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The effects of nano-Y2O3 addition on the structural, superconducting, magnetic and mechanical properties of Bi-2223 superconducting system were investigated in this study. Bulk polycrystalline samples with general formula of Bi1.8Pb0.4Sr2Ca2Cu3O10+δ + (Y2O3) with ( x; weighted % 0.0-0.2-0.4-0.8-1.0) were prepared by solid state reaction method. X-ray diffraction (XRD), Scanning Electron microscope (SEM), Energy dispersive X-ray spectroscopy (EDX) measurement, Vibrating sample measurement (VSM), Resistance- temperature (ρ-T) measurement and Vickers microhardness measurement (VHM) were also used for samples structural characterizations. XRD patterns showed that both Bi -2223 and Bi-2212 phases are coexist in the samples. While a lattice parameter increased, c lattice parameter decreased with increasing nano- Y2O3 addition. In SEM photographs, it is seen that granular structure is plate- like in all samples. The presence of point particles on the layered particles has been seen more clearly with increasing Y2O3 addition. Hole concentration values that calculated from ρ-T measurement, ranges from 0.113 to 0.160. While amount of Y2O3 addition increased, critical transition temperatures decreased. VSM results showed that critical current density values increase with Y2O3 addition. VHM results showed that the hardness value increased until x= 0.4% additive sample and decreased after this value.

A series of the nano-sized Mn polycrystalline-substituted MgB2 samples were synthesized by solid-state reaction method with the ratio of Mg1-xMnxB2 (x = 0.00, 0.01, 0.03 ,and 0.05). Mn substitution emerges shifting (002) peak position to higher angles on MgB2 samples. This shows that isovalent Mn2+ is substituted by Mg2+ ions. Randomly oriented grains were obtained in surface morphology. The presence of Mn nanoparticles was observed with energy-dispersive spectrometry analysis. The superconducting transition temperature was significantly suppressed by Mn ions, from 39.28 to 26.60 K. Spin-flip scattering and pair breaking effect arose from the magnetic nature of Mn. Increasing Mn content ratio in the samples caused narrower magnetization versus applied magnetic field loops, without magnetic flux jumping. Self-field critical current density decreased from 260 to 16 kA cm(-2) with rising Mn substitution ratio. Scaling behavior of the samples was examined between reduced force (f = F/F-max) and reduced applied field (h = H/H-max). Fitting lines showed that pure MgB2 was dominated by normal point pinning mechanism at both lower and higher magnetic fields. However, Mn-substituted MgB2 samples exhibited surface pinning mechanism due to grain refinement.

Graphene's astonishing properties drew attention of many scientists to dedicate a lot of their time to find out more about this extraordinary material. However, challenges continue to produce high-quality graphene in large quantities by using inexpensive and readily available methods. In this study, three different graphite powders have been used as starting materials to produce few-layer graphene sheets, which are pure natural graphite (NGr) and two different electrochemically treated expanded graphite EE1 and EE2. Two simple and time-effective techniques have been applied on the samples interchangeably to investigate the order effect on producing graphene sheets in few-layer form. These techniques are sonication in dimethylformamide (DMF) for one hour and rapid microwave irradiation for 30 s. The study suggests that if the graphite powder is treated first with a strong exfoliation reagent followed by microwave irradiation, the obtained graphene will be high-quality few-layer (similar to 5 layers). Sonication in DMF has worked to increase the inter-planar spacing between graphite layers, while microwave irradiation has worked to decrease the defect density ratio that resulted after sonication process. Our work suggests a novel route to prepare high-quality few-layer graphene sheets, not only with time efficiency, low-cost, and without using harmful chemicals, but also an adequate method for large-scale high-efficiency production of graphene materials.

Due to its outstanding features, graphene has become a vital topic in nanotechnology applications such as optoelectronic devices, sensors, batteries, and biomedical applications. This study has been focused on examining a heavily doped semiconductor in order to fabricate Schottky junction solar cell, where p-type graphene with heavily doped n-type silicon (p-G/n(+)-Si) Schottky junction solar cell with a top-window structure and active area of 0.11 cm(2) has been fabricated using simple techniques without photolithography system. High-quality monolayer graphene sheet was synthesized by CVD method, while the back- and front-metal contacts were achieved by thermal evaporation system using Cr, Ag, and Au. The effect of thermal annealing to the transferred graphene sheet and the p-doping of graphene were also investigated. The results indicate that the annealing treatment has significantly reduced the PMMA residue in the graphene sheet by similar to 75% as well as reduction in the PMMA islands' height. On the other hand, doping graphene with GO dispersion showed an enhancement in both J(sc) = 3.65 mA /cm(2) and V-oc = 420 mV which is an indication of larger graphene's work function. The best obtained power conversion efficiency of this cell after annealing treatment and doping was found to be around 2.24%. The results also showed how it is challenging to deal with heavily doped semiconductor in order to make a Schottky junction between graphene and the semiconductor, where the Fill factor was decreased after each processing step.

