Mechanochemically driven amorphization of nanostructurized arsenicals, the case of β-As4S4

Abstract

The amorphization is studied in mechanically activated b-As 4 S 4 using highenergy ball milling in a dry mode with 100-600 min -1 rotational speeds, employing complementary methods of X-ray powder diffraction (XRPD) related to the first sharp diffraction peak, positron annihilation lifetime (PAL) spectroscopy, and ab initio quantum-chemical simulation within cation-interlinking network cluster approach (CINCA). The amorphous substance appeared under milling in addition to nanostructurized b-As 4 S 4 shows character XRPD halos parameterized as extrapolation of the FSDPs, proper to near-stoichiometric amorphous As-S alloys. The structural network of amorphized arsenicals is assumed as built of randomly packed multifold cycle-type entities proper to As 4 S 4 network. The depressing and time-enhancing tendency in the PAL spectrum peak is direct indicative of milling-driven amorphization, associated with free-volume evolution of interrelated positron-and Ps-trapping sites. At lower speeds (200-500 min -1 ), these changes include Ps-to-positron trapping conversion, but they attain an opposite direction at higher speed (600 min -1 ) due to consolidation of b-As 4 S 4 crystallites. In respect of CINCA modeling, the effect of high-energy milling is identified as destruction-polymerization action on monomer cage-type As 4 S 4 molecules and existing amorphous phase, transforming them to amorphous network of triple-broken As 4 S 4 derivatives. These findings testify in a favor of ''shell'' kinetic model of solid-state amorphization, the amorphous phase continuously generated under speed-increased milling being identified as compositionally authentic to arsenic monosulfide, different in medium range ordering from stoichiometric As 2 S 3 .

Effect of high‐energy mechanical milling on the medium‐range ordering in glassy As‐Se

“…Thus, the FSDP can be ascribed to variations in the underlying cage structure of glass‐forming networks composed by interlinked polyhedrons (network‐forming blocks), producing a variety of interlinked circle‐type entities (small rings), keeping some elements of inter‐planar ordering proper to crystalline counterparts of these glasses. This standpoint occurred to be very useful in the interpretation of crystalline‐to‐amorphous transitions in many arsenic compounds (arsenicals) subjected to high‐energy MM …”

“…The question on topological identity of these molecular entities in over‐stoichiometric arsenoselenide glasses is still remaining open. Indeed, the spatial positioning of barycenter B of As 4 Se 4 (or As 4 Se 3 ) molecules does not change substantially under partial polymerization of these molecules in glassy network, if some elements of these molecules such as small 3‐, 4‐ and/or 5‐folded circles are kept, as it was in the case of MM‐driven amorphization in β‐As 4 S 4 polymorph …”

“…This standpoint occurred to be very useful in the interpretation of crystalline-to-amorphous transitions in many arsenic compounds (arsenicals) subjected to high-energy MM. [45][46][47] Within this approach applied to under-stoichiometric As x Se 100 − x glasses (5 ≤ x ≤ 40), the FSDP can be ascribed to structural networks built of trigonal AsSe 3/2 pyramids interlinked by Se-chains, ie inter-planar order proper to crystalline As 2 Se 3 with character 12-membered corrugated rings, 9,[48][49][50] disturbed by (-Se-Se-) n chains of different lengths n (in dependence on the glass composition).…”

“…Indeed, the spatial positioning of barycenter B of As 4 Se 4 (or As 4 Se 3 ) molecules does not change substantially under partial polymerization of these molecules in glassy network, if some elements of these molecules such as small 3-, 4-and/or 5-folded circles are kept, as it was in the case of MM-driven amorphization in β-As 4 S 4 polymorph. 46,47 . Appearance of such inter-molecular correlations between cage-like As 4 Se 4 and As 4 Se 3 molecules and their partially polymerized remnants in melt-quenched over-stoichiometric As-Se glasses leads to anomalous compositional behavior of the FSDP (drastic decrease in the FSDP position Q 1 and width ΔQ 1 , as it was demonstrated on Figure 5).…”

Cluster Modeling of Network-Forming Amorphization Pathways in AsxS100−x Arsenicals (50 ≤ x ≤ 57) Diven by Nanomilling

“…Thus, at the moderated As content in these thioarsenide alloys close to stoichiometry As 2 S 3 (viz. As 40 S 60 ), competitive matrix amorphization (vitrification) and layer-type conformation (crystallization) processes occur, while in As-rich As x S 100-x compounds (where x exceeds 40) the latter are replaced by molecular-crystallization tendencies accompanied by stabilization of As 4 S n cage-like molecules (n = 5,4,3) [8][9][10].…”