Yazar "Terzioğlu, Cabir" seçeneğine göre listele

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    A-site Pb doping effect on structural, microstructural and magnetotransport properties of La0.5Sm0.2Ca0.3-xPbxMnO3 (x=0, 0.05, 0.10) manganite
    (Elsevier Science SA, 2021) Denbri, Fatih; Mahamdioua, Nabil; Meriche, Faiza; Koç, Nevin Soylu; Terzioğlu, Cabir; Varilci, Ahmet; Altıntaş, Sevgi Polat
    Structural, microstructural and magneto-transport properties of polycrystalline La0.5Sm0.2Ca0.3-x PbxMnO3 (x = 0, 0.05 and 0.10) samples, prepared by conventional solid state reaction, were studied. Refinement of the Powder X-ray diffractograms revealed that all the samples crystallize into orthorhombic structure with Pnma space group and the lattice parameters increase with increasing Pb content. The scanning electron microscope (SEM) micrographs show a granular character and the estimated grain sizes ranges between 10 mu m and 20 mu m. The experimental electrical resistivity and the magnetoresistance in the temperature range 20 K-250 K under magnetic field of zero and 1 Ta, have been recorded using four probe technique. The resistivity curves without magnetic field, exhibit a ferromagnetic-metallic (FM) to paramagnetic-insulating (PI) transition at TMI = 125 K, 91 K and 37 K for x = 0, 0.05 and 0.10, respectively. The magnetoresistance reaches 58% for undoped sample and decrease with Pb doping under 1T. The resistivity values increases drastically with Pb doping. These two results were explained mainly by the increase of the disorder sigma 2 and rA TMI) and for x = 0 and 0.05 samples, the resistivity curves is well fitted by a combination of the residual resistivity, weak localization and electron-electron scatterings; in addition to small polaron contribution or electron-phonon interaction respectively. In the high temperature regime T TMI, all our resistivity curves has been analyzed using adiabatic small polaron hopping model (ASPH) above theta D/2 and variable range hopping model (3D-VRH) (TMI < T < theta D/2). An attempt to use the percolation model to describe the resistivity data in the entire temperature range for both x = 0 and 0.05 samples, was established. Finally, density of state, mean hopping distance Rh and mean hopping energy Eh were calculated and discussed.
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    Ac Susceptibility measurements and mechanical performance of Bulk MgB2
    (Springer, 2015) Öztürk, Özgür; Aşıkuzun, Elif; Kaya, Şeydanur; Erdem, Murat; Safran, Serap; Kılıç,Ahmet; Terzioğlu, Cabir
    The effects of Ar ambient pressure (vacuum and 0, 10, and 20 B) and annealing times (0.5 and 1 h) on microstructural, superconducting, and mechanical properties of bulk superconducting MgB2 are investigated. The samples are produced using the solid-state reaction method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements are performed for determination of the crystal structure and surface morphology of MgB2 samples, respectively. The superconducting properties are studied by AC magnetic susceptibility measurements. Microhardness analyses are made using the Vickers microhardness test for determination of mechanical properties of all samples. Increasing the Ar pressure decreases the lattice parameters and hence the average grain size. Increasing the annealing time results in larger lattice parameters and larger grain formation. The susceptibility measurements revealed a two-step transition which is reminiscent of granular superconductors. The intra-grain transition temperature is determined to be 38.4 K for all samples. The inter-grain transition temperature of 37.2 K is obtained for samples produced under Ar ambient pressure. The samples produced under Ar ambient pressure have better superconducting properties than the ones produced in vacuum. Increasing the annealing time under vacuum further decreases the superconducting properties probably due to Mg loss.
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    Analysis of indentation size effect (ISE) behavior in low-load Vickers microhardness testing of (Sm123)(1-x)(Nd123)(x) superconductor system
    (Springer, 2013) Çelik, Şükrü; Öztürk, Özgür; Coşkun, E.; Sarıhan, Menekşe; Aşıkuzun, Elif; Terzioğlu, Cabir
    Indentation size effect (ISE) for (Sm123)(1-x) (Nd123)(x) superconducting samples which were fabricated by the solid state reaction technique for values of x = 0.00, 0.05, 0.10, 0.20, and 0.30 was investigated by analyzing the theoretical models. When the experimental data of a number of single crystals which have the different crystal structure and different chemical bonding inside the poly-crystallined samples were analyzed with the ISE models, the sample encountering with resistance and elastic deformation was observed as well as plastic deformation. The microhardness values on different surfaces of materials were calculated by using Meyer Law, proportional specimen resistance model, modified proportional specimen resistance model, elastic/plastic deformation model and the Hays-Kendall (HK) approach. The results showed that the HK approach was determined as the most successful model. Furthermore, X-ray powder diffraction and scanning electron microscope measurements were analyzed for superconducting properties of (Sm123)(1-x)(Nd123)(x) superconductor system. The results showed that microhardness values at the minimum load and averaged plateau region of load increased with increase of Nd123 concentration. Nd123 content can be used as to be estimated the microhardness value of (Sm123)(1-x)(Nd123)(x) superconducting sample in the range of 0.878-2.717 GPa. The control of the microhardness value by using Nd123 content in (Sm123)(1-x)(Nd123)(x) superconducting structure can be useful in technological applications in superconductivity industry.
