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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/).
Determination of Possible Maximum Critical Transition Temperatures with Empirical Model Depending on Structural Disorders-Defects for $Bi_{2.1}Sr_{2.0}Ca_{1.1}Cu_{2.0}O_y$ System
(2021) Erdem, Ümit; Yildirim, Gürcan
In this study, we find a strong link depending on the preparation annealing ambient conditions between structural disorders-defects and characteristic transition temperature parameters $(offset, T_c ^{offset} and onset, T_c ^{offset})$ of bulk $Bi_{2.1}Sr_{2.0}Ca_{1.1}Cu_{2.0}O_y$ system for the first time. The superconducting samples are prepared at various annealing temperatures intervals 830°C -850°C with the temperature step of 10°C for annealing time ranging between 24 h and 48 h via traditional solid-state reaction route. The temperature-dependent resistivity measurements are conducted at temperature range of 30-140 K. The most ideal annealing ambient is obtained to be the combination of annealing temperature of 840 °C and annealing time of 24 h because of the enhancement in the formation possibility of strong cooper-pairs and optimization of itinerant charge carrier concentrations in the valence band. Similarly, the positive contributions are observed in the overlapping mechanism of wave functions between Cu-3d and O-2p electrons and especially logarithmic distribution of electronic state densities. The optimum annealing ambient makes the Bi-2212 system refine the structural problems and especially connectivity between the grains in the crystal structure. Conversely, the excess annealing ambient leads to increase considerably the grain misorientation, defects and grain boundary couplings due to the induced permanent problems in the crystal system. The highest correlated model shows that the Bi-2212 superconducting compounds with the minimum structural disorders in the short-range-ordered antiferromagnetic $Cu-O_2$ layers exhibit the maximum $T_c ^{offset} and T_c ^{offset}$ values of about 85.347 K (R2adj=0.9882) and 87.421 K (R2adj=0.97465).
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.
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 sintering parameters and MgO ratio on structural properties in Al7075/MgO composites: A review
(Springer, 2023) Pul, Muharrem; Erdem, Ümit; Türköz, Mustafa Burak; Yıldırım, Gürcan
In this experimental study, Al7075 matrix composites reinforced with different proportions of MgO were produced by powder metallurgy method. Different sintering temperatures and times were applied in the powder metallurgy production process. In the second stage of the experimental study, firstly, the porosity and hardness measurements of the composite materials were made. Then, microstructure images were taken with SEM and optical microscope, and XRD analyzes were performed. Using the obtained data, the effects of different MgO ratios and different sintering parameters on the structural properties of composite materials were evaluated. As the sintering temperature increased, the density of the composite structure increased and then decreased again. Accordingly, the amount of porosity first decreased and then increased again. Significant size growth occurred in all samples sintered at 600 degrees C. This change was associated with the high amount of porosity in the same samples. A more stable microstructure was obtained from the samples sintered at 550 degrees C. Thus, it can be said that the presence of excess MgO particles in the system causes the material quality to deteriorate due to increased microscopic structural problems, wetting rates, intergranular interaction problems between adjacent layers, recovery mechanism and entanglement of voids, and dislocations. Therefore, the ideal rate, time and temperature value for MgO addition should be carefully determined. As a result, it was seen that the sintering temperature of 550 degrees C gave the most suitable results. The sintering time strengthened the phase volume of the Al7075 alloy, making the compound more stable.
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.
