Longitudinal Electrical Conductivity Research Articles

Визначення величини енергетичної невпорядкованості в аморфних оксидних напівпровідниках

The amorphous material films are resistant to high-energy irradiation. Therefore, devices built using the properties of these materials can work in conditions of increased radiation much longer than devices using the properties of crystals. An important characteristic of these materials is their degree of disorder. To determine this characteristic, a model of random fluctuations of the local edge of the conduction band is considered for the theoretical study of magnetoconductivity in amorphous oxide semiconductors. The effective medium approximation is used. An approach to determining the amount of energy disorder based on experimental measurement of changes in longitudinal and transverse electrical conductivity in a magnetic field is proposed.

Quantitative Nondestructive Evaluation of Cold Spray Manufactured Aluminum Alloy 6061 and Copper Samples

Cold spray (CS) is a solid-state process for depositing thick layers of material via the successive high-velocity impact of powder particles onto a solid surface, which leads to high rates of deformation, interparticle bonding, and coating build-up. Although CS is finding commercial utilization in non-load-bearing repair and coating applications, clear nondestructive characterization procedures are necessary to realize its potential in load-bearing structural applications. In this study, the viability of electrical conductivity and through thickness ultrasound wave velocity measurement methods was studied to serve as a means for nondestructive quantitative measurement for quality control in CS and potentially other additive manufacturing (AM) methods. Eddy current, ultrasound, porosity, hardness, and uniaxial tensile strength tests were conducted on CS deposited layers of aluminum alloy 6061 and copper on aluminum alloy 6061 and commercially pure copper substrates, respectively. CS gas dynamic parameters were intentionally and systematically varied to result in corresponding discrete differences in mechanical properties of deposits. Ultrasound measurements of longitudinal wave velocity and eddy current electrical conductivity measurements showed good correlation with process conditions, microstructural characterization results, and destructive mechanical tests (hardness, tensile). The results of this work show that ultrasound wave velocity and electrical conductivity correlate well with increased particle impact velocity in CS deposited aluminum and copper blocks, which evidently show an incremental decrease in porosity, increase in hardness, and increase in tensile strength. The outlined ultrasound and eddy current nondestructive testing methods present effective means for quantitative assessment of cold spray deposited structures while intact with the substrate.

Facile fabrication and characterization of MXene/cellulose composites for electrical properties, electric heating performance

AbstractDeveloping energy-efficient and multifunctional wearable electronic textiles (E-textiles) is a significant challenge. This study investigates MXene-coated cellulose hybrid fibers, focusing on their electrical properties, heating performance, and thermal stability. The fabrication process involves continuous dipping of cellulose fibers into an aqueous MXene solution, resulting in the creation of MXene-coated cellulose hybrid fibers. We confirm the uniform coating of MXene sheets on the cellulose fiber surfaces, with increasing content throughout the dip coating cycle, as evidenced by X-ray diffraction and scanning electron microscopy analysis. The high thermal conductivity of MXene acts as a heat source, impacting the thermal stability of cellulose fibers at lower temperatures. Additionally, the electrical properties of MXene/cellulose hybrid fiber composites are influenced at elevated temperatures. Remarkably, the longitudinal electrical conductivity of the MXene-coated cellulose fiber composites exhibits a notable increase of 0.06 S/cm after the final coating cycle, demonstrating the effective and conductive nature of the layer-by-layer MXene network formed on the cellulose fibers.

On quantifying uncertainty in lightning strike damage of composite laminates: A hybrid stochastic framework of coupled transient thermal-electrical simulations

Lightning strike damage can severely affect the thermo-mechanical performance of composite laminates. It is essential to quantify the effect of lightning strikes considering the inevitable influence of material and geometric uncertainties for ensuring the operational safety of aircraft. This paper presents an efficient support vector machine (SVM)-based surrogate approach coupled with computationally intensive transient thermal-electrical finite element simulations to quantify the uncertainty in lightning strike damage. The uncertainty in epoxy matrix thermal damage and electrical responses of unprotected carbon/epoxy composite laminates is probabilistically quantified considering the stochasticity in temperature-dependent multi-physical material properties and ply orientations. Further, the SVM models are exploited for variance-based global sensitivity analysis to investigate the input parameters' relative influence on the lightning strike-induced damage behavior. Due to the adoption of a coupled SVM-based simulation approach here, it has become possible to carry out a comprehensive uncertainty quantification leading to complete probabilistic descriptions of the electrical and lightning damage parameters despite the requirement of performing a large number of computationally intensive function evaluations. The results reveal that source-uncertainty of the unprotected laminates significantly influences the epoxy matrix decomposition, electrical current density and electric potential, wherein longitudinal electrical conductivity is most sensitive to stochastic variations followed by other electrical, thermal and geometric parameters.

