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    The effect of growth temperature on the irreversibility line of MPMG YBCO bulk with Y2O3 layer
    (Elsevier SCI LTD, 2017) Kurnaz, Sedat; Çakır, Bakiye; Aydıner, Alev
    In this study, three kinds of YBCO samples which are named Y1040, Y1050 and Y1060 were fabricated by Melt-Powder-Melt-Growth (MPMG) method without a seed crystal. Samples seem to be single crystal. The compacted powders were located on a crucible with a buffer layer of Y2O3 to avoid liquid to spread on the furnace plate and also to support crystal growth. YBCO samples were investigated by magnetoresistivity (rho-T) and magnetization (M-T) measurements in dc magnetic fields (parallel to c-axis) up to 5 T. Irreversibility fields (Him) and upper critical fields (11,2) were obtained using 10% and 90% criteria of the normal state resistivity value from rho-T curves. M-T measurements were carried out using the zero field cooling (ZFC) and field cooling (FC) processes to get irreversible temperature (T-irr). Fitting of the irreversibility line results to giant flux creep and vortex glass models were discussed. The results were found to be consistent with the results of the samples fabricated using a seed crystal. At the fabrication of MPMG YBCO, optimized temperature for crystal growth was determined to be around 1050-1060 degrees C. (C) 2017 Elsevier Ltd. All rights reserved.
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    The effect of using different y2o3 layers on the activation energy and ırreversibility line of mpmg ybco bulk at 1050 degrees c growth temperature
    (Springer, 2018) Kurnaz, Sedat; Çakır, Bakiye; Aydıner, Alev
    In this study, three kinds of YBCO samples which are named Y1, Y2 and Y3 were fabricated by a melt–powder–melt–growth (MPMG) method. The Y1 sample was placed into a platinum (Pt) crucible without Y2O3, the Y2 sample was located on a Al2O3 crucible with a freely poured Y2O3 powder and the Y3 sample was located on a Al2O3 crucible with a 1-mm-thick buffer layer of Y2O3. YBCO samples were investigated by magnetoresistivity (?–T ) measurements in dc magnetic fields (parallel to the c-axis) up to 5 T. The effect of the Y2O3 layer on the activation energy and irreversible flux of the samples was studied. The activation energies (U ) were determined using the Arrhenius activation energy law from ?–T . The power law relationship for U with H ?? was investigated. ? was calculated to find out which defects were dominant in the samples. Irreversibility fields (Hirr) and upper critical fields (Hc2) were obtained using 10 and 90% criteria of the normal-state resistivity value from ?–T curves. Irreversibility lines (ILs) were estimated from the equation Hirr ? (1?Tirr(H )/Tirr(0))n. The fitting results to giant flux creep and vortex glass models were discussed