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    Analysis of indentation size effect on mechanical properties of cu-diffused bulk MgB2 superconductor using experimental and different theoretical models
    (Springer, 2013) Doğruer, Musa; Yıldıırm, Gürcan; Öztürk, Özgür; Terzioğlu, Cabir
    This study indicates the change of the electrical, microstructural, physical, mechanical and superconducting properties of Cu-diffused bulk MgB2 superconductors by means of scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), microhardness and dc resistivity measurements. The samples are prepared at different annealing temperatures in the range from 650 to 850 C-a similar to. Electrical and superconducting properties of samples are estimated from the dc electrical resistivity measurements. Moreover, microhardness measurements are performed to investigate the mechanical properties. Further, phase composition, grain sizes and lattice parameters are determined from the XRD measurements. At the same time, the surface morphology and grain connectivity of the samples are examined by SEM investigations. The measurements conducted demonstrate that both the Cu diffusion into the MgB2 system and the increment in the diffusion-annealing temperature increase the critical transition temperatures. Similarly, microstructure and grain size improve while the voids and porosity decrease with the increase of the diffusion-annealing temperature. In addition, the experimental results of the microhardness measurements are investigated using the Meyer's law, PSR (proportional specimen resistance), modified PRS (MPSR), elastic-plastic deformation model (EPD) and Hays-Kendall (HK) approach. The obtained microhardness values of the samples decrease with the increase of the diffusion-annealing temperature up to 850 C-a similar to. The Hays-Kendall approach is found to be the most successful model describing the mechanical properties of the samples studied in this work.
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    Anisotropic nature and scaling of thermally activated dissipation mechanism in Bi-2223 superconducting thin film
    (Elsevier Science Sa, 2013) Yıldırım, Gürcan; Varilci, Ahmet; Terzioğlu, Cabir
    This study deals with the resistive transition of the c-axis oriented Bi-2223 thin film produced on the single crystal MgO (100) substrate using direct current (DC) magnetron reactive sputtering technique at 100 watt in the case of applied field parallel and perpendicular to c-axis up to 3 T, respectively. Peak temperature (T-p) of the sample studied is determined from the variation of dR/dT as a function of temperature plot when the resistance called as R-p at the T-p is deduced from the same curve. It is found that the superconducting translation (onset and offset critical) temperatures reduce with the increment of the applied magnetic field strength and direction. In fact the minimum onset (T-c(onset)) value of 100.94 K and offset (T-c(offset)) value of 55.81 K are observed for 3 T applied field parallel to the c-axis. Moreover, the variation of Delta T-c(T-c(onset) - T-c(offset)) value is found to increase with the enhancement of the field and direction. Similar to the critical transition temperature results, the maximum variation (45.14 K) is observed for the sample in the applied field parallel to c-axis at 3 T. Further, the results obtained show that the dissipative resistivity is well adapted to thermally activated flux motion below the T-p value under the magnetic field and so the R-p values observed are used to examine the temperature and field dependence (mu H-0) of the flux pinning (activation) energy described as the formula U(T, mu H-0) = U-0(1 - T/T-p)H))H-m(-alpha). According to results, while m value is calculated to be about 1.572 and 1.492, alpha value is found to be about 0.546 and 0.498 at H//ab and H//c-axis, respectively, confirming that not only does the film produced show 3D-like behavior but also the thermally activated flux flow is the dominant mechanism on the sample. Additionally, the irreversibility fields (H-irr), upper critical fields (H-c2), penetration depths (lambda) and coherence lengths (xi) are evaluated from the magnetoresistance curves. When the anisotropy ratio of gamma(h) = xi(c)/xi(ab) is estimated to be about 6.42 at 0 K and 7.11 near the transition temperature (R = 0 Omega), the ratio of gamma(lambda) = lambda(c)/lambda(ab) is found to change from 1.97 until 3.28 in the range from 0 K to T-c. Based on the results obtained, it is concluded that both the anisotropy ratios are strongly dependent upon the temperature (particularly the ratio of lambda(lambda)) and the anisotropy ratio lambda(lambda) is more slightly smaller than that of gamma(h). (C) 2012 Elsevier B. V. All rights reserved.
