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Öğe Effect of annealing conditions on the superconducting properties of nano-sized metallic Au-added Bi1.8Sr2Au0.2Ca1.1Cu2.1Oy(Bi-2212) ceramics(Springer, 2020) Ozkurt, BerdanIn this study, the effects of annealing process on the phase formation and electrical and magnetic properties of nano-sized metallic Au-added Bi-2212 ceramics have been investigated. The Bi(1.8)Sr(2)Au(0.2)Ca(1.1)Cu(2.1)O(y)includingx = 0.2 Au content as starting composition was chosen due to the improved transport properties in the Bi-2212 system, as known in the literature. The samples for the post-annealing technique were exposed at different dwell times (10 m, 30 m, 1 h, and 2.5 h) at a fixed temperature of 870 degrees C after the application of normal heat treatment of 850 degrees C for 120 h. The XRD diagrams clearly indicate that a significant part of the phases in all the samples belongs to Bi-2212 phase. SEM results show that all the samples have randomly oriented grain forms as the main characteristic of applied solid-state method. In all cases, the post-annealed samples showed better superconducting properties of Bi-2212 phase, indicating that the increases in the dwell time positively affect its granular polycrystalline character such as inter-connectivity of the grains, the nucleation, and growth of the Bi-2212 phase. Moreover, the sample with dwell time of 2.5 h at 870 degrees C reveals significant enhancement in theM-Hloops compared to the sample with less dwell time, despite the fact that the Bi-2212 phase can easily decompose into secondary phases such as Cu-free and Bi-free due to thermodynamic instabilities of Bi-2212 at temperatures above 860 degrees C. Finally, the intragranular critical current density values (J(c)) have been obtained by using the data from M-H measurements according to the critical Bean model. It has been found that theJ(c)value (16.5 x 10(4) A/cm(2)in 0.15 T at 15 K) of the sample in the dwell time of 2.5 h at 870 degrees C is higher than that of the sample (13.4 x 10(4) A/cm(2)in 0.15 T at 10 K) with the same starting composition reported in the literature.Öğe Effect of nano-sized metallic Au additions at large scale on the phase stability of Bi-2212 ceramics(Springer, 2019) Ozkurt, BerdanBi1.8Sr2AuxCa1.1Cu2.1Oy (Bi-2212) polycrystalline ceramics with x = 0.25, 0.3 and 0.35 have been prepared by the solid-state reaction method. XRD results showed the Bi-2212 phase as the major one in all samples, accompanied by metallic Au, and some secondary phases such as Bi2CaO4. T-c values are very similar for all samples, indicating that the carrier concentration is independent of the amount of Au. Magnetic properties of samples, determined through magnetic hysteresis measurements (M-H) performed at both T = 2 and 10 K, showed that samples maintain their diamagnetic characteristics in all cases. In addition, J(c) values, calculated from their magnetic hysteresis loops using the Bean's model, showed that addition of metallic Au in high contents leads to an important increase when compared to the samples with low Au content.Öğe Effect of postannealing processes on the properties of hot-pressed Bi2Sr2Ca1Cu1.75Na0.25Oy (Bi-2212) ceramics(Springer, 2023) Ozkurt, Berdan; Madre, M. A.; Sotelo, A.In the present work, the effect of different annealing-time on the properties of Bi2Sr2Ca1Cu1.75Na0.25Oy (Bi-2212) superconducting compound is presented. First, the samples were produced by hot-pressing method under 33 MPa pressure at 750 degrees C in accordance with previous works. After annealing, the samples were kept at 840 degrees C for 15, 30 and 60 h, respectively, for postannealing process. XRD results demonstrate the formation of Bi-2212 phase in large amount in all samples. SEM images show the formation of different grain morphologies depending on the postannealing time. The sample postannealed for 60 h at 840 degrees C has the highest superconducting transition temperature (T-c, onset), 91 K, obtained from M-T measurements. The magnetic properties of samples have been investigated using M-H hysteresis loops at 15 K in the range - 1.6 x 10(6) to + 1.6 10(6) A/m. The widest M-H curves were obtained in the postannealed sample for 60 h at 840 degrees C, probably as a result of both the improvement of crystallinity, cleaner grain boundaries and better grain orientation. In addition, the widest hysteresis curve observed in that sample in the entire applied magnetic field range is an indication that it has strong pinning behavior. The critical current density (J(c)) was investigated via Bean's model from these data. Finally, the sample postannealed at 840 degrees C for 60 h reached a J(c) value of 2.903 x 10(6) A/cm(2) at H = 1.9 T and T = 15 K, which is, approximately, 44% higher than the determined in annealed samples (2.015 x 10(6) A/cm(2)).