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Öğe 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, GürcanThis 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.Öğe The effect of Nd (2) O (3) addition on superconducting and structural properties and activation energy calculation of Bi-2212 superconducting system(Springer, 2014) Öztürk, Özgür; Aşıkuzun, Elif; Coşkunyürek, Murat; Soylu, Nevin; Hancerlioğulları, Aybaba; Varilci, Ahmet; Terzioğlu, CabirThe effect of Nd (2) O (3) addition on the micro-structural and the superconducting properties of Bi-2212 superconductor ceramics, prepared by solid state reaction method, was analyzed by performing X-ray diffraction (XRD), scanning electronic microscope (SEM), energy dispersive spectroscopy (EDS) and dc Resistivity (rho-T) measurements. The magnetoresistivity of the samples was measured for different values of the applied magnetic field strengths (0-7 T). Also, the activation energies were calculated using the Arrhenius equation. According to these results, the T (c) (offset) value of the undoped sample was decreased from 79 to 42 K with the growth of magnetic field. In the same way, the activation energy (U (o) ) values were significantly diminished by the increasing of magnetic field. A similar situation was observed in other doped samples. Activation energy for 0.05 % Nd (2) O (3) doped sample under 7 T magnetic field was 550 J/mol the least. In addition, lattice parameter c, calculated by analysis of XRD data, was decreased with doping while lattice parameter a was increased. SEM analysis shows that particles were shrinking with the addition. When compared with other elements for EDS analyses, it was analyzed an important decrease in the percentage of Sr with the increasing of Nd contribution.Öğe Evaluation of microstructural and mechanical properties of Ag-Diffused bulk MgB2 superconductors(Springer, 2014) Yılmazlar, Mustafa; Terzioğlu, Cabir; Doğruer, Musa; Karaboğa, Fırat; Soylu, Nevin; Zalaoğlu, Yusuf; Yıldırım, GürcanElectrical, microstructural, and mechanical properties of undiffused and Ag-diffused bulk MgB2 superconductors are systematically studied using dc resistivity, scanning electron microscopy (SEM), and Vickers microhardness (H (V) ) measurements. The resistivity (at room temperature), critical (onset and offset) temperature, variation of transition temperature, hole-carrier concentration, surface morphology, Vickers microhardness, elastic modulus, and yield strength values of the samples are obtained and compared with each other. One can see that all superconducting parameters given above depend on the Ag diffusion on MgB2 system. The obtained results illustrate that the room temperature resistivity reduces with the increment of diffusion annealing temperature because of the hole filling when the onset () and offset () critical temperatures determined from the resistivity curves are obtained to enhance from 38.4 to 39.7 K and from 36.9 to 38.8 K, respectively. Further, SEM studies carried out for the microstructural characterization demonstrate that the surface morphology and grain connectivity also improve with the increase of the diffusion annealing temperature. In fact, the best surface morphology is observed for the Ag-diffused bulk MgB2 superconductor exposed to 850 A degrees C annealing temperature. Besides, it is obtained that the load-dependent microhardness values reduce nonlinearly as the applied load increases until 2 N, beyond which the curves shift to the saturation region, presenting that all the samples exhibit the indentation size effect (ISE) behavior. Further, the elastic modulus and yield strength values observed decrease with the enhancement of the applied load.Öğe Improved magnetoresistance in Sm0.7-xCexSr0.3MnO3 manganites prepared by a sol-gel route(Springer/Plenum Publishers, 2021) Lakhal, E.; Amira, A.; Chihoub, R.; Soylu, Nevin; Altıntaş, Sevgi Polat; Varilci, Ahmet; Terzioğlu, CabirIn this work, manganite ceramics of Sm0.7-xCexSr0.3MnO3 (0 <= x <= 0.3) are prepared by a citrate sol-gel chemical route and characterized. The structure of the obtained samples is refined in the orthorhombic system with the Pnma space group. The doping causes a change in the lattice parameters leading to a decrease in the cell volume. It also increases slightly the grain size of the crystallites. The temperature dependence of resistivity reveals a metal-insulator transition for all samples. The doping shifts the temperature of this transition towards high values. The extracted magnetoresistance for a 5 T magnetic field is enhanced by doping. The highest obtained value increases from 66.70% for x = 0 to 97.96% for x = 0.3.