On the glass transition temperature Tg against molar volume Vm plotting in arsenoselenide glasses

International audienceDependence of glass transition temperature Tg (K) on overall mean bonding energy E (kJ/mol) in arsenoselenide glass reexamined under per-atom calculations is shown to obey linearized master equation Tg ≅ 418⋅(E–1.13). Compositional variations in Tg against molar volume Vm are plotted for g-AsxSe100- x taken within (0 ≤ x ≤ 65) domain assuming preferential cohesive Van der Waals (VDW) bonding between network-constituting entities. The Tg values are found to vary as inverse-αth power of Vm, attaining distinct values for different networks, in part, 0D-molecular (α=6/3= 2), 1D-chained (α=5/3), 2D-layered (α=4/3), and 3D-spatial (α=3/3=1). These variations originated from macroscopic geometry of VDW interaction are linearized in log-log presentation for networks dominated with chain-like 1D-entities (0 ≤ x<~8) and cross-linked 3D-entities (~8<x<30–33), while demonstrate non-linear behaviour for cross-linked 3D- and layered 2D-entities (30–33 andlt; x andlt; 40), and layered 2D- and molecular 0D-entities (40 andlt; x andlt; 65). Appearance of molecular entities in g-AsxSe100- x (40<x<65) results in self-terminated loop in log–log plotting of Tg(1/Vm) dependence

Mletím indukovaná nanonizace sloučenin AsxS100-x z druhého sklotvorného regionu: případ nízkokrystalických arsenidů (56<x<66)

Competitive intercrystalline phase-transformation and amorphization effects under high-energy mechanical milling are studied in AsxS100-x alloys from low-crystallinity domain (56<x<66) of the second glass-forming region (51<x<66), employing complementary X-ray powder diffraction analysis, micro-Raman scattering spectroscopy, heat flow differential scanning calorimetry and temperature-modulated multifrequency DSC TOPEM® methods. Milling is shown to activate preferential generation of nanosized monoclinic β-As4S4 phase in these AsxS100-x arsenicals at low As content (50<x<60) accompanied by appearance of isocompositional amorphous phase. Principal scenario of milling-driven interphase disproportionality in these arsenicals with high As content (58<x<66) is identified as plastic-crystalline rhombohedral β-As4S3 phase generation supplemented by extraction of As-rich amorphous substance probably of As4S2 composition. Appearance of amorphous a-As4S2 phase with relatively low glass-transition temperature of ~50 °C is supplemented to β-As4S4 polymorph stabilized along with nanostructured plastic-crystalline nc-β-As4S3 phase. Temperature-depressing effects of milling on calorimetric heat-transfer processes are revealed in whole compositional domain of the studied nanoarsenicals.Konkurenční jevy krystalické fázové transformace a amorfizace během vysokoenergetického mechanického mletí byly studovány ve sloučeninách AsxS100-x ve druhé sklotvorné oblasti nízkokrystalinické domény (56<x<66) pomocí komplementárních metod rentgenové práškové difrakce, mikro-Ramanovské spektroskopie, diferenciální skenovací kalorimetrie a teplotně modulované multifrekvenční DSC TOPEM®. Mletí se ukázalo jako schopné aktivace přednostní generace nanokrystalické monoklinické fáze beta-As4S4 ve sloučeninách AsxS100-x s menším obsahem arsenu (50<x<60), doprovázené výskytem izokompoziční amorfní fáze. Primární produkty mletím indukované mezifázové nerovnováhy ve sloučeninách s vyšším obsahem arsenu (58<x<66) pak byly identifikovány jako plasticko-krystalické rhomoedrické beta-As4S3 fáze doprovázené extrakcí na arsen bohatých amorfních sloučenin pravděpodobně složení As4S2. Vznikající amorfní a-As4S2 fáze s relativně nízkou teplotou skelného přechodu cca. 50 °C je doplněna do beta-As4S4 polymorfu stabilizovaném spolu s nanostrukturovanou plasticko-krystalickou nc-beta-As4S3 fází. V rámci celé studované kompoziční oblasti nanoarseničnantů byl potvrzen vliv teplotně indukované deprese mletím na procesy kalorimetrických teplotních transferů

ULTRASHORT LIGHT PULSES IN TRANSPARENT SOLIDS: PROPAGATION PECULIARITIES AND PRACTICAL APPLICATIONS

The peculiarities of the femtosecond filamentation in Kerr media has been studied using a set of time-resoling experimental techniques. These include the temporal self-compression of a laser pulse in the filamentation mode, repulsive and attractive interactions of filaments, and influence of the birefringence on the filamentation. The propagation of femtosecond laser pulses at the 1550-nm wavelength in c-Si is studied for the first time using methods of time-resolved transmission microscopy. The nonlinear widening of the pulse spectrum due to the Kerr- and plasma-caused self-phase modulation is recorded

Bond-changing structural rearrangement in glassy As3Se7 associated with long-term physical aging

International audienceAb initio quantum chemical calculations with RHF/6-311G⁎ basis set are performed to justify destruction-polymerization transformations in glassy g-As3Se7 possible during long-term natural physical aging. It is shown that switching of two double bond; length as m-dashAssingle bondSesingle bondSesingle bondAsdouble bond; length as m-dash bridges into short double bond; length as m-dashAssingle bondSesingle bondAsdouble bond; length as m-dash and long double bond; length as m-dashAssingle bondSesingle bondSesingle bondSesingle bondAsdouble bond; length as m-dash fragments is energetically favorable, testifying thermodynamic possibility for such structural changes. This finding is in good agreement with previous experimental observations for g-As3Se7 performed with Raman scattering, NMR and high-resolution XPS measurements. Simulation data suggest that physical aging in Se-rich As-Se glasses can be treated as a unique cooperative relaxation process accompanied by atomic rearrangement within homopolar single bondSesingle bondSesingle bond bonds incorporated between two neighboring AsSe3/2 pyramids