Amorphization diversity driven by high-energy mechanical milling in β-As4S4 polymorph

Abstract

Amorphization scenarios in multiparticulate nanocomposites based on directly synthesized β-As4S4 activated by high-energy mechanical milling are identified employing X-ray diffraction analysis complemented with ab initio quantum-chemical computational modelling. Coexistance of nanocrystalline and amorphous phases is crucial feature of these nanocomposites, their medium-range structure being reconstructed assuming diffuse halos as arising from remnants of inter-planar correlations with ∼5.3–5.5 Ǻ Bragg-diffraction spacing supplemented by Ehrenfest-diffraction contribution from most pronounced inter-molecular correlations. Full hierarchy of molecular-breaking events comprising transitions from As4S4 cage-like molecule to its network-forming derivatives is computed. The optimally-constrained single-broken clusters keeping one hexagon and two adjacent pentagons in atomic arrangement are supposed to be responsible for amorphization in β-As4S4. The over-constrained triple-broken chains are character for amorphization in monoparticulate (composed exceptionally by β-As4S4 crystallites) and biparticulate (composed by mixed β-As4S4 and magnetite Fe3O4 crystallites) grinding media, the estimated density of accompanied amorphous phase being 3.43 g⋅ cm−3. Strong amorphization scenario obeying “shell” kinetics model occurs in triparticulate β-As4S4-based solution modified by Fe3O4 (few tens nm) and ZnS (below few nm) crystallites. The latter acting as solid solvent provide sufficient energy gained from collisions with hard magnetite particles to soft amorphized substance composed mainly by double-broken As4S4 molecules keeping pentagon rings in atomic arrangement. This effect is identified as ZnS-assisted milling-driven arsenic monosulphide amorphization in 1⋅β-As4S4-4⋅ZnS-1⋅Fe3O4 grinding solution.