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Golovchak R.,Lehigh University | Golovchak R.,Lviv Institute of Materials | Kozdras A.,University of Opole | Balitska V.,Lviv Institute of Materials | And 3 more authors.
Journal of Physics Condensed Matter | Year: 2012

The long-term kinetics of physical ageing at ambient temperature is studied in Se-rich As-Se glasses using the conventional differential scanning calorimetry technique. It is analysed through the changes in the structural relaxation parameters occurring during the glass-to-supercooled liquid transition in the heating mode. Along with the time dependences of the glass transition temperature (Tg) and partial area (A) under the endothermic relaxation peak, the enthalpy losses (ΔH) and calculated fictive temperature (TF) are analysed as key parameters, characterizing the kinetics of physical ageing. The latter is shown to have step-wise character, revealing some kinds of subsequent plateaus and steep regions. A phenomenological description of physical ageing in the investigated glasses is proposed on the basis of an alignment-shrinkage mechanism and first-order kinetic equations. © 2012 IOP Publishing Ltd.

Klym H.,Lviv Polytechnic | Ingram A.,Opole University of Technology | Shpotyuk O.,Lviv Institute of Materials | Shpotyuk O.,Jan Dlugosz University in Czestochowa | Szatanic R.,University of Opole
Physics Procedia | Year: 2015

Positron annihilation lifetime spectroscopy combined with Doppler broadening of annihilation radiation was applied to study free-volume entities in Ge-Ga-S glasses having different amount of CsCl additives. It is shown that the structural changes caused by CsCl additives can be adequately described by positron trapping modes determined within two-state model. The results testify in a favor of rather unchanged nature of corresponding free-volume voids responsible for positron trapping in the studied glasses, when mainly concentration of these traps is a subject to most significant changes with composition. © 2015 The Authors. Published by Elsevier B.V.

Shpotyuk Ya.,Lviv Institute of Materials | Shpotyuk Ya.,Ivan Franko National University of Lviv | Shpotyuk M.,Lviv Institute of Materials | Shpotyuk M.,Lviv Polytechnic
Journal of Non-Crystalline Solids | Year: 2013

The role of destruction-polymerization transformations in radiation-induced effects was considered with the example of As-S chalcogenide amorphous semiconductors. It was shown that γ-irradiation leads to a long-wave shift of the fundamental optical absorption edge for stoichiometric As2S3, while no changes were observed in S-rich AsS2 glass. At the same time, the rejuvenation of annealed samples leads to a long-wave shift of the fundamental optical absorption edge for both glasses. These results are explained within a concept of destruction-polymerization transformations by accepting that metastable charged defects are formed owing to radiation-induced switching of covalent bonds. Crown Copyright © 2013 Published by Elsevier B.V. All rights reserved.

Golovchak R.,Lviv Institute of Materials | Golovchak R.,Lehigh University | Kovalskiy A.,Lehigh University | Shpotyuk O.,Jan Dlugosz University in Czestochowa | Jain H.,Lehigh University
Applied Physics Letters | Year: 2011

Quick scanning extended x-ray absorption fine-structure spectroscopy is used to obtain in situ structural information on the real-time response of network glasses at the nanoscale level of atomic organization to the temperature ramp through the glass transition range. The results testify nonlinear, real-time temperature response indicative of nanoscale dynamic heterogeneity in disordered systems with intermediate fragility, related to the intermetabasin transitions within potential energy/enthalpy landscape. © 2011 American Institute of Physics.

Syvorotka I.I.,Lviv Institute of Materials | Syvorotka I.M.,Lviv Institute of Materials | Kityk I.V.,King Saud University
Journal of Magnetism and Magnetic Materials | Year: 2010

Sc-doped YIG films were grown on (1 1 1) oriented GGG crystalline substrate with disorientation angle within the range 025′. Sc3 ion substitution was varied within the range 0.250.3 per formula unit. The films demonstrate different types of surface morphology versus film growth rate and substrate disorientation. Conditions for existence of these types of the surface morphology were defined. The field dependence of magnetic susceptibility at magnetization reversal in film plane and Faraday rotation at wavelength 633 nm for a magnetic field applied in perpendicular direction were measured to characterize the films grown. Films with "mirror-like" surface demonstrate a planar magnetization at room temperature. © 2010 Elsevier B.V. All rights reserved.

