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Bulk ngB2 superconductor production by excess Mg and hot press methods and their properties
(2017) Yanmaz, Ekrem; Cingi, Didem Odabaşı; Alcan, Pelin; Saraçoğlu, İlkay; Berrio, Claudia Castillo; Alkan, Ümit; Ülgen, Asaf Tolga
Four different nominal compositions MgB, MgB, MgB and MgB were produced by excess Mg method and hot press. These superconducting samples were compared in terms of structural, electric and magnetic properties. The superconducting phase was determined by XRD analysis, which indicated the formation of MgB structure as a main matrix with some amount of nonsuperconducting phases, such as metallic Mg and minor amount of MgO. The electric properties of the samples were characterized by low temperature resistivity measurements under different magnetic fields 0.5, 1.0, 3.0 T. The results showed that the superconducting Tc,onset and Tc,offset transition temperatures moved to lower values. These results indicate that excess Mg method improves the superconducting and magnetic properties of MgB, as well as enhanced the rigidity and ductility of the samples. Experimental results showed the advantages of the proposed methods, established the most suitable transition temperature of the samples, as well as the decline from the superconducting to normal state
Change in transition balance between durable tetragonal phase and stress-induced phase of cobalt surface-layered in Bi-2212 materials by semi-empirical mechanical models
(IOP Publishing Ltd, 2023) Erdem, Ümit; Yıldırım, Gürcan; Türköz, Mustafa Burak; Ülgen, Asaf Tolga; Mercan, Ali
This study has indicated the positive effect of sintering temperature on the mechanical durability, strength, critical stress, deformation degrees, durable tetragonal phase, failure and fracture by fatigue, and mechanical characteristic behavior to the applied test loads for the Co surface-layered Bi-2212 ceramic materials produced by the standard solid-state reaction method. The sintering mechanism has been used as the driving force for the penetration of cobalt ions in the Bi-2212 ceramic matrix. The microindentation hardness test measurements have been performed at the load intervals 0.245 N-2.940 N. The experimental findings have also been examined by the six different semi-empirical mechanical and indentation-induced cracking models. It has been found that all the mechanical performance parameters are improved considerably with increasing the diffusion sintering temperature up to 650 degrees C. On this basis, the Co surface-layered Bi-2212 sample produced at the sintering temperature of 650 degrees C has been observed to improve dramatically the mechanical durability and resistance to the applied test loads as a consequence of the formation of new force barrier regions, surface residual compressive stress regions, and slip systems in the Bi-2212 ceramic system. Similarly, the optimum sintering temperature has extensively enhanced the elastic recovery mechanism, critical stress values, and deformation degree levels, stored internal strain, and crack surface energy through the Bi-2212 ceramic materials. Accordingly, it has been noted that the best sample produced at 650 degrees C is more hardly broken than the other ceramics. Namely, the optimum sintering temperature has decreased the sensitivity to the applied test loads as a result of delaying the beginning of the plateau limit regions. On the other hand, all the mechanism has been found to reverse completely depending on the excess sintering temperature. Lastly, the indentation-induced cracking model has been found to exhibit the closest results to the original Vickers microhardness parameters in the plateau limit regions.
Contribution of vanadium particles to thermal movement of correlated two-dimensional pancake Abrikosov vortices in Bi-2223 superconducting system
(Elsevier, 2023) Ülgen, Asaf Tolga; Erdem, Ümit; Yıldırım, Gürcan; Türköz, Mustafa Burak; Turgay, Tahsin
This article breaks new ground in understanding of variation in the magnetic strength performance, flux pinning and energy dissipation mechanism of polycrystalline bulk Bi1.8Sr2.0Ca2.2Cu3.0Oy (Bi-2223) superconducting materials added with the different vanadium concentration level (0.0 <= x <= 0.30) under the magnetic field strengths applied up to 5 T for the first time. We provide the sophisticated and phenomenological discussions on the magnetoresistivity measurement results in three main sections along the paper. All the findings show that the increase of both the vanadium concentration in the crystal structure and external magnetic field strength damages significantly the magnetic strength performance, vortex dynamics, flux pinning ability and vortex lattice elasticity of bulk Bi-2223 superconducting ceramics. The vanadium addition promotes thermally the movement of correlated two-dimensional (2D) pancake Abrikosov vortices between the in-plane Cu-O-2 layers in the valance band, vortex lattice elasticity, vortex dynamics, distance for interlayer Josephson couplings and flux pinning centers and the theoretical computations confirm the remarkable degradation in the formation of super-electrons in the Bi-2223 crystal system. Thus, the vanadium addition is anticipated to be one of the best selectable materials to examine the differentiation in the thermal movement of correlated 2D Pancake Abrikosov vortices in the bulk Bi-2223 superconducting system. (c) 2022 The Author(s). Published by Elsevier Espana, S.L.U. on behalf of SECV. This is anopen access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/ by-nc-nd/4.0/).