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    Annealing-induced modifications on structural, surface chemical bonding, and electrical characteristics of p-NiO/n-TiO2 heterostructure
    (Springer, 2023) Kaya, Şenol; Soykan, Uğur; Sunkar, Mustafa; Karaboğa, Seda; Doğan, Muhsin Uğur; Terzioğlu, Rıfkı; Yıldırım, Gürcan; Terzioğlu, Cabir
    The influences of annealing temperatures on the electrical characteristics of a p- NiO/n-TiO2 heterojunction diode were thoroughly investigated, taking into account changes in microstructure, morphology, and surface chemistry of the p-NiO/n-TiO2 films, which were deposited on an insulating SiO2/ Si layer. During different annealing processes, considerable stress variations were observed in the p-NiO/n-TiO2 films due to the crystalline evolution of p-NiO and n-TiO2. Notably, the crystallization of the TiO2 layer, which serves as the intermediary between the back contact materials and NiO, led to the evident formation of grain structures. As the annealing temperature increased, the surface roughness also grew from 5.4 to 8.7 nm. At an annealing temperature of 500 degrees C, the formation of a parasitic NiTiOx phase was observed, particularly at the interface between NiO and TiO2. Conversely, the study also revealed that annealing temperature played a significant role in the rectifying behavior, barrier potential, and ideality factor of the diode. Among the various annealing processes, the most favorable results were achieved after annealing at 400 degrees C. At this temperature, the diode demonstrated the lowest ideality factor of 1.89, accompanied by superior rectifying behavior and a barrier potential of 0.70 eV. The findings clearly indicate that any alterations in the surface chemistry and microstructure of the film directly impact the diode's characteristics. Thus, optimizing the annealing temperature becomes crucial for enhancing the performance of the p-NiO/n-TiO2 heterojunction diode.
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    Bi-2223 Süperiletken Seramiklerde Peletizasyon Basıncının Yapısal, Elektriksel ve Mekanik Özellikler Üzerine Etkisi
    (2022) Kara, Emre; Doğan, Muhsin Uğur; Kaya, Şenol; Terzioğlu, Rıfkı; Yıldırım, Gürcan; Terzioğlu, Cabir
    Bu çalışmada Bi-2223 tozlar farklı peletizasyon basınç değerleri ile külçe formuna getirilmiş ardından külçeler 840ºC’de 36 saat tavlanmıştır. Basıncın Bi-2223 külçelerin yapısal, mekanik ve elektriksel özellikleri üzerine etkileri incelenmiştir. Yapısal analizlerin değerlendirilmesi için X-ışını Kırınımı (XRD) spektroskopisi ölçümleri kullanılmıştır. Mekanik analizler için oda sıcaklığında Vickers Mikrosertlik ölçümleri yapılmıştır. Elektriksel analizlerde ise dört kontak I-V ölçümleri kullanılmıştır. Elde edilen sonuçlara göre, Bi-2223 kristal faz yoğunluğunun, sertlik değerinin ve elektrik taşıma kapasitesinin basınca ciddi bir şekilde bağlı olduğu görülmüştür. Bu bağlamda, basıncın artması ile sertlik değerlerinin kristal yapıdaki faz geçişlerine ve yüzey artık basınç gerilim bölgelerinin artışına bağlı olarak yükseldiği tespit edilmiştir. Ayrıca, hesaplanan elastisite modülü ve akma dayanımı gibi genel mekanik performans değerlerinin basınca bağlı olarak arttığı gözlemlenmiştir. Bu bulgu kristal yapıda hali hazırda var olan kovalent ve özellikle iyonik bağ kuvvetlerinin artmasının sonucu olabilir. Bununla birlikte, numunelerin plato limit bölgelerinde yükten bağımsız mikrosertlik değerleri Meyer yasası, Orantılı Numune Direnç (OND) ve Indentation Induced Cracking (IIC) yöntemleri ile analiz edilmiştir. Analiz sonucunda IIC modelin gerçek mikrosertlik değerlerini incelemede daha başarılı olduğu bulunmuştur. Kritik akımın uygulanan basıncın artması ile düştüğü gözlemlenmiştir. Örneklerin yoğunlukları Arşimet yasası kullanılarak ölçülmüştür. Teknolojik kullanım alanına bağlı olarak külçe Bi-2223 örneklerin üretiminde uygulanması gereken optimum basınç değeri detaylarıyla tartışılmıştır.