Klym H.,Lviv Polytechnic | Hadzaman I.,Drohobych Ivan Franko State Pedagogical University | Ingram A.,Opole University of Technology | Shpotyuk O.,Lviv Institute of Materials
Canadian Journal of Physics | Year: 2014

Temperature-sensitive thick films based on spinel-type semiconducting ceramics of different chemical composition Cu0.1Ni 0.1Co1.6Mn1.2O4 (with p +-types of electrical conductivity), Cu0.1Ni 0.8Co0.2Mn1.9O4 (with p-types of electrical conductivity), and their multilayers of p+-p and p-p +-p structures were fabricated and studied. These thick-film elements possess good electrophysical characteristics before and after long-term ageing test at 170 °C. It is shown that degradation processes connected with diffusion of metallic Ag into grain boundaries occur in one-layer p-and p +-conductive thick films. The p+-p structures were of high stability, the relative electrical drift being no more than 1%. Positron trapping processes in so-called free thick-film structures based on spinel-type Cu0.1Ni0.8Co0.2Mn1.9O4 ceramics are studied. It is shown that two-state positron trapping model is appropriate for an adequate description of changes caused by additional glass phase in these materials. The observed behaviour of defect-related component in the fit of the experimentally measured positron lifetime spectra for thick films in comparison with bulk ceramics testifies in favour of agglomeration of free volume entities during technological process. © 2013 Published by NRC Research Press.

Klym H.,Lviv Polytechnic | Ingram A.,Opole University of Technology | Hadzaman I.,Drohobych Ivan Franko State Pedagogical University | Shpotyuk O.,Lviv Institute of Materials | Shpotyuk O.,Jan Dlugosz University in Czestochowa
Ceramics International | Year: 2014

Porous structure evolution in functional humidity-sensitive MgAl 2O4 spinel ceramics prepared at different sintering temperatures is studied. It is shown that the increase in sintering temperature from 1100 to 1400 °C results in the transformation of the pore size distribution in ceramics. It is established that porous ceramics with tri-modal pore size distribution including open macro-, meso- and micropores up to a few nanometer is humidity sensitive in the 25-95% relative humidity range. It is demonstrated that positron annihilation lifetime spectroscopy supported by four-component fitting procedure is a promising tool for nanostructural characterization of MgAl2O4 spinel-type ceramics. Microstructure of these materials is improved with the increase in sintering temperature; the effect mainly results in the decrease of the additional near grain boundaries phases amount. These phase extractions and free-volume entities in ceramic structure serve as specific trapping centers for positrons penetrating ceramics. It is demonstrated that Tao-Eldrup model can be adequately used for the calculation nanopores size in MgAl2O4 ceramics using o-Ps lifetimes of the third and the fourth components. © 2014 Elsevier Ltd and Techna Group S.r.l.

Shpotyuk O.,Lviv Institute of Materials | Shpotyuk O.,Jan Dlugosz University in Czestochowa | Ingram A.,Opole University of Technology | Shpotyuk M.,Lviv Institute of Materials | And 2 more authors.
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms | Year: 2014

A newly modified correlation equation between defect-related positron lifetime determined within two-state trapping model and radius of corresponding free-volume-type defects was proposed to describe compositional variations in atomic-deficient structure of covalent-bonded chalcogenides like binary As-S/Se glasses. Specific chemical environment of free-volume voids around neighboring network-forming polyhedrons was shown to play a decisive role in this correlation, leading to systematically enhanced volumes in comparison with typical molecular substrates, such as polymers. © 2014 Elsevier B.V. All rights reserved.

Bondarchuk A.,Technological University of Mixteca | Shpotyuk O.,Lviv Institute of Materials | Glot A.,Technological University of Mixteca | Klym H.,Lviv Polytechnic
Revista Mexicana de Fisica | Year: 2012

Current-voltage dependence in In 2O 3-SrO ceramics contains a region where the current is increased weaker than the voltage. Such behavior is observed in oxygen atmosphere and is not registered in an inert one. Nonlinear current-voltage dependence is explained in terms of a relation between electronic processes at the grain boundaries and adsorption of oxygen in electric field. The role of adsorption processes is discussed on the basis of obtained data (current-voltage dependences, pore size distribution, secondary electron microscopy, and humidity sensitivity of conductance).

Shpotyuk O.,Lviv Institute of Materials | Shpotyuk O.,Jan Dlugosz University in Czestochowa | Golovchak R.,Lviv Institute of Materials
Physica Status Solidi (C) Current Topics in Solid State Physics | Year: 2011

Network-forming cluster approach is applied to As-Se and Ge-Se glasses to justify their tendency to self-organization. It is shown that reversibility windows determined by temperature-modulated differential scanning calorimetry using short-term aged or as-prepared samples do not necessary coincide with self-organized phase in these materials. The obtained results testify also pseudo-self-organization phenomenon in Ge-Se glasses: over-constrained outrigger raft structural units built of two edge- and four corner-shared tetrahedra are interconnected via optimally-constrained ≡Ge-Se-Se-Ge≡ bridges within the range of compositions identified previously as self-organized phase by temperature modulated differential scanning calorimetry technique. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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