Öğe Investigation of cooling effect on bisrcacuo superconductor by using scanning electron microscopy(Bolu Abant İzzet Baysal Üniversitesi, 2010) Soylu, Nevin; Varilci, AhmetFarklı soğutma oranlarının BSCCO süperiletkenleri üzerindeki etkisi araştırıldı. Bunun için numuneler tavlama işlemlerinden sonra farklı hızlarda oda sıcaklığına soğutuldu. Bu soğutma oranlarına göre sıcaklık düşüş hızları 273°C/dk , 136°C/dk ,55°C/dk, 25°C/dk, 18°C/dk, olarak hesaplandı. Bunların yanında fırın soğutma (5°C/dk) ve hızlı soğutma işlemleri de yapıldı.10 mA lik akım altında 70 K- 160 K sıcaklıkları arasında özdirenç ölçümleri yapıldı. Sıvı nitrojen içinde kritik akımları ölçülerek kritik akım yoğunlukları hesaplandı. Yüzey yapılarını araştırmak için SEM görüntüleri alındı. BSCCO örneklerinin Bi-2212 ve Bi-2223 karakteristik pikleri X-Ray ölçümleri ile görüntülendi ve Bi-2212 ve Bi-2223 oranları hesaplandı.136°C/dk soğutma oranı ile hazırlanan numunede SEM görüntülerinde flake yapının daha fazla olduğu ve bunun da kritik sıcaklık değerinin yüksekliği ile uyumlu olduğu gözlendi. Bi-2223 yapıları için 273°C/dk, 136°C/dk soğutma oranlarının en uygun olduğu saptandı. Kritik akım yoğunluğunun en yüksek olduğu 5°C/dk ile en yavaş soğuma oranına sahip numune olduğu bulundu ve soğuma hızları düştükçe kritik akım yoğunluğunun arttığı gözlendi.Anahtar Kelimeler : Süperiletkenlik, BSCCO Sistemi, Soğutma Oranları, SEM, Kritik Sıcaklık, Kritik Akım Yoğunluğu .Öğe Investigation of microstructural, Vickers microhardness and superconducting properties of YBa2Cu3-xGdxO7-delta (0 a parts per thousand currency sign x a parts per thousand currency sign 0.150) superconducting ceramics via experimental and theoretical approaches(Springer, 2013) Doğruer, Musa; Yıldırım, Gürcan; Öztürk, Özgür; Varilci, Ahmet; Soylu, Nevin; Görür, Osman; Terzioğlu, CabirThis study manifests the change of pinning mechanism, electrical, structural, physical, mechanical and superconducting properties of YBa2Cu3-xGdxO7-delta superconductors samples prepared by the conventional solid-state reaction method (x = 0, 0.025, 0.050, 0.100 and 0.150) by use of dc resistivity, X-ray analysis (XRD), scanning electron microscopy (SEM) and Vickers microhardness measurements. Zero resistivity transition temperatures (T (c) (offset) ) of the samples are deduced from the dc resistivity measurements. Additionally, the lattice parameters are determined from XRD measurements when the microstructure, surface morphology and microhardness of the samples studied are examined by SEM and mechanical measurements, respectively. The results obtained demonstrate that T (c) (offset) values of the samples decrease slowly with the increase in the Gd content. The maximum T (c) (offset) (92.0 K) is obtained for the pure sample prepared at 940 A degrees C for 20 h in air atmosphere while the minimum value of 83.3 K is found for the sample doped with 0.150 Gd content. Moreover, it is obtained that J (c) values reduce from 132 to 34 A/cm(2) with the enhancement of the Gd level in the crystalline structure. Further, the peak intensities belonging to Y123 (major) phase are obtained to decrease whereas the peak intensities of the minor phases such as BaCuO2 and Y211 are found to enhance systematically with the increment in the Gd content in the system, illustrating that partial substitution of Cu2+ ions by Gd3+ ions are carried out successfully. Moreover, SEM images display that the undoped sample obtains the best crystallinity and connectivity between superconducting grains and largest grain size whereas the worst surface morphology is observed for the maximum doped sample (x = 0.150). At the same time, Vickers microhardness, elastic modulus, load independent hardness, yield strength, fracture toughness and brittleness index values, playing important roles on the mechanical properties, are computed for all the samples. The experimental results of the microhardness measurements are examined using the Meyer's law, PSR (proportional specimen resistance), modified PRS, Elastic-Plastic deformation model (EPD) and Hays-Kendall (HK) approach. The microhardness values obtained increase with the enhancement of the Gd content in the samples. Besides, it is noted that the Hays-Kendall approach is the most successful model explaining the mechanical properties of the samples studied in this work.Öğe The structural and electrical study of Lu-Doped YBCO system(Springer, 2013) Soylu, Nevin; Yahşi, C. C.; Altıntaş, Sevgi Polat; Nezir, Saffet; Terzioğlu, CabirWe have prepared a series of bulk superconducting samples with the nominal composition of Y1-xLuxBa2 Cu3Oy (where x = 0.0, 0.05, 0.1, 0.2 and 0.3) by the conventional solid-state reaction method. The samples were characterized structurally by means of X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectrometry. The electrical transport properties of the samples were analyzed in the temperature range between 20-140 K under magnetic fields up to 2 T. The superconducting transition temperature, T-c, and activation energy, U-0, were found to decrease with Lu-doping and with increase in applied magnetic field.
