Sürdürülebilir Kalkınma Amaçları
Yazarlar
- Erdem, O.(6)
- Şenay, Volkan(6)
- Bayram, Ozkan(5)
- Korkmaz, Şadan(5)
- Pat, Suat(5)
- Özen, Soner(5)
- Simsek, Onder(4)
- Yanmaz, E.(4)
- Celik, S.(2)
- Guney, Harun(2)
- Igman, Erdal(2)
- Ozturk, K.(2)
- Yudar, H. Hakan(2)
- Abdioglu, M.(1)
- Cavusoglu, Bulent(1)
- Cuce, Erdem(1)
- Engin, M. Alptekin(1)
- Ertargin, Mehmet Emrah(1)
- Guclu, Tamer(1)
- Guner, S.B.(1)
- Kabaer, M.(1)
- Kirat, G.(1)
- Murat Ozer, Mustafa(1)
- Pat, Zerrin(1)
- Sarıkoç, Selçuk(1)
- Sener, Emre(1)
- Örs, İlker(1)
- Ünalan, Sebahattin(1)
- İgman, Erdal(1)
Yayınlar
- Derleme MakaleAçık Erişim2019Scopus SJRQ2Thermoelectric Coolers (TECs): From Theory to Practice
Guclu, Tamer; Cuce, Erdem
Thermoelectric coolers (TECs) are solid state units, which provide reliable energy conversion with no noise or vibration. They are also lightweight and do not include any moving parts. The current coefficient of performance (COP) range of TECs has shown a trend of improvement, and TECs have a wide range of usage areas. Within the scope of this research, TECs are comprehensively evaluated in terms of several aspects such as type, material, design, modelling, thermal performance, potential applications, economic and environmental issues. It can be achieved through the results that the COP of TECs is highly dependent on the temperature difference between hot and cold side (ΔT), and maximum COP is obtained when ΔT is close to zero. It is also observed that COP can be enhanced by more than 55% when the hot side is thermally regulated by phase change materials (PCMs) or integrated with a water cooling unit.
AtıfScopus69WoS61OpenAlex76
İncele - MakaleAçık Erişim2019Scopus SJRQ2Some physical properties of nanostructured Al doped ZnO thin films synthesized by RF magnetron sputtering at room temperature
Şenay, Volkan
In this research, AZO thin films were deposited on glass substrates with 70 W, 100 W and 125 W RF powers at room temperature by RF magnetron sputtering technique. The structural, optical and surface properties of the produced thin films were investigated. According to the obtained results, the investigated thin films had a crystalline structure and they showed high transparency in the visible region. The increase of RF power produced thicker films. Relatively thicker AZO films produced with higher RF power exhibited greater number of interference fringes in the reflectance and transmittance spectra. The refractive index values of the film produced with 125 W RF power were considerably lower than those of the films produced with 70 W and 100 W due to the decreased packing density. The optical energy band gap values of the produced AZO thin films were higher than that of undoped ZnO films. This expansion resulted from the Burstein–Moss effect. However, the band gap energy value as well as the roughness of the film surface decreased like refractive index with an increase in RF power, especially after 100 W. As a result, the values corresponding to the optical and surface properties can be tuned and AZO thin films can be produced by RF magnetron sputtering technique as promising candidates for optoelectronic devices and transparent conductive oxide applications.
AtıfScopus14WoS14OpenAlex13İncele - MakaleAçık Erişim2019Scopus SJRQ2Experimental Study of Hydrogen Addition on Waste Cooking Oil Biodiesel-Diesel-Butanol Fuel Blends in a DI Diesel Engine
Sarıkoç, Selçuk; Ünalan, Sebahattin; Örs, İlker
In this study, the effects of hydrogen addition on diesel-biodiesel-butanol fuel blends were investigated in terms of engine performance, combustion, and emission characteristics under different engine operating conditions. The experiments were performed with eight different fuel blends at a constant engine speed of 2000 rpm, which is the maximum torque value of all test fuels. The four operating conditions were at 25%, 50%, 75%, and 100% engine loads. Hydrogen was delivered to diesel-biodiesel-butanol fuel blends through the intake manifold with different rates of fuel mass consumption. The experiment results were compared with euro diesel and absence of hydrogen addition for all test fuels. The experimental results have revealed that at 2000 rpm engine speed, the brake torque, in-cylinder pressure, and exhaust gas temperature increased with the addition of hydrogen. Nevertheless, the brake-specific fuel consumption, carbon monoxide (CO), carbon dioxide (CO2), hydrocarbon (HC), nitrogen oxides (NOx), and smoke opacity emissions decreased under various engine conditions. The heat release rate was generally shown to be decreased with higher engine loads and increased with lower engine load conditions, while a rise in thermal efficiency was observed. Therefore, the addition of hydrogen in a diesel engine usually exhibited fewer emissions, improved the combustion process, and increased the brake torques of the engine by comparison to the absence of hydrogen addition.