Degradation in fundamental characteristic features of Bi-2212 superconducting ceramic material with Sr/Ti partial substitution
(Springer, 2019) Ülgen, Asaf Tolga; Yıldırım, Gürcan
The present work investigates the vital differentiations in some basic characteristic properties including the crystallinity quality, flux pinning mechanism, superconducting, dc electrical features, grain boundary coupling problems and strength of connection between the superconducting grains in the poly-crystallized Bi2.1Sr2.0-xTixCa1.1Cu2.0Oy cuprate ceramic materials with the partial aliovalent substitution of Sr2+ impurities for the Ti4+ foreign additives in the crystal system. All the materials are prepared by the standard solid-state reaction method, and the characterization of samples produced is thoroughly performed by the typical experimental measurements such as dc electrical resistivity over the temperature, critical current density and powder X-ray diffraction investigations. It is obvious that all characteristic properties tend to diminish constantly with the augmentation of the aliovalent Sr/Ti partial replacement level, and in case of x=0.10 they reach the global minimum values. To illustrate, the low Bi-2212 superconducting phase diverges from the stabilization because of new induced permanent crystal structure (crystallinity) problems such as the voids, porosity, defects, texturing, cracks, grain boundary coupling problems, grain alignment distributions, stress raisers, omnipresent flaws and crack initiation sites in the crystal system. Besides, the presence of Ti impurities leads to the formation of new impurity phases related to very low superconducting and characteristic TiO2 phase, being favored by either the decrement of c lattice cell parameter or increment of a-axis length. The similar findings are observed in the temperature dependent electrical resistivity measurements. Namely, the electrical resistivities at the normal state are found to increase dramatically from about 74.75-180.47 mcm whereas the offset and onset critical temperature values are recorded to diminish from 82.11K (for the pure sample) to 50.52K (for the sample prepared with x=0.10 substitution level) and 84.03-75.14K, respectively, with the enhancement in the substitution level. Likewise, the Sr/Ti partial replacement affects negatively not only the thermal fluxon motions of correlated two-dimensional pancake vortices but also the ability and strength of vortex lattice period, elasticity, effective and active energy barriers for the flux pinning centers in the Bi-2212 superconducting crystal lattice. In this respect, the Sr/Ti partial substitution mechanism is ploughed to improve the fundamental characteristic features.
A detailed research for determination of Bi/Ga partial substitution effect in Bi-2212 superconducting matrix on crucial characteristic features
(Elsevier Science Sa, 2019) Güner, Sait Barış; Zalaoğlu, Yusuf; Turğay, Tahsin; Özyurt, Ömer; Ülgen, Asaf Tolga; Doğruer, Musa; Yıldırım, Gürcan
This multidisciplinary study paves way to investigate the crucial of fundamental characteristic properties including the bulk density, electrical, superconducting, flux pinning mechanism, crystal structure quality and strength quality of interaction between the superconducting grains in the Bi(2.1)Sr(2.0)Ca(1.1)Cu(2.0)Oy (Bi-2212) superconducting materials with the partial replacement of gallium foreign impurity by bismuth nanoparticles in the crystal structure. Characterizations of polycrystalline ceramic materials prepared by standard ceramic route in the atmospheric air are performed by means of conventional experimental measurement methods such as powder X-ray diffraction, Archimedes water displacement, dc electrical resistivity versus temperature and critical current density examinations. All the bulk Bi-site Ga partial replaced materials exhibit the Bi-2212 superconducting phase within the different fraction levels (%73.1 -94.8), moderate self-field critical current densities 54-96 A/cm(2) and wide-ranging offset and onset critical transition temperature range of 45.65 K-84.52 K and 70.06 K-85.00 K. As for the experimental findings of bulk density and related degrees of granularity (porosity) parameters, the bulk density parameter is found to be between 5.76 g/cm(3) and 6.12 g/cm(3) when the corresponding residual porosity value is also obtained to be in a range of 8.57 % -2.86%. Moreover, the mobile hole carrier concentrations in the short-range-ordered antiferromagnetic Cu-O-2 layers are found to be in the range from 0.085 until 0.152. Additionally, the role of Ga/Bi partial substitution in the crystal lattice on the normal state resistivity, residual resistivity, residual resistivity ratio, vibrational mode intensities, texturing, superconducting volume fractions, mobile hole carrier concentrations, average crystallite sizes, Lotgering indices and cell parameters are discussed in details. All the experimental results and theoretical approaches show that the characteristic properties tend to improve regularly with the increment in the Ga foreign impurity level until x = 0.05 due to the increment in the crystal structure quality and interaction between the superconducting grains. After the critical Ga/Bi substitution level of x = 0.05, every feature degrades considerably. (C) 2018 Elsevier B.V. All rights reserved.
