title: Probing Sub-atomistic Free-Volume Imperfections in Dry-Milled Nanoarsenicals with PAL Spectroscopy.
abstract: Structural transformations caused by coarse-grained powdering and fine-grained mechanochemical milling in a dry mode were probed in high-temperature modification of tetra-arsenic tetra-sulfide known as β-As4S4. In respect to X-ray diffraction analysis, the characteristic sizes of β-As4S4 crystallites in these coarse- and fine-grained powdered pellets were 90 and 40 nm, respectively. Positron annihilation lifetime spectroscopy was employed to characterize transformations occurred in free-volume structure of these nanoarsenicals. Experimentally measured positron lifetime spectra were parameterized in respect to three- or two-term fitting procedures and respectively compared with those accumulated for single crystalline realgar α-As4S4 polymorph. The effect of coarse-grained powdering was found to result in generation of large amount of positron and positronium Ps trapping sites inside arsenicals in addition to existing ones. In fine-grained powdered β-As4S4 pellets, the positron trapping sites with characteristic free volumes close to bi- and tri-atomic vacancies were evidently dominated. These defects were supposed to originate from grain boundary regions and interfacial free volumes near aggregated β-As4S4 crystallites. Thus, the cumulative production of different positron traps with lifetimes close to defect-related lifetimes in realgar α-As4S4 polymorph was detected in fine-grained milled samples.
authors.affiliation: Vlokh Institute of Physical Optics, 23, Dragomanov str., 79005, Lviv, Ukraine. olehshpotyuk@yahoo.com.|Jan Dlugosz University, al. Armii Krajowej, 13/15, 42201, Czestochowa, Poland. olehshpotyuk@yahoo.com.
authors.forename: Oleh
authors.initials: O
authors.lastname: Shpotyuk
authors.affiliation: Opole University of Technology, 75, Ozimska str., 45370, Opole, Poland.
authors.forename: Adam
authors.initials: A
authors.lastname: Ingram
authors.affiliation: Institute of Geotechnics of the Slovak Academy of Sciences, 45, Watsonova str., 04001, Košice, Slovakia.
authors.forename: Zdenka
authors.initials: Z
authors.lastname: Bujňáková
authors.affiliation: Institute of Geotechnics of the Slovak Academy of Sciences, 45, Watsonova str., 04001, Košice, Slovakia.
authors.forename: Peter
authors.initials: P
authors.lastname: Baláž
authors.affiliation: Ivan Franko National University of Lviv, 107, Tarnavskogo str., 79017, Lviv, Ukraine.|Centre for Innovation and Transfer of Natural Sciences and Engineering Knowledge, University of Rzeszow, 1, Pigonia str., 35-959, Rzeszow, Poland.
authors.forename: Yaroslav
authors.initials: Y
authors.lastname: Shpotyuk
keywords: Free-volume void; Nanomaterial; Positron annihilation; Positron trapping