Khaled M. Elsabawy

Narrow range of iridium-substitution on Mg1−xIrxB2 superconductor

Abstract The undoped and iridium-doped samples of the general formula Mg 1− x Ir x B 2 (where x =0.0, 0.02, 0.06 and 0.12 mol%) were prepared via high temperature solid state reaction technique depending upon diffusion mechanism of Mg-vapor through boron-matrix. The maximum iridium solubility limit m was found to be ∼0.06 mol%, which emphasizes that substitution on MgB 2 system is too limited and needs many precautions to be successful. The crystalline lattice constants were evaluated as a function of Ir-doping ratio x and found to confirm that c -axis exhibits slight length compression as x increases while a , b -axes were nearly constant. Furthermore, effect of Ir-doping was investigated carefully on microstructure and superconducting properties of MgB 2 system.

Terbium-neodymium co-doping in Bi sites on the BPSCCO bismuth cuprate superconductor

The parent BiPbSr2Ca2Cu3O10 (BPSCCO) and samples of the general formula Bi1-(x+y)NdxTbyPbSr2Ca2Cu3O10, where x = y = 0.05, 0.1 and 0.2, were prepared using the conventional high-temperature solid-state reaction technique. The superconducting measurements proved that the best value of Tc, 108 K, is for the sample with x = y = 0.1 mol% while the lowest value of Tc, 101 K, is for the sample with maximum dopant concentration x = y = 0.2 mol%. The evaluated crystalline lattice structure of the prepared samples mainly belongs to the superconductive tetragonal phase (2223) besides the secondary (2212) phase. Also, thermogravimetric and differential thermal analyses were studied on the green mixture showing an endothermic peak at 790 °C corresponding to the superconductive phase formation. The microstructures of the prepared samples were investigated by scanning electron microscopy and energy dispersive x-ray analysis.

Two dimensional γ-irradiations for promoted structural properties of MgB2 superconductors

Abstract MgB 2 was prepared via solid state reaction technique by mixing stoichiometric amounts of pure boron and magnesium and sintered at 970 °C under argon atmosphere. X-ray measurements for non-irradiated MgB 2 proved that MgB 2 mainly belongs to hexagonal phase with some MgO and B secondary phases in minor. While γ-irradiated MgB 2 (γ-absorbed dose=10 and 20 MR) exhibits structure quality attributable to enhancing action of γ-ray to the Mg-ions, diffusion and ordering through boron matrix consequently reduce the amount of unreacted boron. Scanning electron microscopy was performed and indicated that the average grain size is in between 0.3 and 1.35 μm and there is no MgO detected in the grain boundaries. The transition temperature for the non-irradiated MgB 2 was found to be ∼37.6 K at the meantime the γ-irradiated MgB 2 (γ-absorbed dose=10 and 20 MR) have been given the same T c while T c =36.1 K was for MgB 2 with γ-absorbed dose=40 MR.

Mechanical tensile promotion and superconducting properties of highly Pb-content HTc-BPSCCO superconductor

Abstract The samples of the general formula (Bi0.8Pb0.2+x)2Sr2Ca2Cu3O10, where 0.0≤x≤0.3 mol% were prepared by the conventional high temperature solid state reaction technique. The extra lead (x) was added as very fine powder of pure Pb-metal with particle size ≤50 μm. The superconducting measurements for HTc-2223-phase proved that, best Tc=109 K is for the sample with x=0.2 (Pb-content=0.4 mol%) while the lowest Tc=98 K is for the sample with x=0.3 mol%. The evaluated crystalline lattice structure of the prepared samples mainly belongs to the superconductive tetragonal phase (2223), besides secondary (2201) and (2212) phases in minor. The c-axis lattice parameter exhibits length elongation as x (Pb-content) increases from x=0.1 to 0.3. The maximum mechanical tensile strength values at 295 K were promoted and found to be 37.5, 38.6 and 41.4 MPa as Pb-content increases from x=0.1 to 0.3, respectively.

