Browsing by Author "Tasci A."

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Comparison of Vickers microhardness of undoped and Ru doped BSCCO glass ceramic materials
(2018-03-01) Ozturk O.; Asikuzun E.; Tasci A.; Gokcen T.; Ada H.; Koralay H.; Cavdar S.
In this study, effect of substitution ratio on the mechanical and structural properties of Bi1−xRuxPb0.2Sr2CaCu2O10+δ system, that is prepared in the ratios of x = 0.0, 0.025, 0.050, 0.075, is investigated. Samples are prepared with glass ceramic method and sintered at 845 °C. XRD and SEM measurements are performed for structural analyses, and Vickers micro-hardness measurements are carried out at different applied load (0.245 ≤ F ≤ 2.940 N) in order to investigate the mechanical performance of the Ru doped Bi1−xRuxPb0.2Sr2CaCu2O10+δ system. Experimental results of Vickers micro-hardness analyses are performed using the Meyer’s law, the proportional samples resistance model, the elastic/plastic deformation model, the Hays–Kendall approach and the indentation induced cracking (IIC) model. All analyses results are exhibited reverse indentation size effect behavior. The measured hardness values increase with increasing the applied load. Finally, IIC model is determined as the most successful model describing the mechanical properties of our samples.
Effect of Zn content on microstructure and mechanical performance in Bi1.8Sr2Ca2Cu3.2-xZn xO10+δ glass ceramic
(2014-01-01) Koralay H.; Hicyilmaz O.; Cavdar S.; Asikuzun E.; Tasci A.; Ozturk O.
In this study, we have investigated the effects of Zn doping on structural and mechanical properties of Bi1.8Sr2Ca2Cu 3.2-xZnxO10+δ ceramic samples with x = 0.0, 0.1, 0.5, 1.0. The prepared samples were characterized by using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray powder diffractometer (XRD) and static microhardness indenter. Surface morphology, orientation of grains and elemental composition analysis of the samples were investigated by SEM and EDS measurements, respectively. Texturing and lattice parameters a, b and c were determined from the XRD measurements. In this work we focused on Vickers microhardness measurements in order to characterize the mechanical properties. Experimental results of Vickers microhardness measurements were analyzed by using Meyer's law, the elastic/plastic deformation model, proportional sample resistance model (PSR), modified PSR model, Hays-Kendall (HK) approach and indentation induced cracking (IIC) model. According to the obtained results, HK approach is the most suitable model for the CZn00 sample showing indentation size effect behavior and IIC Model is the most suitable model for the CZn01, CZn05 and CZn10 samples showing reverse indentation size effect behavior. © 2014 Springer Science+Business Media New York.
Experimental and theoretical approaches on thermal and structural properties of Zn doped BSCCO glass ceramics
(2016-03-01) Koralay H.; Hicyilmaz O.; Cavdar S.; Ozturk O.; Tasci A.
Thermal properties of Cu-Zn partially substituted Bi1.8Sr2Ca2Cu3.2-xZnxO10+δ (x = 0, 0.1 and 0.5) glass-ceramic systems have been investigated with the help of a differential thermal analyzer (DTA) by using Johnson-Mehl-Avrami-Kolmogorov (JMAK) approximation. Non-isothermal crystallization kinetics of the samples has been tested. The calculated values of activation energy of crystallization (E) and Avrami parameter (n) ranged between 306.1 and 338.3 kJ·mol-1 and 1.29 and 3.59, respectively. Crystallization kinetics was compared following the partial substitution, before and after Zn doping of the sample. In addition, by using a scanning electron microscope (SEM) and X-ray powder diffractometer (XRD), structural properties of Zn doped BSCCO glass-ceramic samples were determined. Surface morphology of the samples was studied by SEM measurements. Lattice parameters and volume of the samples were calculated from the XRD measurements.
High-quality c-axis oriented non-vacuum Er doped ZnO thin films
(2016-05-15) Asikuzun E.; Ozturk O.; Arda L.; Tasci A.; Kartal F.; Terzioglu C.
