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Chroneos A.I.,Imperial College London | Vovk R.V.,University of Kharkiv | Goulatis I.L.,University of Kharkiv | Nazyrov Z.F.,University of Kharkiv | And 3 more authors.
Acta Physica Polonica A | Year: 2011

Fluorine (F) doping and the formation of F-vacancy (FnV m) clusters have been extensively studied in silicon (Si) as they can suppress the transient self-interstitial mediated diffusion of boron (B). Recent experimental studies by Bernardi et al. revealed that there is no significant concentration of FnVm clusters (for n ≥ 4, m ≥ 1) in disagreement with a number of density functional theory studies. In the present study we use electronic structure calculations to evaluate the binding energies of FnVm clusters and Vn clusters. The significant binding energies of the Vn clusters reveals that the concentration of the large FnVm clusters (n ≥ 4; m ≥ 1) will be limited compared to the Vn clusters or even smaller clusters. Source


Zavgorodniy A.A.,University of Kharkiv | Vovk R.V.,University of Kharkiv | Obolenskii M.A.,University of Kharkiv | Samoilov A.V.,University of Kharkiv | And 3 more authors.
Functional Materials | Year: 2010

The effect of high hydrostatic pressure on the electric resistance in the ab plane of the oxygendeficient YBa2Cu3O7-δ single crystals has been investigated. It is shown that the pressure-induced redistribution of the labile oxygen results in an intensified phase layering accompanied by structural relaxation processes within the experimental sample volume. A significant displacement of the temperature ranges that correspond to metal-dielectric type transitions and the pseudo-gap realization regime. The description of the excess conductivity as Δσ~(1 - T/T*)exp(Δ*ab/T) can be interpreted in terms of mean field theory where T* is the mean-field temperature of the superconducting transition and the temperature dependence of the pseudo-gap is well described in the framework of the BCS-BEC crossover theory. Increasing the applied pressure results in the narrowing of the temperature range where the PG regime is realized, thus extending the area of linear ρ(T) dependence in the ab plane. © 2010 - STC "Institute fot Scientific Crystals". Source


Vovk R.V.,University of Kharkiv | Obolenskii M.A.,University of Kharkiv | Nazyrov Z.F.,University of Kharkiv | Goulatis I.L.,University of Kharkiv | And 2 more authors.
Journal of Materials Science: Materials in Electronics | Year: 2012

In this work we study the structural and resistivity parameters of the 1-2-3 system HTSC single crystals by substituting yttrium to holmium and with a low (5%) aluminum doping. It was determined that in the case of nonstoichiometric samples, the structure of crystals, directly after the solution-melt growth, is close to tetragonal. In the process of additional oxygen saturation we observed a ferroelastic transition to orthorhombic phase, accompanied by the formation of a domain twin structure. The twin boundaries and the aluminum impurities are efficient scattering centers of normal carriers. At aluminum concentration y B 0.5 the tweed structure is not formed. © 2011 Springer Science+Business Media, LLC. Source


Vovk R.V.,University of Kharkiv | Nazyrov Z.F.,University of Kharkiv | Obolenskii M.A.,University of Kharkiv | Goulatis I.L.,University of Kharkiv | And 2 more authors.
Journal of Alloys and Compounds | Year: 2011

We investigate the influence of the disorientation angle between the direction of a constant magnetic field (up to 15 kOe) and the ab-plane α ≡ ∠(H,ab) to the temperature dependence of the excess conductivity in the temperature interval of the transition to the superconducting state in untwinned YBa2Cu3O7-δ single crystals. We discuss the appearance of low temperature "tails" (para-coherent transitions) on the resistive transitions, corresponding to different phase regimes of the vortex-matter state. At temperatures above the critical temperature, the temperature dependence of the excess para-conductivity is interpreted within the Hikami-Larkin theoretical model of the fluctuation conductivity for layered superconductors. © 2011 Elsevier B.V. All rights reserved. Source


Vovk R.V.,University of Kharkiv | Zavgorodniy A.A.,University of Kharkiv | Obolenskii M.A.,University of Kharkiv | Goulatis I.L.,University of Kharkiv | Pinto Simoes V.M.,Ipa Instituto Superior Autonomo Of Estudos Politecnicos
Journal of Materials Science: Materials in Electronics | Year: 2011

The effect of high hydrostatic pressure on the electric resistance in the ab-plane of the oxygen deficient YBa 2Cu 3O 7-δ single crystals is investigated. It is shown that the pressure induced redistribution of the labile oxygen results in the strengthening of the phase immiscibility in layers. This process is accompanied with structural relaxation and ascending diffusion processes within the volume of the experimental sample. We observe a significant displacement of the temperature range that corresponds to metal-dielectric type transitions and the pseudo-gap realization regime. © 2010 Springer Science+Business Media, LLC. Source

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