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A. Sedky and S.A. Amin

Abstract

Fluctuation induced conductivity by Pr substitution at Y sites of Y1-xPrx:123 superconductors is reported. It is found that the mean field temperature Tc mf, deduced from the peak of dρ/dT versus T plot, gradually decreases by increasing Pr up to 0.40. The order parameter dimensionality (OPD) is estimated from the slope of the logarithmic plot between excess conductivity Δσ and reduced temperature є. Interestingly, the crossover from 2D to 3D is obtained for samples with Pr = 0.00, 0.10 and 0.20, while with increasing Pr up to 0.40, the crossover from 0D to quasi-2D is obtained. On the other hand, the calculated values of interlayer coupling, coherence lengths, critical fields and critical current decrease with increasing Pr up to 0.20, but with the further increase of Pr, up to 0.40, they increase. The hole carriers/Cu ions anisotropy and G-L parameter gradually increase with Pr up to 0.40. Our results are discussed in terms of the effects of Pr substitution at Y site, such as oxygen rearrangements, anisotropy, hybridization and localization of holes in the overdoped region.

Open access

M.M. Ibrahim, S.A. Fayek, G.A.M. Amin and D.M. Elnagar

Abstract

Bulk samples of the BixSe1-x system with (x = 0, 5, and 10) were prepared using conventional melt quenching technique. Thin films were then deposited by thermal evaporation technique under high vacuum conditions from the prepared bulk samples. Effect of Bi substitution on surface morphology, electrical and optical properties of BixSe1-x thin films was studied. X-ray diffraction studies showed the formation of nanocrystalline clusters at Bi concentration x = 10. Formation of these clusters resulted in a rough surface which was confirmed by AFM measurements. The film surface was smooth, with RMS roughness of 0.0124 nm for Bi5Se95. For Bi10Se90, the RMS roughness increased to 3.93 nm indicating the formation of Bi2Se3 clusters. A simple hot probe technique showed a transition from p-type to n-type due to Bi incorporation. Charge transport mechanisms were investigated by temperature dependent DC electrical conductivity measurements in the temperature range of 209 K to 313 K. Electrical activation energy (ΔE) of the films with different Bi concentrations was found to exhibit a notable change at the p to n transition. At low temperature, the conduction was in reasonable agreement with Mott’s condition of variable range hopping. Mott parameters and the density of localized states near Fermi level were evaluated and correlated with the structural changes resulting from Bi addition. In addition, a red shift of the optical absorption edge of the films under study caused by Bi-Se substitution was observed. Slight changes in the optical parameters were observed with the γ-irradiation. Addition of Bi atoms could be used to tailor the structural, electrical and optical properties of chalcogenide materials such as junctionless photovoltaic devices.

Open access

Maksudur R. Khan, M.S.A. Amin, M.T. Rahman, F. Akbar and K. Ferdaus

Electricity generation from the readily biodegradable organic substrate (glucose) accompanied by decolorization of azo dye was investigated using a two-chamber microbial fuel cell (MFC). Batch experiments were conducted to study the effect of dye and substrate concentration on MFC performance. Electricity generation was not significantly affected by the azo dye at 300 mg/L, while higher concentrations inhibited electricity generation. The chemical oxygen demand (COD) removal and decolorization of dye containing wastewater used in the MFC were studied at optimum operation conditions in anode and cathode, 57% COD removal and 70% dye removal were achieved. This study also demonstrated the effect of different catholyte solutions, such as KMnO4 and K2Cr2O7 on electricity generation. As a result, KMnO4 solution showed the maximum electricity generation due to its higher standard reduction potential.