Development of modulation, pairing mechanism, and slip system with optimum vanadium substitution at Bi-sites in Bi-2212 ceramic structure
(Elsevier Science Sa, 2023) Ülgen, Asaf Tolga; Okur, Semih; Erdem, Ümit; Terzioğlu, Cabir; Yıldırım, Gürcan; Turgay, Tahsin
Present study focuses extensively on the change in electrical, superconducting and microhardness parameters with partial substitution of trivalent V+3 impurities replacing Bi+3 ions in Bi-2212 ceramic compound with the aid of dc electrical resistivity and microhardness test measurements. Experimental findings, calculation results, and phenomenological discussions provide that the optimum vanadium substitution level is found to be x = 0.01 in the Bi2.0-xVxSr2.0Ca1.1Cu2.0Oy (Bi-2212) ceramic system for the highest conductivity, crystallinity quality, superconducting, and mechanical performance features depending on the decreased microscopic structural problems. All the findings are wholly verified by scanning electron microscopy (SEM) and X-Ray diffraction (XRD) analyses. The dc electrical measurements indicate that the optimum vanadium ions support the pairing mechanism for the formation of new polaronic states in the clusters of microdomains, and hence expand superconducting energy gap due to the enhancement of amplitude part of pair wave function in the spin-density wave systems. The excess vanadium content degrades all the basic thermodynamics and quantum mechanical quantities mentioned due to the stress-induced phase transformation. Numerically, the Bi-2212 advanced ceramic matrix prepared by the optimum vanadium impurity is noticed to present the smallest residual resistivity value of 0.08 m & omega; cm, room temperature resistivity value of 8.84 m & omega; cm, and broadening degree of 0.36 K. Similarly, the ceramic material is found to possess the highest residual resistivity ratio of 3.05, carrier concen-tration number of 0.153041, critical transition offset and onset value of 84.66 K and 85.02 K, respectively. Besides, the microhardness findings reveal that the same compound with the least sensitivity to the applied test loads exhibits the largest Hv value of 4.799 GPa, Young's moduli of 393.303 GPa, yield strength of (0.969 GPa), and elastic stiffness coefficient of 15.5574 (GPa)7/4 under the applied test load of 0.245 N. The XRD in-vestigations show that the presence of optimum vanadium impurity supports the formation of a high super-conducting phase, c-axis length, and average crystallite size. All the findings are morphologically confirmed by the SEM images. It is found that the crystallographically best crystallinity quality and view of surface morphology is observed for the optimum vanadium substitution level. All in all, new higher properties for the conductivity, crystallinity quality, surface morphology, superconducting, and microhardness parameters based on the optimum vanadium replacement encourage the Bi-2212 crystal system to use in much more application places.
The diffusion of iron (Fe) in the superconducting MgB2 polycrystalline samples
(Bolu Abant İzzet Baysal Üniversitesi, 2016) Ülgen, Asaf Tolga; Belenli, İbrahim; Terzioğlu, Cabir
Bu tezin asıl amacı MgB2 süperiletken külçe örneği içerisinde Fe difüzyonunun araştırılmasıdır. Demir difüzyonu farklı tavlama sıcaklıklarında farklı ısıl işlem süreleri için gerçekleştirildi. Fe difüzyonu için 50 micrometre kalınlığında Fe tabakası vakum altında metal buharlaştırmayla MgB2 üzerine kaplandı. Bu tezin kapsadığı deneysel çalışmalar iki kısma ayrılır. İlk bölümde, süperiletken MgB2 külçe örneklerde Fe difüzyon 650-900C sıcaklığı aralığında 1 saat ısıl işlem uygulanarak çalışılmıştır. Prenslenmiş ama hiçbir ısıl işlem yapılmamış (Set 1N) örnekler ile preslenmiş ve 800C'de 1 saat ısıl işlem yapılmış (Set 1S) olmak üzere iki set külçe MgB2 tabletler üzerine Fe kaplaması yapıldı. Fe difüzyonunun MgB2 kristal yapısı ve süperiletken özellikleri üzerine etkileri X-ışını difraksiyonu (XRD), taramalı elektron mikroskobu (SEM), kızılötesi spektroskopi (IR) ve özdirenç ölçümleri ile incelenmiştir. Her iki set malzemeler için demir difüzyon katsayısı c örgü parametresi ve oda sıcaklığı özdirenç değerleriyle hesaplandı. Bu sıcaklık aralığında demir difüzyonu katsayısının sıcaklığa bağlılığı Arrhenius denklemiyle tanımlandı. Beklendiği gibi tavlama sıcaklığının artmasıyla Fe difüzyon katsayısının arttığı bulunmuştur. Malzemeye demir difüzyonu sayesinde süperiletkenlik özellikler ve micro yapısında gözlenen iyileşmeler tartışılmıştır. İkinci kısımda, kaplama işlemi 800C'de 