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Öğe Activation energy for crystallisation of melt-quenched (Bi1.0Tl0.5Ga0.5)Sr2Ca2Cu3O10+y superconducting glass-ceramics.(Academic Press Ltd, 1997) Yakinci, ME; Aksoy, IA glass of the BiSrCaCuO superconducting system with nominal (Bi1.0Tl0.5Ga0.5)Sr2Ca2Cu3O10+y composition has been prepared by the melt-quenched method. The crystallisation kinetics of the glass was investigated using non-isothermal analysis. The activation energy for crystallisation was found to be 420.6Kjmol(-1). The Superconducting transition and zero resistance temperatures were T-c=118.8K and T-zero=114.6K respectively. The calculated critical current density was J(c)=8.85x10(6) Acm(-2) at 4.5K, In general, substitution of both Tl+3 and Ga+3 for Bi+3 increased the activation energy for crystallisation and enhanced the superconducting phase formation. (C) 1997 Academic Press Limited.Öğe Charging and discharging of particles on the low-potential electrode under bipolar corona conditions(Iop Publishing Ltd, 1998) Aliyev, HZ; Koksal, M; Aksoy, I; Yakinci, MEIn this work, the process of charging and discharging of aerosol particles on the surface of a low-potential electrode and their behaviour depending on the charge that they have are investigated under bipolar corona conditions. A general expression to characterize the kinetics of charging of these particles is developed so that this expression yields many of the special equations that have been reported in the literature and are valid under certain conditions. It is found that the intensity of the corona discharging field affects both the amount of stable charge on the particle and its charging time; in general, the time constant for discharging and the coefficient of bipolarity determine the amount of stable charge. The obtained results indicate that, under suitable conditions, use of a bipolar corona field can be an alternative technique for cleaning and refining impure aerosol mixtures for desired purposes.Öğe Crystallization activation energy and hole concentration properties of the Bi2Sr2Ca1-xCdxCu2O8+y glass-ceramic superconductor rods(Kluwer Academic/Plenum Publ, 2002) Özhanli, Z; Yakinci, ME; Balci, Y; Aksan, MAThe glass rods with the nominal compositions of Bi2Sr2Ca1-xCdxCu2O8+y, where x = 0.0, 0.4, and 0.8, were prepared by melt-casting method. XRD studies exhibited that the Cd substitution caused a transition from Bi-2212 phase to Bi-2201 phase. The multiphase structure was obtained for higher Cd concentration cases. It was determined that the activation energy for crystallization was decreased with the increase of the Cd concentration. When the Cd concentration was increased in the system the superconducting properties decreased. The hole concentration, p, was calculated using the Presland's method. The increase in the Cd concentration increased the hole concentration and the results showed that the Cd-substituted samples were highly in the overdoped region.Öğe Degradation of superconducting properties in MgB2 by Cu addition(Pergamon-Elsevier Science Ltd, 2006) Aksan, MA; Güldeste, A; Balci, Y; Yakinci, METhe (MgB2)(2-x)CUx (x=0-0.5) superconducting system was prepared by a solid-state reaction technique. Microstructural evolution and transport properties including resistivity versus temperature up to a magnetic field of 6 T, activation energy, thermoelectric power and Fermi energy, E-F, and the corresponding velocity, V-F, values of the samples prepared were also investigated. The XRD analysis showed a multiphase formation and no detectable solution of Cu in MgB2. Two different impurity phases, MgCu2 and CuB24, have been identified and their peak intensity increased when the Cu concentration increased. The temperature dependence of the resistivity of the samples showed a metallic behavior down to T-c. But, for the Cu concentrations above 0.3 the superconducting phase transition completely disappeared. The magnetic field strongly affects the electrical properties. For x = 0.0 samples, the transition is found to be sharp, Delta T similar to 1K, but it becomes broader with increasing magnetic field and Cu concentration. The calculated values of carrier concentration, n, of the samples are showed a sharp decrease with increasing Cu content. For x = 0.0 sample the n was calculated to be 12 X 10(21) cm(-3), but for the x = 0.5 sample it decreased to 1.3 X 10(21) cm(-3). We found that the activation energy, U(B), decreased sharply with increasing magnetic field. According to thermoelectric power and Fermi energy, EF, calculations the decrease of the carrier concentration by the additions of Cu into MgB2 gives a decrease in EF and this could be attributed to a shift of the Fermi level towards the top of the sigma-hole band. (c) 2005 Elsevier Ltd. All rights reserved.