DSpace Arşivi :: by Yazar "Yakinci, M. E." değerine göre listeleniyor

Yazar "Yakinci, M. E." seçeneğine göre listele

Listeleniyor 1 - 20 / 49

Adjustable tunneling barrier in bi-based high-Tc cross-whisker junctions
(Iop Publishing Ltd, 2015) Kizilaslan, O.; Simsek, Y.; Aksan, M. A.; Koval, Y.; Yakinci, M. E.; Mueller, P.
We present a study of cross-whisker junctions with electronically modified tunneling barriers. Cross-whisker junctions were successfully prepared by annealing two crossed Bi-based whisker bars at temperatures of around 840 degrees C. In addition to the artificially produced junction at the interface, intrinsic Josephson junctions in the respective bars of the cross were observed. The artificial junction exhibited reproducible and almost ideal junction characteristics. The tunneling barrier/interface properties were controlled by carrier injection in c-axis direction. Using this process, we were able to reduce the tunneling resistance from 408 Omega to 30 Omega. At the same time, the critical current did rise by a factor of 4. Subsequently, the critical current was doubled while the tunneling resistance stayed constant. We interpret this observation in terms of the counter-play between transparency of the barrier and the carrier concentration of the electrodes. In this sense, we can consider the current injection procedure as an electronic gluing process of the two cross-junction whisker bars.
Characterization of Fe3O4 Nano Particles for Biomedical Applications
(Ieee, 2015) Onar, K.; Yakinci, M. E.
Nano particles of Fe3O4 with the range of 30 and 60 nm were synthesized by using chemical coprecipitation method. Particle size effects according to magnetic properties were investigated together with the constant reaction and crystallization temperature. According to calculations peaks were indexed as cubic Fe3O4 for all samples. The hysteresis loops shows superparamagnetic behavior. It was found that when Fe2+/Fe3+ ratio increase to 50% the particle size increases approximately one fold. We realized that chemical coprecipitation method is suitable for biomedical applications of Fe3O4 nano particles.
Current-Voltage Measurements on a Bi2Sr2CaCu2Ox Whisker and Investigation of Its Vortex Dynamics in Self Field
(Springer, 2013) Altin, S.; Aksan, M. A.; Yakinci, M. E.; Bernstein, P.
We report current-voltage measurements carried out on a high quality Bi2Sr2CaCu2Ox whisker in a large temperature range below the critical temperature. When a perpendicular field is applied, the current-voltage curves are typical of the flux flow regime at low fields and resemble flux creep characteristics at high fields. This change, related to what is described as the critical current peak effect is associated to a transition between different vortex phases. In this contribution, we focus on the dynamics of the vortices in self field. We show that the critical current in the flux flow regime can be calculated straightforwardly taking into account inter-vortex forces only, supposing that free vortices run between pinned vortices.
Effect of Bi deficiency on grain alignment of BiPb-2223 thin film fabricated using rf sputtering process and on critical current density properties
(Taylor & Francis Ltd, 2011) Aksan, M. A.; Altin, S.; Yakinci, M. E.; Guldeste, A.; Balci, Y.
In the present study, thin films prepared as a function of the Bi concentration in the BiPbSrCaCuO system were synthesised. Thin films were fabricated using radio frequency sputtering method. Crystal structure of the films fabricated was determined from X-ray diffraction measurements. The crystal orientation was analysed by X-ray pole figure and in-plane alignment. Both X-ray diffraction and pole figure analysis revealed that crystallinity in the films decreased significantly with decreasing Bi concentration in the system. A systematic decrease in the superconducting transition temperature and hole concentration per CuO plane was obtained with decreasing Bi concentration. The J(c) values of the films were calculated using Bean formula. It exhibits a significant dependence on the magnetic field and temperature. It was found that J(c) decreased sharply with increasing applied magnetic field. The highest J(c) value was found to be 1.06 x 10(6) A cm(-2) at 10 K, which corresponded to the best flux pinning among the films fabricated.