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    Breaking point of the harmony between Gd diffused Bi-2223 slabs with diffusion annealing temperature
    (Springer, 2013) Aydin, H.; Babanlı, Arif; Altıntaş, Sevgi Polat; Aşıkuzun, Elif; Soylu, Nevin; Öztürk, Özgür; Doğruer, Musa; Terzioğlu, Cabir; Yıldırım, Gürcan
    This comprehensive study reports the role of annealing temperature on the microstructural, superconducting and mechanical characteristics of the Gd diffused Bi-2223 superconducting ceramics produced by the conventional solid-state reaction route at 840 A degrees C for the annealing duration of 48 h. For the material characterization, the standard experimental methods such as dc resistivity (rho-T), transport critical current density, X-ray powder diffraction, scanning electron microscopy and Vickers microhardness measurements are performed systematically. All the results obtained show that all the measured characteristic properties, being in charge of the applications in the industry, engineering and technology, improve until a certain diffusion annealing temperature of 800 A degrees C beyond which they tend to degrade considerably. The increase in the properties is mostly related to the transition from the inherent overdoped state of the pure Bi-2223 material to optimum doped state with the diffusion annealing temperature, confirming the penetration of the sufficient Gd nanoparticles into the crystal structure. On the other hand, the suppression in the superconducting properties stems from the appearance of the porosity, defects, disorder and localization problem in the polycrystalline Bi-2223 superconducting matrix. This is attributed to the decrement of the average crystallite size and mobile hole concentration in the Cu-O-2 layers and especially the retrogression of the crystallinity in the system. As for the mechanical characteristics, Vickers microhardness measurements exerted in the applied indentation test load range of 0.245-2.940 N indicate that the Gd diffused bulk superconducting samples exhibit the typical indentation size effect behavior. With the enhancement in the annealing temperature up to 800 A degrees C, the significant increase in the elastic modulus, yield strength and fracture toughness is one of the most striking points in the paper. The long and short of it is that the excess diffusion annealing temperature damages the fundamental characteristics of the Bi-2223 system.
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    Calculation of the diffusion coefficient of Au in Bi-2223 superconductors
    (Iop Publishing Ltd, 2007) Öztürk, Özgür; Küçükömeroğlu, Tayfun; Terzioğlu, Cabir
    Undoped Bi-2223 samples were prepared using a conventional solidstate reaction method. Doping of Au in Bi-2223 was carried out by means of diffusion from an evaporated Au film on pellets. We have investigated the effect of Au diffusion and diffusion-annealing duration on the microstructure and superconducting properties of Au-doped samples by performing x-ray diffraction (XRD), scanning electron microscopy (SEM), dc resistivity and critical current density measurements. Gold diffusion in Bi1.8Pb0.35Sr1.9Ca2.1Cu3Oy has been studied over the temperature range 500-800 degrees C using the technique of successive removal of thin layers and the measurements of lattice parameters from XRD patterns at room temperature. The diffusion doping of Bi-2223 by Au causes a significant increase of the lattice parameter c by about 0.19%. This observation is used for calculation of the Au diffusion coefficient in Bi-2223. The Au diffusion coefficient decreases as the diffusion-annealing temperature decreases. The temperature dependence of the Au diffusion coefficient in the range 500-800 degrees C is described by the relation D = 4.4 x 10(-4) exp(-1.08 eV/ k(B)T). Au doping of the sample increased the critical transition temperature and the critical current density from 100 +/- 0.2 to 104 +/- 0.2 K and from 40 to 125 A cm(-2), in comparison with those of undoped samples. The critical transition temperature and critical current density of Au-doped samples increased with increasing diffusion-annealing time from 10 to 50 h. Au doping of the sample also improved the surface morphology and increased the high-T-c phase ratio. The possible reasons for the observed improvement in superconducting properties of the samples due to Au diffusion are discussed.
