Browsing by Author "Asikuzun E."

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Ac Susceptibility Measurements and Mechanical Performance of Bulk MgB2
(2015-07-24) Ozturk O.; Asikuzun E.; Kaya S.; Erdem M.; Safran S.; Kilic A.; Terzioglu C.
The effects of Ar ambient pressure (vacuum and 0, 10, and 20 B) and annealing times (0.5 and 1 h) on microstructural, superconducting, and mechanical properties of bulk superconducting MgB2 are investigated. The samples are produced using the solid-state reaction method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements are performed for determination of the crystal structure and surface morphology of MgB2 samples, respectively. The superconducting properties are studied by AC magnetic susceptibility measurements. Microhardness analyses are made using the Vickers microhardness test for determination of mechanical properties of all samples. Increasing the Ar pressure decreases the lattice parameters and hence the average grain size. Increasing the annealing time results in larger lattice parameters and larger grain formation. The susceptibility measurements revealed a two-step transition which is reminiscent of granular superconductors. The intra-grain transition temperature is determined to be 38.4 K for all samples. The inter-grain transition temperature of 37.2 K is obtained for samples produced under Ar ambient pressure. The samples produced under Ar ambient pressure have better superconducting properties than the ones produced in vacuum. Increasing the annealing time under vacuum further decreases the superconducting properties probably due to Mg loss.
Analysis of indentation size effect (ISE) behavior in low-load Vickers microhardness testing of (Sm123) 1-x (Nd123) x superconductor system
(2013-01-01) Celik S.; Ozturk O.; Coşkun E.; Sarıhan M.; Asikuzun E.; Ozturk K.; Terzioglu C.
Indentation size effect (ISE) for (Sm123) 1-x (Nd123) x superconducting samples which were fabricated by the solid state reaction technique for values of x = 0.00, 0.05, 0.10, 0.20, and 0.30 was investigated by analyzing the theoretical models. When the experimental data of a number of single crystals which have the different crystal structure and different chemical bonding inside the polycrystallined samples were analyzed with the ISE models, the sample encountering with resistance and elastic deformation was observed as well as plastic deformation. The microhardness values on different surfaces of materials were calculated by using Meyer Law, proportional specimen resistance model, modified proportional specimen resistance model, elastic/plastic deformation model and the Hays-Kendall (HK) approach. The results showed that the HK approach was determined as the most successful model. Furthermore, X-ray powder diffraction and scanning electron microscope measurements were analyzed for superconducting properties of (Sm123) 1-x (Nd123) x superconductor system. The results showed that microhardness values at the minimum load and averaged plateau region of load increased with increase of Nd123 concentration. Nd123 content can be used as to be estimated the microhardness value of (Sm123) 1-x (Nd123) x superconducting sample in the range of 0.878-2.717 GPa. The control of the microhardness value by using Nd123 content in (Sm123) 1-x (Nd123) x superconducting structure can be useful in technological applications in superconductivity industry. © 2013 Springer Science+Business Media New York.
Breaking point of the harmony between Gd diffused Bi-2223 slabs with diffusion annealing temperature
(2013-01-01) Aydın H.; Babanli A.; Altintas S.; Asikuzun E.; Soylu N.; Ozturk O.; Dogruer M.; Terzioglu C.; Yildirim G.
This comprehensive study reports the role of annealing temperature on the microstructural, superconducting and mechanical characteristics of the Gd diffused Bi-2223 superconducting ceramics produced by the conventional solid-state reaction route at 840 C for the annealing duration of 48 h. For the material characterization, the standard experimental methods such as dc resistivity (ρ-T), transport critical current density, X-ray powder diffraction, scanning electron microscopy and Vickers microhardness measurements are performed systematically. All the results obtained show that all the measured characteristic properties, being in charge of the applications in the industry, engineering and technology, improve until a certain diffusion annealing temperature of 800 C beyond which they tend to degrade considerably. The increase in the properties is mostly related to the transition from the inherent overdoped state of the pure Bi-2223 material to optimum doped state with the diffusion annealing temperature, confirming the penetration of the sufficient Gd nanoparticles into the crystal structure. On the other hand, the suppression in the superconducting properties stems from the appearance of the porosity, defects, disorder and localization problem in the polycrystalline Bi-2223 superconducting matrix. This is attributed to the decrement of the average crystallite size and mobile hole concentration in the Cu-O 2 layers and especially the retrogression of the crystallinity in the system. As for the mechanical characteristics, Vickers microhardness measurements exerted in the applied indentation test load range of 0.245-2.940 N indicate that the Gd diffused bulk superconducting samples exhibit the typical indentation size effect behavior. With the enhancement in the annealing temperature up to 800 C, the significant increase in the elastic modulus, yield strength and fracture toughness is one of the most striking points in the paper. The long and short of it is that the excess diffusion annealing temperature damages the fundamental characteristics of the Bi-2223 system. © 2013 Springer Science+Business Media New York.