Evolution of dynamics of physico-chemical and mechanical properties of hydroxyapatite with fluorine addition and degradation stability of new matrices
(Elseiver, 2022) Erdem, Ümit; Doğan, Deniz; Bozer, Büşra Moran; Karaboğa, Seda; Türköz, Mustafa Burak; Yıldırım, Gürcan
This multidisciplinary study examined sensitively the change in the dynamics of main mechanical performance, stability of crystal structure, crystallinity quality, strength, corrosion resistance, biocompatibility, resistance to structural degradation/separations and mechanical durability features of hydroxyapatite (HAp) biomedical materials based on the fluorine addition and degradation process to guide future medical and dental treatment studies. In the study, the fluorine ions were used to be the dental coating, filling and supporting material for biologically or synthetically produced bone minerals. The general characteristic properties were investigated by means of standard spectroscopic, structural and mechanical analysis methods including RAMAN, SEM-EDS, TEM, Vickers micro-indentation hardness and density measurements. A time dependent release test was performed to evaluate possible fluorine ion release after the degradation process. It was found that the fundamental charac-teristic properties of HAp biomedical materials are noted to improve with the increase in the fluoride level up to 2% due much more stabilization of HAp crystal system. The combination of RAMAN spectra and powder XRD analyzes indicates that 2% addition level affects positively the formation velocity of characteristic HAP phase. Besides, fluorine doped HAp materials all exhibited the main characteristic peaks after degradation process. This is attributed to the fact that the fluorine ions enabled the hydroxyapatite to enhance the structural quality and stability towards the corrosion environment. However, in case of excess dopant level of 3% the degradation rates were obtained to increase due to higher contribution rate and especially electrostatic interactions. As for the surface morphology examinations, 2% fluorine added HAp with the highest density of 3.0879 g/cm3 was determined to present the superior crystallinity quality (smallest grain size, best smooth surface, honeycomb pattern, regular shaped particles and densest particle distributions through the specimen surface). Conversely, the excess fluorine triggered to increase seriously degree of micro/macro porosity in the surface morphology and microscopic structural problems in the crystal system. Thus, the HAp doped with 3% was the most affected material from the degradation process. Additionally, the fluorine ion values read after the release process were quite far from the value that could cause toxic effects. Lastly, the optimum fluorine addition provides the positive effects on the highest durability, stiffness and mechanical fracture strength properties as a consequence of dif-ferentiation in the surface residual compressive stress regions (lattice strain fields), amplification sites and active operable slip systems in the matrix. Hence, the crack propagations prefer to proceed in the transcrystalline re-gions rather than the intergranular parts. Similarly, it was found that Vickers micro-indentation hardness tests showed that the microhardness parameters increased after the degradation process. All in all, the fluorine addition level of 2% was noted to be good choice to improve the fundamental characteristic properties of hy-droxyapatite biomedical materials for heavy-duty musculoskeletal, orthopedic implant, biological and thera-peutic applications in medicine and dentistry application fields.
Evolution of operable slip systems, lattice strain fields and morphological view of Bi-2223 ceramic system with optimum NiO addition
(Elsevier, 2023) Mercan, Ali; Kara, Emre; Doğan, Muhsin Uğur; Kaya, Şenol; Terzioğlu, Rıfkı; Erdem, Ümit; Yıldırım, Gürcan; Terzioğlu, Cabir
The current work extensively reveals the influence of different nickel oxide (NiO) impurity addition levels on the morphological, microstructural, key mechanical performance, and mechanical characteristic properties of Bi1.8Pb0.4Ca2.2Sr2Cu3Oy (Bi-2223) ceramics using scanning electron microscopy (SEM), powder X-ray diffraction (XRD), and Vickers micro-indentation (Hv) hardness measurements. It was observed that the addition of NiO impurity in the Bi-2223 crystal structure affected seriously the fundamental characteristic features. In the case of the optimum NiO concentration level of x = 0.1, the Bi-2223 materials exhibited the best crystallinity quality and coupling strengths between the adjacent layers, the most uniform surface view, and the densest, and the smoothest crystal structure. Similarly, the compound was noted to possess the hardest, highest mechanical strength, durable tetragonal phase, resistance toward failure by fatigue, and elastic recovery properties. Besides, it was observed that the characteristic Bi-2223 superconducting phase fraction and stabilization of the tetragonal crystal system reached the maximum level for the optimum concentration. Moreover, optimum NiO particles brought about a considerable increase in the number of operable slip systems, surface residual compressive force regions, and lattice strain fields. Correspondingly, the mobility of defects was blocked significantly depending on the preference of defects through transcrystalline