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Shpotyuk O.,Jan Dlugosz University in Czestochowa | Golovchak R.,Lviv Institute of Materials
Journal of Optoelectronics and Advanced Materials | Year: 2012

Compositional trends in topological organization of fully-saturated covalent networks are considered at the example of binary Ge-Se glasses. It is shown that previously announced reversibility window, detected in this system with temperaturemodulated differential scanning calorimetry as compositional range of under-marginal non-reversing heat flow, does not correspond to real intermediate phase in terms of global optimally-constrained connectivity. The observed structural complexity is attributed to topological pseudo-self- organization, e.g. effect originated from mixed over-constrained molecular-clustering and optimally-constrained inter-cluster chain crossing. Source


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. Source


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. Source


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). Source


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. Source

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