1 saatlık ilk sinterlemeli (Set 2S) ve ilk sinterlemesiz (Set 2N) külçe örneklere yapıldı. MgB2 süperiletken malzemeye demir difüzyonu 900C de 15 dakika, 30 dakika, 1 saat, 2 saat, 4 saat ve 8 zaman aralıklarında çalışıldı. Birinci kısıma benzer olarak, MgB2'nin kristal yapısı ve süperiletkenlik özelliklerine demir difüzyonu etkisi XRD, SEM ve özdirenç ölçümleriyle araştırılmıştır. Tavlama işlemi için Fe difüzyon katsayısı c örgü parametresi ve oda sıcaklığı özdirenç değerleriyle hesaplandı. Beklendiği gibi tavlama zamanının artmasıyla Fe difüzyon katsayısının azaldığı bulunmuştur. Sonuç olarak difüzyon katsayısının artan sıcaklıkla artması ve artan ısıl işlem süresi ile azalması süperiletken MgB2 malzemelerin ısıl işlem uygulamalarında dikkate alınmalıdır. Yüksek kaliteli süperiletken külçe, tel/şerit üretiminde düşük sıcaklık ve geniş zaman aralığında ısıl işlem yapılmalıdır.
Effect of annealing ambient conditions on crack formation mechanisms of bulk Bi-2212 ceramic systems
(Taylor & Francis Ltd, 2021) Erdem, Ümit; Akkurt, Bahadır; Ülgen, Asaf Tolga; Zalaoğlu, Yusuf; Turgay, Tahsin; Yıldırım, Gürcan
This study paves way to examine the influence of different annealing conditions (temperature range of 830-850 degrees C and duration intervals 24-48 h) on the fundamental mechanical performance and characteristic quantities of polycrystalline Bi2.1Sr2.0Ca1.1Cu2.0Oy (Bi-2212) superconducting ceramics by means of Vickers microindentation hardness tests at the various indentation test loads (0.245 N <= F <= 2.940 N) and some available theoretical approaches. The annealing ambient plays an important role on the operable slip systems and crystal quality. The bulk Bi-2212 superconducting compound prepared at 840 degrees C and 24 h is found to be the least sensitive to the applied test load due to less structural problems, voids, cracks and stress raisers in the crystal system. Conversely, the excess annealing ambient complicates remarkably the control of crack growth size and velocity. Thus, relatively lower load can lead to the formation of crack and acceleration of crack rate up to the critical size and terminal velocity. The samples exhibit the typical indentation size effect (ISE) behavior as a result of predominant character of elastic recovery mechanism. As for the theoretical examination in the saturation limit regions, the indentation-induced cracking (IIC) model wins the comparison as it provides the most accurate results to the experimental findings.
The effect of Fe diffusion on some physical and superconducting properties of MgB2
(Springer, 2017) Ülgen, Asaf Tolga; Belenli, İbrahim
The iron (Fe) diffusion in superconducting MgB2 bulk samples has been studied over the temperature range of 650-900 degrees C for 1 h. Fe coating on bulk polycrstalline superconducting MgB2 samples was performed in two ways, i.e., on pressed pellets without sintering (set(2)) and on pressed and sintered pellets (set(1)). For both sets, a 50 mu m thick Fe layer was coated on MgB2 by evaporation in vacuum. Effects of Fe diffusion on the crystal structure and superconducting properties of MgB2 have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and resistivity measurements. Fe diffusion coefficients were determined from lattice parameter c and room temperature resistivity values. The temperature dependence of the Fe diffusion coefficient in this temperature range is described by the Arrhenius relation. It has been found that the Fe diffusion coefficient increases with increasing sintering temperature, as expected. The plausible explanations for the observed improvement in microstructure and superconducting properties of the samples due to Fe diffusion are discussed.
Effect of the initial filling density on the critical current of in-situ Fe/MgB2 wires
(Elsevier Science Sa, 2015) Akdoğan, Mustafa; Yetiş, Hakan; Gajda, Daniel; Karaboğa, Fırat; Ülgen, Asaf Tolga; Demirtürk, Emine; Belenli, İbrahim
We report a comparative study on the fabrication of in-situ monofilamentary superconducting Fe sheathed MgB2 wires as a function of the initial tube filling density. The wire samples are fabricated by means of a standard Powder-in-Tube (PIT) method with two different initial powder filling densities. Transport measurements are applied under high magnetic fields, of up to 10 T, obtained in a Bitter magnet. We find that increasing the initial filling density improved the critical current of the Fe/MgB2 wires, and a high I-c (4.2 K) = 140 A at B = 5 T is achieved. (C) 2015 Elsevier B.V. All rights reserved.