Öğe Degradation of superconducting properties in MgB2 by formation of the MgB4 phase(Springer/Plenum Publishers, 2002) Yakinci, ME; Balci, Y; Aksan, MA; Adigüzel, HI; Gencer, ASuperconducting MgB2 polycrystalline samples have been fabricated under two different conditions in order to determine the effect of MgB4 phase. A series of samples was placed in an alpha-alumina container closed with a cup and fired under high purity argon gas. The other series of samples was placed in an a-alumina boot without any lid and fired under similar conditions. For the first series of samples, we have found pure MgB2 phase formation and a narrow transition width at 0.4 K. For the second series of samples, significant amount of MgB4 phase were formed and the T-zero was decreased to 27 K. For both the group of samples magnetization hysteresis loops obtained at various temperature range and applied field up to 2 T. The best J(cmag) for the first series of samples was 1.9 x 10(5) x A/cm(2) at 10 K and 0 T, and for the second series of samples was 0.7 x 10(4) x A/cm(2) at 10 K and 0 T.Öğe Effect of substrates on Ic anisotropy in thick film Bi1.7Ga0.3Sr2Ca2Cu3O10+y glass-ceramic superconductors(Elsevier, 2004) Yakinci, ZD; Balci, Y; Yakinci, ME; Aksan, MABi1.7Ga0.3Sr2Ca2Cu3O10+y material was produced by the glass technique and the glass powders obtained then coated on to YSZ and Al2O3 substrates to fabricate 25-30 mu thick films using spray pyrolsis method. The films were then converted to glass-ceramic structure with suitable heat treatment cycles. The effects of substrates on the J(c) and the I-c anisotropy coefficients have been investigated and the results obtained were presented. (C) 2004 Elsevier B.V. All rights reserved.Öğe Enhanced Jc properties of MgB2 materials processed under a magnetic field(Elsevier, 2004) Aksan, MA; Yakinci, ME; Balci, YSuperconducting MgB2 samples with T-c in the range of 35.9-39.7 K were prepared under a magnetic field up to 1 T for 75 h. Crystallographic and transport properties of the samples were characterized by means of XRD, R-T, M-H, and J(c) analysis. According to XRD results, the intensity of the samples prepared in 1 T magnetic field increased more than 35% compared to standard MgB2 samples. The R-T results showed a slight change, while the transport J(c) and J(cmag) increased significantly. (C) 2004 Elsevier B.V. All rights reserved.Öğe Fabrication and properties of (Hg0.8Re0.2)Ba2Ca2Cu3Ox superconducting thick films(Iop Publishing Ltd, 2005) Yakinci, ME; Aksan, MA; Balci, YApproximately 50 mu m thick epitaxial c-axis orientated (Hg0.8Re0.2)Ba2Ca2Cu3Ox superconducting., films have been prepared on MgO(100) substrates using a spraying process and post-Hg-vapour annealing. The effects of the heating temperature-time combinations and the filling factor of Hg (ff(Hg),) on the physical, electrical and magnetic properties of the thick films have been investigated. The interesting observation was the formation of a similar to 1.5 mu m thick interfacial layer between the film and the substrates. This interfacial layer was found to be protective against excessive diffusion and dissolution of the Mg (2+) ions from the substrate or counter-diffusion of Ba, Ca and Cu ions from the films. The XRD investigations showed that the a-b plane of the HgRe- 1223 phase aligns parallel to the substrate surface. The best T-c and T-zero were found to be 13 1.9 and 129.3 K, respectively. Magnetic properties up to 5 T have been investigated. The calculated value of critical current density, J(c) was found to be 4.82 x 10(5) A cm(-2) at 4.5 K. The results obtained suggested that fabrication of HgRe- 1223 thick film superconductors using a spraying process with 130 K transition is possible and they are very promising particularly for electronic applications.Öğe Fabrication of (BiGaPb)2Sr2Ca2Ca2Cu3O10+y glass-ceramic superconductor rods.(Plenum Publ Corp, 1996) Yakinci, MEGlass samples with a nominal composition of B1.2Ga0.4Pb0.4Sr2Ca2Cu3O10+y were prepared as rods having a diameter of 13mm and 20cm long by melt casting technique. Sintering process was performed by applying a direct current to the glass rods. Three different current application stages were used and crystallisation of the glass rods were obtained. The XRD studies of the material showed that crystallised grains were preferably c-axis oriented. The best T-c was obtained at 107K and T-zero was obtained at 101K. These results were also confirmed by the D.C. Susceptibility measurements. After the optimum processing condition the maximum transport current density was found to be 9700 A/cm(2) at 4.2K.