Water uptake on lightning strike damage of carbon fiber reinforced composites with surface protections

The effect was examined of water uptake on the lightning strike (LS) damage of carbon fiber reinforced composites (CFRCs) and surface-protected CFRCs. First, water absorption (WA) experiments on CFRC, CFRC adhered to a copper mesh (CFRC-Cu) and CFRC bonded with an aluminum coating (CFRC-Al) were performed to obtain specimens with various water contents. Then, simulated LS tests were carried out on the specimens to investigate the LS damage mechanism. The experimental results showed that the LS damage level of the pristine CFRC specimens increased with the addition of water content, primarily due to the decreased glass transition temperature of the matrix, the increased longitudinal electrical conductivity and the gas explosion after WA. In terms of the CFRC-Cu specimens, the decreased interfacial properties between the copper mesh and the insulated adhesive layer are attributed to the aggravated LS damage area of the copper mesh, whereas the gas explosion is the key factor contributing to the increased damage in the CFRC-Al specimens. In addition, an increase in the adhesive layer thickness intensified the LS damage in the CFRC-Cu specimens but reduced the damage in the CFRC-Al specimens after WA.

Heat transport in Weyl semimetals in the hydrodynamic regime

We study heat transport in a Weyl semimetal with broken time-reversal symmetry in the hydrodynamic regime. At the neutrality point, the longitudinal heat conductivity is governed by the momentum relaxation (elastic) time, while the longitudinal electric conductivity is controlled by the inelastic scattering time. In the hydrodynamic regime, this leads to a large longitudinal Lorenz ratio. As the chemical potential is tuned away from the neutrality point, the longitudinal Lorenz ratio decreases because of suppression of the heat conductivity by the Seebeck effect. The Seebeck effect (thermopower) and the open circuit heat conductivity are intertwined with the electric conductivity. The magnitude of the Seebeck tensor is parametrically enhanced, compared to the noninteracting model, in a wide parameter range. While the longitudinal component of Seebeck response decreases with increasing electric anomalous Hall conductivity ${\ensuremath{\sigma}}_{xy}$, the transverse component depends on ${\ensuremath{\sigma}}_{xy}$ in a nonmonotonous way. Via its effect on the Seebeck response, large ${\ensuremath{\sigma}}_{xy}$ enhances the longitudinal Lorenz ratio at a finite chemical potential. At the neutrality point, the transverse heat conductivity is determined by the Wiedemann-Franz law. Increasing the distance from the neutrality point, the transverse heat conductivity is enhanced by the transverse Seebeck effect and follows its nonmonotonous dependence on ${\ensuremath{\sigma}}_{xy}$.

Facile growth of high-yield and -crystallinity vertically aligned carbon nanotubes via a sublimated ferric chloride catalyst precursor

A facile and effective catalyst deposition process for carbon nanotube (CNT) array growth via chemical vapor deposition using a resistively heated thermal evaporation technique to sublimate FeCl3 onto the substrate is demonstrated. The catalytic activity of the sublimated FeCl3 catalyst precursor is shown to be comparable to the well-studied e-beam evaporated Fe catalyst, and the resulting vertically aligned CNTs (VA-CNTs) have a similar diameter, walls, and defects, as well as improved bulk electrical conductivity. In contrast to standard e-beam-deposited Fe, which yields base-growth CNTs, scanning and transmission electron microscopy and X-ray photoelectron spectroscopy characterizations reveal a tip-growth mechanism for the FeCl3-derived VA-CNT arrays/forests. The FeCl3-derived forests have a lower (∼1/3 less) longitudinal indentation modulus, but higher longitudinal electrical conductivity (greater than twice) than that of the e-beam Fe-grown CNT arrays. The sublimation process to grow high-quality VA-CNTs is a highly facile and scalable process (extensive substrate shape and size, and moderate vacuum and temperatures) that provides a new route to synthesizing aligned CNT forests for numerous applications.