Öğe Effects of different dwell-times under low pelletization pressure on the physical properties of the Bi-2212 ceramics(Springer, 2022) Kara, Emine; Ozkurt, Pinar; Ozkurt, BerdanWe reported the evaluation of superconducting properties of Bi-2212 ceramics prepared under different dwell times between 12 and 72 h under 114 MPa constant pelleting pressure using precursors produced through the conventional solid-state reaction. From the XRD patterns, it is clear that all samples contain a high Bi-2212 phase ratio. Moreover, they include only Bi2CaO4 as secondary phase(.) This means that even though the applied pelleting pressure was low, it allowed the formation of the Bi-2212 phase due to its high-thermodynamic stability. SEM results showed that all samples have similar grain morphology with random grain orientation and formation of homogeneous phases, except that they have different grain sizes. T-c values obtained from the M-T curve (magnetization vs. temperature) for all samples are in the range of 77-82 K, indicating that the Bi-2212 phases are formed in the ideal ratio. The magnetic properties of the prepared samples were investigated using M-H (Magnetic hysteresis) and magnetic J(c) curves (critical transport current density calculated in the framework of the Bean model), at 15 K. It has been found that the dwell time of 12 h at constant pelleting pressure of 114 MPa provided the best superconducting properties and the largest J(c) values (1.605 x 10(4) A/cm(2) at T = 15 K and H = 1.5 T) for the Bi-2212 phase in this work. In addition, to better examine the flux pinning properties of samples, the pinning force density (Fp) was calculated from the J(c) and B values. The maximum pinning force (3.929 Oe A/cm(2) at T = 15 K and H = 1.95) has been obtained in the sample including dwell time of 12 h under 114 MPa.Öğe Enhanced critical current density in the nano-sized metallic Au-added Bi1.8Sr2Au0.3Ca1.1Cu2.1Oy (Bi-2212) ceramics by means of optimization of the dwell time at 870 °C(Springer, 2021) Ozkurt, BerdanThis study investigates how the postannealing process applied to Bi1.8Sr2Au0.3Ca1.1Cu2.1Oy (Bi-2212) ceramics at 870 degrees C can improve their J(c) values. Bi1.8Sr2Au0.3Ca1.1Cu2.1Oy has been selected in the present work as initial composition because nano-sized metallic Au additions at large scale positively affect the superconducting properties of Bi-2212 ceramics due to the enhancement of intergranular coupling between the grains, as reported in the literature. These Bi-2212 ceramics were prepared by the solid-state reaction method, including a heat treatment at 860 degrees C for 96 h for sintering. Then, the samples in the postannealing stage are exposed at different dwell times (8 h, 16 h, and 32 h) at 870 degrees C. XRD analysis showed that all the samples have similar chemical composition, with Bi-2212 phase as the major one, and the presence of minor impurity phases such as Au, Bi2CaO4 and Bi4Sr4CaCu3O4. The crystalline size of the samples calculated according to the Debye-Scherrer equation increases with increasing dwell time. Magnetization-temperature (M-T) curves were used to determine the superconducting transition temperatures (T-c(mag)) of all the samples, showing that they are around 70 K. This means that the dwell-time process applied at 870 degrees C in the present study does not degrade their transition temperatures. To observe how both diamagnetic character and grain growth of the Bi-2212 phases affect magnetic properties, as a function of the different dwell times at 870 degrees C, magnetic-hysteresis measurements (M-H) at 15 K were performed. It has been found that the thermal treatment at 870 degrees C for 32 h favors the formation of the widest hysteresis loop due to better intergrain coupling between grains. Finally, the magnetic critical current density (J(c)(mag)) has been obtained through the data from M-H loops according to the critical Bean model. The highest J(c) value, 39.92 x 10(4) A/cm(2) under 0.2 T at 15 K, is higher than the J(c) of for the samples with the same composition reported in the literature (13.42 x 10(4) A/cm(2) under 0.15 T at 10 K). These results clearly show that appropriate postannealing processes can significantly improve superconducting properties of Bi-2212 ceramics.