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    Cation size mismatch effect in (La1-yREy)(1.4)Ca1.6Mn2O7 perovskite manganites
    (Elsevier Science Sa, 2019) Koç, Nevin Soylu; Altıntaş, Sevgi Polat; Mahamdioua, Nabil; Terzioğlu, Cabir
    The size variance (sigma(2)) that indicates random disorder of cations distributed over the A or B-site, has significant influence on the basic quantities on perovskite manganites. In this study, we investigate the effect of A-site variance (sigma(2)(A)) in double layered perovskite manganites. In order to understand how the magneto-electrical properties of layered perovskite type RE2-2xCa1+2xMn2O7 change with sigma(2)(A), we have prepared a series of four samples with optimal doping (x = 0.3) and fixed mean A-cation radius ( = 1.3353 angstrom). A-site disorder is varied by use of different rare earth combinations by co-doping of La with Gd, Sm, Nd and Pr. Based on structural analysis by Rietveld profile fitting, all the samples crystallize in Sr3Ti2O7-type tetragonal phase (space group I4/mmm). As sigma(2)(A) increases, paramagnetic (PM) to ferromagnetic (FM) transition temperature shows a linear decrease. However, metal-insulator transition temperature shows a linear correlation with sigma(2). (C) 2019 Elsevier B.V. All rights reserved.
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    A characterization study on 2,6-dimethyl-4-nitropyridine N-oxide by density functional theory calculations
    (Pergamon-Elsevier Science Ltd, 2011) Yıldırım, Gürcan; Zalaoğlu, Yusuf; Kırılmış, Cumhur; Koca, Murat; Terzioğlu, Cabir
    This study deals with the identification of a title compound, 2,6-dimethyl-4-nitropyridine N-oxide by means of theoretical calculations. The optimized molecular structures, vibrational frequencies, corresponding vibrational assignments, thermodynamic properties and atomic charges of the title compound in the ground state were evaluated using density functional theory (DFT) with the standard B3LYP/6-311G(d,p) method and basis set combination for the first time. Theoretical vibrational spectra were interpreted with the aid of normal coordinate analysis based on scaled density functional force field. The results show that the optimized geometric parameters (bond lengths and bond angles) and vibrational frequencies were observed to be in good agreement with the available experimental results. Based on the results of comparison between experimental results and theoretical data, the chosen calculation level is powerful approach for understanding the molecular structures and vibrational spectra of the 2,6-dimethyl-4-nitropyridine N-oxide. Moreover, we not only simulated frontier molecular orbitals (FMO) and molecular electrostatic potential (MEP) but also determined the transition state and energy band gap. Based on the investigations, the title compound is found to be useful to bond metallically and interact intermolecularly. Infrared intensities and Raman activities were also reported. (C) 2011 Elsevier B.V. All rights reserved.
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    Comparative study on indentation size effect, indentation cracks and superconducting properties of undoped and MgB2 doped Bi-2223 ceramics
    (Springer, 2013) Doğruer, Musa; Karaboğa, Fırat; Yıldırım, Gürcan; Terzioğlu, Cabir
    This study examines the evaluation mechanism of MgB2 doped Bi1.8Pb0.4Sr2(MgB2)(x)Ca2.2Cu3.0Oy (0 <= x <= 1.0) superconducting ceramics prepared by conventional solid-state reaction method via dc resistivity, X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and Vickers micro hardness (Hv) measurements. Variation of room temperature resistivity, critical transition temperatures (onset and offset), phase purity, cell parameter, texturing, grain connectivity, surface morphology, crystallinity and Hv values of the materials are deduced and compared with each other for the determination of the optimum doping level in the Bi-2223 system. It is found that all the properties given above depend strongly on the MgB2 concentration. From dc resistivity investigations, each sample studied exhibits the superconducting behavior below their variable offset critical temperature values. The maximum onset (T-c(onset)) and offset (T-c(onset)) temperatures are found to be about 121.3 and 114.1 K, respectively, for the sample doped with x = 0.05. The minimum T-c(onset) of 118.6 K and T-c(onset) of 109.4 K are observed for the sample doped with x = 1.0. Similarly, XRD and SEM examinations indicate that there is an improvement in the crystal structures and surface morphologies of the superconducting materials with the increment of the MgB2 inclusions in the Bi-2223 system up to x = 0.05 beyond which the crystallinity, grain connectivity and surface morphology start to degrade regularly and in fact reach to the worst structure appearance for the doping level of x = 1.0. Furthermore, the Hv measurement results being analyzed by Meyer's law, proportional sample resistance (PSR), modified PSR, elastic-plastic deformation model, Hays-Kendall (HK) approach, Indentation-induced cracking model (IIC) allow us to derive the mechanical properties of the superconducting samples for the potential technological and industrial applications. According to the results obtained, HK approach, among the mechanical analysis methods, is determined as the most successful model for the samples (doped with x = 0, 0.1, 0.3, 0.5 and 1.0) exhibiting indentation size effect behavior whereas the IIC model is noted to be superior to other models for the other samples (doped with x = 0.01, 0.03 and 0.005) presenting reverse indentation size effect feature.
