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    Influence of Sr/Nd partial replacement on fundamental properties of Bi-2223 superconducting system
    (Springer, 2021) Doğruer, Musa; Aksoy, Canan; Yıldırım, Gülden; Özturk, Özgür; Terzioğlu, Cabir
    This comprehensive work aims to examine the change in flux pinning mechanism, physical, mechanical, and structural characteristics of pure and Sr-site Nd-substituted Bi1.8Pb0.35Sr1.9?yNdyCa2.2Cu3Ox (Bi-2223) systems. The magnetoresistivity performances for all the samples are carried out by magnetotransport experiments in the existence of external magnetic field strength intervals 0–7 T. It is found that the increment of Nd/Sr substitution amount in bulk Bi-2223 system retrogrades the pinning capability of thermal flux motions for interlayer Josephson junction between the isolated grains. Similarly, the coupling probabilities of copper pairs and potential energy barriers are significantly diminished by increasing Nd impurity. This is in association with the enhancement of permanent structural problems in the crystal structure. Therefore, the excessive Nd inclusions improve the reattached linear/split pancake-like nature. In this regard, the best magnetic performance quantities are obtained for the pure sample. Besides, the SEM images show that the grain connectivity and surface morphology damage significantly with the Nd impurity. Additionally, the experimental microhardness findings conducted at various external loads (0.245–2.940 N) display that the Nd purity in the superconducting system degrades dramatically the key design mechanical features. Besides, we analyze the mechanical characteristic properties founded on the theoretical approaches with the proportional sample resistance, elastic/plastic deformation, and Hays–Kendall methods. The results obtained show that the Nd purity causes the indentation size effect behavior to decrease dramatically for all the samples. Furthermore, the findings of Hays–Kendall method are noticed to much more agree with the real hardness parameters. Thus, the Hays–Kendall model is the best methods to find the load-independent Vickers hardness values for the Sr-site Nd-substituted Bi1.8Pb0.35Sr1.9?yNdyCa2.2Cu3Ox (Bi-2223) systems. Moreover, in the dynamic microhardness measurements, the contact depth (hc), elastic modulus (Er), and load (Pmax) of all the samples are experimentally recorded for the first time. The results reveal that the mechanical properties depend strongly on the load and Nd impurity level.
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    Investigation on superconducting and magnetic levitation force behaviour of excess Mg doped-bulk MgB2 superconductors
    (Elsevier Sci Ltd, 2019) Güner, Sait Barış; Savaşkan, Burcu; Öztürk, Ufuk Kemal; Çelik, Şükrü; Aksoy, Canan; Karaboğa, Fırat
    A series bulk samples of MgB2 + x wt% of Mg (x = 0, 5, 10, 15, 20 and 30) were fabricated by solid state reaction method. The structural and electromagnetic properties of MgB2 samples were studied using X-ray diffraction (XRD), scanning electronic microscope (SEM), electrical resistivity (R-T), magnetic hysteresis (M-H), magnetic levitation (F-z) force and lateral force (F-x) measurements. The maximum repulsive and attractive force values of 15 wt% of excess magnesium MgB2 sample compared to the other samples imply that the intergranular connection between grains enhanced while pore and microcrack density decreased which brings an increase in the values of the radius of a shielding current loop (r) and the critical current density (J(c)). It was determined that to obtain the enhancement of the micro and macro structure properties, causing to the higher critical current density, and the maximum levitation and lateral force values, the optimum excess magnesium content was 15 wt % into sample. It is thought that an addition of 10-15% excess magnesium can be tried for spark plasma or other methods -as a further research- and the results showed a potential to guide the researchers to study on the material-fabrication and the magnetic bearing system.
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    Optimized superconducting MgB2 joint made by IMD technique
    (IOP Publishing Ltd, 2023) Avcı, Doğan; Yetiş, Hakan; Gajda, Daniel; Babij, Michal; Tran, Lan Maria; Karaboğa, Fırat; Aksoy, Canan; Zaleski, Andrzej; Belenli, İbrahim
    A novel type of superconducting joining technique has been introduced to join unreacted internal Mg diffusion (IMD) single-core MgB2 wires. Our method is based on fabricating a small diameter joint mould obtained by deforming an Nb/Cu composite tube with a longitudinal semi-cylindrical Mg and B core into a thick round wire. The small diameter of the joint provided advantages such as rapid cooling, low resistance, and the unique core design inside the joint ensured a uniform MgB2 phase formation. Scanning electron microscope analysis revealed that the IMD MgB2 wires had excellent contact with the superconducting MgB2 bulk material inside the joint. The joint resistance, calculated from the decay of the trapped magnetic field over time, is a quite low value of 6.44 × 10−16 Ω at 20 K. The transport critical current (Ic) of the joint is 62 A at 20 K under a self-magnetic field, and the n-value of the joint is 66 at 20 K under 1.5 T. The results showed that the Ic of our joint can be determined precisely, regardless of whether the magnetic field is applied from low to high or from high to low value during I–V measurements.
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    Transport and structural properties of MgB2/Fe wires produced by redesigning internal Mg diffusion process
    (IOP Publishing Ltd, 2022) Yetiş, Hakan; Avcl, Do?an; Karabo?a, Flrat; Aksoy, Canan; Gajda, Daniel; Martínez, Elena; Tanylldlzl, Fatih Mehmet
    We report transport, electromechanical, and structural properties of single core MgB2/Fe wire produced using a new fabrication method, called designed internal Mg diffusion (IMD) process, which relies on the use of non-stoichiometric Mg + B pellets with excess Mg in place of a central Mg rod used in the standard IMD method. Structural analysis revealed the successful formation of a porous MgB2 structure in the center and a dense circular MgB2 layer surrounding this structure in the designed-IMD wire. Fast transport I-V measurements showed that the designed IMD method increased engineering critical current density (J e) up to twice that of the IMD wires in self-field. The central porous MgB2 structure shared the applied current and indirectly behaved as an internal stabilizer against quench damage at high applied currents. © 2022 IOP Publishing Ltd.