Öğe Enhanced Superconducting Properties in Bi2Sr2Ca1Cu1.75Na0.25Oy Ceramics Prepared by Hot-Pressing Under Different Pressures and Temperatures(Springer, 2022) Oner, Bulut; Ozkurt, Pinar; Madre, M. A.; Ozkurt, Berdan; Sotelo, A.Bi2Sr2Ca1Cu1.75Na0.25Oy ceramics have been prepared by the classical solid state reaction method followed by hot-pressing process under several applied pressures and temperatures: 22 and 33 MPa at 750 degrees C, and 22 MPa at 800 degrees C. X-ray diffraction data indicate that the major phase in all samples is the Bi2Sr2Ca1Cu1.75Na0.25Oy phase, accompanied by small amounts of Bi2CaO4 and Bi3Sr4CaCu3O4 secondary phases. Microstructural results clearly showed that the best grain orientation has been obtained under 33 MPa at 750 degrees C. Critical temperatures, T-C (onset) and T-C (offset), of these samples were significantly increased to 96.6 and 85.6 K, respectively, pointing out to a good intergranular coupling. M-H hysteresis curves for all samples display a very large area due to the microstructural characteristics obtained in these samples. The highest critical current density, calculated from M-H measurements according to Bean's model, has been obtained in samples prepared under 33 MPa at 750 degrees C (201.5 x 10(4) A/cm(2) at 1.9 T and 15 K), which are much larger than those reported for samples with the same composition prepared through the classical solid state method.Öğe Enhanced thermoelectric properties in Bi2Sr2-XBaxCo2Oy ceramics by Ba doping(Elsevier, 2022) Ozkurt, Berdan; Madre, M. A.; Sotelo, A.; Torres, M. A.Bi2Sr2-xBaxCo2Oy polycrystalline samples (0.00 <= x <= 0.15) were prepared through the classical solid-state reaction method. It has been found that Ba-doped Bi2Sr2Co2Oy was obtained as major phase in all samples, based on XRD results. On the other hand, SEM studies have shown the presence of small amounts of secondary phases. The electrical resistivity values of all Ba doped samples decreased when compared to the undoped one, being minimum for the 0.075Ba doped ones. Seebeck coefficient increase with the increasing temperature in all samples, reaching the highest values in the 0.025 Ba doped sample. Finally, power factor has been calculated using the Seebeck coefficient and electrical resistivity values to determine the thermoelectric performances of samples. The maximum PF value of 0.14 mW/K2 m at 650 degrees C was obtained for 0.075Ba doped sample, which is around 25% higher than the undoped sample at the same temperature. All these results clearly show that the thermoelectric properties of the Bi2Sr2Co2Oy system can be improved by Ba doping at optimal values.Öğe Enhanced thermoelectric properties in Bi2Sr2-xBaxCo2Oy via doping and texturing for integration in more efficient thermoelectric generators(Elsevier, 2025) Ozkurt, Pinar; Madre, M. A.; Ozkurt, Berdan; Torres, M. A.; Sotelo, A.Bi2Sr2-xBaxCo2Oy (0 <= x <= 0.15) thermoelectric samples have been sintered, and textured through the laser floating zone process using a Nd:YAG laser. Powder XRD studies showed that the thermoelectric phase is the major one in all cases, with higher amount of secondary phases in the textured ones due to their incongruent melting. Microstructural characterization revealed a drastic microstructural modification in the textured samples, when compared to the sintered ones, producing much larger and well oriented grains along the growth direction. These characteristics led to lower electrical resistivity in textured samples, reaching the minimum at 650 degrees C (14.8 mS2 cm) in 0.125Ba-doped samples, which is lower than those typically reported in this system. On the other hand, no significant variation in Seebeck coefficient has been found between the samples. This behaviour is associated to the isovalent doping which does not modify the charge carrier concentration in the material, and the highest values at 650 degrees C (166 mu V/K) are in the order of the reported in the literature. As a consequence, power factor values are mainly driven by the electrical resistivity values, leading to the highest values at 650 degrees C in 0.125Ba-doped textured samples (0.19 mW/K2m) due to their lowest resistivity. These values are higher than the reported for textured materials and in the order of the best reported for this compound in bulk form. All these properties, together with the possibility of the direct integration of these compounds in thermoelectric modules, make them very attractive for practical applications ensuring access to affordable, reliable, and sustainable energy for all.