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Öğe Ac Susceptibility measurements and mechanical performance of Bulk MgB2(Springer, 2015) Öztürk, Özgür; Aşıkuzun, Elif; Kaya, Şeydanur; Erdem, Murat; Safran, Serap; Kılıç,Ahmet; Terzioğlu, CabirThe 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.Öğe Analytical and numerical treatment of partial differential equations in physics(Bolu Abant İzzet Baysal Üniversitesi, 2002) Erdem, Murat; Köşker, DavutÖZET FİZİKTEKİ KISMİ DİFERANSİYEL DENKLEMLERİN ANALİTİK VE NÜMERİK İNCELENMESİ Erdem, Murat Master Tezi, Fizik Bölümü Tez Danışmanı: Prof.Dr.Davut Köşker Temmuz 2002, 65 sayfa Bu tezde öncelikle kısmi diferansiyel denklemleri yapısal özelliklerine göre ayıran bir tekniğe bakılmıştır. Varılan sonuçlardan en önemlisi, bu teknikle fizik sel olayların da dolaylı olarak sınıflandırıldığını görmek olmuştur. Bu sınıflandırma ışığında fizikte sık sık karşılaşılan farklı yapılara haiz önemli birkaç kısmi diferan siyel denklem ele alınarak, analitik ve de nümerik metodlarla incelenmiştir. Her iki metodla elde edilen çözümler karşılaştırıldığında, bu metodların hemen hemen eşdeğer sonuçlar ürettiği anlaşılmıştır. Anahtar sözcükler: Kısmi Diferansiyel Denklemler, Sınıflandırma Tekniği, Analitik Metod, Nümerik MetodÖğe Effect of annealing time on the structural, optical and electrical characteristics of DC sputtered ITO thin films(Springer, 2014) Şenol, Sevim Demirözü; Şenol, Abdulkadir; Öztürk, Özgür; Erdem, MuratUsing an Indium tin oxide (ITO) ceramic target (In2O3:SnO2, 90: 10 wt%), ITO thin films were deposited by conventional direct current magnetron sputtering technique onto glass substrates at room temperature. The obtained ITO films were annealed at 400 degrees C for different annealing times (1, 2, 5, 7, and 9 h). The effect of annealing time on their structural, optical and electrical properties was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microcopy (AFM), ultra violet-visible (UV-Vis) spectrometer, and temperature dependence Hall measurements. XRD data of obtained ITO films reveal that the films were polycrystalline with cubic structure and exhibit (222), (400) and (440) crystallographic planes of In2O3. AFM and Scanning Electron Microscopy SEM have been used to probe the surface roughness and the morphology of the films. The refractive index (n), thickness and porosity (%) of the films were evaluated from transmittance spectra obtained in the range 350-700 nm by UV-Vis. The optical band gap of ITO film was found to be varying from 3.35 to 3.47 eV with the annealing time. The annealing time dependence of resistivity, carrier concentration, carrier mobility, sheet resistance, and figure of merit values of the films at room temperature were discussed. The carrier concentration of the films increased from 1.21 x 10(20) to 1.90 x 10(20) cm(-3), the Hall mobility increased from 11.38 to 18 cm(2) V-1 s(-1) and electrical resistivity decreased from 3.97 x 10(-3) to 2.13 9 10(-3) Omega cm with the increase of annealing time from 1 to 9 h. Additionally, the temperature dependence of the carrier concentration, and carrier mobility for the as-deposited and 400 degrees C annealed ITO films for 2 and 9 h were analysed in the temperature range of 80-350 K.Öğe The effect of Ar ambient pressure and annealing duration on the microstructure, superconducting properties and activation energies of MgB2 superconductors(Springer, 2017) Öztürk, Özgür; Aşıkuzun, Elif; Kaya, Şeydanur; Koç, Nevin Soylu; Erdem, MuratMgB2 samples are produced by ex situ reaction method under vacuum, and various (0, 10, 20 Bar) Ar pressure for 0.5 and 1 h. The effect of ambient pressure and annealing duration on the microstructure and electrical properties of bulk samples are investigated. XRD, SEM, and magnetoresistance measurements are made. The a and c lattice parameters and the grain size values are the highest for the samples produced under vacuum and their values decrease with increasing Ar pressure. Moreover, these values increase when the annealing duration increases from 0.5 to 1 h. The increasing pressure reduces the bond lengths between the atoms thus the grain sizes decrease. Smaller grain size promotes the connection between grains which results in an increase of the critical current density (J(c)). SEM micrographs reveal that the produced samples have granular structure which