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    An electron paramagnetic resonance study on irradiated triphenylphosphinselenid single crystal
    (TAYLOR & FRANCIS LTD, 2014) Aras, Erdal; Karatas, Ozgul; Meric, Yasemin; Abbass, Hind Kh; Birey, Mehmet; Kilic, Ahmet
    The single crystals of triphenylphosphinselenid [C18H15PSe] were produced by slow evaporation of concentrated ethyl acetate solutions. These single crystals were exposed to Co-60 gamma (gamma) rays with a dose speed of 0.980kGy/h at the room temperature for 72h. The free radical over the sample was observed using electron paramagnetic resonance (EPR)-X band spectrometer. The EPR spectra were recorded between 120 and 400K. Furthermore, the sample irradiated was rotated in steps of 10 degrees and analyzed for different orientations of the crystal in the magnetic field. Only one radical structure was determined on the molecule. The hyperfine constants of the sample were found to be anisotropic. The average values of these constants and value of g were calculated as following: g=2.007656, a(Se)=37.47G, a(P)=27.44G, a(Ha)=17.28G, and a(Hb)=18.16G.
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    Effects of Nb2O5 addition on superconducting properties of BSCCO
    (PERGAMON-ELSEVIER SCIENCE LTD, 2007) Ghazanfari, Nader; Kilic, Ahmet; Gencer, Ali; Oezkan, Huesnue
    The effects of Nb2O5 addition on (Bi, Pb)(2)Sr2Ca2Cu3O10 superconducting polycrystalline samples prepared by conventional solid state reaction method in bulk forms have been investigated. Samples were prepared and then characterized by X-ray diffraction, SEM microstructural analysis, DC electrical, and AC susceptibility measurements. X-ray diffraction analysis shows that both (Bi, Pb)-2223 and Bi-2212 phases coexist in the studied samples. I-V characterization and AC susceptibility measurements reveal that Nb addition increases critical current density. The enhancement of the J(c) may be caused by improvement of the grain connectivity with Nb additions. (c) 2007 Elsevier Ltd. All rights reserved.
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    Enhancement in the high-T-c phase of BSCCO superconductors by Nb addition
    (IOP PUBLISHING LTD, 2007) Sozeri, Huseyin; Ghazanfari, Nader; Ozkan, Husnu; Kilic, Ahmet
    Pure and Nb2O5 added Bi1.6Pb0.4Nbx Sr2Ca2Cu3O delta superconductors ( x varies up to 0.30) were synthesized by the solid state reaction method. Structural and superconducting properties of the samples were investigated. The fraction of the high-T-c phase ( 2223) increases with Nb addition up to x = 0.10, for which a nearly single 2223 phase was obtained. The critical temperature of the samples increases from 96 to 104 K with doping up to x = 0.20 and a further increase in Nb decreases the Tc sharply. Similarly, there is a considerable enhancement in the critical current density ( jc) of the samples in the same doping range. Both AC susceptibility and transport measurements showed that the optimum Nb concentration is x = 0.20. The out- of- phase component of the AC susceptibility measurements showed that inter- grain coupling was enhanced up to the same doping level. Nb additions above x = 0.30 decrease the fraction of the high- Tc phase and degrade the superconducting properties. Present measurements indicate that x = 0.20 is the optimum Nb concentration in the BSCCO superconductor to enhance phase purity, inter- grain coupling and superconducting parameters ( Tc and j(c)).
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    EPR study of gamma-irradiated cholesteryl methyl carbonate
    (ELSEVIER SCIENCE BV, 2014) Aras, Erdal; Islek, Yasemin; Karatas, Ozgul; Abbass, Hind Kh; Birey, Mehmet; Kilic, Ahmet
    The electron paramagnetic resonance (EPR) of gamma-irradiated single crystals of cholesteryl methyl carbonate (C29H48O3) has been studied for different orientations of the crystals in a magnetic field. EPR spectra of cholesteryl methyl carbonate (C29H48O3 irradiated by Co-60-gamma were recorded between 125 K and 300 K for different orientations of the crystal in the magnetic field. The spectra were found to be temperature independent. In C29H48O3 single crystal,. the radiation damage centers caused by a Co-60-gamma source were determined as CH3CH2CH radical. For CH3CH2CH radical, a value of spectroscopic splitting factor g was calculated and experimentally results were supported by simulation program (WinEPR). (C) 2014 Elsevier B.V. All rights reserved.
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    EPR STUDY OF GAMMA-IRRADIATED METHYL-4-NITROBENZOATE SINGLE CRYSTALS
    (KAUNAS UNIV TECHNOLOGY PRESS, 2012) Aras, Erdal; Kilic, Ahmet; Cicek, Ekrem; Meric, Yasemin; Karatas, Ozgul; Grigonis, A
    Single crystals of methyl-4-nitrobenzoate C8H7NO4 have been observed and analyzed for different orientations of the crystal in the magnetic field, after being damaged at 300K by Co-60 gamma-irradiation by using Electron Paramagnetic Resonance (EPR) technique. The EPR spectrums of crystals have been taken with X-band EPR spectrometer at 150K temperature range. In C8H7NO4 single crystal, the radiation damage centers were determined to radical. For this free radical, anisotropic hyperfine splitting constants (A) and g-factors were calculated.