Batur, Kübra Nur; Duman, Şeyda; Çakir, Bakiye; Başoğlu, Mehmet; Aydiner, Alev

This study investigates hollow single-crystal top-seeded melt growth (TSMG) YBa2Cu3O7−x (YBCO or Y123) samples welded with Ag-added TSMG YBCO solder materials produced using NdBCO/YBCO/MgO thin-film seeds. Three main samples and one solder material are produced by the TSMG method. In order to increase the dimensions of the bulk YBCO superconductor, two slices of the solder material and the main samples are stacked on top of each other with the c-axis parallel and welded at 1030 °C. X-ray diffraction patterns, polarized optical photographs, and SEM micrographs are taken to determine the structural properties of the samples. A preferential orientation in the c-axis is observed with a good connection. Low-temperature resistance and magnetization measurements are made for the specimens taken from the welding region. A sharp superconducting transition occurs at 0 T around 93 K for welding regions of W-ab and W-bc specimens. The critical current densities (Jc) are high as in the main samples. At the same time, the Jc values at 77 K and 0 T are found as 1.54 × 104, 1.98 × 104, 2.21 × 104, 2.31 × 104, and 2.36 × 104A cm−2 for the W-a, W-ab, W-b, W-bc, and W-c specimens, respectively. The single-grain feature is not impaired; thus, the absence of additional grain boundaries facilitates the current passage.

Başoğlu, Mehmet; Çakir, Bakiye; Duman, Şeyda; Aydiner, Alev

The Y3Ba5Cu8O18 (Y358) superconductors were produced using the Melt-Powder-Melt-Growth (MPMG) method. In the crystal growth process, Y2O3 powder was used as a substrate in both powder and tablet form. The first sample was produced without using any buffer layer, the second sample was produced with a powdered Y2O3 buffer layer, and the third sample was produced with a tablet-form Y2O3 buffer layer. The effect of the Y2O3 substrate on the structural and physical properties of the Y358 superconductor samples was investigated. Superconducting phases were observed in all samples of Y358 through XRD measurements, confirming their presence. Samples fabricated using the powder and tablet forms of the Y2O3 substrate had a better microstructure than the sample fabricated without a Y2O3 substrate. The highest critical current density (J c) value was obtained at 77 K for the Y358 sample produced with a Y2O3 powder substrate, and the J c value was calculated as 1.2 × 104 A cm–2 according to the Bean model.

Duman, Şeyda; Çakır, Bakiye; Başoğlu, Mehmet; Küçükömeroğlu, Tayfur; Aydıner, Alev

In this study, it is aimed to investigate the effects of production methods on the physical properties of 20% Ag2O and different ratios of Y211 added YBCO samples. In this context, the samples with Y123 + x % (x = 20, 25, 30) Y211 + 20%Ag2O compositions were fabricated by MPMG and TSMG methods in two groups to join YBCO main samples. XRD measurements were performed to determine the characteristic peaks. Trapped magnetic fields and vertical levitation forces between the bulk samples and a permanent magnet were measured using a computer-controlled system in ZFC at 77 K. From the XRD measurements, it was found that MPMG YBCO samples had a dominant superconducting structure and partially showed orientation peaks in the c-axis direction, while TSMG YBCO samples were single-crystal samples oriented along the c-axis. From the trapped magnetic field measurement results, the trapped magnetic field value of the Y123 + 25%Y211 + 20%Ag2O (TAg25) sample prepared by the TSMG method was higher than that of the other samples. Among the levitation force measurement results, the maximum repulsive force values of TAg25 and TAg30 (Y123 + 30%Y211 + 20%Ag2O) samples are the highest. At the same time, the hysteresis widths of these samples are also the highest, which proves that their flux-pinning potential is higher than that of the other samples.

Öztürk, Ali; Düzgün, İbrahim; Başoğlu, Mehmet; Çelebi, Selahattin

Partial Re (rare earth elements: Lu, Yb and Dy) substituted YBaCuO (123) superconductors synthesized by solid-state reaction (SSR) procedure have been investigated via x-ray diffraction, scanning electron microscopy, a.c. magnetic susceptibility, and d.c. magnetization, and calculations. The measurements of a.c. magnetic susceptibility have been carried out at constant a.c. field amplitude and constant frequency for the samples studied. The temperature dependence of intergranular critical current density (Jcm) has been estimated from the a.c. magnetic susceptibility data. The d.c. magnetization measurements were performed at the temperatures of 5 K, 20 K, and 77 K separately. The variation of critical current density (Jc) with magnetic field (μ0H) has been evaluated from the d.c. magnetization data by using upper and lower branch of the major hysteresis curve. Lu substituted Y0.5Lu0.5BCO (123) sample shows higher critical current density than Yb and Dy substituted samples at low-temperature (lower than 77 K) regions.