Öğe In-situ single chamber arc sputtering process for YCd0.3Ba2Cu3O7-? superconducting thin films(Kluwer Academic/Plenum Publ, 1999) Yakinci, ME; Balci, Y; Aksan, MA; Aydogdu, Y; Ates, HSuperconducting YCd0.3Ba2Cu3O7-delta thin films have been deposited in-situ onto single crystal MgO substrates using a DC arc-sputtering process. The depositions were carried out in a single chamber deposition system equipped with two target holders. The films deposited at the optimum condition exhibited strong (001) orientation with a high peak: intensity. The best electrical properties were achieved to be 90 K for T-e, 81K for T-zero and the transport critical current density J(c) = 675 A/cm(2) at 77K and 2.3x10(3) A/cm(2) at 4.2 K for the sample deposited at the optimum conditions.Öğe An investigation on the activation energy and the enthalpy of the primary crystallization of glass-ceramic Bi-rich BSCCOHTc superconductors(Elsevier Science Sa, 2001) Balci, Y; Ceylan, M; Yakinci, METhe transformation of amorphous Bi-rich BSCCO (Bi3Sr2Ca2Cu3O12-x) to a superconductive crystalline material has been characterized by structural, thermal and transport measurements. The activation energy and enthalpy data of amorphous materials are examined in terms of analysis developed for non-isothermal crystallization studies. Two groups of samples were prepared. The first group was glass pieces (8 x 8 x 2 mm(3)) of material, and the second group was the same glass material grained and powdered (similar to 1-50 Vm). Four different heating rates were used for differential scanning calorimetry and differential thermal analysis. The both thermal analysis indicated exothermic crystallization peaks at 467-489 degreesC for powdered and 472-490 degreesC for bulk samples depending on the heating rates. The enthalpy of the first crystallization of the samples varied between 40-107 and 30-35 J g(-1) powdered and bulk materials, respectively. The crystallization activation energies of the samples were found to be 299 and 349 kJ mol(-1) for powdered and bulk samples, respectively. The best electrical performance was obtained at 100 K for T-c and 90 K for T-zero. The highest thermal conductivity result was found to be 3.36 mW cm(-1) K-1. The active phonon modes of the system was also found using the Fourier transform infrared analysis. The surface and the polished cross-sections of the samples and evolution of the phases formed were examined by scanning electron microscopy. (C) 2001 Elsevier Science B.V. All rights reserved.Öğe A structural transformation and its effect on the physical properties of the V-substituted Bi2Sr2Ca2Cu3O10+gamma system(Iop Publishing Ltd, 1997) Yakinci, MESystematic substitution of V in the Bi2-deltaVdeltaSr2Ca2Cu3O10+y system (delta = 0, 0.2, 0.4, 0.6, 0.8 and 1) was carried out in order to determine the effect of V ions on the phase formation and on the physical properties of the BSCCO 2223 system. The most interesting observation was structural transformation of the system from tetragonal to orthorhombic after delta = 0.6. A solid solubility limit for V was also found to exist. Resistivity and susceptibility studies have shown that high-T-c superconductivity exists up to delta = 0.6 and that the semiconducting-to-metallic transition or fully semiconducting behaviour occurs after this limit. A fractionally small but very-high-T-c transition at around 210 K was also observed, but it was not reproducible. Among the V-substituted samples the best electrical properties were obtained for delta = 0.2; T-c and T-0 were found to be 112 K and 92 K, respectively, the calculated value of J(c) was found to be 1.11 x 10(5) A cm(2) at 4.5 K and the thermal conductivity parameter kappa was found to be 6.4 mW cm(-1) K-1. By substituting the higher-valence state V5+ ions for Bi3+, the thermal treatment time is significantly reduced. The magnetic properties, IR and thermal conductivity results showed evidence of a strong coupling mechanism in the Bi2-deltaVdeltaSr2Ca2Cu3O10+y system.