AtıfScopus54WoS43OpenAlex54İncele - MakaleAçık Erişim2019Scopus SJRQ2Investigation of structural, morphological and optical properties of Nickel-doped Zinc oxide thin films fabricated by co-sputtering
Bayram, Ozkan; Sener, Emre; İgman, Erdal; Simsek, Onder
In this study, it was aimed to grow Nickel doped (0.0 at.%, 0.16 at.%, 0.20 at. % and 0.24 at. %) Zinc Oxide (NZO) thin films on quartz substrates using Magnetron Sputtering technique. NZO thin films were obtained at a temperature of 450 °C, a pressure of 480 m Torr and a deposition time of 30 min. Co-sputtering process for both Ni and ZnO target was performed using two separate power sources. The DC power of the Ni target material was 20, 30 and 40 W, respectively while the radio frequency (RF) power of the Zinc oxide (ZnO) target material was set to 150 W. Using XRD analysis, thin films were found to have polycrystalline morphology, and the average crystallite size changed significantly depending on the increased Ni doping level. The optical Transmittance of the thin films was greater than 90% in the visible region (550 nm), and this value tends to decrease slightly by Ni doping. The optical band gap (E g ) firstly decreased and then slightly increased with the Nickel doping ratio and these values were found to be 3.23 eV, 3.11 eV and 3.15 eV, respectively, with increase of Ni doping.
AtıfScopus34WoS30OpenAlex37İncele - MakaleYalnız künye2019Scopus SJRQ1Rotation invariant curvelet based image retrieval & classification via Gaussian mixture model and co-occurrence features
Engin, M. Alptekin; Cavusoglu, Bulent
Demand for better retrieval methods continue to outstrip the capabilities of available technologies despite the rapid growth of new feature extraction techniques. Extracting discriminatory features that contain texture specific information are of crucial importance in image indexing. This paper presents a novel rotation invariant texture representation model based on the multi-resolution curvelet transform via co-occurrence and Gaussian mixture features for image retrieval and classification. To extract these features, curvelet transform is applied and the coefficients are obtained at each scale and orientation. The Gaussian mixture model (GMM) features are computed from each of the sub bands and co-occurrence features are computed for only specific sub band. Rotation invariance is provided by applying cycle-shift around the GMM features. The proposed method is evaluated on well-known databases such as Brodatz, Outex_TC_00010, Outex_TC_00012, Outex_TC_00012horizon, Outex_TC_00012tl84, Vistex and KTH-TIPS. When the feature vector is analyzed in terms of its size, it is observed that its dimension is smaller than that of the existing rotation-invariant variants and it has a very good performance. Simulation results show a good performance achieved by combining different techniques with the curvelet transform. Proposed method results in high degree of success rate in classification and in precision-recall value for retrieval.
AtıfScopus8WoS5OpenAlex6İncele - MakaleYalnız künye2018Scopus SJRQ2Investigation of the effect of RF energy on optical, morphological, chemical and antibacterial properties of PolyTerpenol thin films obtained by RF-PECVD technique
Bayram, Ozkan; Simsek, Onder
In this study, it was aimed to obtain PolyTerpenol thin films by radio frequency plasma enhanced chemical vapor deposition technique using Terpinen-4-ol essential oil, which is organic compounds. The surface morphology and chemical properties of polymer thin films were investigated by atomic force microscopy (AFM) and Fourier transform infrared spectroscopy. AFM analyzes of PolyTerpenol thin films revealed that the thin films are homogeneous, smooth and nonporous. The optical properties of the thin films were determined using UV–Vis spectrophotometer. When optical band gaps of thin films were examined, it was found that this value varied from 3.83 to 3.20 eV. The extinction coefficients of the obtained thin films according to the increasing RF energy were calculated as 0.0011, 0.0060, 0.0085 and 0.0150, respectively, at a wavelength of 320 nm. In addition, antibacterial effects of these thin films against Escherichia Coli (E.Coli) bacteria were also investigated. The PolyTerpenol thin films were found to have high antibacterial activity against E. Coli bacteria.
