Turin Polytechnic University in Tashkent

Zafar, Uzbekistan
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Zahedi E.,Islamic Azad University at Shahrood | Hojamberdiev M.,Turin Polytechnic University in Tashkent
European Physical Journal B | Year: 2017

Pressure dependence of the structural and elastic properties of perovskite-type cubic SrWO2.05N0.95 was studied using firstprinciples density functional theory (DFT) utilizing the plane wave pseudopotential and the exchange-correlation functionals within the generalized gradient approximation. The estimated bulk modulus and its pressure derivative values from the P − V data fitted to the third-order Birch-Murnaghan equation of state were close to the data obtained from the independent elastic constants. Based on the generalized Born stability criteria, SrWO2.05N0.95 is mechanically stable up to 139 GPa. The influence of hydrostatic pressure (0 to 139 GPa) on the bulk modulus, shear modulus, Young’s modulus, Pugh’s modulus ratio, Poisson’s ratio, Vickers hardness, sound velocities, Debye temperature, Debye-Grüneisen parameter, minimum thermal conductivity and elastic anisotropy of SrWO2.05N0.95 was particularly studied in detail. It was found that SrWO2.05N0.95 is a ductile and hard solid with large bulk, shear and Young’s modulus and displays an extraordinary low thermal conductivity. Since there are not any experimental or theoretical data available for comparison the results of the present study have revealed an important fundamental information about the elastic properties of perovskite-type cubic SrWO2.05N0.95 for future experimental studies. © 2017, EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.

Zahedi E.,Islamic Azad University at Shahrood | Hojamberdiev M.,Turin Polytechnic University in Tashkent
Journal of Solid State Chemistry | Year: 2017

The crystal structures, electro–optical properties, and charge carrier effective masses of Cs2TeW3O12 and Cs2TeMo3O12 with hexagonal, polar and non–centrosymmetric crystal structure were investigated based on density functional theory. Cs2TeW3O12 and Cs2TeMo3O12 are found to be indirect K (1/3, 1/3, 0) → G (0, 0, 0) band gap semiconductors (Eg > 3 eV) with small effective masses of photogenerated charge carriers. The mixing of octahedrally coordinated d° transition metal cations (W6+ and Mo6+) with the filled p orbitals of the oxygen ligands leads to the formation of some W5+/Mo5+ sites and splitting of d orbitals into the partially filled t2g (dxy, dyz, and dzx) orbitals and empty eg (dz2 and dx2–y2) orbitals. The top of the valence bond is mainly contributed by O 2p orbital of the oxygen ligands mixed with the partially filled t2g orbitals of W 5d/Mo 4d, while the conduction band mainly consists of empty eg orbitals of W 5d/Mo 4d with a little contribution of O 2p orbitals. The dielectric function exhibits a slight anisotropic behavior and optical absorption peak for Cs2TeW3O12 and Cs2TeMo3O12 belonging to the strong electronic transition O 2p → W 5d/Mo 4d within the octahedral units. According to the estimated valence band and conduction band edges, Cs2TeW3O12 and Cs2TeMo3O12 can be applied as visible−light−responsive photocatalysts for the decomposition of organic pollutants and dye molecules. Also, Cs2TeMo3O12 can be used in water splitting for hydrogen generation but Cs2TeW3O12 requires further experimental studies to confirm its ability for water splitting. © 2017 Elsevier Inc.

Kansal I.,University of Aveiro | Goel A.,Pacific Northwest National Laboratory | Tulyaganov D.U.,Turin Polytechnic University in Tashkent | Rajagopal R.R.,University of Aveiro | Ferreira J.M.F.,University of Aveiro
Journal of the European Ceramic Society | Year: 2012

The influence of varying the CaO/MgO ratio on the structure and thermal properties of CaO-MgO-SiO 2-P 2O 5-CaF 2 glasses was studied in a series of eight glass compositions in the glass forming region of diopside (CaMgSi 2O 6)-fluorapatite [Ca 5(PO 4) 3F]-wollastonite (CaSiO 3) ternary system. The melt-quenched glasses were characterized for their structure by infrared spectroscopy (FTIR) and magic angle spinning (MAS)-nuclear magnetic resonance (NMR) spectroscopy. Silicon is predominantly present as Q 2 (Si) species, while phosphorus tends to coordinate in orthophosphate environment. The sintering and crystallization parameters of the glasses were obtained from differential thermal analysis (DTA) while crystalline phase fractions in the sintered glass-ceramics were analyzed by X-ray diffraction adjoined with Rietveld refinement. Diopside, fluorapatite, wollastonite and pseudowollastonite crystallized as the main crystalline phases in all the glass-ceramics with their content varying with respect to variation in CaO/MgO ratio in glasses. The implications of structure and sintering behaviour of glasses on their bioactivity were discussed. © 2011.