regions. Additionally, optimum addition strengthened the typical indentation size effect due to the improvement of the recovery mechanism. In this regard, the NiO-added sample exhibited the least response to the applied loads. Thus, the Bi-2223 sample with the optimum NiO concentration was found to present the highest hardness parameter of 0.496 GPa, greatest elastic deformation value of 16.493 GPa, largest stiffness value of 1.044 MN/m, and smallest contact depth of 5.849 mu m. On the other hand, after the optimum concentration level of x = 0.1, there appeared serious increase in problems including internal defects, impurity residues, microscopic structural problems, and connection problems between the grains. All experimental findings were theoretically supported by semi-empirical mechanical methods. To sum up, the addition of NiO particles was noticed to increase the potential application areas of Bi-2223 ceramic
Fabrication of mechanically advanced polydopamine decorated hydroxyapatite/polyvinyl alcohol bio-composite for biomedical applications: In-vitro physicochemical and biological evaluation
(Elseiver, 2022) Erdem, Ümit; Doğan, Deniz; Bozer, Büşra Moran; Türköz, Mustafa Burak; Yıldırım, Gürcan; Metin, Ayşegül Ülkü
In this study, polydopamine (PDA) coated hydroxyapatite (HA) reinforced polyvinyl alcohol (PVA) films were produced to be used in biomedical applications such as bone tissue regeneration. pDA is coated not only to prevent the agglomeration of HA when encountering interstitial fluids but also to strongly bind the PVA for the interaction between materials so that the mechanical performance becomes more stabilized. pDA was coated on the hydroxyapatite surface using a radical polymerization technique, and the reinforced PVA were produced with pDA-coated HA (pDA-HA/PVA) nanoparticles. Fundamental characteristic properties of pDA-HA/PVA nanocomposite films were examined by morphological/chemical (SEM-EDS), microstructural (XRD, Ft-IR, and Raman), thermodynamic (TGA and TM), mechanical performance (Vickers microhardness) and biological activity analysis (MTT, genotoxicity and antimicrobial efficacy investigations). Physicochemical analysis showed that all the samples studied exhibited homogeneous mineral distributions through the main structures. According to TGA, TMA and hardness tests, the new composite structure possessed higher mechanical properties than neat PVA. Further, pDA-HA/PVA nanocomposites exhibited high antibacterial capacities against Acinetobacter Baumannii (A.Baumannii), Staphylococcus aureus (S. aureus), and Streptococcus mutans (S.mutans). Moreover, the new nanocomposites were noted to present good biocompatibility for fibroblast (L929) cells and to support remarkably MCS cells. All in all, this comprehensive work shows that the thermo-mechanically improved pDA-HA/PVA films will increase the application fields of PVA in biomedical fields especially tooth-bone treatments for coating, filling, or occlusion purposes.
Improvement in deformation degree of Zr surface-layered Bi-2223 ceramics by diffusion annealing temperature
(Elsevier Sci LTD, 2023) Mercan, Ali; Terzioğlu, Rıfkı; Doğan, Muhsin Uğur; Kaya, Şenol; Erdem, Ümit; Yıldırım, Gürcan; Terzioğlu, Cabir; Varilci, Ahmet
This study investigated the effects of different annealing temperatures (650 degrees C <= T <= 840 degrees C) on the surface morphological and mechanical performance properties of Zr surface-layered Bi-2223 materials with scanning electron microscopy (SEM) images, Vickers microhardness (Hv) measurements, and semi-empirical mechanical approaches. It was observed that the ceramic compound exposed to 650 degrees C annealing temperature exhibited the superior performance features due to the enhancement in the deformation degree. This is because the Zr ions behaved as the nucleation centers to prevent the propagations of cracks and dislocations throughout the main matrix depending on the decrease in the degree of granularity and distributions of crystal structure problems over a wider area. Similarly, the SEM pictures indicated that the diffusion mechanism increased the random distributions of the thinner plate-like granular structures (serving as nucleation centers), leading the decrease in the coupling problems between the grains. Among the materials, the highest surface densification was observed for the compound exposed to 650 degrees C. Namely, surface morphological analysis showed a strong correlation be-tween microstructure and mechanical performances. Further, the zirconium ions were found to decrease in the non-recoverable stress concentration sites, crack-initiating defects, and dislocations in the ceramic system. Accordingly, the sensitivity to the applied test load was noted to decrease dramatically. Shortly, crack growth size and velocity were observed to be more easily under control. Correspondingly, the Zr ions delayed consid-erably the beginning points of saturation limit (load-independent) regions for the bulk Bi-2223 superconducting materials. Additionally, the Zr ions led to the change in the mechanical characteristic behavior from typical indentation size effect to reverse indentation size effect. Lastly, the microindentation hardness measurements were semi-empirically analyzed by the different models. According to the comparison, Hays-Kendall mechanical model was noted to provide the closest parameters to the load-independent microhardness results.