AtıfScopus8WoS8OpenAlex11İncele - MakaleAçık Erişim2018Scopus SJRQ2Synthesis and characterization of Zn-doped Mn3O4 thin films using successive ionic layer adsorption and reaction technique: Its structural, optical and wettability properties
Bayram, Ozkan; Ertargin, Mehmet Emrah; Igman, Erdal; Guney, Harun; Simsek, Onder
In this study, it is aimed to obtain Zn doped Mn3O4 (manganese oxide) nanostructured thin films on the soda lime glass substrates by successive ionic layer adsorption and reaction technique. The tetragonal crystal structure of the all thin films was detected using XRD spectroscopy. The average crystallite size of undoped Mn3O4 thin films was calculated to be 29 nm and for Zn-doped thin films, this value decreased to 23 nm with increasing Zn concentration. Characteristic peaks for thin films were also confirmed by RAMAN spectroscopy. The morphological structures of zinc-doped manganese oxide nano-sheets thin films were revealed by SEM. Using UV–Vis spectroscopy, it was found that the optical band gap of Mn3O4 thin films decreased from 2.05 to 1.73 eV with Zn doping. It has also been understood from the wettability analyzes of thin films that all thin films have a hydrophilic character. From all these analyzes, it is thought that the Zn doped Mn3O4 thin films have the potential to be used in supercapacitor applications.
AtıfScopus25WoS22OpenAlex25İncele - MakaleYalnız künye2018Scopus SJRQ2Influence of coronene addition on some superconducting properties of bulk MgB2
Erdem, O.; Kirat, G.
This study reports the effect of coronene (C24H12) addition on some superconducting properties such as critical temperature (Tc), critical current density (Jc), flux pinning force density (Fp), irreversibility field (Hirr), upper critical magnetic field (Hc2), and activation energy (U0), of bulk MgB2 superconductor by means of magnetisation and magnetoresistivity measurements. Disk-shaped polycrystalline MgB2 samples with varying C24H12 contents of 0, 2, 4, 6, 8, 10 wt%, were produced at 850 °C in Ar atmosphere. The obtained results show an increase in field-Jc values at 10 and 20 K resulting from the strengthened flux pinning, and a decrease in critical temperature (Tc) because of C substitution into MgB2 lattice, with increasing amount of C24H12 powder. The Hc2(0) and Hirr(0) values are respectively found as 144, 181, 172 kOe, and 128, 161, 145 kOe for pure, 4 wt% and 10 wt% C24H12 added samples. The U0 depending on the magnetic field curves were plotted using thermally activated flux flow model. The maximum U0 values are respectively obtained as 0.20, 0.23 and 0.12 eV at 30 kOe for pure, 4 wt% and 10 wt% C24H12 added samples. As a result, the superconducting properties of bulk MgB2 at high fields was improved using C24H12, active carbon source addition, because of the presence of uniformly dispersed C particles with nanometer order of magnitude, and acting as effective pinning centres in MgB2 structure.
AtıfScopus12WoS12OpenAlex11İncele - MakaleAçık Erişim2018Scopus SJRQ2Effect of the number of cycles on the optical and structural properties of Mn3O4 nanostructures obtained by SILAR technique
Bayram, Ozkan; Simsek, Onder; Guney, Harun; Igman, Erdal; Murat Ozer, Mustafa
In this study, nanostructured Mn3O4 (manganese oxide) thin films were successfully obtained by successive ionic layer adsorption and reaction (SILAR) method on the soda lime glass substrates using Manganese Nitrate (Mn(NO3)2) and Ammonium hydroxide (NH4(OH)) as cationic and anionic precursors respectively. Structural and morphological characterizations of the Mn3O4 films obtained at different cycles were determined using X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The crystal structure of the thin films were also confirmed by RAMAN spectroscopy. Optical properties such as absorption, transmission, reflection, extinction coefficient and optical band gap of nanostructured Mn3O4 thin films were determined by UV–Vis spectroscopy. SEM images showed that the manganese oxide nanosheets formed uniformly on substrate surface. As the deposition cycles increased, nano-sheets structure deteriorated. The optical band gap of Mn3O4 thin films varied from 2.12 to 2.59 eV, depending on the increase in number of cycles. From contact angle measurements of thin films, it was determined that thin films had hydrophilic character.