Öğe Improvement in electrical properties of Bi-2212 superconducting materials substituted with large-scale nano-sized tin(Springer Heidelberg, 2024) Aytekin, Mehmet Ersin; Akyol, Mustafa; Ozkurt, BerdanIn the current work, the effect of nano-sized Sn (50 nm)/Sr partial replacement on the superconducting properties such as crystal structure, quality of intra- and intergrain boundary coupling, dc electrical resistivity, and dc magnetization in the Bi-2212 ceramic superconductors were investigated. Ceramic superconductors with nominal composition of Bi2Sr2-x(Sn)(x)Ca1Cu1.75Na0.25Oy where x = 0.25, 0.30, 0.35 and 0.40 were prepared by solid-state reaction method and characterized by powder X-ray diffraction (XRD), dc electrical resistivity, scanning electron microscopy (SEM) and magnetic hysteresis (M-H) measurements. Phase examination of by XRD indicated that the doping of x = 0.25 ratio nano-sized SnO2 to the strontium sites improved the formation of the Bi-2212 high-temperature superconducting phase. SEM micrographs showed that the morphological structure of all samples consisted of plate-like grains, which were separated from each other by grain boundaries, indicating the Bi-2212 superconducting phase. The highest superconductivity transition temperature among the samples was measured as the T-c(onset) = 86 K at x = 0.25 in Bi2Sr2-x(Sn)(x)Ca1Cu1.75Na0.25Oy. M-H loops of the Bi2Sr2-x(Sn)(x)Ca1Cu1.75Na0.25Oy sample at x = 0.25 ratio is larger compared to other examples, indicating improvement intergrain connectivity as well as enhanced flux pinning centers. In addition, the critical current (J(c)) values of the samples were calculated from M-H measurement using Bean's critical current model. The best J(c) values were obtained as 570 A/cm(2) at 15 K, which is a relatively high value for BSCCO superconductors with polycrystalline structure.Öğe Improving thermoelectric properties of Ca3Co4O9+ through both Na doping and K addition at optimal values(Springer, 2019) Ozkurt, Berdan; Aytekin, M. Ersin; Madre, M. A.; Sotelo, A.; Torres, M. A.Ca2.93Na0.07Co4Oy/x wt% K2CO3 (x=0.00, 0.01, and 0.03) polycrystalline ceramics were prepared by conventional solid-state method. XRD results have shown that all samples predominantly include Ca3Co4O9 phase together with small amounts of secondary phases. SEM images show that all samples have randomly oriented plate-like grains in different sizes. The electrical resistivity measurement showed that electrical properties of Ca3Co4O9 ceramics can be improved significantly by both, Na doping and K addition at their optimal values. The effect of dopants on thermoelectric properties of Ca3Co4O9 was examined by both, Seebeck coefficient and power factor, being higher in K-added than in the pure samples, indicating that thermoelectric properties of samples are positively affected when alkaline elements enter into their structure.Öğe Large Jc Enhancement of Bi-2212 Ceramics by Triple Doping of Li, K, and Na in Bi1.8-x(Li,Na,K)xSr2Ca1.1Cu2.1Oy (x=0.05, 0.1, and 0.25) Composition(Springer, 2021) Ozkurt, BerdanThe samples with compositions of Bi1.8-x(Li,Na,K)(x)Sr2Ca1.1Cu2.1Oy (x = 0.05, 0.1, 0.25) were prepared by the solid-state reaction method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and DC magnetization measurements. XRD data indicates that all samples have an ideal ratio of Bi-2212 phase; moreover, some impurity phases such as Bi2CaO4 and Bi4Sr4CaCu3O4 are observed to disappear in the maximum alkaline-doped sample (x = 0.25). SEM observations have shown that, with the increase in the amount of alkaline-doped elements, the grain sizes grow significantly. The highest onset superconducting transition temperature obtained from M-T data belongs to the alkaline-doped (Na, K, and Li) samples at high contents (x > 0.05). It has been found that the sample with x = 0.25 (Na, K, Li) has the largest magnetic hysteresis loop, indicating that high level of triple alkaline element doping positively affects the superconductivity properties of the Bi-2212 phase due to the better intergranular coupling. In addition, Bean's critical model has been used for determining the critical current density. It has been found that maximum J(c) of 141.42 x 10(4) A/cm(2) at H = 1 kOe and T = 15 K is achieved in the x = 0.25 alkaline-doped sample, which is higher than the pure samples obtained by the same initial conditions in literature.