Effect of vanadium addition on fundamental electrical quantities of Bi-2223 crystal structure and semi-empirical model on structural disorders-defects
(Springer, 2020) Ülgen, Asaf Tolga; Erdem, Ümit; Zalaoğlu, Yusuf; Turğay, Tahsin; Yıldırım, Gürcan
The primary contribution of the present study is to determine the effect of vanadium addition on the fundamental aspects of characteristic crystalline and electrical quantities for the Bi1.8Sr2.0Ca2.2Cu3.0VxOy (0.00 <= x <= 0.30) crystal system using the powder X-ray diffraction (XRD), temperature-dependent electrical resistivities and semi-empirical approaches founded on the structural disorders-defects. The de electrical resistivity results show that every electrical quantity is found to degrade regularly with the increment in the addition level as a consequence of the induced permanent structural disorders-defects, intergranular grain boundary coupling interaction problems and non-superconducting barrier regions in the bulk Bi-2223 superconducting system. The vanadium addition brings also about the characteristic transition from over-doped state to under-doped state due to the suppression in the overlapping of Cu-3d and O-2p wave functions. The XRD results indicate that the vanadium addition leads to shift the characteristic peaks towards the larger/lower angles in terms of the peak positions in the reference data, enlarge the diffraction peak widths (line broadening of X-ray diffraction), appear or disappear new peaks, increase/decrease the average grain size, lattice cell parameters and superconducting phase fractions founded on the diffraction intensities. Based on the evidences, the presence of vanadium particles in the bulk Bi-2223 superconducting phase damages crucially the fundamental characteristic features. Moreover, it is found that characteristic two-stage (bulk genuine, T-c(mid) and coherence, T-co) transition temperatures decrease systematically with the addition level. On this basis, the presence of vanadium impurity in the system leads to degrade the stabilization of superconductivity in the small homogeneous clusters in the paths and especially effective electron-phonon coupling (bipolaron in the polarizable lattices) probabilities due to the reduction of hole trap energy per Cu ions in the valence band of system. Additionally, the results display that the vanadium particles affect negatively on both the dirty limit characteristic feature and gap coefficient of Bi-2223 ceramic compound as a result of the decrement in the minimum required energy for breaking up the cooper-pairs in the system. At the same time, the electrical resistivity curves enable us to develop a sensitive semi-empirical approach to find the possible highest onset critical transition temperature for the ideal crystallinity. The model founded on the crystallinity quality displays that the possible highest onset transition temperature is about 116.037 K +/- 1.25587 K with R-adj(2) = 0.948.
Evaluation of crystallographic and electrical-superconducting features of Bi-2223 advanced ceramics with vanadium addition
(Springer, 2021) Akkurt, Bahadır; Erdem, Ümit; Zalaoğlu, Yusuf; Ülgen, Asaf Tolga; Turğay, Tahsin; Yıldırım, Gürcan
In the current study, the effect of vanadium particles on the electrical, superconducting, crystallographic, key structural and morphological features of Bi1.8Sr2.0Ca2.2Cu3.0VxOy superconducting materials is examined with the aid of powder X-ray diffraction (XRD), scanning electron microscope (SEM), electron-dispersive X-ray (EDX) and dc electrical resistivity over the temperature (?-T). The vanadium-added Bi1.8Sr2.0Ca2.2Cu3.0VxOy (Bi-2223) superconducting materials are prepared within the molar ratios between x = 0.00 and 0.30 using the conventional solid-state reaction technique. The temperature-dependent electrical resistivity measurements show that the existence of vanadium atom in the superconducting system damages seriously the Bi-2223 (high-Tc) phase content in the crystal structure as a result of the formations/disappearances of new impurity phases. On this basis, the amplitude ?0 of wave function founded on the super-electrons is considerably reduced with the vanadium addition. The critical onset and offset transition temperature values truncate from the values of 110.92 K and 97.45 K to 103.17 K and 18.38 K in case of the maximum vanadium addition level of x = 0.30. Similarly, the XRD results present that the average crystallite size and c-axis length parameters are noted to decrease considerably whereas a-axis length, strain and relativistic dislocation density ratios are calculated to enlarge harshly depending on the addition content level. It is also obtained that the vanadium inclusions lead to increase seriously the permanent crystal structure problems, disorders, misorientations, lattice strains, crack-producing omnipresent flaws and grain boundary coupling problems in the active Cu–O2 consecutively stacked layers in the superconducting core, being assured by SEM analyses. Besides, the SEM results show that the enhancement of vanadium addition level in the crystal structure damages remarkably the flaky layers of platelet-like shape for the grains. In fact, the excess vanadium addition seriously damages the general characteristic view (flaky layer structure) of Bi-2223 compound. Based on the EDX findings, the main reason for the degradation of fundamental characteristic properties of Bi-2223 system may stem from the possible replacement of aliovalent vanadium impurities for the copper-sites in the crystal structure. Namely, the vanadium addition in the crystal structure is ploughed to improve the fundamental crystallographic and electrical-superconducting features of bulk Bi-2223 superconducting materials.
