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Effect of Bi deficiency on grain alignment of BiPb-2223 thin film fabricated using rf sputtering process and on critical current density properties
(Taylor & Francis Ltd, 2011) Aksan, M. A.; Altin, S.; Yakinci, M. E.; Guldeste, A.; Balci, Y.
In the present study, thin films prepared as a function of the Bi concentration in the BiPbSrCaCuO system were synthesised. Thin films were fabricated using radio frequency sputtering method. Crystal structure of the films fabricated was determined from X-ray diffraction measurements. The crystal orientation was analysed by X-ray pole figure and in-plane alignment. Both X-ray diffraction and pole figure analysis revealed that crystallinity in the films decreased significantly with decreasing Bi concentration in the system. A systematic decrease in the superconducting transition temperature and hole concentration per CuO plane was obtained with decreasing Bi concentration. The J(c) values of the films were calculated using Bean formula. It exhibits a significant dependence on the magnetic field and temperature. It was found that J(c) decreased sharply with increasing applied magnetic field. The highest J(c) value was found to be 1.06 x 10(6) A cm(-2) at 10 K, which corresponded to the best flux pinning among the films fabricated.
Effect of Bi2O3 Addition on the Single-Crystal BiSrCaCuO Whisker Growth
(Springer, 2011) Altin, S.; Aksan, M. A.; Altin, E.; Balci, Y.; Yakinci, M. E.
Bi-2212 superconducting whiskers have been fabricated by annealing a melt-quenched precursor using suitable heat-treatment cycles for Bi3+x Sr2Ca2Cu3O8+delta where x=1 and 2. Approximately 1-3 mm long whiskers were fabricated for x=1 and x=2 and their physical, electrical and magnetic properties were investigated. Crystallization activation energies of the materials were calculated according to Kissinger and Augis-Bennet method using the DTA data. Microstructural changes from glass to heat-treated glass-ceramic materials at different temperatures were investigated with SEM, EDX and XRD analyses. It was observed that the structure of the whiskers has high c-axis oriented single-crystalline Bi-2212 phase. The whiskers fabricated for x=1 and 2 showed very smooth surface without cracks and dislocations. T (c) of the whiskers for x=1 and 2 were obtained to be 83.2 K and 79.8 K respectively. The change of magnetization with applied magnetic fields (M-H) was investigated at three different temperatures, 10, 20 and 40 K, and J (c mag) was determined using the Bean model.
Effect of Ce substitution on superconducting properties of Bi2Sr2Ca2Cu3O10+? system fabricated by glass-ceramic technique
(Springer, 2011) Ozturk, R.; Aksan, M. A.; Altin, S.; Yakinci, M. E.; Balci, Y.
In this study, the samples with nominal composition of Bi2-x Ce (x) Sr2Ca2Cu3O10+delta , where x=0, 0.05, 0.1, 0.2, 0.4 and 0.6, are synthesized by using conventional glass-ceramic technique. Effects of the Ce substitution on the structural/microstructural and electrical properties of the Bi-2223 system have been investigated in detail. Ce has a solid solubility limit on glassification, which is found to be x=0.2. It is seen that glassification is destroyed for the Ce substitutions above x=0.2. Further, XRD investigations showed that main phase in all the heat-treated samples is identified to be Bi-2212. From SEM-EDX investigations of heat-treated samples, it is revealed that the highly Ce-substituted samples had complex and deformed structure. It is also found that electrical properties degraded with increasing the Ce concentration. Especially in high Ce substitution level, superconductivity is destroyed and an insulating behavior is observed.
Effect of grain size on the electrical and magnetic properties of MgB2 thick films deposited on the Al2O3 single crystal substrates
(Springer, 2014) Onar, K.; Balci, Y.; Yakinci, M. E.
MgB2 films having thicknesses of approximately 10 mu m have been prepared on the Al2O3 single crystal substrates by using ultrasonic spray pyrolysis technique. The films fabricated were then analyzed by means of microstructural, structural, transport and magnetic properties. The influence of grain size, depending on the ex-situ and in situ heating, were investigated. The results obtained showed that the size of MgB2 grains has an effect on the transport and magnetic properties of the films. Films prepared with in situ heating have small particle size (< 50 nm) and were found to be much better properties than the films prepared ex-situ heating, which have larger grains (similar to 1 mu m). The best T (c) value and critical current density, J (c) (mag) , were obtained to be similar to 36 K and 9.88 x 10(5) A cm(-2) respectively for the films prepared with small grains. The results were showed that the smaller grain size and in situ heating cycles are essential points for quality thick film MgB2 fabrication.
The effect of Mo addition on the microstructure and Jc properties of MgB2 tapes fabricated by PIT method
(Elsevier Science Sa, 2008) Bayazit, E.; Altin, S.; Yakinci, M. E.; Aksan, M. A.; Balci, Y.