Low temperature electrical transport in microwave plasma fabricated free-standing graphene and N-graphene sheets

In this paper, the electrical transport in free-standing graphene and N-graphene sheets fabricated by a microwave plasma-based method is addressed. Temperature–dependent resistivity/conductivity measurements are performed on the graphene/N-graphene sheets compressed in pellets. Different measurement configurations reveal directional dependence of current flow—the room-temperature conductivity longitudinal to the pellet’s plane is an order of magnitude higher than the transversal one, due to the preferential orientation of graphene sheets in the pellets. SEM imaging confirms that the graphene sheets are mostly oriented parallel to the pellet’s plane and stacked in agglomerates. The high longitudinal electrical conductivity with values on the order of 103 S/m should be noted. Further, the current flow mechanism revealed from resistivity-temperature dependences from 300K down to 10K shows non-metallic behavior manifested with an increasing resistivity with decreasing the temperature usually observed for insulating or localized systems. The observed charge transport shows variable range hopping at lower temperatures and thermally activated behaviour at higher temperatures. This allows us to attribute the charge transport mechanism to a partially disordered system in which single graphene sheets are placed predominantly parallel to each other and stacked together.

Continuous intercalation compound fibers of bromine wires and aligned CNTs for high-performance conductors

This work presents macroscopic fibers of aligned double-walled carbon nanotubes (DWCNTs) intercalated with long-range ordered bromine, with a stoichiometry close to C17Br. Tribromide ions lie inside interstitial sites between hexagonally-packed DWCNTs and extend parallel to their axis as ordered supramolecular “wires”. First-principles simulations confirm this structure and a transfer of 0.13 electrons per Br atom. The structure of nested bundles of CNTs with a homogeneous distribution of bromine species in the interstitial sites of the superlattice is directly imaged by cross-sectional HRTEM, showing full intercalation of highly dense and aligned fibers. The presence of Br2 and Br3– is confirmed by Raman spectroscopy, and their supramolecular organization is resolved by 2D wide-angle X-ray scattering. Intercalation increases room-temperature longitudinal electrical conductivity by a factor of 8.4. Through low-temperature transport measurements in the longitudinal and transverse directions, we show that the intercalate reduces the tunneling-dominated resistance associated with transport between adjacent CNTs, rather than exclusively acting as a dopant that increases conductance of individual CNTs. By preserving the separation between CNTs, the exceptional mechanical properties of the CNT fiber host are retained. The combined tensile strength above 2.46 GPa and conductivity of 10.68 MS/m makes intercalated CNT fibers attractive lightweight conductors with combined properties superior to metals and graphite intercalation compounds.

Colossal Nernst power factor in topological semimetal NbSb2

Today solid-state cooling technologies below liquid nitrogen boiling temperature (77 K), crucial to quantum information technology and probing quantum state of matter, are greatly limited due to the lack of good thermoelectric and/or thermomagnetic materials. Here, we report the discovery of colossal Nernst power factor of 3800 × 10-4 W m-1 K-2 under 5 T at 25 K and high Nernst figure-of-merit of 71 × 10-4 K-1 under 5 T at 20 K in topological semimetal NbSb2 single crystals. The observed high thermomagnetic performance is attributed to large Nernst thermopower and longitudinal electrical conductivity, and relatively low transverse thermal conductivity. The large and unsaturated Nernst thermopower is the result of the combination of highly desirable electronic structures of NbSb2 having compensated high mobility electrons and holes near Fermi level and strong phonon-drag effect. This discovery opens an avenue for exploring material option for the solid-state heat pumping below liquid nitrogen temperature.

Effect of dynamical screening on quantized longitudinal electrical conductivity in neutron star mergers

We present the calculation of longitudinal electrical conductivity in magnetized plasma considering dynamical screening in the context of binary neutron star mergers. We consider strongly quantizing domain for significant modification in the transport coefficient due to magnetic field. Boltzmann equation is solved to obtain dissipative component of the electrical conductivity tensor in presence of magnetic field. The longitudinal electrical conductivity is formulated considering dynamically screened medium with magnetically modified screening. Numerical evaluations show that the effect of screening on electrical conductivity is less whereas inclusion of dynamical screening results in profound modification. Dynamical screening reduces electrical conductivity leading to a reduction in relevant magnetic field decay time scale.