Evaluation of load-independent microhardness values in Plateau regions of Vanadium substituted Bi-2212 ceramics
(IOP Publishing Ltd, 2022) Ülgen, Asaf Tolga; Okur, Semih; Erdem, Ümit; Pakdil, Murat; Turgay, Tahsin; Yıldırım, Gürcan
This study reveals extensively effect of homovalent V/Bi partial replacement in Bi2.0-xVxSr2.0Ca1.1Cu2.0Oy ceramic matrix (0.00 <= x <= 0.30) on the key mechanical design performance parameters and load-independent Vickers microhardness parameters in plateau limit region by means of experimental microhardness tests and semi-empiric approaching models. It is found that the vanadium substitution level of x = 0.01 is observed to be optimum amount in the Bi-2212 crystal lattice for refinement of fundamental mechanical properties due to the enhancement in stabilization of durable tetragonal phase, surface residual compressive stress and elastic recovery mechanism. Conversely, from the replacement level of x = 0.01 onwards, the lattice strain field and stress concentration sites enhance significantly depending on the increase of microscopic structural problems, interaction problems between adjacent layers and crack-initiating flaws in Bi-2212 ceramic system. Correspondingly, stress-induced phase transformation begins to play predominant role, and excess vanadium substituted ceramic materials are easily broken at relatively smaller test load. Moreover, the models indicate that every ceramic compound shows standard indentation size effect (ISE) feature due to predominant behavior of elastic recovery in crystal structure. Hence, presence of optimum vanadium ions strengthens typical ISE characteristic behavior. Furthermore, among semi-empirical models the indentation-induced cracking (IIC) model exhibits the highest performance to inspect real microhardness values of Bi2.0-xVxSr2.0Ca1.1Cu2.0Oy ceramic compounds in the plateau limit region.
Improved transport properties of MgB2 superconducting round wires via minute addition of gold nanoparticles
(Elsevier Sci Ltd, 2019) Ülgen, Asaf Tolga; Karaboğa, Fırat; Karakaya, Mehmet; Podila, Ramakrishna; Rao, Apparao M.; Belenli, İbrahim
This study investigates the effect of gold nanoparticles (Au-NPs) on structural, morphological, electrical and magnetic properties of Fe/MgB2 wires 1.00 mm in diameter. Au-NPs were obtained by pulsed laser ablation of gold in acetone and mixed with Mg + 2B powder mixture for in-situ powder-in-tube wire making process. Resulting drawn wires were subjected to inert atmosphere heat treatments at different temperatures. Transport measurements were performed on 1.00 mm round wires samples in a closed cycle cryostat under magnetic fields perpendicular to wire axis.
Mechanical properties and uniformity of Fe-MgB2 wires upon various wire drawing steps
(Elsevier Science Sa, 2018) Karaboğa, Fırat; Ülgen, Asaf Tolga; Yetiş, Hakan; Akdoğan, Mustafa; Pakdil, Murat; Belenli, İbrahim
Effect of drawing process on the mechanical properties and cross-sectional uniformity of Fe/MgB2 mono-filamentary wires were investigated in this study. Successive cold drawing steps were applied with and without intermediate strain relief annealing steps. Micro-hardness measurements of the drawn wires were taken from the polished cross-sections. Tensile tests were performed on the 120 mm long wires samples. Microstructural properties of the sheathing material and that of the superconducting core were studied using SEM. Uniformity of the cross-sectional area in final mono filamentary wires was studied on SEM images of the polished cross sections. Excessive mechanical deformation of the soft iron sheathing metal via drawing was assessed and discussed.