Effect of Bi2O3 Addition on the Single-Crystal BiSrCaCuO Whisker Growth
(Springer, 2011) Altin, S.; Aksan, M. A.; Altin, E.; Balci, Y.; Yakinci, M. E.
Bi-2212 superconducting whiskers have been fabricated by annealing a melt-quenched precursor using suitable heat-treatment cycles for Bi3+x Sr2Ca2Cu3O8+delta where x=1 and 2. Approximately 1-3 mm long whiskers were fabricated for x=1 and x=2 and their physical, electrical and magnetic properties were investigated. Crystallization activation energies of the materials were calculated according to Kissinger and Augis-Bennet method using the DTA data. Microstructural changes from glass to heat-treated glass-ceramic materials at different temperatures were investigated with SEM, EDX and XRD analyses. It was observed that the structure of the whiskers has high c-axis oriented single-crystalline Bi-2212 phase. The whiskers fabricated for x=1 and 2 showed very smooth surface without cracks and dislocations. T (c) of the whiskers for x=1 and 2 were obtained to be 83.2 K and 79.8 K respectively. The change of magnetization with applied magnetic fields (M-H) was investigated at three different temperatures, 10, 20 and 40 K, and J (c mag) was determined using the Bean model.
Effect of Ce substitution on superconducting properties of Bi2Sr2Ca2Cu3O10+? system fabricated by glass-ceramic technique
(Springer, 2011) Ozturk, R.; Aksan, M. A.; Altin, S.; Yakinci, M. E.; Balci, Y.
In this study, the samples with nominal composition of Bi2-x Ce (x) Sr2Ca2Cu3O10+delta , where x=0, 0.05, 0.1, 0.2, 0.4 and 0.6, are synthesized by using conventional glass-ceramic technique. Effects of the Ce substitution on the structural/microstructural and electrical properties of the Bi-2223 system have been investigated in detail. Ce has a solid solubility limit on glassification, which is found to be x=0.2. It is seen that glassification is destroyed for the Ce substitutions above x=0.2. Further, XRD investigations showed that main phase in all the heat-treated samples is identified to be Bi-2212. From SEM-EDX investigations of heat-treated samples, it is revealed that the highly Ce-substituted samples had complex and deformed structure. It is also found that electrical properties degraded with increasing the Ce concentration. Especially in high Ce substitution level, superconductivity is destroyed and an insulating behavior is observed.
Effect of Co addition on the critical current density of MgB2 superconductor
(Elsevier, 2014) Kirat, G.; Kizilaslan, O.; Aksan, M. A.; Yakinci, M. E.
In this study, the (MgB2),Co-1-x(x), samples, where x-0.0. 0.1, 0.3, 0.6 and 0.8, were prepared by using the solid-state reaction technique. Effect of the Co-addition on the structural, magnetic, critical current density. J(c), and flux pinning properties of the superconducting MgB2 system was investigated. A magnetic transition was observed with increasing the Co-concentration in MgB2. For the pure MgB2, J(c), was obtained to be 2.78 x 10(4) A cm(-2) at 5 K and 1.7 kOe, but J(c) was suppressed by addition of Co to the system. It was found that a large amount of Co in MgB2 did not act as pinning centers which improves J(c) The magnetic behavior observed by the Co-addition originates from the magnetic properties of cobalt itself. (C) 2014 Elsevier B.V. All rights reserved.
Effect of Fe Substitution for Cu on Microstructure and Magnetic Properties of Laser Floating Zone (LFZ) Grown Bi-2212 Rods
(Springer, 2013) Ozabaci, M.; Sotelo, A.; Madre, M. A.; Yakinci, M. E.
