Structure, electronic, and vibrational properties of amorphousAsS2andAgAsS2: Experimentally constrained density functional study

Abstract

Density functional/molecular dynamics simulations and experimental data (x-ray and neutron diffraction, extended x-ray absorption fine structure) have been combined to determine structural and other properties of amorphous AsS 2 and AgAsS 2 . These semiconductors represent the two small regions of the Ag-As-S ternary diagram where homogeneous glasses form, and they have quite different properties, including ionic conductivities. We find excellent agreement between the experimental results and large-scale (over 500 atoms) simulations, and we compare and contrast the structures of AsS 2 and AgAsS 2 . The calculated electronic structures, vibrational densities of states, ionic mobilities, and cavity distributions of the amorphous materials are discussed and compared with data on crystalline phases where available. The high mobility of Ag in solid state electrolyte applications is coupled to the large cavity volume in AsS 2 and local modifications of the covalent As-S network in the presence of Ag.

Structure of amorphous Ag/Ge/S alloys: experimentally constrained density functional study

“…Effective charges in Ag/Ge/S have been computed by the method of Bader [52,53] to be +0.29e for Ag, +0.10e for Ge, and −0.20e for S. Despite the low effective charges, the cationic nature of Ag + is clear. The effect of adding Ag atoms is similar to our findings for Ag-AsS 2 and AsS 2 [28].…”

“…Silver forms bonds mostly with sulphur as demonstrated by the sharp Ag-S peak at 2.55Å. The Ag-Ge PDF has a well-defined first peak, which differs from the weak shoulder for Ag-As found in Ag-AsS 2 [28]. The average coordination numbers in Ge/S and Ag/Ge/S are given in Table 2.…”

“…than in standard Car-Parrinello simulations. The PBEsol approximation [40] for the exchange-correlation energy is a modification of the popular PBE functional [41] that is intended to improve equilibrium properties for extended systems, and we used it also in recent calculations on Ag/As/S [28] and Ge/Sb/Te [42] alloys. The electron-ion interaction was described by scalarrelativistic pseudopotentials of Troullier-Martins form [43] with valence configurations Ag: 4d 10 5s, Ge: 4s 2 4p 2 , and S: 3s 2 3p 4 .…”

Structural elucidation of AgAsS2 glass by the analysis of clusters formed during laser desorption ionisation applying quadrupole ion trap time‐of‐flight mass spectrometry

“…[2] The addition of ionic silver results in various structural changes in the material, which in turn modify the band structure and hence its electrical properties. [3][4][5] Silver arsenic sulfides are found in nature as constituents of the minerals smithite, trechmannite (AgAsS 2 ) and proustite (Ag 3 AsS 3 ), [6,7] and ternary Ag-As-S compounds were synthesised as far back as the nineteenth century. [8] Nowadays, Ag-As-S glasses can be prepared by thin film deposition, and following optically induced silver dissolution and diffusion into an As-S film.…”

“…However, the conventional melt-quench technique is the most commonly used method for the synthesis of Ag-As-S chalcogenide glasses. [3,5,9] Silver-doped chalcogenide glasses can be prepared by doping with metallic silver or with silver compounds such as AgX (X = Cl, Br, I) or Ag 2 Ch (Ch = S, Se, Te). [4] AgAsS 2 glass shows some interesting physical and electronic properties.…”