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    Comparative study on mechanical properties of undoped and Ce-doped Bi-2212 superconductors
    (Springer, 2013) Zalaoğlu, Yusuf; Bekiroğlu, Erdal; Doğruer, Musa; Yıldırım, Gürcan; Öztürk, Özgür; Terzioğlu, Cabir
    This study discusses the mechanical performances of Bi1.8Sr2.0CexCa1.1Cu2.1Oy ceramics with x = 0, 0.001, 0.003, 0.005, 0.01, 0.03, 0.05 and 0.1 by way of Vickers microhardness (H-v) measurements performed at different applied loads in the range of 0.245-2.940 N. For the potential industrial applications, the important mechanical characteristics such as Vickers microhardness, elastic modulus, yield strength, fracture toughness and brittleness index values of the samples studied are extracted from the microhardness measurements. All the results obtained indicate that the Vickers hardness, Young's (elastic) modulus, yield strength, fracture toughness and brittleness index values suppress with the increment of the Ce concentration in the system as a consequence of the degradation in the connectivity between superconducting grains. The decrement in the H-v values with the applied load is attributed Indentation Size Effect behaviour of the samples studied. Moreover, the experimental results of Vickers microhardness measurements are estimated using the 5 different models such as Kick's law, proportional sample resistance model, modified proportional sample resistance model, elastic/plastic deformation model and Hays-Kendall approach. According to the results obtained from the simulations, Kick's law is not useful model to obtain information about the origin of the indentation size effect feature of the Ce-doped bulk Bi-2212 superconductors. On the other hand, the Hays-Kendall approach is determined as the most suitable model for the description of the mechanical properties of the superconducting samples. In addition, the bulk porosity analysis for the samples reveals that the porosity increases monotonously with the Ce inclusion in the Bi-2212, leading to the degradation of the grain connectivity.
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    A comprehensive study on mechanical properties of Bi1.8Pb0.4Sr2MnxCa2.2Cu3.0Oy superconductors
    (Springer, 2013) Doğruer, Musa; Karaboğa, Fırat; Yıldırım, Gürcan; Terzioğlu, Cabir; Öztürk, Özgür
    This study manifests the crucial change in the mechanical performances of Bi1.8Pb0.4Sr2MnxCa2.2Cu3.0Oy superconductor samples (x = 0, 0.03, 0.06, 0.15, 0.3 and 0.6) prepared by conventional solid-state reaction method by use of Vickers microhardness (H-v) measurements carried out at different applied loads, (0.245 N a parts per thousand currency sign F a parts per thousand currency sign 2.940 N). Load dependent microhardness, load independent microhardness, Young's (elastic) modulus and yield strength values being account for the potential technological and industrial applications are evaluated from the hardness curves and compared with each other. It is found that the H-v, elastic modulus and yield strength obtained decrease (increase) with the enhancement of the applied load for the undoped (doped) samples. Surprisingly, the results of the H-v values illustrate that the samples doped with x = 0.03, 0.06, 0.15, 0.3 and 0.6 exhibit reverse indentation size effect (RISE) feature whereas the pure sample obeys indentation size effect (ISE) behavior. Furthermore, the experimental results are examined with the aid of the available methods such as Meyer's law, proportional sample resistance model (PSR), elastic/plastic deformation (EPD), Hays-Kendall (HK) approach and indentation-induced cracking (IIC) model. The results inferred show that the hardness values calculated by PSR and EPD models are far from the values of the plateau region, meaning that these models are not adequate approaches to determine the real microhardness value of the Mn doped Bi-2223 materials. On the other hand, the HK approach is completely successful for the explanation of the ISE nature for the pure sample while the IIC model is obtained to be the best model to describe the hardness values of the doped materials exhibiting the RISE behavior. Additionally, the bulk porosity analysis for the samples reveals that the porosity increases monotonously with the increment in the Mn inclusions inserted in the Bi-2223 system, presenting the degradation of the grain connectivity.