In this paper, the laser floating zone (LFZ) technique has been used to fabricate Bi2Sr2Ca1Cu2-x Fe (x) O (x=0,0.01,0.03,0.05,0.1) superconducting fibers. The effects of Fe substitution on grain alignment and superconducting properties of annealed fibers were studied using SEM/EDX microanalysis in addition to phase analysis and magnetic measurements realized through XRD, M-T, and M-H loops. In the same growth conditions, higher Fe contents lead to a more compact microstructure with lower porosity but also caused the formation of poor superconducting phases followed by the decrease of T (c) and J (cmag). No evidence of enhanced pinning capability was found in the magnetic measurements. Annealed rods indicated a weakly ferromagnetic-like behavior at relatively high doping levels.
Effect of grain size on the electrical and magnetic properties of MgB2 thick films deposited on the Al2O3 single crystal substrates
(Springer, 2014) Onar, K.; Balci, Y.; Yakinci, M. E.
MgB2 films having thicknesses of approximately 10 mu m have been prepared on the Al2O3 single crystal substrates by using ultrasonic spray pyrolysis technique. The films fabricated were then analyzed by means of microstructural, structural, transport and magnetic properties. The influence of grain size, depending on the ex-situ and in situ heating, were investigated. The results obtained showed that the size of MgB2 grains has an effect on the transport and magnetic properties of the films. Films prepared with in situ heating have small particle size (< 50 nm) and were found to be much better properties than the films prepared ex-situ heating, which have larger grains (similar to 1 mu m). The best T (c) value and critical current density, J (c) (mag) , were obtained to be similar to 36 K and 9.88 x 10(5) A cm(-2) respectively for the films prepared with small grains. The results were showed that the smaller grain size and in situ heating cycles are essential points for quality thick film MgB2 fabrication.
The Effect of K Substitution on Magnetoresistivity and Activation Energy of Bi-2212 System
(Springer, 2015) Ozcelik, B.; Yalaz, E.; Yakinci, M. E.; Sotelo, A.; Madre, M. A.
In the present work, magnetoresistivity performance of polycrystalline Bi2Sr2Ca1-x K (x) Cu-2 O (8+y) superconductor with x=0.0,0.05,0.075, and 0.1 has been studied by change of flux pinning mechanism, using magnetoresistivity measurements. The samples were prepared using a polymer solution technique. The effects of K substitution for Ca on the irreversibility field, upper critical magnetic field, coherence length, and activation energies have been investigated. The magnetoresistivity of the samples has been measured under applied magnetic fields ranging from 0 to 9 T. Broadening of superconducting transition is observed under magnetic field, explained on the basis of thermally activated flux flow (TAFF) model. The upper critical magnetic field H (C2)(0) and the coherence length (zeta(0)) at T = 0 K were calculated using the resistivity data and from H (C2)(0) ,respectively. H (C2)(0) and xi(0) values have been calculated as 62, 72, 75, and 53 T and 23, 21, 20, and 25 for the 0.0, 0.05, 0.075, and 0.10 K doped samples, respectively. TAFF model has been studied in order to calculate the flux pinning energies. In particular, the flux pinning energies of Bi2Sr2Ca1-x K (x) Cu-2 O (8+y) where x = 0.075 are calculated as 0.0147 eV for 9 T and 0.29 eV for 0 T.
The effect of Mo addition on the microstructure and Jc properties of MgB2 tapes fabricated by PIT method
(Elsevier Science Sa, 2008) Bayazit, E.; Altin, S.; Yakinci, M. E.; Aksan, M. A.; Balci, Y.
We investigated the effect of Mo addition to MgB2/Ag tapes fabricated by the ex situ PIT method. The heat treatments were carried out at 600 degrees C for 24 h under At atmosphere. The structural development, microstructures, superconducting properties and critical current density were characterized by means of XRD, SEM, M-T and M-H measurements. XRD and SEM studies indicated that Mo, not reacting with matrix of MgB2, was formed. The T-c of the tapes decreased in all the addition levels. The maximum J(c) value was obtained to be 1.2 x 10(5) A cm(-2) at 10 K for pure MgB2 tape. Decrease of J(c) was observed with increasing the Mo concentration. The J(c)-H characteristics of the tapes were decreased by the addition of Mo. This is considered to be due to the reduced flux-pinning force in the material. (C) 2007 Elsevier B.V. All rights reserved.