We investigated the effect of Mo addition to MgB2/Ag tapes fabricated by the ex situ PIT method. The heat treatments were carried out at 600 degrees C for 24 h under At atmosphere. The structural development, microstructures, superconducting properties and critical current density were characterized by means of XRD, SEM, M-T and M-H measurements. XRD and SEM studies indicated that Mo, not reacting with matrix of MgB2, was formed. The T-c of the tapes decreased in all the addition levels. The maximum J(c) value was obtained to be 1.2 x 10(5) A cm(-2) at 10 K for pure MgB2 tape. Decrease of J(c) was observed with increasing the Mo concentration. The J(c)-H characteristics of the tapes were decreased by the addition of Mo. This is considered to be due to the reduced flux-pinning force in the material. (C) 2007 Elsevier B.V. All rights reserved.
Effects of In-situ and Ex-situ Heat-Treatment Procedures on the Transport Properties of the MgB2 Superconducting Thin Films Fabricated by Ultrasonic Spray Pyrolysis (USP) System
(Springer, 2011) Yakinci, M. E.; Aydogdu, Y.; Aksan, M. A.; Balci, Y.; Altin, S.
Superconducting MgB2 thin films have been prepared using Ultrasonic Spray Pyrolysis (USP) system. 2.4 MHz USP system and various solutions which contain different Mg, B and de-ionized water and LAPSA concentrations and gas atmospheres were used to obtain 500 nm to 1.0 mu m thick MgB2 films. Some of the films produced were heat treated in-situ in the spraying chamber during deposition and some of them were annealed ex-situ in the tube furnace under Mg vapor. T (c) and T (zero) of the samples were obtained to be 39.5 K and 37.4, 39.5 and 37.0 for ex-situ and in-situ prepared films, respectively. The highest critical current density was obtained to be 4.12x10(6) A cm(-2) for ex-situ annealed films and 4.01x10(6) A cm(-2) for in-situ produced films. The result obtained indicated that the ex-situ preparation method provides improvement in the transport and magnetic properties.
Effects of SnO on growth and physical properties of BSCCO whiskers
(Maney Publishing, 2010) Altin, S.; Aksan, M. A.; Balci, Y.; Yakinci, M. E.
Superconductor whiskers doped with SnO have been fabricated by annealing a melt quenched (Bi2Sn1)-223 precursor using suitable heat treatment cycles. Approximately 5 mu m thick, 90 mu m wide and 5 mm long whiskers were fabricated, and their physical, electrical and magnetic properties were investigated. Crystallisation activation energies of glass phase fabricated were calculated to be 390 kJ mol(-1) using Kissinger method based on the differential thermal analysis data. The T-c value of the whiskers was found to be 94 K from M-T measurement. The magnetisation of whiskers before superconducting transition increased with decreasing temperature, and after superconducting transition, the magnetisation of whiskers decreased, from positive to negative, due to the diamagnetic nature of superconductivity. The change on magnetisation dependence of applied magnetic fields (M-H) showed that whiskers have paramagnetic-diamagnetic multiphase structure.
Magnetoresistance properties of MgB2 thick films on YSZ substrate using spray pyrolysis method
(Iop Publishing Ltd, 2009) Altin, S.; Aksan, M. A.; Yakinci, Z. D.; Oezabaci, M.; Balci, Y.; Yakinci, M. E.
The MgB2 thick films have been fabricated on the polycrystalline YSZ substrates using spray pyrlosis technique. Structural/microstructural, electrical and magnetic properties were investigated by XRD, SEM-EDX and R-T measurements. The films fabricated showed dense and homogenous structural formation with strong grain connections. The electrical properties of MgB2 thick films were investigated under different magnetic fields. It was seen that resistive transition broadened with increasing the applied magnetic fields. It was believed that the broadening is due to the thermally activated flux flow (TAFF). The activation energy, U(H), of the MgB2 films was calculated using Arhenius law.
Nano-sized Spherical MgB2 Superconducting Powder Fabrication Using MHz Range Ultrasonic Spray Pyrolysis (USP) System
(Springer, 2011) Yakinci, M. E.; Aksan, M. A.; Balci, Y.; Altin, S.; Onal, Y.; Aydogdu, Y.
We have fabricated 40-150 nm sized MgB2 superconducting spherical powders by using a 2.4 MHz ultrasonic spray pyrolysis system and consecutive high temperature heating and powder collection chamber. Various chemical solutions, which contain Mg, B, de-ionized water, acetone and LAPSA in different concentrations and gas atmosphere, were used to obtain MgB2 superconducting powders. Microstructural, transport and magnetic characterizations of the powders were performed using XRD, SEM-EDX, R-T, M-H analysis and critical current density calculations, which is found in the range of 10(6) Acm(-2), indicating improved flux pinning properties.
Oxidation Behavior of Bi(Pb,Ga) SrCaCuO System
(Springer, 2011) Balci, Y.; Ceylan, M.; Aksan, M. A.; Yakinci, M. E.