Change of formation velocity of Bi-2212 superconducting phase with annealing ambient
(2013-11-01) Ozturk O.; Yildirim G.; Asikuzun E.; Coskunyurek M.; Yilmazlar M.; Kilic A.
This exhaustive study enables the researchers to recognize the role of the annealing conditions (temperature and time) on the microstructural, mechanical, electrical and superconducting properties of the Bi-2212 superconducting material with the aid of ρ-T, X-ray diffraction, scanning electron microscopy and Vickers microhardness (Hv) measurements. For this aim, the superconducting samples are elaborated by standard solid-state reaction route at different annealing temperature and different annealing duration. The results show that the annealing temperature of 840 C and the annealing duration of 72 h are the best for the formation velocity of Bi-2212 superconducting phase. In this study we have focused on microhardness measurements to investigate the mechanical properties. Vickers microhardness, Young's modulus, fracture toughness and yield strength values are calculated separately for all samples. Experimental results of hardness measurements are analyzed using the some models. Finally, the Hays-Kendall model is determined as the most successful model describing the mechanical properties of our samples. © 2013 Springer Science+Business Media New York.
Comparison of theoretical and experimental microhardness of tetrahedral binary Zn1-xErxO semiconductor polycrystalline nanoparticles
(2019-03-01) Asikuzun E.; Ozturk O.
Zn1−xErxO polycrystalline nanoparticles with various compositions (x=0.01,0.02,0.03,0.04,0.05, and 0.10)were prepared using sol–gel techniques, for which zinc acetate dihydrate and erbium 2–4 pentanedionate are used as precursors. Nanoparticles were pressed under a pressure of 4 tons for 5 min into disk-shaped compacts with 2 mm thicknesses and 10 mm diameters. The pressed samples were annealed at 400 °C for 30 min. X-ray diffraction (XRD), scanning electron microscopy (SEM), and Vickers microhardness analyses of the produced Er-doped ZnO bulk nanomaterials were performed. Specifically, in this study we focused on the analysis of their mechanical properties. Undoped and Er-doped bulk samples were investigated according to Meyer's law; the proportional sample resistance (PSR), elastic/plastic deformation (EPD), and indentation-induced cracking (IIC) models; and the Hays–Kendal (HK) approach. As a result, the IIC model was more suitable to determine the micromechanical properties and the reverse indentation size effect (RISE) behavior of Er-doped ZnO semiconductors.
Comparison of Vickers microhardness of undoped and Ru doped BSCCO glass ceramic materials
(2018-03-01) Ozturk O.; Asikuzun E.; Tasci A.; Gokcen T.; Ada H.; Koralay H.; Cavdar S.
In this study, effect of substitution ratio on the mechanical and structural properties of Bi1−xRuxPb0.2Sr2CaCu2O10+δ system, that is prepared in the ratios of x = 0.0, 0.025, 0.050, 0.075, is investigated. Samples are prepared with glass ceramic method and sintered at 845 °C. XRD and SEM measurements are performed for structural analyses, and Vickers micro-hardness measurements are carried out at different applied load (0.245 ≤ F ≤ 2.940 N) in order to investigate the mechanical performance of the Ru doped Bi1−xRuxPb0.2Sr2CaCu2O10+δ system. Experimental results of Vickers micro-hardness analyses are performed using the Meyer’s law, the proportional samples resistance model, the elastic/plastic deformation model, the Hays–Kendall approach and the indentation induced cracking (IIC) model. All analyses results are exhibited reverse indentation size effect behavior. The measured hardness values increase with increasing the applied load. Finally, IIC model is determined as the most successful model describing the mechanical properties of our samples.