Improvement in fundamental electronic properties of Bi-2212 electroceramics with trivalent Bi/Tm substitution: A combined experimental and empirical model approach
(SPRINGER, 2021) Zalaoğlu, Yusuf; Erdem, Ümit; Bolat, Fevzi Çakmak; Akkurt, Bahadır; Turğay, Tahsin; Yıldırım, Gürcan
This study delves into the variation in the fundamental aspects of electrical quantities with the partial substitution of Tm impurities at Bi-site in the Bi2.1-xTmxSr2.0Ca1.1Cu2.0Oy (0.00 <= x <= 0.30) ceramic system with the derivatives of electrical resistivity examinations and theoretical approaches. It is found that all the electrical characteristic properties tend to improve with the trivalent Bi/Tm substitution level up to x = 0.07 beyond which they degrade considerably due to the increment of non-superconducting barrier regions, permanent disorders, inhomogeneity, porosity, grain misorientation distribution, internal and surface omnipresent defects, microscopic cracks, and coupling interaction problems throughout the grain boundaries in the Bi-2212 crystal system. Thus, the optimum dopant level of x = 0.07 results in the transition from the over-doped state to optimally doped state in the Bi-2212 crystal system as a consequence of augmented hybridization mechanism. Further, the characteristic two-stage transition temperatures, gap coefficient, Josephson coupled, and thermal energies for the isolated grains and inter-grains are explored. The findings show that the optimum Bi/Tm substitution leads not only to stabilize the superconductivity in the homogeneous superconducting clusters as a result of the increment in the formation of active Cooper pairs but also to decrease significantly the location of resistivity in long-range coherent state due to the increment of hole trap energy. Additionally, a strong link is established between the structural disorders-defects and onset/offset (T-c(onset)/T-c(offset)) transition temperatures using the electrical resistivity features for the first time. The empirical model based on the impurity scattering and lattice strain in the crystal lattices displays that it is possible to achieve the possible highest T-c(onset) and T-c(offset) values of about 86.558 K and 86.445 K, respectively. To sum up, the paper with strong methodology between electrical quantities and structural disorders-defects depending on Tm impurity may be a pioneering research to explain why the characteristic features improve with the optimum substitution and especially open up a novel and feasible area for the advanced engineering, heavy industrial technology, and large-scale applications of ceramic materials.
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.
Refinement of fundamental characteristic properties with homovalent Er/Y partial replacement of YBa2Cu3O7-y ceramic matrix
(Elsevier Science SA, 2021) Erdem, Ümit; Türköz, Mustafa Burak; Yıldırım, Gürcan; Zalaoğlu, Yusuf; Nezir, Saffet
In the current work, the effect of partial substitution of Er-sites for the Y-sites in the bulk YBa2Cu3O7-y (YBCO) crystal system on the fundamental superconducting, electrical, crystallinity and structural morphology features is examined together with the reasons by means of powder X-ray diffraction (XRD), temperature-dependent electrical resistivity (rho-T), scanning electron microscopy (SEM), electron dispersive X-ray (EDX) investigations and deduced calculation parameters. All the experimental test results show that the erbium impurities are suc-cessfully substituted by the yttrium sites in the bulk Y-123 crystal system, confirmed by sensitively the EDX and rho-T measurement results. Moreover, it is found that all the fundamental characteristic quantities improve with the increment in the Er/Y partial substitution level up to the value of x = 0.03 beyond which the features tend to degrade dramatically. In this respect, the bulk Y1-xErxBa2Cu3O7-y ceramic compound prepared within the molar ratio of x = 0.03 crystallizes in the orthorhombic space group P-4/ mmm with a little distortion due to the refinement in the crystallinity quality, crystallite growth, oxygen ordering degree, scattering mechanism, intra and intergrain boundary couplings, grain alignment distributions and orientations. The XRD results show that the optimum erbium content enables to develop seriously the fundamental crystallographic features (lattice strain, lattice cell constants, crystallite size distribution, dislocation density ratio, oxygen concentrations in the unit cells) of Y-123 crystal structure. However, the excess Er/Y substitution leads to enhance considerably the systematic structural problems and inhomogeneous distribution of strains (formed by the structural defects) in the YBCO crystal structure. Thus, the phase transition from orthorhombic to tetragonal (structural O-T transition) crystal structure is observed. In fact, the XRD result displays that the trivalent Er3+ particles may partially be replaced by the divalent Cu2+ host atoms in the bulk Y-123 crystal structure after the critic substitution level of x = 0.03. The optimum Er concentration causes to form more thermodynamically activated super-electrons in the homogeneous superconducting cluster percentages in the paths due to the induced polaronic effect, and accordingly the intrinsic overdoped nature of Y-123 ceramic system transits into optimally doped state. Similarly, the erbium ions enable to increase the mobile hole carrier concentration and homogeneities in the oxidation state of superconducting grains. Namely, the amplitude of pair wave function (Psi=Psi(0)e(-i phi)) is strength enough to form bipolarons in the polarizable lattices and localize of densities of electronic states (DOS) at Fermi level. SEM investigations picture that the surface morphology view and crystallinity quality develop remarkably with the increment in the erbium content up to the critical dopant level of x = 0.03 where the sample exhibits the best grain alignment orientations, densest and smoothest surface morphology with the combination of lowest porous and largest particle distributions well linked each other. All in all, this comprehensive work based on the analysis of Er/Y partial replacement mechanism along the YBa2Cu3O7- y ceramic matrix may open up a newly/novel and feasible area for the advanced engineering, heavy-industrial technology and large-scale applications of type-II superconducting materials. (C) 2021 Elsevier B.V. All rights reserved.