A nominal compositions of BiSrCaCuO (3:2:2:3), (2:2:2:3), (4:3:3:4), and BiPbGaSrCaCuO (3:0.5:2:2:3), (3:0.3:0.3:2:2:3) have been prepared by conventional melt-quenching method. The oxidation behaviors of samples prepared were analyzed using a thermogravimetric analyser, TGA. Total mass gains of samples, average oxidation rates and maximum oxidation rates were calculated separately. TGA measurements of all samples were carried out under the normal atmosphere pressure.
Pinning Properties of Bi-2212 Single Crystal Whiskers
(Iop Publishing Ltd, 2009) Altin, S.; Aksan, M. A.; Balci, Y.; Yakinci, M. E.
Bi-2212 single crystal whiskers have been fabricated on the surface of the bulk glass BSCCO pieces prepared by the melt-quenching process. The characterizations of the whiskers were made using XRD, SEM-EDX, M-T, M-H analysis. Pinning force calculations were performed using magnetic hysteretic loops taken at different temperatures and results obtained were analyzed using scaling law equation. The whiskers fabricated showed higher pinning at low temperature. The pinning force at 10 K was calculated to be 3,83x10(11) N/m(3) under 2 T applied magnetic field. The results obtained showed that a decrease on the flux pinning force decreases the critical current density of whiskers.
Power Law Dependence of I-V Characteristics of Bi-2212 Whiskers at Low Magnetic Fields
(Springer, 2011) Altin, S.; Altin, E.; Aksan, M. A.; Balci, Y.; Yakinci, M. E.
In this study, BiSrCaCuO superconducting whiskers were fabricated by using a glass-ceramics process. The T (c) value of the whiskers fabricated was found to be 90.2 K. I-V characteristics of the whiskers were studied in the temperature range of 10-70 K under low magnetic fields. The transport critical current density of whiskers was calculated between 19 and 0.63x10(4) A/cm(2) at 10-60 K. I-V data were fitted using the Levenberg-Marquardt technique. Results were discussed and so was their dependence on magnetic and electrical properties of the superconductors.
The single crystal superconducting Bi-2212 whiskers fabrication and their thermal transport properties
(Elsevier Science Sa, 2010) Altin, S.; Aksan, M. A.; Yakinci, M. E.; Balci, Y.
In this study, we have fabricated the superconducting single crystal whiskers using glass-ceramic BiSr-CaCuO material. The crystallization kinetic studies (crystallization activation energy, E-a, and the Avrami parameter, n,) were carried out using DTA data. The oxygen diffusion energy was calculated using TG data. XRD and SEM analysis of the whiskers showed Bi-2212 phase formation and the c-axis orientation. The in-plane resistivity, rho(ab), and the out-of-plane resistivity, rho(c), properties of the whiskers were investigated. The thermoelectric power. S(T), value between 10 and 300 K is found to be positive, indicating that charge carriers in the whiskers are holes. We analyzed the thermoelectric power as a function of temperature with Two band model with linear T-term Linear temperature dependence in the thermal conductivity down to T-c and then a sharp rise just below T-c were obtained. (C) 2010 Elsevier B.V. All rights reserved.
Transport Properties under Magnetic Field and Jc(H) Peak Effect on Single-Crystal Bi-2212 Whiskers
(Springer, 2009) Altin, S.; Aksan, M. A.; Balci, Y.; Yakinci, M. E.
In this study, 50 nm-18 mm in length superconducting single-crystal Bi-2212 whiskers have been fabricated using glass-ceramic BSCCO material. The microstructure, transport and magnetic properties were characterized by XRD, SEM-EDX, R-T, I-V and M-H analysis. Highly c-axis oriented single-crystal whiskers were produced without any grain boundaries in any crystallographic direction. T-c and T-zero were obtained to be 94.8 K and 92.8 K, respectively, and decreased with increasing the magnetic field. Magnetic properties, M-H curves of the whiskers, were investigated at 3 different constant temperatures up to 5 T. Symmetric hysteresis loops for all temperature and field cases were obtained and maximum J(c)(mag) value was calculated to be 4.58 x 10(6) Acm(-2) at 10 K for 0 T but dropped to 1.61 x 10(6) Acm(-2) at 30 K for 0 T. Transport critical current density, J(c)(trans), of the whiskers in low magnetic field (between 0 and 270 Oe) and in a wide temperature region (5-75 K) was investigated. It was obtained that initially J(c)(trans) increased with increasing the magnetic field but then started to decrease with further increase on the magnetic field at all temperature values. We have investigated this problem in terms of the Bulk pinning model, the Geometrical barrier model and the Bean-Livingston surface barrier model. We have noticed that all these models were not fitted well to our data. However, we have modified the Bean-Livingstone model by adding a new parameter. It was found that this modified formula fitted well to the data obtained in this work and can give successful explanations to the other results obtained by other groups.

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