Fernandes H.R.,University of Aveiro | Tulyaganov D.U.,University of Aveiro | Tulyaganov D.U.,Turin Polytechnic University in Tashkent | Goel A.,Pacific Northwest National Laboratory | Ferreira J.M.F.,University of Aveiro
Journal of the European Ceramic Society | Year: 2012

Glass compositions with formula (71.78-x)SiO2-2.63Al2O3-(2.63+x)K2O-23.7Li2O (mol.%, x=0-10) and SiO2/Li2O molar ratios far beyond that of stoichiometric lithium disilicate (Li2Si2O5) were prepared by conventional melt-quenching technique to investigate the influence of K2O content on structural transformations and devitrification behaviour of glasses in the Li2O-SiO2 system. The scanning electron microscopy (SEM) examination of as cast non-annealed glasses revealed the presence of nanosized droplets in glassy matrices suggesting occurrence of liquid-liquid phase separation. An overall trend towards depolymerization of the silicate glass network with increasing K2O content was demonstrated by employing magic angle spinning-nuclear magnetic resonance (MAS-NMR) spectroscopy. The distribution of structural units in the experimental glasses was estimated using 29Si MAS-NMR spectroscopy suggesting the appearance of Q2, enhancement of Q3 and diminishing of Q4 groups with increasing K2O contents. X-ray diffraction (XRD) and differential thermal analysis (DTA) were used to assess the influence of K2O on devitrification process and formation of lithium disilicate (Li2Si2O5) and/or lithium metasilicate (Li2SiO3) crystalline phases. © 2011 Elsevier Ltd.

Kansal I.,University of Aveiro | Goel A.,Pacific Northwest National Laboratory | Tulyaganov D.U.,Turin Polytechnic University in Tashkent | Santos L.F.,University of Lisbon | Ferreira J.M.F.,University of Aveiro
Journal of Materials Chemistry | Year: 2011

We report on the structure, apatite-forming ability and physicochemical degradation of glasses along the fluorapatite [FA; Ca5(PO 4)3F]-diopside (Di; CaMgSi2O6) join. A series of glasses with varying FA/Di ratio have been synthesised by melt-quenching technique. The amorphous glasses could be obtained only for compositions up to 40 wt.% of FA. The detailed structural analysis of the glasses has been made by infrared spectroscopy (FTIR), Raman spectroscopy and magic angle spinning-nuclear magnetic resonance spectroscopy (MAS-NMR). Silicon was predominantly present as Q2 (Si) species while phosphorus was found in an orthophosphate type environment in all the investigated glasses. The apatite forming ability of glasses was investigated by immersion of the glass powders in simulated body fluid (SBF) for times varying between 1 h-28 days. An extensive precipitation of calcite (CaCO3) after immersion in SBF was found in all the glasses, which considerably masked the formation of hydroxyapatite [HA; Ca5(PO4)3OH]. The possible mechanism favouring the formation of calcite instead of HA has been explained on the basis of experimental results obtained for the structure of the glasses, leaching profile of glass powders in SBF solution and pH variation in SBF solution. Furthermore, the physico-chemical degradation of the glasses has been studied in accordance with ISO 10993-14 "Biological evaluation of medical devices - Part 14: Identification and quantification of degradation products from ceramics" in Tris HCl and citric acid buffer. All the FA containing glasses exhibited a weight gain (instead of weight loss) after immersion in citric acid buffer due to the formation of different crystalline products. © 2011 The Royal Society of Chemistry.

Masuda S.,James Franck Institute | Masuda S.,Tohoku University | Nakamura K.,Turin Polytechnic University in Tashkent | Nakamura K.,Osaka City University | Del Campo A.,Los Alamos National Laboratory
Physical Review Letters | Year: 2014

A protocol is proposed for the rapid coherent loading of a Bose-Einstein condensate into the ground state of an optical lattice, without residual excitation associated with the breakdown of adiabaticity. The driving potential required to assist the rapid loading is derived using the fast-forward technique, and generates the ground state in any desired short time. We propose an experimentally feasible loading scheme using a bichromatic lattice potential, which approximates the fast-forward driving potential with high fidelity. © 2014 American Physical Society.