AtıfScopus14WoS14OpenAlex16İncele - MakaleYalnız künye2018Scopus SJRQ2Determination of the optical and chemical properties of aniline doped plasma polymerized cineole thin films synthesized at various RF powers
Bayram, Ozkan
Aniline-doped plasma polymerized cineole (PPCin) thin films were produced on glass substrates by plasma polymerization technique under varying Radio Frequency (RF) power levels. PPCin thin films were produced at 30 min deposition time and at 50, 75 and 100 W RF energies. Surface morphologies of pure and aniline-doped PPCin thin films obtained on glass substrates were investigated by AFM. It was found that the average surface roughness of pure PPCin thin films increased from 0.19 to 30.6 nm due to the dopant effect and RF energies. The optical band gap for pure polymer thin film was 3.65 eV, but with the effect of doping, these value was found to be 3.54, 3.29 and 3.93, respectively, with increasing RF energy. The extinction coefficient and refractive indices of PPCin thin films were calculated as between 0.065 and 0.92 and between 1.24 and 1.57 respectively, at the wavelength of 400 nm. Wettability analyzes of PPCin thin films were also determined using the water contact angle (WCA) measurement and all thin films were found to have hydrophilic character.
AtıfScopus8WoS7OpenAlex9İncele - MakaleAçık Erişim2017Scopus SJRQ3Enhanced Pinning Properties of Laser-Irradiated Bulk MgB2 Superconductors
Erdem, O.; Yanmaz, E.
In order to investigate the effect of laser irradiation on the superconducting properties of MgB2, a pellet-shaped sample was produced and cut into two pieces. The dot-shaped molten patterns, with the distance of 100 µm between them, were formed on the surface of one of the pieces by using an Nd:YVO4 laser. The grains of the irradiated sample were significantly grown due to the laser-induced sintering. The modified surface appeared to have dense and compacted grains as a result of increasing interconnectivity among the superconducting grains. The critical current densities at 5 K in a field of 3 T were found to be 5.38 × 104 and 8.96 × 104 A cm−2 for the reference and the irradiated samples, respectively. The increment of critical current density for the irradiated sample is presumably connected with the changing of pinning mechanism after the laser irradiation. For the irradiated sample which showed a higher value of critical current density at 5 K under high fields, Δκ pinning was obtained as a dominant pinning mechanism, while the normal point pinning was dominant for the reference one. These results point out that the superconducting properties of bulk MgB2 can be changed and improved via laser irradiation in a short time.
AtıfScopus12WoS10OpenAlex11İncele - MakaleAçık Erişim2017Scopus SJRQ2Effect of laser irradiation on superconducting properties of bulk MgB2 sintered at different temperatures
Erdem, O.; Yanmaz, E.
The surfaces of MgB2 bulk samples produced by a pellet/closed tube method at two different sintering temperatures of 650 and 850 °C, after hot pressing at 200 °C, were irradiated with the same irradiation dose by using an Nd:YVO4 laser in order to study the possible potentiality of laser irradiation to improve pinning performances and critical current density of MgB2 superconductor. The measurements showed that the magnetic field dependence of the critical current density values of irradiated sample sintered at 650 °C slightly increased with a narrowing in superconducting transition region as compared to the reference sample sintered at same temperature. However, irradiated sample sintered at 850 °C showed a decrease in pinning performance and similar critical temperature values as compared to the corresponding reference sample. From these results it can be said that the same laser irradiation dose affects superconducting properties of bulk MgB2 in different ways depending on sintering temperature of the superconductor.
AtıfScopus4WoS4OpenAlex4İncele - MakaleAçık Erişim2017Scopus SJRQ2The substrate effect on Ge doped GaN thin films coated by thermionic vacuum arc
Özen, Soner; Korkmaz, Şadan; Şenay, Volkan; Pat, Suat
This study focuses on characterization and understanding of the substrate effect on Ge doped GaN thin films coated onto transparent substrates. The produced films were deposited onto unheated glass and unheated polyethylene terephthalate by using thermionic vacuum arc technique. Gallium nitride and germanium pellets were used in the thin film production. Reflectance, refractive index and thicknesses of Ge doped GaN thin films were measured by optical interferometer using Cauchy model for fitting. The transmittances were determined in the wavelength range between 200 and 1000 nm by using UV–Vis double beam spectrophotometer. The optical Tauc method was used to determine the band gap energies of produced thin films. Surface morphologies of produced thin films were characterized by atomic force microscopy and also field emission scanning electron microscopy. In conclusion, the substrate effect on the optical and morphological properties of the produced thin films was observed.