Resorbable membrane design: In vitro characterization of silver doped-hydroxyapatite-reinforced XG/PEI semi-IPN composite
(Elseiver, 2023) Doğan, Deniz; Erdem, Ümit; Bozer, Büşra Moran; Türköz, Mustafa Burak; Yıldırım, Gürcan; Metin, Ayşegül Ülkü
In this study, the production and characterization of silver-doped hydroxyapatite (AgHA) reinforced Xanthan gum (XG) and Polyethyleneimine (PEI) reinforced semi-interpenetrating polymer network (IPN) biocomposite, known to be used as bone cover material for therapeutic purposes in bone tissue, were performed. XG/PEI IPN films containing 2AgHA nanoparticles were produced by simultaneous condensation and ionic gelation. Characteristics of 2AgHA-XG/PEI nanocomposite film were evaluated by structural, morphological (SEM, XRD, FT-IR, TGA, TM, and Raman) and biological activity analysis (degradation, MTT, genotoxicity, and antimicrobial activity) techniques. In the physicochemical characterization, it was determined that 2AgHA nanoparticles were homogeneously dispersed in the XG/PEI-IPN membrane at high concentration and the thermal and mechanical stability of the formed film were high. The nanocomposites showed high antibacterial activity against Acinetobacter Baumannii (A.Baumannii), Staphylococcus aureus (S.aureus), and Streptococcus mutans (S.mutans). L929 exhibited good biocompatibility for fibroblast cells and was determined to support the formation of MCC cells. It was shown that a resorbable 2AgHA-XG/PEI composite material was obtained with a high degradation rate and 64% loss of mass at the end of the 7th day. Physico-chemically developed biocompatible and biodegradable XG-2AgHA/PEI nanocomposite semi-IPN films possessed an important potential for the treatment of defects in bone tissue as an easily applicable bone cover. Besides, it was noted that 2AgHA-XG/PEI biocomposite could increase cell viability, especially in dental-bone treatments for coating, filling, and occlusion.
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 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.
Spectral analysis and biological activity assessment of silver doped hydroxyapatite
(TAYLOR & FRANCIS LTD, 2021) Erdem, Ümit; Bozer, Büşra Moran; Türköz, Mustafa Burak; Metin, Ayşegül Ülkü; Yıldırım, Gürcan
In this study, the hydroxyapatite biomaterials are produced by the precipitation method and the role of silver doping within the different molar ratios of 2.0, 5.0, and 10.0% are investigated with some fundamental analysis, including powder XRD, SEM, EDS, FTIR, Raman, and material densities. In vitro biocompatibility assessment is conducted with cytotoxicity and agar diffusion tests. Moreover, genotoxicity tests determine whether the biomaterials produced cause the mutations or not. In addition, a hemolytic effect test examines the variation of hemolytic behavior of compounds. Also, the cell migration experiments inspect the influence of silver ion levels in biomaterials on many biological processes. The experimental results reveal that the honeycomb-patterned morphological structures are obtained for all the products. FTIR and Raman analyses reveal that the dramatic changes in the characteristic functional group peaks are obtained with the increment in the amount of silver ions. The experimental parts related to the biocompatibility assessment of the study show that there seems to be deterioration in biocompatibility as the silver ion-doping level increases in the system. To sum up, the ideal doping value for bone tissue engineering applications is found to be 2%.

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