Öğe Study on the physical and electrical properties of Bi2-?Zn?Sr2Ca2Cu3O10+y glass-ceramic superconductors(Kluwer Academic/Plenum Publ, 2002) Aksan, MA; Yakinci, ME; Balci, YWe have fabricated a series of glass-ceramic (Bi2-deltaZndelta) Sr2Ca2Cu3O10+y, where delta = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0, and investigated the effect of Zn ions on the glass formation, crystallization, thermal, electrical, and on the magnetic properties of the BSCCO-2223 superconductor system. The structural symmetry was found to be tetragonal in all the substitution levels. The best electrical performance was obtained from the 6 = 0 sample, the T-c and T-zero was obtained at 110 K and 107 K, respectively. The J(c) values of the samples were determined using the magnetization hysteresis and Bean's model. The crystallization kinetics were investigated using nonisothermal models of Augis-Bennett. The calculated activation energy, E-a, of the system was found to be in the range of 258-336 kJ/mol.Öğe Synthesis and characterization of asbestos-silane hybrid materials(Elsevier, 2005) Onal, Y; Yakinci, ME; Seçkin, T; Içduygu, MGIn this study, interaction of the silane coupling agent 3-(trimethoxysilyl)propylmethacrylate (A-174) and asbestos was investigated. A-174 grafted onto the surface of the asbestos was polymerized by radical initiator. FT-IR, thermogravimetric analysis (TGA), X-ray diffractometer (XRD), differential thermal analyzer (DTA) and scanning electron microscopy (SEM) were used to characterize modified particles. The effects of temperature on modified particles and were evaluated by differential thermal analysis. After modification with A-174, the effects of grafting on asbestos were discussed in terms of structural change and thermal stability. These results lead us to conclude that the silane coupling agent in asbestos serve as polymeric precursor to form polymer onto asbestos matrix resulting the hybrid materials in which the harmful effect of asbestos was prevented by covering the asbestos particles with polymer. (c) 2004 Elsevier B.V. All rights reserved.Öğe Synthesis and characterization of Er-substituted Bi-2223 H-Tc glass-ceramic superconductors(Elsevier Science Sa, 2004) Aksan, MA; Yakinci, METhe Bi2Sr2Ca2Cu3-xErxO10+delta (x = 0.5 and 1.0) H-T-c system was prepared by glass-ceramic technique to investigate the microstructural formation. thermal and transport properties. We have found that Er+3 ions have a solid solubility limit in the Bi-2223 system and this limit was passed at x = 1.0. Below this limit glass samples were prepared and converted to the glass-ceramic form easily, but after the solid solubility limit glass formation was diminished and crystallized samples were formed after melt quenching. The substitution had considerable effect on the electrical properties comparing with the unsubstituted Bi-2223 material. The T-c values of the x = 0.5 and 1.0 sample were found to be 71 +/- 0.1 K. The thermoelectric power data were analyzed in view of two band model with linear T-term and Xin's two band model. Thermoelectric power was obtained to be positive for the both samples, indicating that the hole type conductivity is dominant in the materials prepared. The magnitude of thermal conductivity, kappa, was also influenced by the Er concentration. When the Er concentration was increased the magnitude of kappa was suppressed. It strongly indicates that the impurities play a significant role in limiting the heat transport due to a strong increase of the electron-phonon-impurity scattering rate. (C) 2004 Elsevier B.V. All rights reserved.Öğe Synthesis and characterization of glass-ceramic Bi2-xGaxSr2Ca2Cu3O10+y superconductors(Iop Publishing Ltd, 2000) Aksan, MA; Yakinci, ME; Balci, YWe have melt quenched a series of Ga substituted Bi2-xGaxSr2Ca2Cu3O10+y samples with the compositions with x = 0.2, 0.4, 0.6, 0.8 and 1.0. Microstructure, thermal properties including crystallization activation energy, magnetic and superconducting properties were investigated. We have found that Ga3+ ions have a solid solubility limit in the BSCCO system and this limit was passed at x = 0.6. Below this limit HTc BSCCO n = 3 phase was obtained, but after the solid solubility limit samples yield multiphase superconducting properties. Extended heat treatment at 840 degrees C displayed no suppression of the solid solubility Limit. The crystallization kinetic studies were investigated using non-isothermal kinetic models of Kissinger and Augis-Bennet. Higher crystallization activation energies, E-a, were obtained compared to unsubstituted BSCCO materials, glassification improved and glass handling time increased. The substitution had a slight effect on J(c), the flux pinning in the material was improved and better J(c) values were obtained below the solid solubility limit.