Effect of doping on microstructure and optical properties of ternary structure of Zn1−x−yBxCyO (B=Cu, C=Co) nano thin films
(2020-12-01) Asikuzun E.; Ozturk O.; Terzioglu R.; Arda L.; Terzioglu C.
We report the results of an in depth study of optical and microstuctural properties of thin films of Zn1−x−yCuxCoyO system (x = 0,00 and 0.02, y = 0.00, 0.01, 0.02, 0.03, 0.04. and 0.05) which are grown by the sol–gel method. We have performed differential thermal analysis, and thermo gravimetric analysis/difference thermogravimetric analysis, x-ray diffraction, scanning electron microscopy, energy dispersive spectrometer, atomic force microscopy and UV–VIS spectrophotometer experiments. We have found that all of the studied samples are in hexagonal wurtzite structure and oriented along the (002) direction with a very weak signal for the (101) reflection. We have also found that the lattice parameter c increases with doping. All the films showed wrinkle network structure with nano-sized crystals and the grain size was observed to decrease with increasing Co doping. The bandgap was found to decrease from 3.28 to 3.22 eV with doping. All the above results will be discussed in detail.
Effect of Zn content on microstructure and mechanical performance in Bi1.8Sr2Ca2Cu3.2-xZn xO10+δ glass ceramic
(2014-01-01) Koralay H.; Hicyilmaz O.; Cavdar S.; Asikuzun E.; Tasci A.; Ozturk O.
In this study, we have investigated the effects of Zn doping on structural and mechanical properties of Bi1.8Sr2Ca2Cu 3.2-xZnxO10+δ ceramic samples with x = 0.0, 0.1, 0.5, 1.0. The prepared samples were characterized by using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray powder diffractometer (XRD) and static microhardness indenter. Surface morphology, orientation of grains and elemental composition analysis of the samples were investigated by SEM and EDS measurements, respectively. Texturing and lattice parameters a, b and c were determined from the XRD measurements. In this work we focused on Vickers microhardness measurements in order to characterize the mechanical properties. Experimental results of Vickers microhardness measurements were analyzed by using Meyer's law, the elastic/plastic deformation model, proportional sample resistance model (PSR), modified PSR model, Hays-Kendall (HK) approach and indentation induced cracking (IIC) model. According to the obtained results, HK approach is the most suitable model for the CZn00 sample showing indentation size effect behavior and IIC Model is the most suitable model for the CZn01, CZn05 and CZn10 samples showing reverse indentation size effect behavior. © 2014 Springer Science+Business Media New York.
Experimental and theoretical approaches on mechanical evaluation of Y123 system by Lu addition
(2013-07-01) Turkoz M.; Nezir S.; Ozturk O.; Asikuzun E.; Yildirim G.; Terzioglu C.; Varilci A.
This work is the continuation of a systematic study on the characterization of the Lu-added Y123 bulk superconducting materials prepared by the nitrate compounds and derivatives at 970 C for 20 h. In this part, the effect of Lu inclusions on the physical and mechanical properties of the Y123 superconductors is examined with the aid of microhardness measurements performed at various applied loads in the range of 0.245-2.940 N. The microhardness measurement results allow us to determine the important mechanical characteristics such as Vickers microhardness, elastic (Young's) modulus, yield strength and fracture toughness values being responsible for the potential industrial applications. It is found that all the properties given above are strongly dependent upon the Lu concentration in the Y123 matrix. Especially, Vickers microhardness (H v ) values of the samples studied in this work are found to suppressed considerably with the enhancement of the Lu addition in the system due to the degradation in the connectivity between superconducting grains. Moreover, the Hv values of the pure Y123 sample are observed to increase with increasing the applied load whereas those of the Lu-doped superconducting materials are obtained to decrease with the load. In other words, the pure sample exhibits the reverse indentation size effect (RISE) behavior while the others obey the indentation size effect (ISE) feature, confirming the degradation in the mechanical properties with the Lu inclusions in the Y123 matrix. In addition, the microhardness measurement results are estimated using the 5 different models such as Meyer's law, proportional sample resistance model, elastic/plastic deformation model, Hays-Kendall (HK) approach and indentation-induced cracking (IIC) model. According to the results obtained from the simulations, of the mechanical analysis models, the Hays-Kendall (HK) approach is determined as the most successful model for the description of the mechanical properties of the Lu-doped superconducting materials (exhibiting the ISE behavior) where both the both the reversible (elastic) and irreversible (plastic) deformations are produced. On the other hand, the IIC model is found to be superior to other approaches for the pure sample (presenting the RISE feature) where the irreversible deformation becomes more and more dominant compared to the reversible deformation. © 2013 The Author(s).