In this work, quick and practical approach has been used to produce few-layered graphene sheets (FGs). Graphene sheets are synthesized by electrochemical exfoliation method using H2SO4 as an electrolyte with two graphite rods as anode and cathode electrodes. The graphite source in this work is three different grades of softness of pencil leads; B, 4B, and 8B. Then the few-layered graphene sheets are obtained by quick exfoliation of microwaves radiation. The prepared graphene sheets are characterized using various characterization tools such as Raman spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The obtained results have showed that, the highest softness of pencil lead used, the fewer layers of exfoliated graphene sheets acquired. This electrochemical exfoliation method with microwave-assisted is a very promising method that suggests convenient, low-cost, and efficient way to produce few-layered graphene sheets with high yield.

In this work, Bi1.7Pb0.3Sr2Ca2Cu3-xAgxOy (x = 0.00, 0.03, 0.06, 0.09, 0.12) ceramics were prepared by conventional solid state reaction method. The effects of Ag substitution on the structural and mechanical properties of the samples were investigated by Vickers microhardness, X-ray powder diffraction (XRD) measurements and scanning electron microscope (SEM) analysis. The phase formation, volume fraction and lattice parameters were characterized by using XRD measurements. Surface morphology and grain connectivity of the samples were identified by using SEM. The mechanical properties were analyzed by microhardness measurements. Load dependent microhardness, elastic modulus, yield strength and fracture toughness were obtained by hardness measurements. XRD results indicated that the lattice parameter c decreases with increasing Ag addition. It was also observed that volume fraction of Bi-2223 phase decreases with increasing Ag addition from XRD measurements. SEM results showed that the surface morphology and grain connectivity improve, the grain sizes and porosity of the samples decrease with increasing Ag addition. Vickers microhardness (H-v), Young's modulus (E), yield strength (Y) and fracture toughness (K-IC) values were calculated separately for all samples. In our study, Young's modulus, yield strength, and fracture toughness of the samples indicated dependency on applied load. It was seen that the load dependent H-v, E, Y, and K-IC increase with increasing Ag and decreasing applied load. Experimental results of the microhardness measurements were analyzed using two models such as elastic-plastic deformation model and the energy dissipative model. Energy dissipative model was determined as the most successful model describing the mechanical properties of our samples.

In this work, we investigate the effects of Sb substitution on structural and superconducting properties of Bi1.75-xPb0.25SbxSr2Ca2Cu3Oy superconductor for x = 0.00-0.20. Powder X-ray diffraction analysis showed that the samples consist of the Bi-2212 phase is dominant in all samples and the impurity phases was observed to increase with increasing the substitution ratio. Moreover, the intensity of the (115) peak for the low phase and the (117) peak of the high temperature phase decrease with increasing Sb substitution. The grain size, grain connectivity and surface morphology of the samples are identified from SEM microphotographs. Temperature dependence of resistivity revealed the highest Tc value at 110 K for x = 0.1 Sb substitution ratio. The density of all prepared samples were determined and was found to decrease with increasing Sb substitution, while porosity found to increase with increasing the substitution ratio.

In this study, the effects of addition of magnesium oxide powders with average particle size < 100 nm to Bi-2223 superconducting system were investigated. Bulk samples with general formula of Bi1.7Pb0.3Sr2Ca2Cu3Oy + (MgO)(x) nominal composition (x = 0.00, 0.05, 0.10, 0.15 and 0.20 wt%) were prepared by conventional solid state reaction method. The critical temperature (T-c) and hole concentration (p) of nano MgO added samples were determined by AC susceptibility measurements. X-ray powder diffraction measurement (XRD) was used to examine phase formation, volume fraction and lattice parameters. The microstructure and surface morphology analyses of the samples were determined by scanning electron microscope. As Nano Mg addition was increased, surface morphology and grain connectivity of the samples were observed to degrade. XRD results showed that the lattice parameters do not change with increasing nano Mg addition. It was also observed from XRD measurements that volume fraction of Bi-2223 phase decreases with increasing nano Mg addition. The volume fraction of Bi-2223 phase for the non-added sample showed the highest value as 62.7% and further increasing nano MgO, the volume fraction of Bi-2223 phase decreases while Bi-2212 phase increases. The sample with 0.20 wt% MgO addition showed the highest volume fraction of Bi-2223 phase (similar to 56%) and the highest superconducting transition temperature, T-c (similar to 106 K) compared to added samples with nano MgO. The effect of nano Mg addition on magnetic properties of Bi1.7Pb0.3Sr2Ca2Cu3Oy superconductors were investigated by AC susceptibility measurements performed at ac fields of 1 Oe with f = 1000 Hz. The results revealed that critical temperature (T-c) decreases with increasing nano Mg addition down to 99.16 K.