AtıfScopus8WoS8OpenAlex9İncele - MakaleAçık Erişim2017Scopus SJRQ2Zn/ZnSe thin films deposition by RF magnetron sputtering
Yudar, H. Hakan; Pat, Suat; Korkmaz, Şadan; Özen, Soner; Şenay, Volkan
In this paper, Zn/ZnSe thin films were deposited on glass substrates by RF magnetron sputtering system. XRD analyses were done. Zn and ZnSe phases were obtained. Miller indices of obtained Zn phases were detected in (320), (620) and (112) crystal formation. For the ZnSe phases, only one peak of (110)/(220) was observed. The surface morphology of the samples was investigated by an atomic force microscopy tools. It found that average roughness of the films was increased by raised RF power. The thin films around 80 % of high transmittance were measured. The band gap values were calculated as to be ~2.80 eV by the Cauchy model. The calculated refractive indices values were approximately 2.25 by a relation between the refractive index and the band gap.
AtıfScopus31WoS24OpenAlex29İncele - MakaleAçık Erişim2017Scopus SJRQ3Lateral Position Effect of Auxiliary Permanent Magnets on the Magnetic Force Properties of Cylindrical YBCO
Abdioglu, M.; Kabaer, M.; Ozturk, K.; Erdem, O.; Celik, S.
The magnetic levitation force (MLF) and the guidance force (GF) should be improved for loading capacity and stability of Maglev systems, respectively. Although there are some ways to increase these properties, using of auxiliary onboard permanent magnets (PMs) can be considered as the most efficient one. The auxiliary PMs increase the MLF significantly but, at the same time, decrease the GF. We have searched a solution to overcome this problem in this study. Firstly, we have determined the optimum vertical positions of the auxiliary PMs and then we have investigated the vertical levitation force and lateral guidance force of hybrid Maglev system depending on lateral position of auxiliary PMs in different cooling heights (CHs). A cylindrical YBCO superconductor, fabricated by a top seeding method with the diameter of 45 mm and the height of 15 mm, was used as a high-temperature superconductor (HTS). The maximum increment rate in MLF and the minimum decrement rate in GF were observed as 277 and 54 %, respectively. The increment in MLF was obtained five times more than the decrement in GF, and this reality points out that the results of this study can be useful for improving the loading capacity and thus enhancing the practical applicability of Maglev systems.
AtıfScopus16WoS14OpenAlex14İncele - MakaleAçık Erişim2017Scopus SJRQ2Effect of XRD relative intensities of the Li (002) on surface, optical and electrochemical impedance spectroscopy analyses of the deposited LiCoO2 thin film
Yudar, H. Hakan; Pat, Suat; Özen, Soner; Şenay, Volkan; Korkmaz, Şadan; Pat, Zerrin
In this paper, the effect of RF power on LiCoO2 thin films was investigated using X-ray diffractometer (XRD), atomic force microscopy, UV–Vis spectrophotometer, and potentiostat. The microstructural, surface, optical and electrochemical impedance measurements were performed to LiCoO2 thin films, are used to for the fully solid-state battery cathode material. According to obtained results, the relative intensities of the Li (002) crystal phase in XRD patterns of deposited LiCoO2 thin films were increased by increasing applied RF power, for the first time. The intensity of the LiCoO2 (104) plane is nearly invariant. The relative intensities of the LiCoO2 (113) plane were decreased by increasing RF power. The peak locations of the Li (002) and LiCoO2 (104) were not changed. It was found that Li (002) relative intensities affect the all investigated parameters for the LiCoO2 thin films. Especially, transmittance value increased about 20%. The band gap of the deposited film was changed 100–300 meV drastically. Deposited samples are shown high transparency in the visible region. Randles circuit was used for the equivalent circuit model. Nyquist plots, fitting parameters values and value of the circuit elements were estimated by ZSim software.
AtıfScopus4WoS3OpenAlex4İncele - MakaleAçık Erişim2016Scopus SJRQ2Effect of laser irradiation on activation energy, irreversibility field and upper critical magnetic field of bulk MgB2 superconductor
Erdem, O.; Yanmaz, E.
