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Article Citation - WoS: 5Citation - Scopus: 6Synthesis, X-Ray Data, and Hall Effect Measurements of Li-Doped Tl-Ba Superconductor(Wiley-v C H verlag Gmbh, 2003) Kayed, TSLithium-doped Tl-based superconductor was prepared by adding an amount of 0.3 mol.% to the Tl1.8Ba2Ca2.2Cu3Ox compound. The usual solid-state reaction method has been applied under optimum conditions. The x-ray data of the sample show a tetragonal structure with a high ratio of Tl-2223 superconducting phase. The sample showed a transition at 125 K and the zero resistance was observed at 117 K. Longitudinal (transport) and transverse (Hall) resistivities were measured at different temperatures under different magnetic fields and the data were interpreted. A positive Hall coefficient was observed at normal state and a sign reversal appears at temperatures lower than the critical temperature. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Article Citation - WoS: 9Citation - Scopus: 9Electrical Properties of Bi1.5znsb1.5< Pyrochlore Ceramics(Wiley-v C H verlag Gmbh, 2003) Kayed, TS; Mergen, ABi1.5ZnSb1.5O7 pyrochlore samples were prepared by solid state reaction method. They were examined by x-ray diffraction and scanning electron microscopy. Single phase, belongs to the cubic pyrochlore structure, with a lattice parameter of 10.442 Angstrom and grain size that varies from 16 to 20 mum was obtained. The electrical properties were measured at different temperatures in the range 15-330 K under different applied magnetic fields up 1.4 T. In our measurements for Hall coefficient, Hall resistivity, and mobility; we noticed an anomalous behavior at two temperatures (around 250 and 310 K) which was supported by the I-V measurements (double transition of the slope of I-V characteristics (beta) at the same temperatures). This was discussed in terms of polarization phenomenon and mixed ionic-electronic conduction. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Article Citation - WoS: 7Citation - Scopus: 9Properties of Boron Doped Ti-Ba Superconductors(Pergamon-elsevier Science Ltd, 2003) Kayed, TSThe effects of boron doping on the formation and properties of the Tl-based superconductors have been studied. Up to 10 wt.% boron has been added to the oxides having the nominal composition, Tl1.8Ba2Ca2.2Cu3Ox, by the usual solid-state reaction method. Boron additions in the range 0.8-1.0% increase the fraction of the Tl-2223 phase and significantly improve the critical temperature of the samples. Higher amounts of boron additions eliminate the Tl-2223 phase, reduce the fraction of Tl-2212 phase and cause separate non-superconducting phases to be formed. The formation of non-superconducting phases does not allow us to obtain pure Tl-2212 phase. (C) 2002 Elsevier Science Ltd. All rights reserved.Conference Object Citation - WoS: 10Production of Anorthite From Kaolinite and Caco3 Via Colemanite(Trans Tech Publications Ltd, 2004) Mergen, A; Kayed, TS; Bilen, M; Qasrawi, AF; Gürü, MBoron oxide has been found to be useful flux for the preparation of dense anorthite ceramics (CaO.Al2O3.2SiO(2)). Inexpensive starting materials of kaolinite, calcium carbonate and silica were used for anorthite ceramic production. Colemanite (2CaO.3B(2)O(3).5H(2)O) was added into the mixtures and the effects of colemanite upon the transformation towards anorthite and on the densification were investigated between 900-1400 degreesC. Single phase anorthite ceramic formed at lower temperatures in boron containing mixtures. Boron containing powder compacts were sintered above 90% theoretical density at 1350 degreesC.Article Citation - WoS: 5Citation - Scopus: 5Electrical Behavior of Pb1.83mg0.29< Pyrochlore Ceramics(Elsevier Science Bv, 2004) Mergen, A; Kayed, TSPb1.83Mg0.29Nb1.71O6.39 pyrochlore was produced via a simple partial oxalate method. It was examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Single phase, belonging to the cubic pyrochlore structure, with a lattice parameter of a = 10.60125 +/- 0.001 Angstrom and grain size that varies from 5 to 10 mum was obtained. The electrical properties were measured at different temperatures in the range 15-320 K without and with applied magnetic field of 1.4 T. Current-voltage characteristics data were fitted to a power law expression V=I-beta(T) in which the exponential parameter beta takes values around 1 at all temperatures except at 300 K. Resistance starts from 3.3 x 10(10) Omega at 15 K and increases gradually to 4.8 x 10(10) Omega at 240 K. It drops to approximately 1.2 x 10(10) Omega at 300 K, after which it increases again to around 1.6 x 10(10) Omega at 320 K. (C) 2004 Elsevier B.V. All rights reserved.Article Citation - WoS: 6Citation - Scopus: 5Magnetoresistance, Voltage-Current Characteristics, and Hall Effect Measurements of Bulk Mgb2 Superconductors(Wiley-v C H verlag Gmbh, 2004) Kayed, TSBulk MgB2 samples were prepared from the commercially available powder (Alfa-Aesar). One of the samples was used in measuring the transport properties by the DC four-probe technique while the other was used in measuring Hall effect using the van-der-Pauw configuration. From the transport measurements, we noticed that the R-T curves shift to lower temperatures under applied magnetic field without any observed enlargement of the transition width. T-c gradually decreases from 37 K at zero field to 32 K at B = 1.4 T. Our V-I data were found to obey a power law expression V proportional to I-beta(T,I- B). The change of beta with temperature and magnetic field was shown and discussed. R-H is positive under positive applied magnetic field. The 1/R-H linear dependency on T, usually observed in high temperature superconductors, could not be observed in our case. