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  • Küçük Resim
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    The effect of cooling rates on properties of Bi1.7Pb0.35Sr1.9Ca2.1Cu3Oy superconductors produced by solid-state reaction method
    (Elsevier Science Bv, 2007) Öztürk, Özgür; Yeğen, Dinçer; Yılmazlar, Mustafa; Varilci, A.; Terzioğlu, Çağlar
    We have investigated the effect of the cooling rates in the Bi-2223 superconducting samples prepared by standard solid-state reaction method using electrical resistivity, transport critical current density, and XRD (X-ray diffraction) measurements. We estimated the transition temperature values from the DC resistivity measurements. We observed that transition temperature, T-c, and transport critical current density, J(c)(trans), depend on the cooling rates of the samples. They both increase with increasing cooling rates. We estimated the peak temperature, T-P, from our previous ac susceptibility measurements. The pinning force density increased with increasing the cooling rate. XRD patterns are used to calculate lattice parameter c and obtain information about Bi-2223 phase ratio. (c) 2006 Elsevier B.V. All rights reserved.
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    Experimental and theoretical approaches on mechanical evaluation of Y123 system by Lu addition
    (Springer, 2013) Turkoz, M. B.; Nezir, S.; Ozturk, O.; Asikuzun, E.; Yildirim, G.; Terzioglu, C.; Varilci, A.
    This work is the continuation of a systematic study on the characterization of the Lu-added Y123 bulk superconducting materials prepared by the nitrate compounds and derivatives at 970 degrees C for 20 h. In this part, the effect of Lu inclusions on the physical and mechanical properties of the Y123 superconductors is examined with the aid of microhardness measurements performed at various applied loads in the range of 0.245-2.940 N. The microhardness measurement results allow us to determine the important mechanical characteristics such as Vickers microhardness, elastic (Young's) modulus, yield strength and fracture toughness values being responsible for the potential industrial applications. It is found that all the properties given above are strongly dependent upon the Lu concentration in the Y123 matrix. Especially, Vickers microhardness (H-nu) values of the samples studied in this work are found to suppressed considerably with the enhancement of the Lu addition in the system due to the degradation in the connectivity between superconducting grains. Moreover, the H-nu values of the pure Y123 sample are observed to increase with increasing the applied load whereas those of the Lu-doped superconducting materials are obtained to decrease with the load. In other words, the pure sample exhibits the reverse indentation size effect (RISE) behavior while the others obey the indentation size effect (ISE) feature, confirming the degradation in the mechanical properties with the Lu inclusions in the Y123 matrix. In addition, the microhardness measurement results are estimated using the 5 different models such as Meyer's law, proportional sample resistance model, elastic/plastic deformation model, Hays-Kendall (HK) approach and indentation-induced cracking (IIC) model. According to the results obtained from the simulations, of the mechanical analysis models, the Hays-Kendall (HK) approach is determined as the most successful model for the description of the mechanical properties of the Lu-doped superconducting materials (exhibiting the ISE behavior) where both the both the reversible (elastic) and irreversible (plastic) deformations are produced. On the other hand, the IIC model is found to be superior to other approaches for the pure sample (presenting the RISE feature) where the irreversible deformation becomes more and more dominant compared to the reversible deformation.