Experimental and DFT characterization of argyrodite type Ag8SiS6 multidispersed powders and ceramics

Herein we present a detailed study of silver-based argyrodite Ag₈SiS₆ in the form of micro- and nanopowders and corresponding ceramics. The microcrystalline fraction has a particle size of 10–20 μm. The average particle size of nanopowders, as determined by SEM, are ∼140 nm (30 min of grinding) and ∼115 nm (60 min of grinding). XRD analysis confirms the formation of orthorhombic low temperature modification of Ag₈SiS₆ and the absence of degradation during the ball milling process. The nature of the optical transition and the change in the E_g with dispersion were determined by combining DFT calculations and diffuse reflectance spectroscopy. The microstructural analysis of ceramics indicates a presence of quite homogeneous ceramics (with an average crystallite size of ∼0.41 μm, ∼0.37 μm and ∼0.34 μm) and uniformly distributed microvoids. The compositional homogeneity of the ceramics was established by EDS. The electrical conductivity and activation energy of the studied ceramics were characterized by the impedance spectroscopy. The Ag₈SiS₆ ceramics are characterized by increase of ionic conductivity (up to 1.1 × 10⁻⁴ S/cm) and a decrease in its activation energy (to 0.234 eV) with decreasing of average crystallite sizes in ceramics. The influence of the recrystallization process and grain size on the electrical parameters of Ag₈SiS₆ ceramics is discussed.