The Effect of Ru Substitution on the Thermal, Structural and Magnetic Properties of Bi3Sr2Ca2Cu3O ? Superconducting System
(Springer, 2010) Aksan, M. A.; Yakinci, M. E.; Kadowaki, K.
We have investigated the effect of Ru substitution on the thermal, structural/microstructural and magnetic properties of Bi-3223 system prepared using solid-state technique. The crystallization studies were made using DSC data with four different uniform heating rates. The formation temperature of Bi-2212 did not change significantly with increasing the Ru concentration; however, it was found that the thermal decomposition temperatures decreased. The activation energy for crystallization, E (a) , decreased by increasing the Ru concentration. X-ray diffraction and SEM measurements showed that substitution of Ru for Bi caused significant changes in the crystal structure of the BSCCO material. A distorted and multiphase crystalline structure was observed. The M--T measurement exhibited that superconducting onset temperature (T (c) ) decreased with increasing the Ru concentration in the system. The substitution of Ru for Bi caused the formation of ferromagnetic clusters in the materials, which destroyed the superconductivity in the system. Symmetric M(H) loops were obtained for lower Ru substitution, but in the case of high level substitution of Ru, a typical weak ferromagnetic-like hysteresis loop was found. It is believed that the Ru ions in the system are responsible for ferromagnetic behavior in the highly substituted materials.
The effect of Sn content on mechanical, magnetization and shape memory behavior in NiMnSn alloys
(Elsevier Science Sa, 2016) Aydogdu, Y.; Turabi, A. S.; Kok, M.; Aydogdu, A.; Yakinci, Z. D.; Aksan, M. A.; Yakinci, M. E.
The effects of the composition alteration on the magnetization and shape memory behavior of Ni50Mn40-xSn10+x (x = 0, 1, 2, 3) alloys were systematically investigated by thermal, magnetic and mechanical experiments. Phase transformation from ferromagnetic austenite to weakly magnetic martensite was observed during thermal cycling under magnetic field and transformation temperatures were decreased with increasing Sn (or decreasing Mn). Moreover, the saturation magnetization of martensite increased with Sn content. Ni50Mn40Sn10 showed the recoverable strain of 2.1% during thermal cycling under 300 MPa and the reversible superelastic strain of 2% at 190 degrees C. Mechanical experiments exhibited that the largest compressive deformation of about 7% at 650 MPa occurred in Ni50Mn39Sn11 while Ni50Mn40Sn10 had fractured at 4% and 390 MPa at room temperature. (C) 2016 Elsevier B.V. All rights reserved.
Effect of Substrates on Superconducting Properties of MgB2 Thick Films Fabricated by Spraying Method
(Springer, 2011) Ozabaci, M.; Aksan, M. A.; Yakinci, M. E.
MgB2 thick films have been prepared on Al2O3, MgO and SrTiO3 ceramic substrates using the spray method with two different heat-treatment cycles, 925 A degrees C with 10 min (Group A) and 610 A degrees C with 24 h (Group B). The structural/microstructural (XRD, SEM) and transport (R-T, MR-T) properties of the films prepared were investigated. XRD analysis showed that the films in Groups A and B consisted mainly of MgB2, but the peaks originating from the substrates were also observed in films fabricated on the Al2O3 substrate. From scanning electron microscopy, it was seen that the surface of MgB2 thick films prepared is not sufficiently homogeneous. Some cracks and heaps with different sizes were observed. The best electrical results were obtained for films in Group A on Al2O3 substrate. The T (c) value for films in Group A was found to be 36.1 K, 36 K and 35 K, for Al2O3, MgO and SrTiO3 substrates, respectively. No superconducting state was reached for films in Group B on the SrTiO3 substrate. In all the films which showed a superconducting state, the magnetic field strongly affected T (c) . A tail in the resistance curves was observed with increasing magnetic field for films in Group A on the MgO and SrTiO3 substrates. At magnetic fields above 1 T for films in Group A on the SrTiO3 substrate and above 2 T for films in Group A on the MgO substrate, the zero-resistance temperature, T (0), was not obtained.