High-quality c-axis oriented non-vacuum Er doped ZnO thin films
(2016-05-15) Asikuzun E.; Ozturk O.; Arda L.; Tasci A.; Kartal F.; Terzioglu C.
Preparation, growth, structure and optical properties of high-quality c-axis oriented non-vacuum Er doped ZnO thin films were studied. Zn1-xErxO (x=0.0, 0.01, 0.02, 0.04, and 0.05) precursor solutions were prepared by sol-gel synthesis using Zn, and Er based alkoxide which were dissolved into solvent and chelating agent. Zn1-xErxO thin films with different Er doping concentration were grown on glass substrate using sol-gel dip coating. Thin films were annealed at 600 °C for 30 min, and tried to observe the effect of doping ratio on structural and optical properties. The particle size, crystal structure, surface morphologies and microstructure of all samples were characterized by X-Ray diffraction (XRD) and Scanning Electron Microscope (SEM). The UV-vis spectrometer measurements were carried out for the optical characterizations. The surface morphology of the Zn1-xErxO films depend on substrate nature and sol-gel parameters such as withdrawal speed, drying, heat treatment, deep number (film thickness) and annealing condition. Surface morphologies of Er doped ZnO thin films were dense, without porosity, uniform, crack and pinhole free. XRD results showed that, all Er doped ZnO thin films have a hexagonal structure and (002) orientation. The optical transmittance of rare earth element (Er) doped ZnO thin films were increased. The Er doped ZnO thin films showed high transparency (>85) in the visible region (400-700 nm).
Improvement of the nature of indentation size effect of Bi-2212 superconducting matrix by doped Nd inclusion and theoretical modeling of new matrix
(2014-01-01) Ozturk O.; Asikuzun E.; Kaya S.; Yildirim G.; Turkoz M.; Kilic A.
Neodmium (Nd) inclusions at different stoichiometric ratios (x=0.0, 0.001 %, 0.005 %, 0.01 %, 0.05 %, 0.1 %) are doped in the Bi-2212 superconducting samples and the samples obtained are subjected to the sintering process at 840 °C constant temperature for 72 hours. The effect of Nd doping on the structural and mechanical properties of prepared samples is investigated by the standard characterization measurements. XRD and SEM measurements are performed to obtain information about surface morphology, phase ratios, lattice parameters and particle size. Moreover, Vickers microhardness (H V ) measurements are exerted to investigate the mechanical properties of the all samples in detail. It is found that all the properties given above retrogress with the increase of the Nd concentration in the Bi-2212 superconducting core. However, the ISE nature of the materials improves systematically. Additionally, the experimental results of microhardness measurements are analyzed using Meyer's law, PSR, MPSR, EPD models and HK approach. The results show that Hays-Kendall approach is determined as the most successful model. © 2014 Springer Science+Business Media New York.
Influence of different boron precursors on superconducting and mechanical properties of MgB 2
(2014-01-01) Safran S.; Kılıç A.; Asikuzun E.; KIlIçarslan E.; Ozturk O.; Gencer A.