In this study, the role of laser irradiation on the upper critical field (Hc2), the irreversibility field (Hirr) and the activation energy (U0) of bulk MgB2 superconductor was first time investigated with the aid of magnetoresistivity measurements conducted at different applied magnetic fields in a range of 0–15 kOe as a function of temperature from 25 to 40 K. For this aim, a disk shaped MgB2 superconductor was produced and cut into two pieces. One of the pieces was irradiated under high vacuum conditions by using an Nd:YVO4 laser. The obtained results showed an increase in the critical temperature (Tc) by about 1 K after irradiation. Also, the values of Hc2(0) were respectively found to be around 143 and 151 kOe while the values of Hirr(0) were about 122 and 130 kOe for the reference and the irradiated samples. Using the thermally activated flux flow model the dependence of U0 on magnetic field was determined. The maximum U0 values of 0.43 and 0.83 eV in zero magnetic field were respectively obtained for the reference and the irradiated samples. Also, the magnetic field dependence of the critical current density Jc(B) values at different temperatures were slightly increased after the irradiation. These results point out that the superconducting properties of bulk MgB2 can be improved via laser irradiation.
AtıfScopus11WoS10OpenAlex8İncele - MakaleAçık Erişim2015Scopus SJRQ2Characterization of a fast grown GaAs:Sn thin film by thermionic vacuum arc
Özen, Soner; Şenay, Volkan; Pat, Suat; Korkmaz, Şadan
In this research, a tin doped gallium arsenide thin film was grown on a glass substrate by means of the TVA technique in a very short period of time (70 s) and it’s morphological, compositional, and optical properties were examined. The deposited GaAs:Sn structures were characterized via both atomic force microscope (AFM) and field emission scanning electron microscope (FESEM). In this context, current research aims to reach a conclusion about the structure of the produced GaAs:Sn film by combining AFM, FESEM and energy dispersive X-ray spectroscopy data. From the optical investigation, the refractive index and extinction coefficient values for the produced film were obtained as 3.68 and 0.03 at the wavelength of 632.8 nm, respectively. The direct optical band gap energy of the deposited thin film was determined by two different models. Estimated optical band gap values were compared with each other. The results showed that TVA technique is suitable for a GaAs:Sn coating on glass substrate.
AtıfScopus6WoS5OpenAlex6İncele - MakaleAçık Erişim2015Scopus SJRQ2Deposition of a Mo doped GaN thin film on glass substrate by thermionic vacuum arc (TVA)
Özen, Soner; Şenay, Volkan; Pat, Suat; Korkmaz, Şadan
Current research presents a new deposition method for GaN thin films that produces in a very short production time for GaN-based solid-state applications. A Mo doped GaN thin film on a glass substrate was produced by thermionic vacuum arc (TVA) technique. The TVA technique is a novel non-reactive plasma technique. The optical properties were determined by Filmetrics F20 interferometer and UV–Vis double beam spectrophotometer. The surface morphology was analyzed using field emission scanning electron microscopy and atomic force microscopy. The mean thickness value was measured as 100 nm by Filmetrics interferometer. The crystalline structure of the produced thin film has a Wurtzite crystal structure (004) as obtained by X-ray diffraction. Hardness value was determined as 14 GPa with the Oliver–Pharr method. The obtained properties are consistent with the values reported in related literature. The findings indicate that the TVA method provides advantages for optical and industrial applications.
AtıfScopus20WoS20OpenAlex22İncele - MakaleYalnız künye2014Scopus SJRQ2Effects of initial cooling conditions and measurement heights on the levitation performance of bulk MgB2 superconductor at different measurement temperatures
Erdem, O.; Ozturk, K.; Guner, S.B.; Celik, S.; Yanmaz, E.
The levitation properties of MgB2 prepared by hot press at 200 ° C and then pellet/closed tube method has been investigated. The vertical and lateral levitation forces (Fz and Fx) on a cylindrical NdFeB permanent magnet (PM) below a disk-shaped bulk MgB2 were measured during the vertical and lateral traverses of the PM in different cooling heights (CHs) and measurement heights (MHs) at temperatures of 20, 25 and 30 K to investigate the effect of the initial CH and MH on the levitation performance of MgB2. For temperatures below 30 K, it was observed that Fz increases with increasing CH. However, a minute variation in Fz and a big hysteresis loop are observed at 30 K. From the lateral traverses, it was obtained that the Fz with attractive character increases with decreasing MH and the hysteresis effect increases for small MHs due to the increment of the magnetic field intensity which the sample feels with decreasing MH. In addition, it was seen that the character of Fx varies depending on both MH and measurement temperature. The higher hysteresis obtained in Fx than in Fz during lateral traverses implies that the motion of the flux lines in MgB2 is especially in lateral rather than vertical direction. Finally in this study, it was shown that the levitation performance of MgB2 depends not only on the measurement temperature but also on the CH and MH conditions. These results can be useful for optimizing the levitation performance of MgB2 superconductors for potential applications.
AtıfScopus20WoS21OpenAlex21İncele