is a characteristic feature of MgB2. The decrease of grain sizes and thus enhancement in grain connectivity with increasing pressure is also confirmed by SEM images. Magneto resistivity measurements show that T-c values of the samples produced under vacuum are the highest. Tc values decrease with increasing ambient pressure and applied magnetic field. The activation energies (U-0) of the samples are calculated using Arrhenius plots due to thermally activated flux flow theory. Existence and increase of Ar pressure causes increase of activation energies. The samples produced with 0.5-h annealing have higher activation energies than the ones produced with 1-h annealing.Öğe Effect of high valancy cations on the intergranular pinning energies of (Bi-Pb)(2)Sr2Ca2Cu3O10+delta samples(Springer, 2012) Yazıcı, Duygu; Erdem, Murat; Özçelik, BekirIn the present work, Bi-Pb-V-Sr-Ca-Cu-Ti-O bulk samples with nominal composition (BiPb)(2)VxSr2Ca3Cu4-y TiyO12+delta with x = 0.2 and y = 0.1, 0.2 and 0.3 compounds have been prepared by the melt-quenching method. The magnetoresistance of the samples has been measured for different values of the applied magnetic field. Using the resistivity data, the upper critical magnetic field H-c2(0) at T = 0 K was calculated. The coherence lengths at T = 0 K were calculated from H-c2(0) values. The thermally activated flux creep model has been studied in order to calculate the flux pinning energies. The results showed that H-c2(0) varied from 152.5 to 60.4 T and the flux pinning energies varied from 515 to 184 meV at 0 T, with the content y.Öğe The Effect of PbSe Addition on the Mechanical Properties of Bi-2212 Superconductors(Springer, 2012) Çavdar, S.; Deniz, E.; Koralay, H.; Öztürk, Özgür; Erdem, MuratThe effects of PbSe addition and heat treatment on the structure and mechanical properties of Bi-2212 superconductors are analyzed. Glass ceramic method is used to produce PbSe added samples. The mechanical properties are derived using Vickers microhardness measurement results. Well known analysis methods like Meyer's law, PSR (Proportional Sample Resistance) Model, EDP (Elastic/Plastic Deformation Model), Hays-Kendall approach and IIC (Indentation-Induced Cracking Model) are used to calculate load independent microhardness values of the samples. HK approach produces successful results for the samples A, E, F, G and H indicating ISE (Indentation Size Effect) behavior. The IIC model successfully explains RISE (Reverse Indentation Size Effect) behavior for the samples B, C and D. RISE behavior is observed only for the samples where the plastic deformation is dominant. ISE behavior is observed for the samples where both elastic and plastic deformation are produced. The results of XRD and SEM analysis show improvement with PbSe addition in the crystal structures and surface morphologies of superconducting samples.Öğe Hydrothermal synthesis of Li co-doped Zn0.98Mg0.02O nanoparticles and their structural, optical and electrical properties(Elsevier Sci Ltd, 2016) Şenol, Sevim Demirözü; Erdem, MuratZn0.98-xMg0.02LixO (x=0.0, 0.01, 0.02, 0.03) nanoparticles were synthesized by the hydrothermal method. The structural, optical and electrical properties of the samples were analyzed by X-ray diffraction (XRD), Scanning Electron Microscope (SEM), Diffuse Reflectance UV-vis spectroscopy, and Hall effect measurements. XRD results showed that Zn0.98-xMg0.02LixO with wurtzite structure are obtained without impurities and additional phases. The lattice parameters (a, c) initially decrease, but they increase with further Li doping. The optical measurements exhibited blue-shift of optical band edge and widening of the band gap. Temperature dependent transport measurements using Van der Pauw method showed that Li doping increased the resistivities and charge carrier density, while it decreased the Hall mobility.Öğe Improvement of the intergranular pinning energy in the (BiPb)(2)Sr2Ca2Cu3O10+delta superconductors doped with high valancy cations(Springer, 2012) Yazıcı, Duygu; Erdem, Murat; Özçelik, BekirIn the present work, Bi-Pb-V-Sr-Ca-Cu-Ti-O bulk samples with nominal composition (BiPb)(2)V (x) Sr2Ca3Cu4-y Ti (y) O12+delta with x=0.1 and y=0.050, 0.10, 0.2, and 0.3 have been prepared by the melt-quenching method. The magnetoresistance of the samples has been measured for different values of the applied magnetic field. The thermally activated flux creep model has been studied in order to calculate the flux pinning energies. The flux pinning energies calculated increase with increasing Ti-content, and decrease with applied magnetic field.