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    Decrement of crack propagation in bulk Bi-2223 superconducting ceramics with Sn-diffusion annealing temperature
    (Springer, 2015) Doğruer, Musa; Terzioğlu, Cabir; Yıldırım, Gürcan; Pakdil, Murat; Zalaoğlu, Yusuf
    The effect of Sn diffusion at different annealing temperature on the Bi1.8Pb0.4Sr2.0Ca2.1Cu3.0Oy superconducting materials is performed with the aid of Vickers microhardness (H-v) measurements at different applied loads in the range of 0.245-2.940 N. The measurement results observed show that all the samples exhibit typical indentation size effect behavior, meaning that both the elastic and plastic deformations play dominant role on the inorganic structures owing to the presence of the elastic recovery. Likewise, the mechanical characteristics increase with the Sn additives as a consequence of improvement of the local structural distortions and boundary weak-links between the grains. Furthermore, the increased Sn inclusions in the crystal lattice make the cracks propagate slower than before. This may be related to the fact that the Sn particles prefer to accumulate throughout the grain boundaries (defect locations) similar to the propagation of the cracks in the materials. In other words, the ductility (nondirectional interactions) of the ceramics tends to improve with the increment in the Sn concentration level in the crystal lattice as a consequence of the enhancement of the tensile strength, fracture toughness and especially Griffith critical crack length values. Hence, the mechanical flexibility takes place rapidly in the crystal structure. Moreover, the hardness measurements allow us to discuss the load dependent and independent microhardness, elastic modulus, yield strength and fracture toughness parameters. At the same time, the experimental data of the Vickers hardness are studied by the available models regarding Meyer's law, proportional sample resistance model, elastic-plastic deformation model and Hays-Kendall (HK) approach for the first time. According to the results obtained, the load dependence of Vickers microhardness is fitted with the HK approach rather than the other methods. Based on the electrical and superconducting results observed before, it is to be mentioned here that the significant improvement of electrical performance may contribute to enhancement in mechanical characteristics.
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    Deformation of mechanical properties and failure behavior of Hays-Kendall approach in Bi-2223 superconducting core after Eu inclusions
    (Springer, 2014) Doğruer, Musa; Zalaoğlu, Yusuf; Yıldrım, Gürcan; Terzioğlu, Cabir
    Mechanical features of Bi1.8Pb0.4Eu (x) Sr2Ca2.2Cu3O (y) superconductor samples (x=0, 0.01, 0.03, 0.05, 0.07, 0.1, and 0.3) are elaborated by traditional solid-state reaction route. The deformation of the mechanical properties belonging to the Bi-2223 crystal structure by Eu impurities with the aid of Vickers hardness (H (v) ) measurements are conducted at different indentation loads from 0.245 N to 2.940 N for the first time. Further, the H (v) values extracted from experimental results are investigated using five different models so as to demonstrate the role of Eu addition on Bi-2223 samples. Based on these results, we observed that the undoped sample reveals the indentation size effect (ISE) feature, whereas the Eu-doped Bi-2223 superconducting core demonstrates the reverse indentation size effect (RISE) nature. Additionally, it is attained that the models (Meyer's law, EPD, and PSR) fail to determine the estimate of the microhardness with the applied load. Nonetheless, the HK approach is observed to be superior to other models for the pure sample showing the ISE feature, while the IIC model is found to be the most successful model for the explanation of the mechanical characteristics of the Eu impurities in Bi-2223 bulk ceramics obeying RISE nature.
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    Density functional theory study on the identification of 3-[(2-morpholinoethylimino)methyl]benzene-1,2-diol
    (Pergamon-Elsevier Science Ltd, 2011) Parlak, Cihan; Akdoğan, Mustafa; Yıldırım, Gürcan; Karagöz, Nurettin; Budak, Erhan; Terzioğlu, Cabir
    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 (OFT) 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, C-13 and H-1 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. (C) 2011 Elsevier B.V. All rights reserved.