The superconducting, structural and mechanical properties of MgB 2 bulk samples have been studied as a function of precursor B powder particle size by means of AC susceptibility, XRD and microhardness measurements, respectively. The in situ processed MgB 2 samples have been prepared by means of conventional solid state reaction method with magnesium powder (99.8 %, 325 mesh) and four different types of boron powders (95.2, >95, 91.9 and 86.7 %) from two sources, Pavezyum and Sigma Aldrich. The XRD measurements showed that the diffraction peaks for our samples belong to the main phase of the MgB 2 diffraction patterns. The highest critical temperature T c = 37.7 K was achieved for the MgB 2 sample which was fabricated by using >95 % purity amorphous boron. Microhardness measurements were performed to investigate the mechanical properties. Load independent hardness, Vickers microhardness, Young's modulus, fracture toughness, and yield strength values were calculated separately for all samples. The results were analyzed by using the Meyer's law, proportional sample resistance model, elastic-plastic deformation model, Hays Kendall approach, and indentation induced cracking (IIC) model. It was found that the IIC model is the most successful model to describe the mechanical properties of our samples. © 2014 Springer Science+Business Media New York.
Investigation of indentation size effect (ISE) and micro-mechanical properties of Lu added Bi2Sr2CaCu2Oy ceramic superconductors
(2013-01-01) Ozturk O.; Erdem M.; Asikuzun E.; Yildiz O.; Yildirim G.; Varilci A.; Terzioglu C.
In this study, we investigated the effect of the Lutetium (Lu) addition on microstructure and mechanical properties of the Bi-2212 superconductors annealed at 840 C for 50 h. The samples were prepared by the widely used conventional solid-state reaction method. For comparison, undoped sample was prepared in the same conditions. The prepared samples were characterized using X-ray powder diffraction (XRD), scanning electron microscope (SEM), and microhardness measurements (H v ). The volume fraction and lattice parameters were determined from the XRD measurements. The microstructure, surface morphology and orientation of the grains were investigated by SEM. In this study we have focused on microhardness measurements to investigate the mechanical properties. Vickers microhardness, load independent hardness, Young's modulus, fracture toughness and yield strength values were calculated separately for doped and undoped samples. Experimental results of hardness measurements were analyzed using the Meyer's law, proportional sample resistance (PSR)model, modified proportional sample resistance (MPRS) model, Elastic-Plastic deformation model (EPD), and Hays-Kendall (HK) approach. Finally, the Hays-Kendall (HK) approach was determined as the most successful model describing the mechanical properties of our samples. Moreover, lattice parameter c and volume fraction of Bi-2212 phase decreased with increasing Lu content. SEM measurements show that not only the surface morphology and grain connectivity were obtained to degrade but also the grain sizes of the samples were found to decrease with the increase of the Lu addition, as well. © 2012 Springer Science+Business Media, LLC.
Investigation of mechanical and superconducting properties of iron diffusion-doped Bi-2223 superconductors
(2011-09-01) Ozturk O.; Cetinkara H.A.; Asikuzun E.; Akdogan M.; Yilmazlar M.; Terzioglu C.
The mechanical and superconducting properties of the Fe diffusion-doped (Bi-Pb)-2223 superconductor have been investigated. First, iron was evaporated on Bi-2223 superconductor and then the Fe layered superconductor was annealed at 830 °C for 10, 30 and 60 h. Static Vickers hardness, dc electrical resistivity, X-ray diffraction and scanning electron microcopy have been carried out to assess the effects of Fe doping. These measurements indicates that Fe doping, in comparison with the undoped samples, increased the critical transition temperature, and improved formation of high Tc phase, while decreasing the number and size of voids. Moreover, both microhardness and grain size were also enhanced by increasing the amount of diffusion. The values of microhardness were found to be load dependent. In addition, we have investigated the indentation size effect (ISE) behavior using some models such as the Kick's law, modified proportional specimen resistance (MPRS) model and the Hays- Kendall (HK) approach. Among them, both HK and MPRS models are successful. In this study, the possible reasons of noticed improvement on mechanical and physical properties due to iron diffusion are discussed. © Springer Science+Business Media, LLC 2011.
Investigation of structural, superconducting and mechanical properties of Co/Cu substituted YBCO-358 ceramic composites
(2019-01-01) Ozturk O.; Arebat R.; Nefrow A.; Bulut F.; Guducu G.; Asikuzun E.; Celik S.