A novel research on the subject of the load-independent microhardness performances of Sr/Ti partial displacement in Bi-2212 ceramics
(Springer, 2020) Zalaoğlu, Yusuf; Turğay, Tahsin; Ülgen, Asaf Tolga; Erdem, Ümit; Türköz, Mustafa Burak; Yıldırım, Gürcan
This work is interested in the critical changes in the load-independent microhardness performance parameters with the partial substitution of Sr2+ inclusions for the Ti4+ impurities in the Bi-2212 inorganic solids with the help of the theoretical approximations as regards Meyer's law (ML), proportional sample resistance (PSR), modified proportional sample resistance (MPSR), elastic/plastic deformation (EPD), Hays-Kendall (HK) and indentation-induced cracking (IIC) models found on the experimental microhardness tests applied to a variety of test loads between 0.245 and 2.940 N for the first time. Moreover, Ti-substituted Bi-2212 bulk ceramics (Bi2.1Sr2.0-xTixCa1.1Cu2.0Oy) are prepared within mole-to-mole ratios of x = 0.000, 0.010, 0.030, 0.050, 0.070, 0.100 by the standard solid-state reaction method in the atmospheric pressure conditions. It is provided that Ti partial substitution in the superconducting system descends unsmilingly the mechanical durability, stability, strength, toughness, critical stress, stiffness and flexural strengths of Bi-2212 superconducting solids studied owing to the increment of crystal structural problems. Moreover, it is obtained that the degradation in the crystal structural leads to diminish the typical ISE characteristic of Bi-2212 superconducting ceramic compounds. At the same time, the results show that all the models (especially IIC approach) can serve as the suitable descriptors for the determination of the variation in the load-independent mechanical performances of the Bi-2212 superconducting materials.
Role of active slip systems induced with holmium impurity in Bi-2212 ceramics on mechanical design performance and morphological properties
(Elsevier, 2022) Ülgen, Asaf Tolga; Çetin, Samet; Zalaoğlu, Yusuf; Türköz, Mustafa Burak; Erdem, Ümit; Yıldırım, Gürcan
Effect of Ho/Bi partial replacement in Bi2.1-xHoxSr2.0Ca1.1Cu2.0Oy (Bi-2212) superconductors on the fundamental structural, morphological and mechanical performance properties are investigated by Scanning Electron Mi-croscopy (SEM) and Vickers hardness (Hv) measurement techniques. Crystallinity quality and surface morphology including the microcrystal coalescence orientations, grain alignment distributions, microscopic structural problems, microvoids, internal defects, uniform surface view, porosity and particle growth distribution are visually examined with the aid of SEM. Basic mechanical performance and characteristic features of Bi/Ho substituted Bi-2212 superconducting ceramics (0.00 <= x <= 0.10) are also determined with Vickers tests con-ducted at various loads intervals 0.245-2.940 N. Experimental findings show that the characteristic features enhance seriously in case of x = 0.01 due to refinement of crystallinity quality and slip systems. Thus, the op-timum Ho concentration presents the highest mechanical fracture strength to the load applied as a result of better uniform surface appearance and grain orientations, well-connected flaky layers, larger particle size distribution and denser structure, confirmed by the SEM investigations. Namely, much more load is required to accelerate the dislocation movement and crack propagation to the terminal velocity for critical size growth. The fracture predominantly takes place in the transcrystalline regions and hence the propagations are easily controlled with the optimum Ho dopant ions. On the other hand, the increase in the Ho ions in Bi-2212 structure induces the crack-initiating defects for new stress concentration sites. In conclusion, the permanent and non-recoverable deformations appear at even lower indentation test loads. All samples present indentation size effect feature depending on the dominant character of elastic recovery mechanism. Further, original hardness parameters are semi-empirically analyzed in the plateau limit regions using mechanical modelling approaches for the first time. Based on the analyses, Hays-Kendall model exhibits the closest results to the experimental findings.
