Synthesis and characterization of novel polyacrylate-clay sol-gel materials

Organo-functional silanes which were able to form chemical bonds with kaolinite and could also have an affinity to the materials of concern here, were studied by the sol-gel process. Polymethacrylate with trialkoxy silyl functional groups were prepared, hydrolysed and co-condensed with kaolinite. The progress of the hydrolysis, which proceeded very slowly, was followed by Karl-Fischer titration. Thermal behavior was investigated by differential thermal analysis. The extent of the reaction leading to network formation was qualitatively followed by Fourier transform-infrared spectroscopy and X-ray diffraction. Free-radical polymerization was carried out ultrasonically in the presence of a catalyst. Trimethoxy silane end-capped silane was found to be covalently bonded to kaolinite. The copolymers, with various amounts of kaolinite, were then hydrolysed and co-condensed in the presence of a catalyst to yield sol-gel materials which have a controllable combination of properties of both the polymer and kaolinite.     

Oxidation Behavior of Bi(Pb,Ga) SrCaCuO System

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.     

Hysteresis loops of MgB2 + Co composite tapes

The (MgB₂)_1?x Co _x composite tapes fabricated by the ex situ PIT method were investigated. The structural and magnetic properties were characterized. Only MgB₂ and Co phases were observed in the composites while x ≤ 0.2. A superconducting transition temperature was stable for these samples. Enhancement of the critical current density is found for x = 0.1.     

Effect of Fe Substitution for Cu on Microstructure and Magnetic Properties of Laser Floating Zone (LFZ) Grown Bi-2212 Rods

In this paper, the laser floating zone (LFZ) technique has been used to fabricate Bi₂Sr₂Ca₁Cu_2?x Fe _x O (x=0,0.01,0.03,0.05,0.1) superconducting fibers. The effects of Fe substitution on grain alignment and superconducting properties of annealed fibers were studied using SEM/EDX microanalysis in addition to phase analysis and magnetic measurements realized through XRD, M–T, and M–H loops. In the same growth conditions, higher Fe contents lead to a more compact microstructure with lower porosity but also caused the formation of poor superconducting phases followed by the decrease of T _c and J _cmag. No evidence of enhanced pinning capability was found in the magnetic measurements. Annealed rods indicated a weakly ferromagnetic-like behavior at relatively high doping levels.     

Structural and Superconducting Properties of Magnetically Doped Bi-2212 Textured Rods Grown by Laser Floating Zone (LFZ) Technique

In this work, we have applied the laser floating zone technique, a well-known method to produce highly aligned crystals and dense morphology, with improved transport properties, to obtain Bi₂Sr₂Ca₁Cu_2?x Ni _x O (x=0, 0.01, 0.03, 0.05 and 0.1) fibers of about 1.8 mm diameter ×12 cm length. Microstructural and magnetic properties of textured materials grown in the optimum conditions were analyzed through scanning electron microscope (SEM), energy dispersive X-ray analysis (EDX), powder XRD patterns, M–T and M–H loops. XRD analysis showed that addition of Ni at x=0.1 level caused the formation of small amounts of Bi-2201 phase. Thermal treatment has produced the agglomeration of Ni particles up to a few μm, detected by dot mapping EDX. Both T _c-onset and J _cmag values of the annealed rods decreased with the increasing Ni substitution rate, determined from the M–T and M–H loops, respectively.     

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

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 ??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 4.12×10⁶ A?cm^?2 for ex-situ annealed films and 4.01×10⁶ 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 grain boundaries on electrical and magnetic properties of melt-processed SmBa2Cu3Ox superconductors

In the present study, we examine the energy dissipation mechanisms and grain boundary effects on the superconducting properties of high-T_c SmBa₂Cu₃O_7?x samples. Sm-123 was synthesized with the top-seeded-melt-growth technique. Grain sizes, as determined by optical microscopy, ranged between 0.5 mm and 1.5 mm. Thus, each specimen, on which the electrical and magnetic measurements were carried out, contained several grains. Some of our findings are as follows: (1) the intragrain T_c is 93.5 K and the intergrain T_c is 87.5 K. Superconducting transition width is narrow and is not affected much by the magnetic field. (2) The intragrain J_c is 110,000 A cm^?2 while the intergrain J_c is 210 A cm^?2 at 10 K. (3) The intergrain J_c shows a secondary peak with the increase in temperature from 10 K to 30 K. The main reasons behind these observations are discussed in detail.     

Power Law Dependence of I?CV Characteristics of Bi-2212 Whiskers at Low Magnetic Fields

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?CV characteristics of the whiskers were studied in the temperature range of 10?C70?K under low magnetic fields. The transport critical current density of whiskers was calculated between 19 and 0.63??10⁴ A/cm² at 10?C60?K. I?CV data were fitted using the Levenberg?CMarquardt technique. Results were discussed and so was their dependence on magnetic and electrical properties of the superconductors.     

Physical, electrical, transport and magnetic properties of Nd(Ba,Nd)2.1Cu3O7−δ system

In this study, the superconducting Nd(Ba,Nd)_2.1Cu₃O_7?δ system has been prepared using conventional solid-state reaction technique. Transport properties including structural/microstructural evolution, electrical, magnetic and critical current density properties were investigated. After high temperature heat treatments at over 1,000 °C, large and strongly connected grains were obtained but weakly connected and small in size granular formation were obtained for the low temperature heat treated samples at around 900 °C. The best T _c and T ₀ values were obtained as 93 and 89 K respectively for the sample prepared at 1,020 °C for 24 h, which is very close to peritectic temperature of YBCO material. Magnetization of the sample heat treated at 1,020 °C was investigated in detail. The magnetization hysteresis loops are expounded to be the product of Nd-123 grains and unscreened Nd³⁺ ions within intergranular boundaries and vortex cores. The peak effect on the magnetization curves was described by the extended critical state model. Temperature dependencies of the irreversibility field, the peak field and the full penetration field correlate and there is scaling behavior of the pinning force as well. Thermoelectric power data was analyzed by “Modified two band model with linear T-term for superconductors”. Temperature dependence of thermal conductivity of the samples showed small peak with broad maximum just below the T _c value. Thermal conductivity of samples prepared was calculated by using “The Modified Callaway Model and Wiedermann–Franz law” and results obtained discussed.     

Thermal Conductivity Properties of Glass-Ceramic (Bi2-δ-γGaδTlγ)Sr2Ca2Cu3O10+x High-Tc Superconductors

Glass-ceramic BSCCO superconductors with nominal (Bi _2-- Ga Tl )Sr ₂ Ca ₂ Cu ₃ O _10+x compositions, where =0.20, 0.40, 0.60 and =0.10, 0.30, 0.40, have been prepared by the melt quenching method. The thermal conductivity (T) measurements were performed between 30K and 285K and results obtained found to be between 3.1 and 9.9 mW/cm.K depending on the substitution levels and temperature. Results obtained showed that the phonon-defect scattering dominates above the T _c for all samples but below the T _c a strong coupling mechanism occurs. The best electrical performance was obtained to be 113K and 107K for T _c and T _zero respectively.