In this study, we have examined the structural, superconducting and mechanical properties of Y 3 Ba 5 Cu 8−x Co x O 18 − δ system (x = 0, 0.05, 0.1, 0.15, 0.2 and 0.5), which is produced by conventional solid-state reaction method. Produced samples have been examined using X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS), Vicker’s hardness (H v ) and electrical resistance measurement (R–T). According to the XRD patterns, we have obtained that the Co nanopowder doping has been caused some changes on the average grain size, characteristic peak intensities and lattice parameters of the Y 3 Ba 5 Cu 8 O 18 − δ crystal system. Furthermore, according to the electrical resistance measurements, the critical temperature (T c ) values of all the samples have tended to decrease constantly with the increment in the doping ratio in the Y358 crystal structure. As for the variation in the microhardness parameters of superconducting materials, the H v parameters and other related computations (Young’s modulus and yield strengths) have been found to increase regularly with the Co/Cu substitution level. Besides, the characteristic H v curves have confirmed that the whole bulk of Bi-2212 samples showed untypical reverse indentation size effect (RISE) behavior.
Mechanical, microstructural and magnetic properties of the bulk BSCCO superconductor prepared by two different methods
(2015-04-01) Safran S.; Kılıç A.; Kılıçarslan E.; Ozturk H.; Alp M.; Asikuzun E.; Ozturk O.
BSCCO bulk samples have been prepared by solid-state reaction and ammonium nitrate precipitation methods with Bi1.65Pb0.35Sr2Ca2Cu3O10±y stoichiometry. Structural, mechanical and magnetic characterizations of the samples were performed by the X-ray powder diffraction (XRD), the scanning electron microscopy (SEM), Microhardness measurements, AC susceptibility measurements. The XRD patterns showed that the diffraction peaks for our samples belong to the two main phase, namely 2223 and 2212 of the BSCCO. In this study we have focused on microhardness measurements to investigate the mechanical properties. Vickers microhardness, Young’s modulus and yield strength values were calculated separately for all samples. In addition to these, we calculated the load independent hardness values of samples. Experimental results of hardness measurements were analyzed using the Meyer’s law, proportional sample resistance (PSR) model, Elastic–Plastic deformation model (EPD) and indentation induced cracking (IIC) model. The critical transition temperature, phase purity, lattice parameter, surface morphology and crystallinity of the prepared bulk samples were compared with each other.
Microstructural and electrical characterizations of transparent Er-doped ZnO nano thin films prepared by sol–gel process
(2017-10-01) Asikuzun E.; Ozturk O.; Arda L.; Terzioglu C.
In this study, rare earth element (Er) doped ZnO nano thin films which have dual structure of (Zn1−xErx)O (x = 0.0, 0.01, 0.02, 0.03, 0.04 and 0.05) are prepared by using sol–gel method. The microstructure and electrical properties of prepared nano thin films are investigated. Nano thin films are coated on the glass substrate by using the dip coating method. The films are annealed at 600 °C for 30 min. The X-ray diffractometer (XRD), scanning electron microscopy and atomic force microscopy are used to determine the structural properties such as crystal structures, grain sizes, surface morphology; Hall effect measurements system is used to investigate the electrical properties of materials. XRD results showed that all Er doped nano thin films have a hexagonal structure and (002) orientation. Surface morphologies of ZnErO thin films are denser and more uniform than the undoped ZnO thin film. According to the Hall effect measurements, the resistivity of the films decreased with increasing Er concentration from 0 to 4 % and then slightly increased at 5 % Er.
Physical properties and diffusion-coefficient calculation of iron diffused BI-2223 system
(2012-10-01) Ozturk O.; Asikuzun E.; Kaya S.; Coskunyurek M.; Yildirim G.; Yilmazlar M.; Terzioglu C.
