G. Yildirim

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.

Ab initio Hartree-Fock and density functional theory study on characterization of 3-(5-methylthiazol-2-yldiazenyl)-2-phenyl-1H-indole

The optimized molecular structures, vibrational frequencies, corresponding vibrational assignments, thermodynamic properties, UV-vis spectra and atomic charges of 3-(5-methylthiazol-2-yldiazenyl)-2-phenyl-1H-indole molecule have been investigated using ab initio Hartree-Fock (HF) and density functional theory (B3LYP) methods at 6-31G (d,p) basis set. The obtained bond lengths and bond angles have been seen to be good agreement with the experimental data. After calculated vibrational frequencies have been compared with each other, the correlation coefficient has been determined. Moreover, we have not only simulated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) but also determined the transition state and energy band gap. Infrared intensities and Raman activities have been also reported.

Density functional theory study on the identification of 3-[(2-morpholinoethylimino)methyl]benzene-1,2-diol

This study deals with the identification of a title compound, 3-[(2-morpholinoethylimino)methyl]benzene-1,2-diol by means of quantum chemical calculations. The optimized molecular structures, vibrational frequencies and corresponding vibrational assignments, thermodynamic properties, charge analyses, nuclear magnetic resonance (NMR) chemical shifts and ultraviolet-visible (UV-vis) spectra of the title molecule in the ground state were evaluated using 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 of the title compound were interpreted with the aid of normal coordinate analysis based on scaled density functional force field. The results show that the obtained optimized geometric parameters (bond lengths, bond angles and bond dihedrals) and vibrational frequencies were observed to be in good agreement with the available experimental results. Moreover, the calculations of the electronic spectra, (13)C and (1)H chemical shifts were compared with the experimental ones. Furthermore, we not only simulated the frontier molecular orbitals (FMO) and molecular electrostatic potential (MEP) but also determined the transition states and energy band gaps, as well. It was found that charge analyses supported the evidences of MEP. Infrared intensities and Raman activities were also reported.

Effect of diffusion-annealing time (0.5 h ≤ t ≤ 2 h) on the mechanical and superconducting properties of Cu-diffused bulk MgB2 superconductors by use of experimental and different theoretical models

This study reports the effect of different annealing time (0.5 h ≤ t ≤ 2 h) on the electrical, physical, microstructural, mechanical and superconducting properties of Cu-diffused bulk magnesium diboride (MgB2) system by means of dc resistivity, X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and microhardness measurements (Hv). The room temperature resistivity (at 300 K), critical transition (Tcoffset and Tconset) temperature, variation of transition temperature, grain size, phase purity, lattice parameter, texturing, surface morphology, crystallinity and Vickers microhardness values of the samples are evaluated and compared with each other. The resistivity results obtained reveal that the (Tcoffset and Tconset) values of the samples produced ascend with the enhancement in the annealing time up to 1 h beyond which these values start to reduce systematically and in fact the smallest Tconset of 38.1 K and Tcoffset of 36.2 K are observed for the sample annealed for 2 h. Similarly, the SEM micrographs display that the surface morphology, crystallinity and grain connectivity improve until a certain diffusion-annealing time (1 h), and after this point, all the properties obtained start to degrade with the increase of the annealing time. Furthermore, the peak intensities, grain sizes and lattice parameters deduced from the XRD measurements illustrate that a systematic elongation in the a and c axis lengths is detected with the annealing time until 1 h beyond which a regular contraction in the lattice parameters is observed for the samples. Likewise, the peak intensities belonging to MgB2 phase enhance with the increment of the annealing time up to 1 h after which they reduce slowly; however, a new peak belonging to Mg2Cu phase appears in the sample annealed for the duration of 2 h, confirming both the reduction of the grain size and degradation of the critical temperature. Additionally, we have focused on the microhardness measurements for the examination of the mechanical properties of the samples studied. Experimental results of microhardness measurements are estimated using the various models such as Meyer’s law, proportional sample resistance model, modified proportional sample resistance model and Hays-Kendall (HK) approach. Based on the simulation results obtained, the Hays-Kendall (HK) approach is determined as the most suitable model describing the mechanical properties of samples prepared.