De Martino A.,City University London | Klopfer D.,Heinrich Heine University Düsseldorf | Matrasulov D.,Turin Polytechnic University in Tashkent | Egger R.,Heinrich Heine University Düsseldorf
Physical Review Letters | Year: 2014

We study electric dipole effects for massive Dirac fermions in graphene and related materials. The dipole potential accommodates towers of infinitely many bound states exhibiting a universal Efimov-like scaling hierarchy. The dipole moment determines the number of towers, but there is always at least one tower. The corresponding eigenstates show a characteristic angular asymmetry, observable in tunnel spectroscopy. However, charge transport properties inferred from scattering states are highly isotropic. © 2014 American Physical Society.

Dzhalilov A.,Turin Polytechnic University in Tashkent | Mayer D.,Clausthal University of Technology | Safarov U.,National University of Uzbekistan
Nonlinearity | Year: 2015

Let fi, i = 1, 2, be orientation preserving circle homeomorphisms with a finite number of break points , at which the first derivatives Dfi have jumps, and whose irrational rotation numbers coincide. Denote by the jump ratio of fi at a break point and by its total jump ratio, given by the product of the jump ratios over all break points. We prove that, for two such circle homeomorphisms fi, i = 1, 2, which on each interval of continuity of Dfi are C2+ε, ε > 0, and whose total jump ratios and do not coincide, the map h conjugating f1 and f2 is a singular function. © 2015 IOP Publishing Ltd & London Mathematical Society.

Fernandes H.R.,University of Aveiro | Tulyaganov D.U.,University of Aveiro | Tulyaganov D.U.,Turin Polytechnic University in Tashkent | Pascual M.J.,CSIC - Institute of Ceramics and Glass | Ferreira J.M.F.,University of Aveiro
Ceramics International | Year: 2014

The role of each oxide component on the structure of molten glass and on their densification and crystallization behaviours is expected to be more easily assessed for compositions comprising a small number of components. In the present work, binary (Li2O-SiO2), ternary (Li 2O-Al2O3-SiO2), and quaternary (Li2O-K2O-Al2O3-SiO2) glass compositions were selected. The aim was to investigate the relationships between the compositions and structure of the glasses, namely, the effects of each component on the extent of liquid-in-liquid phase separation, their thermal behaviour and the phase assemblage in the disilicate glass-ceramics. The distribution of structural units in the experimental glasses was assessed using 29Si MAS-NMR spectroscopy. Adding Al2O3 played a dual role as network former and modifier when added to the binary system by enhancing Q2 and diminishing Q3 structural units. The processing window for sintering, the difference between the onset of crystallisation and glass-transition temperature (Tc-Tg), was too narrow for the less polymerised network structures (binary and ternary systems), hindering the densification of the corresponding glass powder compacts. Oppositly, compositions in the quaternary system featured excellent densification behaviour coupled with high mechanical strength. These features derive from a more rigid glass network comprising four coordinated (AlO 4/2)- units and K+ cations in its vicinity. © 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Kansal I.,University of Aveiro | Tulyaganov D.U.,Turin Polytechnic University in Tashkent | Goel A.,University of Aveiro | Pascual M.J.,CSIC - Institute of Ceramics and Glass | Ferreira J.M.F.,University of Aveiro
Acta Biomaterialia | Year: 2010

Glass-ceramics in the diopside (CaMgSi2O6)- fluorapatite (Ca5(PO4)3F)-wollastonite (CaSiO3) system are potential candidates for restorative dental and bone implant materials. The present study describes the influence of varying SiO2/CaO and CaF2/P2O5 molar ratio on the structure and thermal behavior of glass compositions in the CaO-MgO-SiO2-P2O5-Na2O-CaF 2 system. The structural features and properties of the glasses were investigated by nuclear magnetic resonance (NMR), infrared spectroscopy, density measurements and dilatometry. Sintering and crystallization behavior of the glass powders were studied by hot-stage microscopy and differential thermal analysis, respectively. The microstructure and crystalline phase assemblage in the sintered glass powder compacts were studied under non-isothermal heating conditions at 825 °C. X-ray diffraction studies combined with the Rietveld-reference intensity ratio (R.I.R) method were employed to quantify the amount of amorphous and crystalline phases in the glass-ceramics, while scanning electron microscopy was used to shed some light on the microstructure of resultant glass-ceramics. An increase in CaO/SiO2 ratio degraded the sinterability of the glass powder compacts, resulting in the formation of akermanite as the major crystalline phase. On the other hand, an increase in P2O5/CaF2 ratio improved the sintering behavior of the glass-ceramics, while varying the amount of crystalline phases, i.e. diopside, fluorapatite and wollastonite. © 2010 Published by Elsevier Ltd. on behalf of Acta Materialia Inc.

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