Role of Bi/Tm substitution in Bi-2212 system on crystal structure quality, pair wave function and polaronic states
(Elsevier Science Sa, 2018) Ülgen, Asaf Tolga; Turğay, Tahsin; Terzioğlu, Cabir; Yıldırım, Gürcan; Öz, Muhammed
This comprehensive study finds strongly out the crucial variations in the dc electrical resistivity, superconducting, crystal structural and flux pinning mechanisms with the partial replacement of homovalent Tm+3 inclusions by Bi+3 impurity in the active layers of Bi-2212 superconducting material. Materials of type Bi2.1-xTmxSr2.0Ca1.1Cu2.0Oy with molar ratio changes of 0.00 <= x <= 0.30 are prepared by conventional solid-state reaction route in atmospheric pressure and the characterizations are exerted by the bulk density, dc electrical resistivity (rho-T), powder X-ray diffraction (XRD), critical current density (J(c)), scanning electron microscopy (SEM) and electron dispersive X-ray (EDX) experimental measurements. The combination of experimental results evaluated from the bulk density, dc electrical resistivity, XRD and EDX measurements points out that the Tm foreign impurities mostly incorporate successfully into the Bi-2212 crystal lattice. In fact, the EDX investigations verify that the thulium impurities may mostly be substituted for the bismuth sites in the crystal structure. All the experimental results declare that the characteristic features improve regularly with the increment in the Tm impurity level up to x = 0.07 beyond which the properties degrade dramatically. In this respect, the sample with x = 0.07 exhibits highest electrical conductive/metallic characteristics as a consequence of the refinement in the crystal structure quality and connectivity between the superconducting grains, being favored by bulk density and related relative degrees of granularity surveys. Likewise, the material presents the maximum offset-onset critical transition temperature values of 85.61 K-85.85 K due to the increment in the formation of effective and strong electron-phonon coupling probabilities and optimization of mobile hole carrier concentrations in the Cu-O-2 consecutively stacked layers. In other words, the optimum content level leading to transit inherently over-doped nature into optimally doped state strengthens the amplitude of pair wave function for the Bi-2212 material. In more sophisticated interpretations, the presence of optimum dopant in the crystal structure changes the vibrational mode intensities of O (1)CuA1g, B1g phonons and O (2)SrA1g phonon so that the formation possibility of bipolaron out of two polarons increases strongly in a polarizable lattice (polaronic effect). Additionally, the highest self-field J(c) of 95 A/cm(2) confirms the fact that the optimum dopant augments the effective nucleation centers along the intragrain and inter-grain boundaries in the crystal system. Similarly, the material prepared with x = 0.07 presents the smoothest, densest, largest average crystalline distribution, lowest porosity and most uniform surface appearance with the finest connection between the superconducting grains. The XRD results (the increased high phase, c-axis length and average grain size but decreased a-axis length) also show the optimum dopant level of x = 0.07 for Bi-2212 crystal system. All in all, the paper developing a strong methodology about why the characteristic properties improve with the presence of Tm impurity in the Bi-2212 system may be a pioneering research to construct newly, novel and feasible market areas for the Bi-2212 superconducting ceramics in the universe economy. (C) 2018 Elsevier B.V. All rights reserved.
Role of trivalent Bi/Tm partial substitution on active operable slip systems in Bi-2212 crystal structure
(Elsevier Ltd, 2021) Erdem, Ümit; Zalaoğlu, Yusuf; Ülgen, Asaf Tolga; Turğay, Tahsin; Yıldırım, Gürcan
This study delves into three main subjects: (I) A strong definition on the variation of fundamental key mechanical design performance and general mechanical characteristic features founded on the formation of active operable slip systems and elimination of structural problems in the Tm substituted Bi-site Bi2.1-xTmxSr2.0Ca1.1Cu2.0Oy (0.00 ? x ? 0.30) ceramic materials; (II) Preference of propagation of cracks and dislocation movements (III) An examination of differentiation in the load-independent microhardness parameters in the saturation limit regions with the Bi/Tm partial replacement. It is found that all the mechanical performance (mechanical strength, stiffness, durability and resistant towards to the failure by fatigue) properties considerably improve with the increment in the Bi/Tm substitution level up to x = 0.07 due to the augmentation in the new active operable slip systems and crystallinity quality of Bi2.1Sr2.0Ca1.1Cu2.0Oy (Bi-2212) system. Accordingly, in case of the optimum Bi/Tm substitution the propagation of dislocation and crack movements is more and more easily controlled in the Bi-2212 ceramic system. However, the excess Tm concentrations in the ceramic system make the stress-induced phase transformation remarkably activate as a consequence of the degradation in the crack orientation and geometry. Hence, any deformation at even lower applied test loads is much more permanent and non-recoverable due to the enhancement of unconstrained dislocation motions and especially entanglement of cracks and dislocations. This fact is also confirmed from the reduction of typical indentation size effect (ISE) behavior in the event of excess Tm concentration. To conclude, the optimum Bi/Tm partial replacement in the Bi-2212 crystal structure is successful to improve the economic lives of Bi-2212 inorganic ceramics in the new, novel, innovative, feasible and potential design areas for the universe economy.
Sintering time dependence of iron diffusion in MgB2 and its effect on superconducting properties
(American Institute of Physics Inc., 2017) Ülgen, Asaf Tolga; Belenli, İbrahim
We have investigated the effects of the iron diffusion on the crystal structure and superconducting properties of pelletised magnesium diboride (MgB2) bulk samples employing X-ray diffraction (XRD), critical transition temperature, and room temperature resistivity measurements. The Fe diffusion into MgB2 bulk pellets upon sintering at 900°C has been studied for sintering time durations of 15 minutes, 30 minutes, 1 hour, 2 hours, and 4 hours. We have carried out XRD and room temperature resistivity determinations along the depth starting from iron coated surface by successive removal of thin layers from the surface mechanically. Sintering time dependence of the Fe diffusion coefficients has been calculated from depth profiles of lattice parameter c and room temperature resistivity values. It has been found that the Fe diffusion coefficient decreases with increasing sintering time. © 2017 Author(s).

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