This study includes two parts: (I) investigation of the effect of different annealing time (10 h, 30 h, and 60 h) on physical, superconducting, and microstructural properties of Fe-diffused Bi-2223 superconductor ceramics prepared by the conventional solid-state reaction method with the aid of the X-ray diffraction (XRD), scanning electron microscopy (SEM), dc resistivity (φ-T ) and transport critical current density (Jc) measurements, and (II) determination of the diffusion coefficient and the activation energy of iron in the Bi-2223 system. In the former part, the zero-resistivity transition temperature (Tc), phase purity, volume fraction, hole-carrier concentration, lattice parameters, surface morphology, texturing, crystallinity, grain connectivity, grain size, and room temperature resistivity values of the bulk samples are found and compared with each other. The results obtained show that both the zero resistivity transition temperature (Tc) and transport critical current density (Jc) regularly enhance with the increment in the diffusion-annealing time. The maximum Tc of 107 ± 0.2 K and Jc of 50.0 Acm-2 are observed for the sample annealed at 830 °C for 60 h. As for the XRD investigations, according to the refinement of cell parameters done by considering the structural modulation, the enhance-ment in the diffusion-annealing is confirmed by both a decrease of the cell parameter a and an increase of the lattice parameter c of the samples, meaning that the greatest Bi-2223 phase fraction belongs to the sample annealed at 830 °C for 60 h. Moreover, SEM images display that the sample has the best crystallinity, grain connectivity, and largest grain size. Based on the results, the superconducting and microstructural properties improve with the increase in the diffusion-annealing time. In the latter part, Fe diffusion in the Bi-2223 system is examined in a range of 500-830 °C by the variation of the lattice parameters evaluated from the XRD patterns. The temperature dependence of the Fe diffusion coefficient is described by the Arrhenius relation D = 4.27 × 10-5 exp(-1.27 ± 0.10) eV/kBT, and the related activation energy of the iron in the Bi-2223 system is found to be about 1.27 eV. The relatively low value of activation energy obtained illustrates that the migration of the Fe ions primarily proceeds through defects such as pore surfaces and grain boundaries in the polycrystalline structure, leading to the improvement of the microstructural and superconducting properties of the samples, supported by the results of part I. All in all, the aim of the present study is not only to analyze the role of diffusion-annealing time on superconducting and microstructural properties of Fe-diffused Bi-2223 superconductors, but also to find the diffusion coefficient and activation energy of Fe in the Bi-2223 system. © Springer Science+Business Media, LLC 2012.
Preparation, growth and characterization of nonvacuum Cu-doped ZnO thin films
(2018-08-05) Asikuzun E.; Ozturk O.; Arda L.; Terzioglu C.
We investigated the effects of increasing Cu dopant concentration on the microstructure and optical properties of Zn1−xCuxO thin films. The transparent Zn1−xCuxO solution concentrations were varied from x = 0.0 to x = 0.05 with an increment of 0.01. All nano films were prepared by dip coating system using the sol-gel method. X-ray diffraction (XRD) measurements, scanning electron microscopy (SEM) observations, energy-dispersive X-ray spectroscopy (EDS) analyses, and atomic force microscopys (AFM) analyses revealed a fine-grained structure resulting from doping of Cu into the ZnO structure. In addition, UV–Vis spectrophotometer was used to determine the optic properties of ZnO based nano thin films. XRD analysis also showed that the undoped ZnO and Cu-doped ZnO films oriented along the (002) as the dominant plane. In the 400–700 nm wavelength range, a decrease in transparency was observed in the Zn1−xCuxO thin films with increasing Cu concentration. Although the optical band gap of the Cu-doped ZnO thin films was lower than that of the undoped ZnO thin film, the Urbach energy of the all of the doped thin films was higher than the undoped ZnO thin film.
Preparation, structural and micromechanical properties of (Al/Mg) co-doped ZnO nanoparticles by sol–gel process
(2015-10-22) Asikuzun E.; Ozturk O.; Arda L.; Akcan D.; Senol S.; Terzioglu C.
Zn0.90Mg0.10−xAlxO (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.10) nanoparticles were prepared by using sol–gel technique. The effects of Al and Mg doping on the structural and mechanical properties were investigated by using X-Ray diffraction (XRD), scanning electron microscopy (SEM) and digital micro-hardness tester, respectively. The grain size, a and c lattice parameters and morphology of nanoparticles were characterized by XRD and SEM measurements. The grain sizes of Al/Mg co-doped ZnO nanoparticles were also calculated by Scherrer–Warren equation. a and c lattice parameters are calculated from XRD peaks. According to the results it was observed that the grain sizes increased with increasing the Al doping. c lattice parameter partially decreased with Al doping. The experimental results of hardness measurements were analyzed using Meyer’s law, proportional specimen resistance model, elastic/plastic deformation model, and Hays–Kendall (HK) approach. It was observed that HK approach is the most successful model for the micro-hardness analysis of Al/Mg co-doped ZnO materials.