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

J Mater Sci MECHANOCHEMICAL SYN THESIS Mechanochemical Synthesis Mechanochemically driven amorphization of nanostructurized arsenicals, the case of b-As4S4 Oleh Shpotyuk1,2,* , Peter Baláž3, Zdenka Bujňáková3, Adam Ingram4, Pavlo Demchenko5, and Yaroslav Shpotyuk5,6 1 Jan Dlugosz University, Al. Armii Krajowej, 13/15, 42201 Czestochowa, Poland Vlokh Institute of Physical Optics, 23, Dragomanov Str., Lviv 79005, Ukraine 3 Institute of Geotechnics of the Slovak Academy of Sciences, 45, Watsonova Str., 04001 Kosice, Slovakia 4 Opole University of Technology, 75, Ozimska Str., 45370 Opole, Poland 5 Ivan Franko National University of Lviv, 107, Tarnavskogo Str., Lviv 79017, Ukraine 6 Centre for Innovation and Transfer of Natural Sciences and Engineering Knowledge, University of Rzeszow, 1, Pigonia Str., 35-959 Rzeszow, Poland 2 Received: 2 February 2018 ABSTRACT Accepted: 3 May 2018 The amorphization is studied in mechanically activated b-As4S4 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-As4S4 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 As4S4 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-As4S4 crystallites. In respect of CINCA modeling, the effect of high-energy milling is identified as destruction–polymerization action on monomer cage-type As4S4 molecules and existing amorphous phase, transforming them to amorphous network of triple-broken As4S4 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 As2S3.  The Author(s) 2018 Address correspondence to E-mail: https://doi.org/10.1007/s10853-018-2404-3 J Mater Sci Introduction The high-entropy disordered state of substances (viz. amorphous materials) is typically derived from a melt owing to rapid cooling, which allows avoid kinetically competitive crystallization processes [1]. That is why different melt-quenching (MQ) routes freezing a liquid state for room-temperature conditions are widely used in commercial glass-preparation technologies [2]. However, amorphous state can be also achieved in an alternative way ensuring generation of a large amount of structural defects in a crystal over a critical density. In this view, the high-energy mechanochemical milling (MM) reducing substantially grain sizes of the appeared nanoparticles (NPs) [1] seems to be one of the most promising technological solutions. More commonly, the appearance of amorphous phase was detected in different substances possessing extensive row of glassy-prone compositions and inter-crystalline equilibriums like over-stoichiometric As–S alloys [2–5], also referred to (preferentially in biomedical literature) as arsenicals [6]. Recently [7], some of the current authors reported the first results on observation of complete amorphization in semicrystalline As45S55 alloy subjected to MM in a dry mode under protective Ar atmosphere. The amorphous phase possessing double-Tg relaxation originated from intrinsic separation on distinct highand low-temperature glass components was identified as close to alloy of the same nominal chemical composition. Careful inspection with X-ray powder diffraction (XRPD) related to the first sharp diffraction peak (FSDP) revealed this amorphous phase as extension of MQ As-rich glass-forming structural motifs stretching beyond As2S3 stoichiometry. Generation of amorphous phase in addition to parent crystalline compound, albeit not exactly defined, was also detected in high-temperature polymorph of tetraarsenic tetrasulfide b-As4S4 after dry or wet MM, studied in view of promising anticancer activity [8–12]. Recently, the macroscopic evolution processes associated with intrinsic sub-nanometer free-volume voids were comprehensively studied in this b-As4S4 polymorph subjected to high-energy MM, using different mathematical treatment procedures applied to reconstructed positron annihilation lifetime (PAL) spectra [12]. The identified stages of MM-induced interaction between generated NPs include non-interacting accumulation, adhesion-enhanced aggregation, and irreversible agglomeration. This work is aimed to characterize the microstructure picture of amorphization in b-As4S4, driven by high-energy ball MM at different rotational speeds, employing experimental methods of intermediate-range structural probing with FSDP-related XRPD, free-volume voids study with PAL spectroscopy, supported by atomic clustering simulation with ab initio quantum-chemical models developed for covalent-bonded glass-forming networks known as CINCA (the cation-interlinking network cluster approach [13]). Experimental Commercial arsenic sulfide b-As4S4 (98% in purity, purchased in Sigma-Aldrich, USA) was used as initial precursor for MM. The small pieces of this arsenical were coarse-grained, powdered, and sieved under 200 lm. Then, this powder (3 g) was subjected to MM in a dry mode under protective Ar atmosphere, using planetary ball mill Pulverisette 6 (Fritsch, Germany) loaded with 50 tungsten carbide balls of 10 mm in diameter (the MM conditions being described in more details elsewhere [9]). The overall MM duration was 60 min for each sample at different rotational speed of the planet carrier n, for example, REHE-0 (coarse-grained powdered sample), REHE-100 (n = 100 min-1), REHE-200 (n = 200 min-1), REHE500 (n = 500 min-1), and REHE-600 (n = 600 min-1). Finally, the samples were compressed by compacting inside a stainless steel die under the same 0.7 GPa pressure to prepare disk-like pellets (6 mm in a diameter and 1 mm in a thickness). The crystal structures of the arsenical pellets were identified by XRPD method, the data being collected in a transmission mode using STOE STADI P diffractometer (STOE & Cie GmbH, Darmstadt, Germany) with linear position-sensitive detector (Cu-Ka1 radiation, curved Ge(111) monochromator) as was described elsewhere [7, 9]. The crystal (...truncated)