In this work, nano-SnO2 (

The effects of Mg substitution in Bi-2223 superconductor system has been studied for the Bi1.7Pb0.3Sr2Ca2Cu3-x Mg (x) O (y) nominal composition (x=0.00, 0.05, 0.10, 0.15 and 0.20) which was prepared by the conventional solid-state reaction. The properties of these compounds have been investigated by measuring the electrical resistivity, X-ray diffraction (XRD) and density. Also, scanning electron microscopy (SEM) was employed to investigate the surface microstructure of the samples. It has been found that the effects of Mg substitution support the development of both the Bi-2212 and Bi-2223 phases. These measurements and analyses enable us to discuss the effects of Mg dopant on superconducting properties. We found that onset critical temperatures (T (c, onset)) decrease with addition x > 0.10 in resistivity measurements. The presence of Mg influenced the microstructure of the samples and decreased the mean grain size of Bi-2223 grains up to x=0.10.

The effects of Gd addition on the structural and magnetic properties of Bi1.7-xPb0.3GdxSr2Ca2Cu3Oy (x = 0.00-0.20) superconducting samples were investigated. The samples were prepared by conventional solid state reaction method. The phase formation, phase fraction and lattice parameters were determined from X-ray diffraction (XRD) measurements, while the microstructure, surface morphology analyses of the samples were carried out using scanning electron microscope. As Gd addition was increased, surface morphology and grain connectivity of the samples were observed to degrade. XRD results indicated that the lattice parameter c decrease with increasing Gd addition while Bi-2223 phase disappear and Bi-2212 phase become dominant. AC susceptibility measurements were performed at various ac fields (ranging from 20 to 160 A/m) to understand the effect of Gd addition on magnetic properties of Bi1.7-xPb0.3GdxSr2Ca2Cu3Oy superconductors. The results showed that both critical temperature (T-c) and critical current densities (J(c)) were found to decrease with increasing Gd addition. It was found that T-c values decrease from 108 to 70 K with increasing Gd addition.

The effects of Ag dopants on the superconducting properties of YBCO bulk samples, prepared under solid-state reaction method, have been studied by resistivity–temperature (ρ–T), X-ray diffraction (XRD), scanning electron microscope (SEM), bulk density, AC susceptibility, DC magnetization measurements, and theoretical analysis. Small Ag substitutions (x≤0.10) do not effect T c of pure YBa2Cu3−x Ag x O7−δ , while we observed small decreases of 1.5 K for larger doping levels (x≥0.15). AC susceptibility measurements for sintered YBCO pellets have been performed as a function of temperatures at constant frequency and AC field amplitude in the absence of DC bias field. The critical current densities (J c ) have been estimated as a function of magnetic field from the magnetization data employing Bean’s critical state model. The increase in Ag amount (x) in YBa2Cu3−x Ag x O7−δ (x≥0.10) system effectively decreases the intragrain critical current density, which is attributed to the reduced connectivity between the grain boundaries. In the case of small additions (x=0.05), Ag atoms fill partly the pores, leading better crystallization of the grains.

In this study, the effects of partial Sb 3+ ion substitutions for the Y sites and the Cu sites on the superconducting properties of YBa 2Cu 3O y (Y123) ceramic superconductors were investigated. The samples were prepared by the conventional solid-state reaction method and the properties of the samples were investigated by means of X-ray diffraction, AC magnetic susceptibility measurements, scanning electron microscope, and energy dispersive X-ray analysis. The critical temperatures were determined to be in the range of 80-92 K for both Systems I and II. It was found that Sb-addition leads to the formation of the non-superconducting YBa 2SbO 6 phase, which has a negative effect on the critical temperature, since the highest critical temperature was measured for pure Y123. However, the increasing substitution level has a negligible effect on the X-ray diffraction analysis peak intensities of the superconducting phases. In addition, SEM images showed that Sb substitution decreases the grain size and modifies the microstructure development, which makes the samples denser.