Öğe Investigation of physical properties of Gd doped Bi-2223 superconductors(Bolu Abant İzzet Baysal Üniversitesi, 2009) Erdem, Murat; Terzioğlu, Cabir; Belenli, İbrahimBirçok araştırmacı farklı elementlerin yüksek sıcaklık süperiletkenlere katkılanmasının etkilerini araştırmaktadır. Bu araştırmaların iki amacı vardır; yüksek sıcaklık süperiletkenliğin temel mekanizmasını anlamak ve yüksek sıcaklık süperiletkenlerin mekanik ve süperiletkenlik özelliklerini geliştirmek. İkinci amaç yüksek sıcaklık süperiletkenlerin teknolojik uygulamaları açısından oldukça önemlidir. Yüksek sıcaklık süperiletkenler içerisinde bakır oksitler (kupratlar) en önemli gruptur. Bakır oksitler arasında BSCCO sistemi, yaygın olarak incelenmiş ve bazı teknolojik uygulamaları gerçekleştirilmiştir. Bu tezde, Bi-2223 fazına Gd katkılamanın süperiletkenlik ve mekanik özelliklerine etkisi incelenmiştir. Gd iyonlarının BSCCO sisteminde Ca iyonlarının yerine geçtiği düşünülmektedir. Bu düşünce taşıyıcı yük yoğunluğuna bağlı olan geçiş sıcaklığındaki (Tc) ve birim hücrenin c parametresindeki azalma ile desteklenmektedir. Gd iyonlarının yarıçapı Ca iyonlarının yarıçapından küçüktür ve c parametresindeki azalma iyon yarıçaplarının farkı ile açıklanabilir. Kritik akım yoğunluğu (Jc) değerlerindeki azalma ve SEM görüntüleri, Gd içeriği arttıkça numunlerin tanecik bağlantılarının zayıfladığını göstermektedir. Gd katkısı arttıkça zayıf bağlantı özelliği artmaktadır. Gd katkısı 2223 fazının oluşumunu zayıflatmış ve sonuçta Gd katkısı arttıkça 2223 fazının oranı azalmış ve 2212 fazının oranı artmıştır. Gd elementinin yüksek manyetik momentinin süperiletken durumda Cooper çiftlerini etkilediği düşünülmektedir. Çiftlerin spinleri Gd elementinin manyetik momenti olumsuz etkileyerek çift-ayrışması etkisi de taşıyıcı yoğunluğunun azalmasına neden olabilir. Bu tez sonucunda BSCCO sistemine Gd katkılanmasının süperiletkenlik ve mekanik özelliklerini olumsuz etkilediği görülmüştür.Öğe Investigation of the magnetic field angle dependence of resistance, irreversibility field, upper critical field and critical current density in DC sputtered Bi-2223 thin film(Elsevier Science Bv, 2011) Yıldırım, Gürcan; Akdoğan, Mustafa; Altıntaş, Sevgi Polat; Erdem, Murat; Terzioğlu, Cabir; Varilci, AhmetWe measured resistivity and transport critical current density, J(c), as a function of DC magnetic field and the angle (phi) between the surface of the film and the magnetic field on ex-situ annealed, c-axis oriented Bi-2223 thin films fabricated by DC sputtering method. Irreversibility field (mu(0)H(irr)) and upper critical field (mu(0)H(c2)) were determined from the resistivity versus the applied magnetic field graph. It is observed that critical temperature (T(c)), mu(0)H(irr), mu(0)H(c2) and J(c) of the films strongly depend on the direction and strength of the field. While T(c) of the film without magnetic field is observed to be about 102 K, it is found to decrease to 90 K (85 K) for the applied field perpendicular (parallel) to c-axis of the film. Not only were mu(0)H(irr)(0) and mu(0)H(c2)(0) values determined from the mu(0)H(irr) and mu(0)H(c2) versus temperature graphs, respectively, but also penetration depths and coherence lengths were interpreted. Anisotropy of the film was also discussed by means of the change of irreversibility as a function of angle. Moreover at 4.2 K, J(c) was observed to be 3000 A/cm(2) at zero field; however, it was found to abruptly decrease to 1982 (1 1 2 0) A/cm(2) under low magnetic field at phi=0 degrees (phi=90 degrees), which indicates that anisotropic J(c) behavior of the film is intrinsic. Furthermore, we provided a theoretical analysis of the obtained results in the framework of intrinsic pinning theory of superconductors. Microstructural properties of the produced films were also reinvestigated by X-ray diffractometer (XRD) and scanning electron microscopy (SEM) measurements. XRD patterns indicate that the films are c-axis oriented based on the prominent (0 0 l) peaks. SEM images show needle-like grain structures dominate the surface morphology of the films. (C) 2011 Elsevier B.V. All rights reserved.