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Conference Object Citation - WoS: 9Citation - Scopus: 11Effect of Lithium Doping on the Properties of Tl-Based Superconductors(Iop Publishing Ltd, 2001) Kayed, TS; Özkan, H; Gasanly, NMThe effects of lithium doping on the formation and properties of the T1-based superconductors have been studied. Lithium atoms up to around 3 mol.% have been added to the oxides of nominal composition Tl1.8Ba2Ca2.2Cu3Ox, and the usual solid-state reaction method has been applied. Lithium additions in the range 0.23-0.29 mol.% increase the fraction of the Tl-2223 phase and significantly improve the critical temperature of the samples. Higher amounts of lithium additions diminish the Tl-2223 phase, reduce the fraction of the Tl-2212 phase, and cause separate non-superconducting phases to be formed.Article Citation - WoS: 2Citation - Scopus: 2Voltage-Current Characteristics of Bi-2223 Superconducting Tape Near Tc Under Γ Irradiation(Wiley-v C H verlag Gmbh, 2004) Kayed, TS; Ercan, IVoltage-current characteristics at four different applied magnetic fields (7, 20, 30, and 40 mT) of Bi2Sr2Ca2CU3Ox superconducting tape were measured in the temperature range from 100 to 115 K. They were also measured at zero magnetic field before and after gamma irradiations up to 10 MRad at different temperatures just below the critical temperature. The data were fitted to a power law expression V = I (beta(T)) in which the exponential parameter P under 20 mT field and after irradiation is found to fluctuate around three and then drops to unity near the critical temperature which may be interpreted as a sign of Kosterlitz-Thouless transition. The electrical properties of the tape were found to be very sensitive to gamma irradiation where most of the changes take place in low gamma doses.Article Citation - WoS: 11Citation - Scopus: 11Microstructural, thermal, and electrical properties of Bi1.7V0.3Sr2Ca2Ca3Ox glass-ceramic superconductor(Wiley-v C H verlag Gmbh, 2004) Kayed, TS; Calinli, N; Aksu, E; Koralay, H; Günen, A; Ercan, I; Cavdar, SA glass-ceramic Bi1.7V0.3Sr2Ca2Cu3Ox superconductor was prepared by the melt-quenching method. The compound was characterized by scanning electron microscopy, x-ray diffraction, differential thermal analysis, current-voltage characteristics, transport resistance measurements, and Hall effect measurements. Two main phases (BSCCO 2212 and 2223) were observed in the x-ray data and the values of the lattice parameters quite agree with the known values for 2212 and 2223 phases. The glass transition temperature was found to be 426 degreesC while the activation energy for crystallization of glass has been found to be E-a = 370.5 kJ / mol. This result indicates that the substitution of vanadium increased the activation energy for the BSCCO system. An offset T-c of 80 K was measured and the onset T-c was 100 K. The Hall resistivity rho(H) was found to be almost field-independent at the normal state. A negative Hall coefficient was observed and no sign reversal of rho(H) or RH could be noticed. The mobility and carrier density at different temperatures in the range 140-300 K under different applied magnetic fields up to 1.4 T were also measured and the results are discussed.Article Citation - WoS: 26Citation - Scopus: 26Fabrication and Some Physical Properties of Agin5s8< Thin Films(Elsevier Science Sa, 2004) Qasrawi, AF; Kayed, TS; Ercan, IAgIn5S8 thin films are deposited on glass substrates, kept at 300 K, by thermal evaporation of AgIn5S8 single crystals under the pressure of 10-5 Torr. The X-ray fluorescence analysis revealed that the films have a weight percentage of similar to11.5% Ag, 61.17% In, and 27.33% S which corresponds to 1:5:8 stoichiometric composition. X-ray analysis of the films reveals the polycrystalline nature of the films. The lattice parameter (a) of the films was calculated to be 10.784(5) Angstrom. The dark n-type electrical conductivity of the films was measured in the temperature range of 30-350 K. The conductivity data analysis shows that the thermionic emission of the charge carriers having activation energies of 147 and 224 meV in the temperature ranges of 130-230 and 240-350 K, respectively, are the dominant transport mechanism in the films. The variable range hopping transport mechanism is dominant below 130 K. The room temperature photocurrent-photon energy dependency predicts a band gap of 1.91 eV of the films. The illumination intensity-photocurrent dependency measured in the intensity range of 13-235 W cm(-2) reveals monomolecular recombination (linear) in the films and bimolecular recombination (sublinear) at the film surface corresponding to low and high applied illumination intensities, respectively. The time-dependant photocurrent measured at fixed illumination intensity reveals a response time of 0.85, 2.66 and 10.0 s in the time periods of 0-0.5, 0.5-1.0, and 1.0-10.0 s, respectively. (C) 2004 Elsevier B.V. All rights reserved.