Effects of In-situ and Ex-situ Heat-Treatment Procedures on the Transport Properties of the MgB2 Superconducting Thin Films Fabricated by Ultrasonic Spray Pyrolysis (USP) System
(Springer, 2011) Yakinci, M. E.; Aydogdu, Y.; Aksan, M. A.; Balci, Y.; Altin, S.
Superconducting MgB2 thin films have been prepared using Ultrasonic Spray Pyrolysis (USP) system. 2.4 MHz USP system and various solutions which contain different Mg, B and de-ionized water and LAPSA concentrations and gas atmospheres were used to obtain 500 nm to 1.0 mu m thick MgB2 films. Some of the films produced were heat treated in-situ in the spraying chamber during deposition and some of them were annealed ex-situ in the tube furnace under Mg vapor. T (c) and T (zero) of the samples were obtained to be 39.5 K and 37.4, 39.5 and 37.0 for ex-situ and in-situ prepared films, respectively. The highest critical current density was obtained to be 4.12x10(6) A cm(-2) for ex-situ annealed films and 4.01x10(6) A cm(-2) for in-situ produced films. The result obtained indicated that the ex-situ preparation method provides improvement in the transport and magnetic properties.
Effects of SnO on growth and physical properties of BSCCO whiskers
(Maney Publishing, 2010) Altin, S.; Aksan, M. A.; Balci, Y.; Yakinci, M. E.
Superconductor whiskers doped with SnO have been fabricated by annealing a melt quenched (Bi2Sn1)-223 precursor using suitable heat treatment cycles. Approximately 5 mu m thick, 90 mu m wide and 5 mm long whiskers were fabricated, and their physical, electrical and magnetic properties were investigated. Crystallisation activation energies of glass phase fabricated were calculated to be 390 kJ mol(-1) using Kissinger method based on the differential thermal analysis data. The T-c value of the whiskers was found to be 94 K from M-T measurement. The magnetisation of whiskers before superconducting transition increased with decreasing temperature, and after superconducting transition, the magnetisation of whiskers decreased, from positive to negative, due to the diamagnetic nature of superconductivity. The change on magnetisation dependence of applied magnetic fields (M-H) showed that whiskers have paramagnetic-diamagnetic multiphase structure.
Enhanced physical properties of single crystal Fe0.99Te0.63Se0.37 prepared by self-flux synthesis method
(Elsevier Science Sa, 2016) Onar, K.; Oezcelik, B.; Guler, N. K.; Okazaki, H.; Takeya, H.; Takano, Y.; Yakinci, M. E.
In this study, we have systemically studied the physical, electrical and magnetic properties of Fe0.99Te0.63Se0.37 single crystalline samples prepared by self-flux method. We found that the self-flux method is a suitable synthesis technique for this alloys if setting of experimental parameters made carefully. The M-H curve affirms that samples are typical type-II superconductor. Strong sign of bulk superconductivity, even after high field measurements, were seen. Calculated J(c)(mag) values, at zero field, were found to be 7.7 x 10(5) Acm(-2) and 2.6 x 10(4) Acm(-2) for 5 K and 10 K respectively. The upper critical field H-c2(0) has been determined with the magnetic field parallel to the sample surface and yielding a maximum value of 65 T. At the zero field coherence length, xi, value was calculated to be 2.24 nm for 10% T-c(offset) which is significantly larger (approximately 6 fold) than the unit cell, a, and indicating the absence of weak link behavior in the sample. Calculated mu H-0(c2)(0)/k(B)T(c) rate indicated comparably higher value (3.66 T/K) than the Pauli limit (1.84 T/K) and obtained results were suggested unconventional nature of superconductivity in our samples. (C) 2016 Elsevier B.V. All rights reserved.
