Browsing by Author "Altintas S.P."

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Effect of Gd addition on the activation energies of Bi-2223 superconductor
(2011-02-01) Erdem M.; Özturk O.; Yucel E.; Altintas S.P.; Varilci A.; Terziolu C.; Belenli I.
We have investigated the effect of addition of Gd in Bi 1.8Pb0.35Sr1.9Ca2.1Cu 3GdxOy superconductor with x=0, 0.1, 0.2, 0.3, 0.4 and 0.5. The samples were prepared using the standard solid-state reaction method. The activation energies, irreversibility fields (Hirr), upper critical fields (Hc2) and coherence lengths at 0 K (ξ(0)) were calculated from the resistivity versus temperature (RT) curves under DC magnetic fields up to 7 T. The superconducting transition temperature, Tc, and activation energy, U0, were found to decrease with increase in Gd concentration and with increase in applied magnetic field. The offset transition temperature of the pure (Gd00) sample without applied magnetic field is 108 K, whereas for Gd05 sample, the offset transition temperature drops to 5 K with 7 T applied magnetic field. The activation energy of the Gd00 sample without applied magnetic field is 34,980 K, and for Gd05 sample with 7 T applied field it is 98 K. Hirr and Hc2 values also decrease with increase in Gd addition. The possible reasons for the observed degradation in microstructural and superconducting properties due to Gd addition were discussed. © 2010 Elsevier B.V. All rights reserved.
Enhancing magnetoresistive features of iron-substituted La0·8Sr0·2MnO3 ceramic manganites
(2022-10-15) Karadavut S.; Denbri F.; Terzioglu C.; Ozturk O.; Altintas S.P.
The influence of iron content on the structural, microstructural, magnetic, and electrical-transport features of the ceramic perovskite manganites of the form La0·8Sr0·2Mn1-xFexO3 (x=0.0, 0.05, 0.1, and 0.2) was investigated. A single phase of rhombohedral-distorted structure with an R 3‾ c space group was confirmed for all synthesized ceramic samples. The microstructures of the manganite ceramics were improved by iron substitution. The magnetic and electrical-transport studies show that samples with x=0.0, 0.05, and 0.1 display phase transitions from ferromagnetic to paramagnetic state and metallic to insulating one with increasing temperature. The phase transition temperatures, i.e., Curie temperature, TC, and the resistance transition temperature TMI, are found to be lowered with the increase in the Fe concentration. The temperature coefficient of resistance (TCR) value for the x=0.0 sample is obtained ∼2.16% K−1 and slightly decreased to ∼1.55% K−1 with a 5% Fe substituted sample. As x rise to 0.1, we obtain the maximum TCR value of ∼8.23% K−1. At the same time, the maximum magnetoresistance is obtained as 48.1% at 233 K for the x=0.1 sample. One of the most important findings in this paper is that Fe substitution is very useful for improving magneto-electrical features of the La0·8Sr0·2MnO3 ceramics. Moreover, to better understand the temperature dependence of the electrical resistivity data, the experimental findings were fitted to the equations of several models.