Sr-doping for promoted high-Tc BPSCCO superconductors

Abstract Nearly single phase superconducting samples of the general formula (Bi/Pb) 2 (Sr 2− x Ca x ) 2 Cu 3 O 10 were prepared by the usual high temperature solid state reaction technique and ceramic procedures. The prepared sample with x =0.6, with optimally nominal oxygen content (over doped) shows T c of 107 K. The increase in T c is also accompanied by an increase in the room temperature c -axis length. The crystal structure of the sample was determined by Cu-K α X-ray diffractometry. This crystal belongs to a tetragonal system and has a space group of I4/mmm with a =3.6732 A and c =34.3176 A. The TGA and DTA thermal analyses on the green samples included steps of thermal decomposition of CuCO 3 (300–400 °C), CaCO 3 (660–710 °C), SrCO 3 (710–800 °C) and finally to the high temperature solid state formation of superconductive phase at 820 °C. Finally a proposed crystalline structure symbol was put forward.

Synthesis and 3D-AFM surface topology of nanographene-like material extracted from sulfonated tri-, di- and monochloroacetic acid

Abstract In this study a graphene-like material was synthesized by chemical exfoliation of sieved graphite powder with an average particles size ≤100 µm in dispersing medium from tri-, di- and monochloroacetic acid sulfonated with 55 % H2SO3. The results indicated that the yield of graphene-like material was the best in case of trichloroacetic 55 % H2SO3, taking into account structure quality and amount of obtained material. Layered graphene-like material was carefully collected after reduction of GO formed by 50 % dimethylhydrazine. AFM-investigations were performed to characterize nanostructural features of produced graphene and expected surface area which is surface topology dependent. Furthermore, Raman spectra were measured to confirm graphene formation.

New Thorium-Doped YBa2(1 − x)Sr x Th x Cu3O7 − δ High-Tc Superconductors

Thorium-doped YBa2(1 − x)SrxThxCu3O7 − δ high-Tc ceramic superconductors (with x = 0.1, 0.15, 0.2, and 0.3) have been carefully prepared by the usual ceramic procedure and sintering technique, with intermediate grindings and annealing under a stream of compressed-air atmosphere. The structural parameters of the prepared samples are calculated and interpreted using X-ray diffraction analysis. The electrical properties are also carefully investigated in the present work using the four-probe technique. Results obtained were compared, explained, interpreted, and discussed in detail; meanwhile, the major goal of the present work and promising deductions are attained at.

Soft Synthesis and Nano -Structural Features of Highly Crystalline Asprin An AFM-Investigations

The present investigations introduce new trend of applying AFM-microscopy to visualize a real 3D-imaging of samples surface topography. High resolution AFM-investigations indicated that crystalline asprin has regular arrays of atomic arrangement with no violation in the bulk of asprin .TM deflection AFM- gave us good approximation to the diffusion of grain throughout the surface topology of investigated asprin . The AFM-deflection centers imaging indicated that the numbers of grains distribute in circular arrangements on the surface and material bulk .3D-visualized imaging introduce precise determination of exposure surface area interacting with dissolving agent.

BSCCO 2212 Defective Tellurium Ions on Bi-Site

BSCCO 2212 superconducting samples, doped Tellurium, with the chemical formula Bi2-xTexSr2CaCu2O8, were prepared by the conventional solid state reaction technique. The prepared samples were studied utilizing XRD, DC-electrical conductivity and SEM. XRD spectra indicated that 2212 with tetragonal structure is the major phase, whereas Bi-2201 and CaTeO4 are minor phases. At higher Te-additions x, traces from some other semi conducting phases were detected. The critical transition temperature Tcoffset was found to decrease non-linearly with x, which attributed to the hole filling caused by the liberated electrons of Te4+ ions. For x–values in the range 0.1 ≤ x ≤ 0.4, the steepness of (ρ vs T) relationship increases abruptly around 150 K; this was attributed to change in the oxygen vacancy feature (phase-like transition). SEM photographs revealed that as Te-content increases the compactness of the surface and the connectivity of the grains decreases, while pores and voids increase as a result of decreasing the amount of Bi and presence of multiple-phases in the sample.