O. Ozturk

The effect of Pr addition on superconducting and mechanical properties of Bi-2212 superconductors

In this work, the effects of Pr doping on the superconducting, structural and mechanical properties of the samples are analyzed. Pr doped Bi-2212 superconductors are obtained using solid state reaction method. Dc resistivity measurements are made to investigate the superconducting properties, microhardness measurements are made to analyze the mechanical properties, XRD and SEM measurements are done for crystal structure determination and calculation of the lattice parameters. Using EDS measurements, the change in the elemental composition with doping is analyzed. The Vickers microhardness is calculated for undoped and doped samples. The experimental results of the microhardness measurements are analyzed using Kick’s Law, PSR (proportional specimen resistance), modified PRS (MPSR) and Hays–Kendall (HK) approach. The microhardness values of the samples decrease with Pr addition. The results can be successfully explained by HK approach.

The influence of cooling rates on microstructure and mechanical properties of Bi1,6Pb0,4Sr2Ca2Cu3Oy superconductors

We investigated the effect of cooling rates on the microstructure and mechanical properties of Bi1,6Pb0,4Sr2Ca2Cu3Oy superconductors prepared by standard solid state reaction methods. The samples were annealed under identical condition and cooled with different cooling rates. The investigations consisted of Vickers microhardness, SEM and XRD measurements. XRD examination of the samples showed that high percentage of Bi-2212 phase was observed and low-Tc phase increased with increasing the cooling rates. From SEM analysis, flake-like grains were more pronounced with increasing cooling rates. The indentation load versus diagonal length of the samples under different indentation loads in the range of 0.245-2.940 N were presented. We calculated Vickers hardness, Youngs modulus, yield strength, fracture toughness values. These mechanical properties of the samples were found to be load and cooling rate dependent. In addition, we calculated the load independent microhardness, Youngs modulus, and yield strength and fracture toughness of the samples using different models. The possible reasons for the observed changes in microstructure and mechanical properties of the samples due to cooling rates were discussed.

Theoretical investigations of α,α,α-trifluoro-3, -p and o-nitrotoluene by means of density functional theory

This study reports the optimized molecular structures, vibrational frequencies including Infrared intensities and Raman activities, corresponding vibrational assignments, (1)H and (13)C 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.

Mechanical, microstructural and magnetic properties of the bulk BSCCO superconductor prepared by two different methods

BSCCO bulk samples have been prepared by solid-state reaction and ammonium nitrate precipitation methods with Bi1.65Pb0.35Sr2Ca2Cu3O10±y stoichiometry. Structural, mechanical and magnetic characterizations of the samples were performed by the X-ray powder diffraction (XRD), the scanning electron microscopy (SEM), Microhardness measurements, AC susceptibility measurements. The XRD patterns showed that the diffraction peaks for our samples belong to the two main phase, namely 2223 and 2212 of the BSCCO. In this study we have focused on microhardness measurements to investigate the mechanical properties. Vickers microhardness, Young’s modulus and yield strength values were calculated separately for all samples. In addition to these, we calculated the load independent hardness values of samples. Experimental results of hardness measurements were analyzed using the Meyer’s law, proportional sample resistance (PSR) model, Elastic–Plastic deformation model (EPD) and indentation induced cracking (IIC) model. The critical transition temperature, phase purity, lattice parameter, surface morphology and crystallinity of the prepared bulk samples were compared with each other.

Effect of re-pelletization on structural, mechanical and superconducting properties of BSCCO superconductors

We have examined the effect of re-pelletization on structural, mechanical and superconducting properties of high temperature superconducting (HTS) bulk samples using Bi1.85Pb0.35Sr2Ca2Cu3Oy stoichiometry. Conventional solid state reaction method is used for preparation of three different bulk samples. XRD measurement of the samples shows that a high percentage of high-Tc phase is determined. Superconducting critical transition temperature of the samples have been obtained from the curves of ρ-T and χ-T. Vickers micro-hardness are also calculated for all samples. Re-pelletization has a positive effect on structural, mechanical and superconducting properties of bulk samples.

Influence of gold diffusion-doped on phase formation, superconducting and microstructure properties of Bi1.8Pb0.35Sr1.9Ca2.1Cu3Oy superconductors

We report on low-field magnetic properties of gold diffusion-doped Bi1.8Pb0.35Sr1.9Ca2.1Cu3Oy superconducting bulk samples by performing ac susceptibility measurements. The undoped samples were prepared by the standard solid-state reaction method. Doping of Bi1.8Pb0.35Sr1.9Ca2.1Cu3Oy was carried out by means of Au-diffusion during sintering from an evaporated gold film on pellets. To investigate the effect of gold-diffusion and diffusion-annealing duration on transport, magnetic and microstructure properties of the superconducting samples we performed magnetoresistivity, scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements. The ac susceptibility as a function of temperature measurements were carried out at different values of the ac magnetic field amplitudes (Hac) in the range between 20A/m and 320 A/m for 211 Hz. The imaginary part of ac susceptibility measurements is used to calculate intergranular critical current density Jc(Tp) using the Bean Model. Jc(Tp) is seen to increase from 60 A cm-2 to 90 A cm-2 with increasing diffusion-annealing time from 10 h to 50 h. The peak temperature, Tp, in the imaginary part of the ac susceptibility is shifted to a lower temperature with decreasing diffusion-annealing duration as well as increasing ac magnetic fields. The force pinning density (αjj (0)) increased with increasing diffusion annealing time. The value of Tc in gold-diffused samples, in comparison with the undoped samples, increased from 100 ± 0.2 K to 104 ± 0.2 K. It was observed that the value of Tc-offset of the gold-doped samples enhanced with further increasing diffusion-annealing duration. XRD patterns and SEM micrographs are used to obtain information about Bi-2223 phase ratio, lattice parameters and grain size of the samples. Gold doping enhanced the formation high-Tc phase and increased the grain size. The possible reasons for the observed improvements in transport, microstructure and magnetic properties due to Au diffusion and diffusion-annealing time were discussed.

Experimental and theoretical approaches on thermal and structural properties of Zn doped BSCCO glass ceramics

Abstract 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.