Influence of carbon fibers discontinuity on the transverse conductivity of a unidirectional carbon fiber reinforced plastics

AbstractIn this work, a numerical simulation was carried out to analyze the influence of contact points as well as fibers breakage on the transverse conductivity of unidirectional (UD) carbon fiber reinforced plastics (CFRP). The analysis is based on the calculation of the distribution of the electric scalar potential on a geometry inspired by a cross‐section along the axis of the fibers taken by scanning electron microscopy (SEM) on a CFRP. The observation of the cross‐section allows us to capture the microstructure of the material which served as a basis for our model, in which numerical analysis using the finite element method (FEM) was performed. This simulation allows us to highlight the electric current pathways and evaluate their influence on both longitudinal and transversal electric conductivity. The obtained results give a good agreement with those found in the literature.

Scaling of the anomalous Hall effect in perpendicularly magnetized epitaxial films of the ferrimagnet NiCo2O4

We investigate the anomalous Hall effect in perpendicularly magnetized ferrimagnet $\mathrm{Ni}{\mathrm{Co}}_{2}{\mathrm{O}}_{4}$ epitaxial films 3 to 30 nm thick. We find that the anomalous Hall conductivity ${\ensuremath{\sigma}}_{\mathrm{AHE}}$ has complex relations with the longitudinal electrical conductivity ${\ensuremath{\sigma}}_{\mathrm{xx}}$. When the ${\ensuremath{\sigma}}_{\mathrm{xx}}$ is relatively large (larger than ${10}^{3}\phantom{\rule{0.16em}{0ex}}{\mathrm{\ensuremath{\Omega}}}^{--1}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{--1}$), the ${\ensuremath{\sigma}}_{\mathrm{AHE}}$ is almost independent of the ${\ensuremath{\sigma}}_{\mathrm{xx}}$, but scales with the magnetization. This unique scaling behavior of ${\ensuremath{\sigma}}_{\mathrm{AHE}}$ indicates that the anomalous Hall effect is of intrinsic origin dominated by the Berry curvature of occupied electronic states. On the other hand, when the ${\ensuremath{\sigma}}_{\mathrm{xx}}$ is lowered, the scaling relation is changed to ${\ensuremath{\sigma}}_{\mathrm{AHE}}\ensuremath{\sim}{\ensuremath{\sigma}}_{\mathrm{xx}}^{1.6}$, indicating a crossover of the dominant contribution to ${\ensuremath{\sigma}}_{\mathrm{AHE}}$, from the intrinsic Berry phase to the impurity scatterings. Our results show the intrinsic contribution from Berry curvature plays a crucial role in the anomalous Hall effect in $\mathrm{Ni}{\mathrm{Co}}_{2}{\mathrm{O}}_{4}$ films.

Resummation for the field-theoretical derivation of the negative magnetoresistance

We show detailed derivation of the electric conductivity of quark matter at finite temperature and density under a magnetic field. We especially focus on the longitudinal electric conductivity along the magnetic direction and establish the field-theoretical description of the negative magnetoresistance as observed in chiral materials. With increasing magnetic field our microscopic calculation leads to changing behavior from approximately quadratic to asymptotically linear dependence of the electric conductivity, while the magnetic dependence is quadratic in the conventional relaxation time approximation. The presented formulation founds a firm basis for the physical interpretation of the negative magnetoresistance in terms of the particle and the hydrodynamic contributions, as well as it offers general methodology applicable for various transport coefficients.

The Influence of External Factors on Quantum Magnetic Effects in Electronic Semiconductor Structures

A theory is constructed of the temperature dependence of quantum oscillation phenomena in narrow-gap electronic semiconductors, taking into account the thermal smearing of Landau levels. Oscillations of longitudinal electrical conductivity in narrow-gap electronic semiconductors at various temperatures are studied. An integral expression is obtained for the longitudinal conductivity in narrow-gap electronic semiconductors, taking into account the diffuse broadening of the Landau levels. A formula is obtained for the dependence of the oscillations of longitudinal electrical conductivity on the band gap of narrow-gap semiconductors. The calculation results are compared with experimental data.