Öğe Structural, electrical and magnetic properties of Au doped Bi-2212 superconductors(Pamukkale Univ, 2021) Gun, Esen; Ozkurt, Berdan; Aytekin, Mehmet Ersin; Ocakoglu, KasimIn this work effect of nano sized Au additions on the physical and magnetic properties of Bi-2212 phase with general formula of Bi(1.8)Sr(2)Ca(1.1)Oy+Au-x (x=0.0, 0.05, 0.1 and 0.2) are reported. The samples were prepared by solid state reaction method. Au element used in the material preparation process was obtained by reduction of HAuCl4 center dot 3H(2)O. The physical, morphological and superconducting properties of the samples have been characterized by XRD, scanning electron microscopy (SEM), dc electrical resistivity and magnetic-hysteresis loop measurements. It is observed that pure and Au added samples have plate like grain structure, indicating predominantly the formation of Bi-2212 phase. The results of dc electrical resistivity showed that the sample including x=0.2 HAuCl4 center dot 3H(2)O has the highest transition temperature (T-c) due to the formation of optimum hole concentration in copper oxide layers. Also, M-H measurements were carried out at T=10 K and T=25 K The Largest hysteresis loop due to its stronger coupling between grains was obtained on maximum HAuCl4 center dot 3H(2)O added sample.Öğe The Influence of Nano-Sized SnO2 Doping on Physical and Magnetic Properties of the Bi2Sr2-x(SnO2)xCa1Cu1.75Na0.25Oy Superconductors(Springer, 2020) Aytekin, Mehmet Ersin; Ozkurt, BerdanIn this study, we have investigated the effect of nano-sized SnO2 (50 nm) doping on the superconducting properties of Bi-2212 ceramics. In the first stage of the the experiment, the composition Bi2Sr2-xSnxCa1Cu1.75Na0.25Oy where x = 0, 0.05, 0.1 and 0.2 is selected due to the positive effect of sodium substitution on the grain sizes of the Bi-2212. X-ray diffraction results indicate that all the samples have considerable amount of Bi-2212 phases. Scanning electron microscopy (SEM) analysis of all samples clearly shows significant grain growth due to lower crystallization temperature formed by sodium. The lowest resistivity in the nano-sized SnO2-doped samples at 150 K is obtained for the sample of x = 0.05. The M-H hysteresis loops for all the samples have been measured within +/- 2 T externally applied magnetic field range at T = 15 and 25 K, respectively. The undoped and the sample with x = 0.05 SnO2 have both large M-H loops, indicating the improvement of flux pinning properties of the Bi-2212 as well as enhanced intergrain connectivity. However, the width of the hysteresis loop in samples including high (x > 0.05) SnO2 contents significantly decreased, indicating deterioration in superconducting properties of the Bi-2212 system. Additionally, the critical current densities (J(c)) of all the samples at 15 K are calculated from their hysteresis loop measurements by using Bean's critical state model. When compared with other samples, a slight increase in J(c) is obtained for x = 0.05 SnO2. The results indicate that the optimal contents of sodium (x = 0.25) and nano-sized SnO2 (x = 0.05) in the Bi-2212 system are effective for achieving enhanced superconductivity properties.Öğe Wavelength-induced modifications of thermoelectric properties of laser-textured Bi2Sr2-xBaxCo2O8 ceramics for sustainable energy generation(Elsevier, 2025) Ozkurt, Pinar; Madre, M. A.; Ozkurt, Berdan; Torres, M. A.; Sotelo, A.; Rasekh, Sh.Ba-doped Bi2Sr2-xBaxCo2O8 samples have been directionally grown using the Laser Floating Zone technique using two different lasers, leading to significant differences between the samples. Powder XRD patterns revealed that the major phase in all samples is the thermoelectric one, without notable differences with the type of laser. On the other hand, microstructure studies showed significant differences between Nd:YAG and CO2-grown samples. Use of CO2 laser promoted a reduction of secondary phases content and a higher grain alignment. Furthermore, Ba-doping further decreases the secondary phases content and increases grain alignment. The electrical resistivity was affected by the different microstructures, being lower for the CO2-grown samples, reaching the lowest values at 650 degrees C in 0.125Ba-doped samples, 12.8 m Omega cm, which are among the best reported in the literature. However, S is maintained practically unchanged independently of the laser and composition. As a consequence, PF values mainly depend on the electrical resistivity and, consequently, the highest values at 650 degrees C, 0.22 mW/K2m, have been achieved in 0.125Ba samples textured with CO2 laser. These values are around the best ones presented in the literature for this material. Additionally these textured materials possess the advantage of avoiding the typical machining processes which are necessary in bulk materials for their integration into thermoelectric modules. These characteristics may enhance the interest on these materials in order to be used in practical devices to help their use to produce affordable, reliable and sustainable energy for all mankind.
