Investigation of Structural, Electronic and Thermoelectric Properties of Two-Dimensional Graphdiyne/Borophene Monolayers and Hetero-bilayers

The integration of dissimilar 2D materials is important for nanoelectronic and thermoelectric applications. Among different polymorphs and different bond geometries, borophene and graphdiyne are two promising candidates for these applications. In the present paper, we have studied hetero-bilayers comprising graphdiyne-borophene (GDY-BS) sheets. Three structural models, namely S0, S1 and S2 have been used for borophene sheets. The optimum interlayer distance for the hetero-bilayers was obtained through binding energy calculations. Then, the structure and electronic properties of the monolayers and hetero-bilayers were individually examined and compared. Graphdiyne monolayer was shown to be a semiconductor with a band gap of 0.43 eV, while the borophene monolayers, as well as all studied hetero-bilayers showed metallic behavior. The thermoelectric properties of borophene and graphdiyne monolayers and the graphdiyne-borophene bilayers were calculated on the basis of the semi-classical Boltzmann theory. The results showed signs of improvement in the conductivity behavior of the hetero-bilayers. Furthermore, considering the increase in Seebeck coefficient and the conductivity for all the structures after calculating figure of merit and power factor, a higher power factor and more energy generation were observed for bilayers. These results show that the GDY-BS hetero-bilayers can positively affect the performance of thermoelectric devices,

A phenomenological approach to anomalous transport in complex or disordered media

We aim to derive a phenomenological approach to link the theories of anomalous transport governed by fractional calculus and stochastic theory with the conductivity behavior governed by the semi-empirical conductivity formalism involving Debye, Cole-Cole, Cole-Davidson, and Havriliak-Negami type conductivity equations. We want to determine the anomalous transport processes in the amorphous semiconductors and insulators by developing a theoretical approach over some mathematical instruments and methods. In this paper, we obtain an analytical expression for the average behavior of conductivity in complex or disordered media via using the fractional-stochastic differential equation, the Fourier-Laplace transform, some natural boundary-initial conditions, and familiar physical relations. We start with the stochastic equation of motion called the Langevin equation, develop its equivalent master equation called Klein-Kramers or Fokker-Planck equation, and consider the time-fractional generalization of the master equation. Once we derive the fractional master equation, then determine the expressions for the mean value of the variables or observables through some calculations and conditions. Finally, we use these expressions in the current density relation to obtain the average conductivity behavior.

Temperature glass and conductivity behavior of epoxy deproteinized natural rubber in ternary blend of EDPNR/PMMA/LiCF3SO3

The temperature glass behavior of epoxy deproteinized natural rubber/polymethylmethacrylate/lithium trifluoromethanesulfonate (EDPNR/PMMA/LiCF3SO3) and the conductivity behavior of EDPNR in the ternary blends were studied by DSC and multichannel potentiostat. The DSC result revealed the temperature glass of the EDPNR was shifted to the right with the increase of lithium salt amount in these binary blends composition. However, in the ternary blends of EDPNR/PMMA/LiCF3SO3 the temperature glass revealed the miscibility of these ternary blends. Two different temperature glass values were obtained when the ratio of EDPNR in EDPNR/PMMA was less than 80 wt.%. The ionic conductivity of EDPNR could be improved by increasing the amount of lithium salt up to 35 wt.%, after this amount the ionic conductivity of EDPNR was significantly decreased. While in the ternary blends, the highest ionic conductivity value was found at the ratio 80/20 of EDPNR/PMMA. Furthermore, the factors influencing the temperature glass and conductivity behavior of EDPNR were systematically studied in this work. The results demonstrated an intimate correlation between temperature glass and conductivity behavior of EDPNR.

Hydraulic conductivity behavior of soilcrete specimens created from dredging sand, cement, and bentonite

Dredging sand is an inexpensive material utilized to rise elevations of highway embankments and earth levee bodies in the Southern Vietnam. However, high permeability of the dredging sand can cause failures due to seepage flows during annual flood seasons. The dredging sand mixing cement with or without bentonite is expected to be suitable low permeability as an impermeable material. However, hydraulic conductivity of soilcrete and bentonite specimens created from dredging sand taken in the Mekong delta has limit research data. This study aims at better understanding the hydraulic conductivity of dredging sand samples taken in Dong Thap province mixed with cement and bentonite. The effects of the hydraulic conductivity of soilcrete and bentonite soilcrete specimens on time, cement contents, bentonite contents, cement types, and hydraulic gradients were investigated. The tests followed the ASTM D5084 standard using the both falling head-constant tailwater and falling head-rising tailwater methods. The results indicate that: (1) the hydraulic conductivity of the soilcrete and bentonite specimens decreased with increasing in testing duration and cement contents; (2) the hydraulic conductivity of the soilcrete specimens was lower 104 to 105 times than that of the compacted sand; (3) the hydraulic conductivity of the bentonite soilcrete specimens was lower 10 times than those of the soilcrete specimens; (5) the PCS cement can induce long-term reduction of soilcrete hydraulic; (6) effect of hydraulic gradients on soilcrete hydraulic conductivity was ignorable; (6) the soilcrete hydraulic conductivity varies from 10− 9 to 10− 10 m/s.

Structure evolution, dielectric, and conductivity behavior of (K0.5Na0.5)NbO3-Bi(Zn2/3Nb1/3)O3 ceramics

Abstract(1−x)K0.5Na0.5NbO3−xBi(Zn2/3Nb1/3)O3 ((1−x)KNN−xBZN, x = 0.010, 0.015, 0.020, 0.025, and 0.030) lead-free ceramics were fabricated via a traditional solid-state method. The crystal structure, microstructure, dielectric, and conductivity behavior of this system were studied. Combined with X-ray diffraction (XRD) patterns, Rietveld refinement, and dielectric spectroscopy, an orthorhombic phase was determined for x = 0.010, an orthorhombic-tetragonal mixed phase was identified for x = 0.015, and a rhombohedral symmetry appears in 0.020 ⩽ x ⩽ 0.030. Both 0.98KNN−0.02BZN and 0.975KNN−0.025BZN ceramics exhibit stable permittivity and low dielectric loss tangent (tanδ) in wide temperature ranges owing to the combination of rhombohedral-tetragonal step-like feature and the diffuse phase transition from tetragonal to cubic. The activation energies of dielectric relaxation and conductivity behavior at high temperatures initially decrease slightly, then drop sharply, and finally decline slowly, which could be attributed to microstructure morphologies and the concentration of oxygen vacancies.