Modeling on the temperature dependence of the magnetic susceptibility and electrical conductivity oscillations in narrow-gap semiconductors

Electrical conductivity oscillations, magnetic susceptibility oscillations and electronic heat capacity oscillations for narrow-gap electronic semiconductors are considered at different temperatures. A theory is constructed of the temperature dependence of quantum oscillation phenomena in narrow-gap electronic semiconductors, taking into account the thermal smearing of Landau levels. Oscillations of longitudinal electrical conductivity in narrow-gap electronic semiconductors at various temperatures are studied. An integral expression is obtained for the longitudinal conductivity in narrow-gap electronic semiconductors, taking into account the diffuse broadening of the Landau levels. A formula is obtained for the dependence of the oscillations of longitudinal electrical conductivity on the bandgap of narrow-gap semiconductors. The theory is compared with the experimental results of [Formula: see text]. A theory is constructed of the temperature dependence of the magnetic susceptibility oscillations for narrow-gap electronic semiconductors. Using these oscillations of magnetic susceptibility, the cyclotron effective masses of electrons are determined. The calculation results are compared with experimental data. The proposed model explains the experimental results in [Formula: see text] at different temperatures.

On Temperature Dependence of Longitudinal Electrical Conductivity Oscillations in Narrow-gap Electronic Semiconductors

On Temperature Dependence of Longitudinal Electrical Conductivity Oscillations in Narrow-gap Electronic Semiconductors

Investigation of the State of an Earth Dam by Geophysical Methods

Operational nondestructive monitoring is presently used actively for assessing the stability and predicting the physical state of earth dams. An investigation by several methods of such physical parameters as density, dielectric constant, electrical resistance, longitudinal electrical conductivity, and frequency dispersion coefficient was carried out on an earth dam located in the Sverdlovsk Oblast.

Developing high-performance laminated Cu/TiC composites through melt infiltration of Ni-doped freeze-cast preforms

Abstract Nacre-inspired laminated composites have been proven to possess a unique combination of strength and toughness. In this study, we fabricated nacre-mimetic Cu/TiC composites via unidirectional freezing of aqueous TiC slurries containing different amounts of NiO additives, followed by ice sublimation, carbothermal reduction of NiO to Ni during sintering and then gas-pressure infiltration of the Cu melt. The introduction of Ni greatly facilitated the densification of ceramic lamellae and enhanced the interfacial bonding between Cu and TiC. The resultant composites displayed outstanding damage tolerance and anisotropic electrical conductivities. Specifically, for an ∼31 vol% TiC–Cu composite containing 24 wt% Ni in the ceramic lamellae (based on the TiC content), a fracture toughness (KJc) of 72.5 ± 1.0 MPa·m1/2, work of fracture of 53.4 ± 3.5 kJ/m2, bending strength of 725 ± 11 MPa and longitudinal electrical conductivity of 22.7 MS/m (∼60% of the Cu matrix) were achieved, which were approx. 81%, 536%, 122% and 97% higher than those of the Ni-free composite, respectively. Noticeable toughening was demonstrated to be a consequence of multiple cracking, plastic deformation and uncracked-ligament bridging of the metal layers, as well as crack deflection and blunting. On the other hand, significant strengthening resulted from tailoring the microstructures in the ceramic layers and at the Cu/TiC interface as a result of Ni doping. We believe that the facile strategy adopted herein provides an effective way to solve the problems of wetting and bonding related to metal infiltration and can be readily extended to the preparation of other nacre-inspired metal−ceramic composites.

Simplified Calculation of the Electrical Conductivity of Composites with Carbon Nanotubes

The electrical conductivity of two groups of polymer nanocomposites filled with the same NC7000 carbon nanotubes (CNTs) beyond the percolation threshold is described with the help of simple formulas. Different manufacturing process of the nanocomposites led to different CNT network structures, and, as a consequence, their electrical conductivity, at the same CNT volume, differed by two orders of magnitude. The relation between the electrical conductivity and the volume content of CNTs of the first group of composites (with a higher electrical conductivity) is described assuming that the CNT network structure is close to a statistically homogeneous one. The formula for this case, derived on the basis of a self-consistent model, includes only two parameters: the effective longitudinal electrical conductivity of CNT and the percolation threshold (the critical value of CNT volume content). These parameters were determined from two experimental points of electrical conductivity as a function of the volume fraction of CNTs. The second group of nanocomposites had a pronounced agglomerative structure, which was confirmed by microscopy data. To describe the low electrical conductivity of this group of nanocomposites, a formula based on known models of micromechanics is proposed. Two parameters of this formula were determined from experimental data of the first group, but the other two — of the second group of nanocomposites. A comparison of calculation and experimental relations confirmed the practical expediency of using the approach described.