement with the measured Ag+ distribution within the unit cell.

Phase transitions in jalpaite, Ag3CuS2

“…Therefore, we conclude that model 5 (cations are distributed over ideal tetrahedral 8(c) and ideal octahedral 4(b) sites) describes fcc-Ag 3 CuS 2 in the optimal way (see the quality of the simultaneous fit in the figure 2). The same structural model was recently reported for superionic fcc-Ag 2 S [15] and fcc-(AgI) x -(PbI 2 ) 1-x with x= 5 4 and 3 2 [17]. In order to investigate the high-temperature behaviour of superionic fcc-Ag 3 CuS 2 , we analyzed synchrotron diffraction data in the temperature range from 543 K up to sample's melting on the basis of the model with random occupation of the tetrahedral 8(c) site at ( 4 1 , 4 1 , 4 1 ) and the octahedral 4(b) site at ( 2 1 , 2 1 , 2 1 ).…”

“…The analysis of the diffraction check-pattern from the sample after the heat treatment in argon during the diffraction measurements shows no changes with respect to the initial state. The systematics of the phase transitions of related copper-and silver-based superionics was considered by Hull et al [15], where the disordered fcc structure (or related hcp structure) was suggested to be always the lower temperature modification, with the bcc -AgI-like structure occurring at the highest temperature. Despite this assumption, the fcc structure was found to be the high temperature phase for Ag 2 S in a reference [15] which was stated to be anomalous.…”

Silver sulphide growth on Ag(111): A medium energy ion scattering study

“…Based on these observations, they attributed the (√7×√7)R19° pattern to the formation of an epitaxial film of the high temperature phase of Ag 2 S (referred to as the γ-phase in the very limited report of its structure [6]). This bulk structural phase of Ag 2 S has been characterised more fully by neutron scattering [7 ] and confirmed to have a facecentred cubic lattice with a lattice parameter of 6.27 Å. As such the S-S spacing in the (111) plane is 4.43 Å, an almost perfect match to the √(7/3) spacing 4.41 Å required for epitaxial growth on Ag(111) with a (√7×√7)R19° registry mesh.…”

Ultralong Single‐Crystalline Ag2S Nanowires: Promising Candidates for Photoswitches and Room‐Temperature Oxygen Sensors

“…[11][12][13] It has significant applications in optical and electronic devices such as photoconductors, photovoltaic cells, and superionic conductors. [14][15][16] Single-crystalline Ag 2 S nanowires can be expected to have superior properties owing to their anisotropic geometry, large surface-to-volume ratio, and carrier and photon confinement in two dimensions. However, because the synthesis of Ag 2 S nanowires with high aspect ratios, good quality, and high yield is a great challenge, nanodevices based on Ag 2 S semiconductor nanowires are limited.…”