Experimental and theoretical studies on the identification of p-biphenyloxycarbonylphenyl acrylate

This study presents the identification of a title compound, p-biphenyloxycarbonylphenyl acrylate by means of experimental and theoretical evidences. The spectroscopic properties of the compound were experimentally investigated by Fourier transformation-infrared spectra (in the region 400-4000 cm(-1)) and nuclear magnetic resonance (NMR) chemical shifts (with a frequency of 400 MHz). Moreover, the optimized molecular structures, vibrational frequencies including infrared intensities and Raman activities, corresponding vibrational spectra interpreted with the aid of normal coordinate analysis based on scaled density functional force field, thermodynamic properties, atomic charges and ultraviolet-visible (UV-vis) spectra were analyzed utilizing ab initio Hartree-Fock (HF) and Density Functional Theory (B3LYP) methods at 6-31G(d,p) calculation level. It was found that the vibrational frequencies and chemical shifts obtained were shown to have a good agreement with available experimental results. We not only simulated frontier molecular orbitals (FMO) and molecular electrostatic potential (MEP) but also evaluated the transition state and energy band gap clearly.

Research on MgB2 bulk superconductors exposed to Ag nanoparticles diffusion

Studies of microstructural, mechanical and superconducting properties of Ag diffused MgB2 superconductors by way of scanning electron microscopy, X-ray diffraction and Vickers microhardness measurements. A systemic examination of the magnetoresistance measurements for our prepared samples is exerted under applied magnetic fields started from 0.0 up to 7 T, and their results are described according to thermally activated flux creep. Further, this study reveals explanations of the diffusion coefficient (diffusivity) and activation energy of Ag impurities in the MgB2 materials using the resistivity measurements for the first time. Additionally, all the samples display the indentation size effect nature under the applied indentation test load. Regarding the theoretical modeling of the microhardness evidences, the calculations performed by HK approach are quite closer to the values of the load dependent microhardness.

Experimental and theoretical approaches for identification of p-benzophenoneoxycarbonylphenyl acrylate.

The aim of this multidisciplinary study is to characterize a title compound, p-benzophenoneoxycarbonylphenyl acrylate (BPOCPA) synthesized by condensation reaction of p-acryloyloxybenzoyl chloride (ABC) with 4-hydroxybenzophenone (HBP) by means of experimental and theoretical evidences. The spectroscopic properties of the compound are experimentally examined by Fourier transformation-infrared (FTIR) spectra (in the region 400-4000 cm(-1)) and nuclear magnetic resonance (NMR) chemical shifts (with a frequency of 400 MHz). For the theoretical studies, the optimized molecular structures, vibrational frequencies including infrared intensities and Raman activities, corresponding vibrational spectra interpreted with the aid of normal coordinate analysis based on scaled density functional force field, atomic charges, thermodynamic properties, (1)H and (13)C NMR chemical shifts, JCH and JCC coupling constants belonging to the BPOCPA compound are analyzed in the ground state by the way of the density functional theory (B3LYP) with the standard 6-311++G(d,p) level of theory for the first time. All the results obtained show that the calculated vibrational frequencies and chemical shifts are observed to be in good agreement with the available experimental findings. According to the comparison between experimental results and theoretical data, the calculation level chosen plays an important role in understanding of dynamics of the title compound studied in this work. The self-consistent field (SCF) energy of the molecule in six different solvent media is also analyzed at the same basis set by applying both the Onsager and Polarizable Continuum Model (PCM). It is found that the SCF energies deduced from the methods reduce with the enhancement of the solvent polarity as a consequence of the increment in the stability of the compound studied. Besides, the changes of the PCM calculations are found to be higher than those of the Onsager ones, confirming that the former method displays a more stable structure than latter model.

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.

Decrement in metastability with Zr nanoparticles inserted in Bi-2223 superconducting system and working principle of hybridization mechanism

Abstract This exhaustive study experimentally deals with the role of Zr foreign impurities on the electrical, superconducting and flux pinning properties of the bulk Bi-2223 superconducting compounds by the typical experimental characterization methods such as dc resistivity (ρ–T), transport critical current density (Jc) and powder X-ray diffraction (XRD) surveys. All the experimental findings show that the curial characteristics, being in charge of the varied attractive and feasible applications, retrograde significantly with the enhancement of the Zr nanoparticles in the Bi-2223 superconducting system due to the presence of two trap levels for mobile holes. This leads to the degradation of the metastability of the superconducting materials. In more detail, based on the dc resistivity and transport critical current density measurements, the Zr additives give rise to the localization problem as a consequence of the change in the dynamics of electron–electron interaction. Thus, the room state conductivity,