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Öğe The effect of excess Y2O3 addition on the mechanical properties of melt-processed YBCO superconductor(Springer, 2010) Aydıner, Alev; Başoğlu, Mehmet; Yanmaz, Ekrem; Çakır, BakiyeIn this study, two kinds of melt-processed YBCO samples with Y2O3 addition were fabricated and their microstructures were defined by XRD analysis and polarized light optical microscopy. The mechanical properties of these compounds have been investigated by measuring the Vickers hardness. The superconducting transition temperature was determined by inductive measurements for oxygenated and non-oxygenated samples. The compacted powders were located on a crucible with a buffer layer of Y2O3 and a crucible with Y2O3 powder freely poured to avoid liquid to spread on the furnace plate. It was found that the sample located on crucible with freely poured Y2O3 powder has shown almost single crystal and indicated a very sharp transition curve.Öğe The Effect of Y2O3 on AC susceptibility measurements of MPMG YBCO superconductor(Springer, 2013) Çakır, Bakiye; Aydıner, Alev; Başoğlu, Mehmet; Yanmaz, EkremIn this study, two kinds of melt-powder-melt-growth (MPMG) YBCO sample grown on a buffer layer of Y2O3 addition were fabricated. The compacted powders were located on a crucible with Y2O3 powder freely poured and a buffer layer of pressed Y2O3. AC susceptibility measurements of the samples as a function of temperature was reported for several different AC magnetic-field amplitudes (H (ac) ) in the presence of static bias magnetic field (H (b) ) directed along H (ac) . The loss peaks are found to shift towards lower temperatures as the AC field strength is increased. The frequency effect on the AC susceptibility was also measured. As the frequency increases, the peak temperature shifts to higher temperature. This effect can be interpreted in terms of flux creep.Öğe Magnetic Properties of YBCO Single-Crystal Grown on Y2O3 Layer by a Cold Top-Seeding Method(Springer, 2012) Aydıner, Alev; Çakır, Bakiye; Başoğlu, Mehmet; Seki, Hironori; Wongsatanawarid, Atikorn; Murakami, Masato; Yanmaz, EkremIn this work, single-crystal samples 20 mm in diameter were grown by a cold top-seeding method. In order to study the effect of an Y2O3 buffer layer, a compacted precursor was located in a crucible on a buffer layer of freely poured Y2O3 powder. The YBCO bulk samples were carefully prepared in the same chemical composition. In order to examine the homogeneity of the samples, rectangular specimens were cut from a sample. The structural orientation of the specimens was measured by a X-ray diffractrometer (XRD). The microstructure was observed with a Scanning Electron Microscope (SEM). The magnetic properties were measured using a Vibrating Sample Magnetometer (VSM) at 77 K with the applied magnetic field parallel to the c-axis. As a result only (00l) peaks were observed in X-ray diffraction data, indicating that all specimens are highly oriented with the c-axis perpendicular to the top surface. Also the cut samples exhibited very fine Y211 inclusion distributed in the bulk sample observed in SEM micrographs. The critical current density J (c) (A/cm(2)) has been estimated by the extended Bean model. The maximum value of the critical current density at 77 K is 5.2x10(4) A/cm(2) in a self-field. The trapped magnetic field measurements of the samples were performed by using Hall probe scanning device with static field of 0.5 T at 77 K. The single-domain sample exhibits a trapped field of 1140 G at 77 K.Öğe The effect of Y₂O₃ buffer layer on the magnetic properties of melt-processed YBCO superconductor(Springer New York LLC, 2011) Aydıner, Alev; Çakır, Bakiye; Seki, Hironori; Başoğlu, Mehmet; Wongsatanawarid, Atikorn; Murakami, Masato; Yanmaz, EkremIn this study, two kinds of melt-processed YBCO samples (Y₁₀₅₀₋₁ andY₁₀₅₀₋₂) grown on a buffer layer of Y₂O₃ addition were fabricated. The compacted powders were located on a crucible with Y₂O₃ powder freely poured and a buffer layer of pressed Y₂O₃ to avoid liquid to spread on the furnace plate. The superconducting transition temperature was determined by a standard four-point method at temperatures between 40 and 100 K. The transition temperatures of Y₁₀₅₀₋₁ and Y₁₀₅₀₋₂ were found to be 91.6 and 92.9 K at zero magnetic fields, respectively. The magnetization measurements were performed using a vibrating sample magnetometer (VSM) on the same system at 5, 40, and 77 K. The critical current densities for Y₁₀₅₀₋₁ and Y₁₀₅₀₋₂ samples were determined to be 6.5×10 3 and 5.6×10 3 A/cm 2 at 77 K in zero magnetic fields, respectively. The trapped magnetic field measurements of the samples were performed by using a Hall probe scanning device and a Fe-Nd-B permanent magnet at 77 K. It was found that the trapped magnetic field of the Y₁₀₅₀₋₁ sample is higher than that of the Y₁₀₅₀₋₂ sample.