Preparation, growth, structure and optical properties of high-quality c-axis oriented non-vacuum Er doped ZnO thin films were studied. Zn1-xErxO (x=0.0, 0.01, 0.02, 0.04, and 0.05) precursor solutions were prepared by sol-gel synthesis using Zn, and Er based alkoxide which were dissolved into solvent and chelating agent. Zn1-xErxO thin films with different Er doping concentration were grown on glass substrate using sol-gel dip coating. Thin films were annealed at 600 °C for 30 min, and tried to observe the effect of doping ratio on structural and optical properties. The particle size, crystal structure, surface morphologies and microstructure of all samples were characterized by X-Ray diffraction (XRD) and Scanning Electron Microscope (SEM). The UV-vis spectrometer measurements were carried out for the optical characterizations. The surface morphology of the Zn1-xErxO films depend on substrate nature and sol-gel parameters such as withdrawal speed, drying, heat treatment, deep number (film thickness) and annealing condition. Surface morphologies of Er doped ZnO thin films were dense, without porosity, uniform, crack and pinhole free. XRD results showed that, all Er doped ZnO thin films have a hexagonal structure and (002) orientation. The optical transmittance of rare earth element (Er) doped ZnO thin films were increased. The Er doped ZnO thin films showed high transparency (>85) in the visible region (400-700 nm).
Structural, electrical and mechanical properties of selenium doped thallium based high-temperature superconductors
(2016-01-01) Cavdar S.; Kol N.; Koralay H.; Ozturk O.; Asikuzun E.; Tasci A.
In this study, highly-refined chemical powders were synthesized by having them ready in appropriate stoichiometric proportions with conventional solid state reaction method so that they would produce the superconductor TlPb0.3Sr2Ca1-xSexCu2Oy (x = 0; 0.4; 0.6; 1.0). This study aims to understand effect of the selenium doping on the superconducting, structural and mechanical properties of the aforementioned superconducting material. The effect of the doping rates on the structural and electrical properties of the sample has been identified. Electrical characteristics of the TlPb0.3Sr2Ca1-xSexCu2Oy material were measured using standard four point probe method. Structural characteristics were examined with the powder X-ray diffractometer (XRD) and scanning electron microscope (SEM). Mechanical properties were analyzed with Vickers microhardness measurements on the sample surface. According to the results, it was observed that the reflection comes from the (00l) and parallel planes increased with Se doping. Particle size increases with increasing doping ratio. According to results of the mechanical measurements, all samples exhibit indentation size effect (ISE) behavior. Comparing the obtained results with theoretical studies, it was understood that Hays Kendall approach is the best method in determination of mechanical properties and analyzing microhardness of the materials.
Theoretical investigations of α,α,α-trifluoro-3, -p and o-nitrotoluene by means of density functional theory
(2012-01-01) Yildirim G.; Senol S.; Dogruer M.; Ozturk O.; Senol A.; Tasci A.; Terzioglu C.
This study reports the optimized molecular structures, vibrational frequencies including Infrared intensities and Raman activities, corresponding vibrational assignments, 1H and 13C NMR chemical shifts, the magnitudes of the JCH and JCC coupling constants, Ultraviolet-visible (UV-vis) spectra, thermodynamic properties and atomic charges of the title compounds, α,α,α-trifluoro-3, -p and o-nitrotoluene, in the ground state by means of the density functional theory (DFT) with the standard B3LYP/6-311++G(d,p) method and basis set combination for the first time. Theoretical vibrational spectra were interpreted by normal coordinate analysis based on scaled density functional force field. The results show that the vibrational frequencies and chemical shifts calculated were obtained to be in good agreement with the experimental data. Based on the comparison between experimental results and theoretical data, the calculation level chosen is powerful approach for understanding the identification of all the molecules studied. In addition, not only were frontier molecular orbitals (HOMO and LUMO), molecular electrostatic potential (MEP) and electrostatic potential (ESP) simulated but also the dipole moment, softness, electronegativity, chemical hardness, electrophilicity index, transition state and energy band gap values were predicted. According to the investigations, all compounds were found to be useful to bond metallically and interact intermolecularly; however, the thermodynamic properties confirm that the α,α,α-trifluoro-p- nitrotoluene was more reactive and more polar than the others. © 2011 Elsevier B.V. All rights reserved.