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    Detailed analysis on electrical conduction transition from 2D variable range hopping to phonon-assisted 3D VRH mechanism belonging to Bi-site La substituted Bi-2212 system
    (Elsevier Science Sa, 2015) Zalaoğlu, Yusuf; Yıldırım, Gürcan; Terzioğlu, Cabir; Görür, Osman
    The main scope of this comprehensive study is to determine the critical dopant level of metal to insulator transition (MIT) for Bi-site La substituted Bi-2212 superconducting ceramics by means of bulk density, Xray diffraction (XRD), scanning electron microscopy (SEM), electron dispersive X-ray (EDX), dc resistivity (rho-T) and transport critical current density (J(c)) experimental methods. The samples produced in this work are prepared by the conventional solid state reaction technique at the constant temperature of 840 degrees C for the annealing duration of 60 h. All the experimental evidences obtained indicate that the microstructural, electrical and superconducting properties suppress with the increment of the La dopant level in the Bi-2212 superconducting matrix up to x = 0.20 beyond which the crucial characteristics diminish rapidly due to not only the deformation between the Bi-2212 layers and grain boundaries but also the disorder and hole localization (filling) problem in the crystal structure. As for the numerical values, onset and offset critical temperatures systematically decrease from 85.67 K and 84.49 K to 82.74 K and 59.38 K with the impurity content until x = 0.15. However, the sample doped with the content level of x = 0.20 exhibits further pseudo-critical transition (related to Bi-2201 phase) at about 23 K as a consequence of the existence of inhomogeneities in the oxidation state of superconducting grains. This fact is even verified by the degree of the broadening. Moreover, residual resistivity (temperature-independent) value tends to increase rapidly because of the impurity scattering and defect interfaces such as grain boundaries, stacking faults, voids, planar and micro defects, being favored by the bulk density and porosity analyses. Similarly, critical current density is measured to be in the range of 771 A/cm(2) (for the pure sample)-78 A/cm(2) (for the compound doped with x = 0.20). The critical current densities and temperatures are not measurable for the compounds substituted by the excess La concentration level (x>0.20) due to the beginning point of the metal to insulator transition (nonsuperconducting behavior). In other words, the disappearance of the superconductivity results from the destruction of the phase coherence (phase breaking). Additionally, surface morphology and interaction between the superconducting grains retrograde significantly with the La concentration. EDX measurement evidences also show that during the sample preparation procedure the elements each successfully enter into the Bi-2212 crystal structure and the observed peaks of Cu and especially Bi degrade regularly with the La inclusions, meaning that the foreign particles may substitute for the elements (especially Bi). Based on the XRD measurement results, a axis length is observed to elongate regularly due to both the induced electrons into anti-bonding orbital and ionic radius of La3+ > that of Bi3+ whereas the cell parameter c is obtained to shrink considerably as a result of the required extra energy for the bond formation in the orbital hybrid process. Moreover, the electrical conduction transition from the 2D variable range hopping (VRH) to phonon-assisted 3D VRH mechanism is theoretically discussed with the aid localization length, probable jump distance, average hopping energy and inelastic diffusion length parameters. (C) 2014 Elsevier B.V. All rights reserved.
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    Detailed survey on minimum activation energy for penetration of Ni nanoparticles into Bi-2223 crystal structure and temperature-dependent Ni diffusivity
    (Springer, 2018) Zalaoğlu, Yusuf; Terzioğlu, Cabir; Turgay, Tahsin; Yıldırım, Gürcan
    The primary contributions of this study are not only to explore the role of diffusion annealing temperature interval 650 to 850 A degrees C on the formation of effective electron-phonon coupling or cooper-pair probabilities (percentage of clusters in the superconducting path), densities of active and dynamic electronic states at Fermi energy level, stabilization of superconductivity in the homogeneous regions, overlapping of Cu-3d and O-2p wave functions and bond strengths in the crystal matrix of Ni surface-layered Bi-2223 polycrystalline ceramics, but also to determine the temperature-dependent diffusion fast-rate and required minimum activation energy for the diffusion of Ni foreign impurities into the bulk Bi-2223 superconducting crystal structure for the first time. The dc electrical measurement results obtained show that the optimum diffusion annealing temperature is found to be 700 A degrees C for the penetration of optimum Ni concentration into the Bi-2223 crystal lattice so that the ceramic compound exposed to 700 A degrees C annealing temperature exhibits the highest electrical and superconducting properties. In this respect, the material with the minimum electrical resistivity parameters of Delta rho, rho (115K) , rho (res) and rho (norm) obtains the maximum superconducting characteristics of , and RRR. Accordingly, the annealing temperature of 700 A degrees C promotes the Bi-2223 ceramics for usage in the engineering, electro-optic, industrial and large scale applications. At the same time, the diffusion coefficients [D = D(o)exp(E/k(B)T)] determined at annealing temperature ranging from 650 to 850 A degrees C are observed to be much more significant at rather higher temperatures as compared to lower temperatures. The temperature-dependent Ni diffusion coefficient is determined to be D = 3.9707 x 10(- 7)exp[- 1.132 eV/k(B)T] for the Bi-2223 particulate solid material. Namely, the diffusion coefficient is calculated to be about 3.9707 x 10(- 7)cm(2) s(- 1) when the required minimum activation energy for the introduction of heavy metal Ni ions to the bulk Bi-2223 crystal structure is computed to be about 1.132 eV, being one of the most striking points deduced form this work.