Öğe Synthesis and characterization of novel polyacrylate-clay sol-gel materials(Chapman Hall Ltd, 1996) Seckin, T; Onal, Y; Aksoy, I; Yakinci, MEOrgano-functional silanes which were able to form chemical bonds with kaolinite and could also have an affinity to the materials of concern here, were studied by the sol-gel process. Polymethacrylate with trialkoxy silyl functional groups were prepared, hydrolysed and co-condensed with kaolinite. The progress of the hydrolysis, which proceeded very slowly, was followed by Karl-Fischer titration. Thermal behavior was investigated by differential thermal analysis. The extent of the reaction leading to network formation was qualitatively followed by Fourier transform-infrared spectroscopy and X-ray diffraction. Free-radical polymerization was carried out ultrasonically in the presence of a catalyst. Trimethoxy silane end-capped silane was found to be covalently bonded to kaolinite. The copolymers, with various amounts of kaolinite, were then hydrolysed and co-condensed in the presence of a catalyst to yield sol-gel materials which have a controllable combination of properties of both the polymer and kaolinite.Öğe Synthesis of melt-quenched Bi1.7V0.3Sr2Ca2Cu3O10+y superconducting glass-ceramics(Springer, 1996) Yakinci, ME; Aksoy, I; Ceylan, MA glass in the BSCCO system with Bi1.7V0.3Sr2Ca2Cu3O10+y nominal composition was prepared by the melt-quenching (glass) method. The suitability of the glass ceramic method has been assessed in terms of physical and electrical properties. Using an analysis developed for non-isothermal crystallization studies, information on some aspects of crystallization has been obtained. The result obtained indicated that substitution of vanadium for bismuth increased the activation energy compared to the unsubstituted BSCCO system but did not enhance the superconducting phase formation. The activation energy for crystallization of glass has been found, E(a)=355 kJ mol(-1). The crystal structure was found to differ from that in the unsubstituted BSCCO system. Most importantly, the HT, phase was formed by reaction between the constituent phases at lower temperatures and not directly from the glass material. The best electrical properties were obtained at T-0=75 K and J(c)=12 x 10(3) A cm(-2) at 4.2 K.Öğe Synthesis, characterization and thermal properties of bentonite-polyacrylate sol-gel materials(Royal Soc Chemistry, 1997) Seckin, T; Gultek, A; Onal, Y; Yakinci, ME; Aksoy, IA new type of material incorporating bentonite with an alkoxide, H2C=C(CH3)COO(CH2)(3)Si(OCH3)(3), has been prepared successfully using a sol-gel process. The structures and structural changes upon heating, of the bentonite and the sol-gel material. were investigated by FTIR, XRD and DSC. Using the metal alkoxide and the corresponding clay mineral as precursors, the additive reaction followed by free radical polymerization resulted in a novel material in which polymer was attached covalently to, silicate sheets of bentonite via hydroxy bonding.Öğe Thermal analysis study of Bi2Sr2Ca2Cu3-xErxO10+? glass-ceramic system(Springer, 2005) Aksan, MA; Yakinci, ME; Balci, YWe have fabricated glasses in the Bi-2223 HTc superconductor system with Bi2Sr2Ca2Cu3-xErxO10+delta nominal composition, where x=0.5 and 1.0, by the glass-ceramic technique. Using an analysis developed for non-isothermal crystallization studies, information on some aspects of crystallization temperature and thermal properties has been obtained. The crystallization studies were made using DTA with several uniform rates. The calculations of crystallization activation energies, E-a, and the Avrami parameters, n, were made based on the non-isothermal kinetic theory of Kissinger and the Ozawa's equations. The DTA data of the samples showed that the first crystallization temperature, T-x1, increases and the second crystallization temperature, T-x2, decreases by increasing the Er concentration. This suggests that the Er substitution had significant effect on the glassification of the BSCCO material due to change on the surface nucleation and increased ionic activities at high temperature region. The activation energy for crystallization, E., of the samples was also showed an increase at high Er concentration case. However, the Avrami parameter, n, decreased from 2.5 to 1.7 for x=0.5 and 1.0 samples, respectively. This suggests that the growth mechanism is diffusion-controlled and three-dimensional parabolic growth takes place near the first crystallization temperature. The oxidization rates and the activation barrier for oxygen out-diffusion process, E, was calculated using the TG data. It was found that the total mass gain in the x=0.5 sample is comparably smaller than that of the x=1.0 sample. This shows that the oxygen absorption of the x=1.0 sample is faster than the x=0.5 sample, leading to increase in the oxidization rate in the x=1.0 material.