Enhanced thermoelectric properties induced by chemical pressure in Ca3Co4O9
(Elsevier Sci Ltd, 2014) Demirel, S.; Avci, S.; Altin, E.; Altin, S.; Yakinci, M. E.
We report the investigation of boron substitution on structural, electrical, thermal, and thermoelectric properties of Ca-3_xBxCo4O9 (x=0, 0.5, 0.75, and 1) in the temperature range between 300 K and 5 K. X-ray diffraction studies show that the Ca3Co4O9 phase is successfully preserved as the majority phase in the x=0.5 sample despite the small size of boron ions. Electrical transport measurements confirm that B3+ substitution for Ca2+ causes an increase in resistivity due to the decrease in carrier concentration. x=0.5 sample is found to have a Seebeck coefficient of 181 mu V/K at room temperature which is similar to 1.5 times higher than that of the pure Ca3Co4O9. Our results indicate that the chemical pressure due to the large ionic radii difference between B3+ (0.27 angstrom) and Ca2+ (1 angstrom) enhances the thermoelectric properties as long as the unique crystal structure of Ca3Co4O9 is preserved. (c) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Enhancement of Magnetic and Transport Properties of Superconducting Fe1-xMnxSe0.5Te0.5 Single Crystals
(Springer, 2019) Ozabaci, M.; Yakinci, K.; Yakinci, M. E.
In this article, we provide the synthesis and characterization of manganese-substituted FeSe0.5Te0.5 single crystals in the nominal composition range of Fe1-xMnxSe0.5Te0.5 (x = 0.01, 0.05, 0.1) via the self-flux method. It is observed that Mn-substitution improved the bulk superconducting properties of FeSe0.5Te0.5 considerably by increasing the superconducting transition temperatures determined from both resistive and magnetic transitions. Our results reveal that x = 0.05 Mn-substituted sample yields the most appropriate superconducting performance, considering all the samples employed. The corresponding value is computed to be 4.7 x 10(4) A/cm(2) for x = 0.05 sample at 8 K under 0.2 kOe, and it decreases to the values 2.54 x 10(4) A/cm(2) and 1.34 x 10(4) A/cm(2) for the x = 0.01 and x = 0.1 samples, respectively.
Fabrication of NdCeCuO and effects of binding agents on the growth, micro-structural and electrical properties
(Elsevier Science Bv, 2011) Altin, S.; Aksan, M. A.; Turkoglu, S.; Yakinci, M. E.
NdCeCuO superconducting samples were fabricated using ethyl alcohol, acetone and ethylenediaminetetraacetic acid (EDTA) as binding agents. For evaporation of binding agents, the samples were heat treated at 1050 degrees C for 24 h and then at 950 degrees C for 6-48 h under argon atmosphere to obtain the superconducting phase. The best superconducting performance was found in the sample heat treated at 1050 degrees C for 24 h and then 950 degrees C for 12 h which was fabricated by using acetone as binding agent. The T(c) and T(0) value was found to be similar to 25 K and 23.4 K, respectively. Grain size in the samples fabricated was calculated using Scherer equation and SEM data. It was found that grain size strongly depends on the binding agents and heat treatment conditions. Some cracks and voids on the surface of the samples were observed, which influences the superconducting and electrical transport properties of the samples. (C) 2011 Elsevier B.V. All rights reserved.

Yazar "Yakinci, M. E." seçeneğine göre listele

Sayfa Başına Sonuç

Sıralama seçenekleri