Thermoelectric,electronic and structural properties of CuNMn3 cubic antiperovskite

Using first-principles calculations, in this work we report the structural, electronic and, for the first time, thermoelectric properties of CuNMn3 cubic antiperovskite. The structural properties are explored using GGA and \(\hbox {GGA}{+}\hbox {U}\) approximations. Structural optimization shows that the compound is stable in the ferrimagnetic phase, and the electronic properties confirm the metallicity of this compound. At room temperature, high values of the Seebeck coefficient are obtained between \(-\) 0.8 and 0.5 \(\upmu (\hbox {eV})\) chemical potential, whereas outside this region the Seebeck coefficient diminishes. Also, thermal conductivities are minimal in this region of chemical potential; therefore, the material can be used to achieve thermocouples. Thermal conductivity is high for 900 K. The maximum electrical conductivity is obtained at 0.38 \(\upmu (\hbox {eV})\) chemical potential, with a value of \(4.15\times 10^{20}(\Omega ~\hbox {ms})^{-1}\). The figure of merit ZT values obtained are still low, so for thermoelectric applications of the material, it is necessary to improve the figure of merit coefficient by doping the material with a suitable element.     

Study of electronic and magnetic properties of binary zinc sulfide and ternary manganese- and iron-substituted alloys

A series of first principles calculations have been carried out to investigate magnetic and electronic properties of zinc manganese sulfide ZnMnS for three different manganese concentrations and for zinc iron sulfide ZnFeS. The electronic structures and properties of ZnMnS and ZnFeS were calculated by the local spin density approximation method based on density functional theory. The electronic-state densities in ZnFeS show that the density of states near Fermi energy level is mainly derived from the orbital (d) of the transition metal. Moreover, ZnMnS for a concentration of 6.25% and 12.5% behaves as a semiconductor and has a weak ferromagnetic behavior for a concentration of 18.75%. Consequently, ZnMnS is unsuitable for spintronics. In contrast, ZnFeS is half-metallic and ferromagnetic for low concentration of Fe, so it is a promising candidate for applications in spintronics.     

Investigation of Transport Properties of Some Superconductor Nickel-Based Antiperovskite XNNi<Subscript>3</Subscript> (X = Mg,Al, Cu,Zn, Ga,Ag, Cd,In, Sn,Sb, Pt and Pb)

We report, in this work, a theoretical study of electronic and transport (thermoelectric) properties of some superconductor nickel-based antiperovskite XNNi₃ (X = Mg, Al, Cu, Zn, Ga, Ag, Cd, In, Sn, Sb, Pt and Pb) using first-principles calculations with the full-potential linearized augmented plane wave (FPLAPW) method based on the density functional theory (DFT) as implemented in the WIEN2k package. Electronic properties are calculated and show that the studied materials are of metallic type which is in good agreement with experimental data. The Seebeck coefficient, thermal conductivity, electrical conductivity and figure of merit were reported. The results obtained show that the zinc (Zn) and silver (Ag) materials are characterized by a high value of the figure of merit at room temperature (300 K) which is respectively 0.86 and 1.02 in a p-type region. In the case of the transition metals, the maximum values of S increase in going from the Pt atom to the Zn atom and then decrease for the Cd atom. Furthermore, the Wiedemann–Franz law which states that the ratio of thermal to electrical conductivity for metals is constant is well verified in this work. The electric conductivity values are almost invariant with the temperature except for the case of MgNNi₃ and AgNNi₃ compounds in which it increases with T slightly. So, the superconducting materials based on silver and zinc are the best for the thermoelectric applications at room temperature due to the very important value of the factor of merit and the Seebeck coefficient obtained.     

Flow characteristics of surfactant stabilized water-in-oil emulsions

In this paper, an investigation was carried out to study the effect of water fraction and flow conditions on the flow characteristics of surfactant stabilized water-in-oil emulsion. Pressure drop measurements were conducted in 2.54-cm and 1.27-cm horizontal pipes. The influence of water fraction and the flow conditions on emulsion stability, type, conductivity, droplet size distribution, viscosity and pressure drop were reported. The results showed a significant increase in the emulsion stability, viscosity and pressure drop with increasing water fraction up to 70%. In addition, shear thinning behavior was observed for the emulsions especially at high water fractions. Furthermore, pressure drop measurements of high concentrated emulsions showed pipe diameter dependency especially at high Reynolds (Re) numbers. Moreover, drag reduction was observed with decreasing water fraction. The viscosity of surfactant-stabilized water-in-oil emulsions was modeled with a modified fluidity-additivity model.