Nanomilling-driven volumetric changes in multiparticulate As4S4-bearing nanocomposites recognized with a help of annihilating positrons

Abstract

Employing positron annihilation lifetime (PAL) spectroscopy, nanomilling-driven volumetric changes driven are identified in multiparticulate nanocomposites of As4S4–ZnS–Fe3O4 system, considered in transitions between their respective hierarchical derivatives from triparticulate (1⋅As4S4/4⋅ZnS/1⋅Fe3O4) to biparticulate (1⋅As4S4/1⋅Fe3O4, 1⋅As4S4/4⋅ZnS) and monoparticulate (As4S4) ones. Unconstrained three-component PAL spectra of nanocomposites are parameterized in terms of positron-Ps trapping conversion obeying x3-x2-CDA (coupling decomposition algorithm). Coexistence of nanocrystalline nc-β-As4S4 and amorphous a-AsS phase is shown to be crucial feature of these nanocomposites, the latter being generated continuously due to reamorphization of initial disordered phase and/or vitrification of nc-β-As4S4 phase. The inverse positron-to-Ps trapping conversion prevails in transition from biparticulate (1⋅As4S4/1⋅Fe3O4) and monoparticulate (As4S4) nanocomposites (both dominated by trapping in As4S4-bearing sub-system) to triparticulate (1⋅As4S4/4⋅ZnS/1⋅Fe3O4) one, disappeared positron traps being vacancy defects in a-As–S matrix, and Ps-decay sites formed instead being triple junctions between amorphized nc-β-As4S4 grains. The normal Ps-to-positron-trapping conversion prevails in transition from biparticulate (1⋅As4S4/4⋅ZnS) nanocomposite dominated by positron trapping in ZnS sub-system to triparticulate (1⋅As4S4/4⋅ZnS/1⋅Fe3O4) one, disappeared Ps-decay sites being triple junctions between amorphized nc-β-As4S4 grains, and positron traps formed instead being vacancy-type defects in the packing of the finest ZnS crystallites (~ 2–3 nm).