The effect of Ag substitution on the properties of high-temperature superconductor Bi1.7Pb0.3Sr2Ca2−x Ag x Cu3O y system have been investigated. The electrical and structural properties of the samples, prepared by the conventional solid-state reaction method, have been characterized by X-ray diffraction (XRD), electrical resistance and scanning electron microscopy (SEM) studies. XRD analysis reveals a multiphase structure of the samples, whereas SEM micrographs indicate some morphological changes induced by silver addition. It was found that an increase of the amount of Ag2O addition leads to an enhancement of the critical temperature and the percentage of Bi-2223 phase in the phase mixture.

In this work, effects of compaction pressure on the structural and superconducting properties of BSCCO ceramic superconductors were investigated. The study was carried out on two systems which were, System I: Bi 1.7Pb 0.3Sr 2Ca 2Cu 3O y and System II: Bi 1.6Pb 0.3Ag 0.1Sr 2Ca 2Cu 3O y, respectively. Ceramic powders were prepared by conventional solid-state reaction method and sintered at 850°C after compaction at five different pressures in the 150-750 MPa range. Critical temperatures of samples were determined by resistivity-temperature determinations made by four-point probe method in liquid nitrogen conditions. XRD analysis was conducted by powder X-ray diffraction method. Morphology of the grains present in the samples were determined by using scanning electron microscope (SEM) photographs at 2 K× and 2.5 K× magnifications for System I and System II, respectively. Sintered densities of the superconducting ceramics were measured by Archimedes water displacement method and unit cell parameters were additionally obtained from XRD data. T c values for System I was determined to be in the 109-115 K with sample D having the highest T c of 115 K while T c varied in the 104-109 K range and sample B had the highest T c value of 109 K for System II. The transition width, which is a sign of the purity of the samples, was determined to be narrow for both systems. The data obtained from X-ray diffraction measurements have shown that 2223 high-T c phase was dominant in both systems. The determination of the optimum pellet compaction pressure for BSCCO ceramic superconductors was the main purpose of this work. The results of this work indicated that compaction at around 450 MPa improves the superconducting and structural properties of the BSCCO ceramic superconductors. © 2009 Springer Science+Business Media, LLC.

The effect of partial substitution of Ca by Zn in Bi1.7Pb0.3Sr2Ca2−x Zn x Cu3O y at x=0.00, 0.05, 0.10, 0.15 and 0.20 levels on the electrical and structural properties was investigated in this work. The characterization of the ceramics prepared by the conventional solid-state reaction method were done by resistance–temperature measurements, XRD, SEM and density analysis. Low levels of Zn substitution of Ca caused significant changes in the properties of the ceramics. The low-T c superconducting properties were enhanced and the fraction of the low-T c (2212) phase were found to increase at x=0.15 level of Zn substitution at 830 °C sintering temperature. Zero resistance was observed only in sample D with x=0.15 and the T c was determined as 92 K. The SEM micrographs and the density analysis have shown that this was the densest packed ceramic.

In this study, the effects of sintering temperature on the Bi-2223 phase formation and the influence of minor phases on the intergranular properties of Sb substituted Bi-2223 samples were investigated. The samples were prepared by solid-state reaction method with different sintering temperatures ranging from 800 to 855 A degrees C. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and density measurements. We observed the optimal temperature of the Sb + Pb substituted Bi-2223 system as 845 A degrees C.

The effect of partial substitution of Cu in Bi 1.7 Pb 0.3 Sr 2 Ca 2 Cu 3-x Sb x O y at x = 0.0, 0.05, 0.1, 0.15, and 0.2 levels on the electrical and structural properties was investigated in this work. X-ray diffraction analysis shows that these materials have a multiphase structure. Two different types of particles with different morphologies were observed in scanning electron micrographs, The T c values decreased from 103.5 to 87 K for x = 0.1 Sb substitution level with a subsequent increase to 101 K at x = 0.2.

The effect of silver doping on the superconducting properties and structure of the BiPbSrCaCuO ceramics have been investigated in this work. The critical temperature, Tc, of ceramics without Ag doping was measured as 104 K. Sintered Ag doped Bi1.6Pb0.4-xAgxSr2Ca 2Cu3Oy ceramics (with x values of 0.0, 0.1, 0.2 and 0.3) were characterized by electrical conductivity measurements, XRD analysis and SEM. The Tc of the ceramics were observed to decrease with increasing levels of Ag doping ( while decreasing the Pb content). The electrical conductivity of samples with the highest level of Ag content (x = 0.3) was found to be not equal to zero even at 77 K. These observations were in aggrement with structural analysis. The low Tc and impurity phase contents of the ceramics was observed to increase with increasing Ag content as evidence by XRD patterns of the samples.