Measurements Of Transport Properties Research Articles

Ion Correlations and Their Impact on Transport in Polymer-Based Electrolytes

Author(s): Fong, KD; Self, J; McCloskey, BD; Persson, KA | Abstract: The development of next-generation polymer-based electrolytes for energy storage applications would greatly benefit from a deeper understanding of transport phenomena in these systems. In this Perspective, we argue that the Onsager transport equations provide an intuitive but underutilized framework for analyzing transport in polymer-based electrolytes. Unlike the ubiquitous Stefan-Maxwell equations, the Onsager framework generates transport coefficients with clear physical interpretation at the atomistic level and can be computed easily from molecular simulations using Green-Kubo relations. Herein we present an overview of the Onsager transport theory as it applies to polymer-based electrolytes and discuss its relation to experimentally measurable transport properties and the Stefan-Maxwell equations. Using case studies from recent computational work, we demonstrate how this framework can clarify nonintuitive phenomena such as negative cation transference number, anticorrelated cation-anion motion, and the dramatic failure of the Nernst-Einstein approximation. We discuss how insights from such analysis can inform design rules for improved systems.

Quantitative thermosensation in a single touch

Thermosensation is the skin perception of thermal stimuli, including temperature and temperature changing rate. Measurements of the thermal transport properties of materials in the environment by robotic hand can help robots analyze environment conditions and make decisions. Existing methods for bulk materials demand ideal measurement conditions or complex measuring systems for material heating and temperature measurement. This paper introduces a flexible thermal sensor that can be used on robotic fingers to achieve rapid measurement of thermal conductivity and thermal diffusivity for different materials. A theoretical transient heat conduction model is proposed based on a touch-and-heat scenario in which the combination of robot finger, sensor and test material is regarded as semi-infinite object. According to this feature, an ultra-thin flexible thermal sensor composed of a central thermoresistor and a surrounding heater is designed and fabricated. The sensor is heated after contacting with different materials, and the temperature change on the sensor surface is recorded. Thermal conductivity and thermal diffusivity of the contacting materials are fitted using the proposed heat transfer model with fitting errors less than 4.5 % and 8.5 %, respectively. In this way, the thermal conductivity and thermal diffusivity of an object can be measured with a single touch by the robot finger in less than 2 s. The device and method presented in this work show the potential of the application in tactile sensing for robotic dexterous hand and manipulation.

A model for dynamical solvent control of molecular junction electronic properties

Experimental measurements of electron transport properties of molecular junctions are often performed in solvents. Solvent-molecule coupling and physical properties of the solvent can be used as the external stimulus to control the electric current through a molecule. In this paper, we propose a model that includes dynamical effects of solvent-molecule interaction in non-equilibrium Green's function calculations of the electric current. The solvent is considered as a macroscopic dipole moment that reorients stochastically and interacts with the electrons tunneling through the molecular junction. The Keldysh-Kadanoff-Baym equations for electronic Green's functions are solved in the time domain with subsequent averaging over random realizations of rotational variables using the Furutsu-Novikov method for the exact closure of infinite hierarchy of stochastic correlation functions. The developed theory requires the use of wideband approximation as well as classical treatment of solvent degrees of freedom. The theory is applied to a model molecular junction. It is demonstrated that not only electrostatic interaction between molecular junction and solvent but also solvent viscosity can be used to control electrical properties of the junction. Alignment of the rotating dipole moment breaks the particle-hole symmetry of the transmission favoring either hole or electron transport channels depending upon the aligning potential.

Wireless, soft electronics for rapid, multisensor measurements of hydration levels in healthy and diseased skin

Precise, quantitative measurements of the hydration status of skin can yield important insights into dermatological health and skin structure and function, with additional relevance to essential processes of thermoregulation and other features of basic physiology. Existing tools for determining skin water content exploit surrogate electrical assessments performed with bulky, rigid, and expensive instruments that are difficult to use in a repeatable manner. Recent alternatives exploit thermal measurements using soft wireless devices that adhere gently and noninvasively to the surface of the skin, but with limited operating range (∼1 cm) and high sensitivity to subtle environmental fluctuations. This paper introduces a set of ideas and technologies that overcome these drawbacks to enable high-speed, robust, long-range automated measurements of thermal transport properties via a miniaturized, multisensor module controlled by a long-range (∼10 m) Bluetooth Low Energy system on a chip, with a graphical user interface to standard smartphones. Soft contact to the surface of the skin, with almost zero user burden, yields recordings that can be quantitatively connected to hydration levels of both the epidermis and dermis, using computational modeling techniques, with high levels of repeatability and insensitivity to ambient fluctuations in temperature. Systematic studies of polymers in layered configurations similar to those of human skin, of porcine skin with known levels of hydration, and of human subjects with benchmarks against clinical devices validate the measurement approach and associated sensor hardware. The results support capabilities in characterizing skin barrier function, assessing severity of skin diseases, and evaluating cosmetic and medication efficacy, for use in the clinic or in the home.

A cylindrical SiC heater for an externally heated diamond anvil cell to 1500 K.

Semiconductor-based heaters for diamond anvil cells (DACs) have advantages over metal wire heaters in terms of repeated use and the ability to reach higher temperatures. We introduce a cylindrical SiC heater for an externally heated DAC (EHDAC) that works satisfactorily at temperatures up to 1500K and pressures around 90GPa. The heater is reusable and inexpensive, and only slight modifications to the DAC are required to fit the heater. Experiments on melting of NaCl and gold are conducted at ambient pressure to test the temperature accuracy of the EHDAC system, and resistance measurements on iodine at high pressures and temperatures are performed to assess the heater assembly. These test runs show that a uniform and accurate temperature can be maintained by the EHDAC assembly, which has potential applications to a variety of transport property measurements.

The solvation structure, transport properties and reduction behavior of carbonate-based electrolytes of lithium-ion batteries.

Despite the extensive employment of binary/ternary mixed-carbonate electrolytes (MCEs) for Li-ion batteries, the role of each ingredient with regards to the solvation structure, transport properties, and reduction behavior is not fully understood. Herein, we report the atomistic modeling and transport property measurements of the Gen2 (1.2 M LiPF6 in ethylene carbonate (EC) and ethyl methyl carbonate (EMC)) and EC-base (1.2 M LiPF6 in EC) electrolytes, as well as their mixtures with 10 mol% fluoroethylene carbonate (FEC). Due to the mixing of cyclic and linear carbonates, the Gen2 electrolyte is found to have a 60% lower ion dissociation rate and a 44% faster Li+ self-diffusion rate than the EC-base electrolyte, while the total ionic conductivities are similar. Moreover, we propose for the first time the anion–solvent exchange mechanism in MCEs with identified energetic and electrostatic origins. For electrolytes with additive, up to 25% FEC coordinates with Li+, which exhibits a preferential reduction that helps passivate the anode and facilitates an improved solid electrolyte interphase. The work provides a coherent computational framework for evaluating mixed electrolyte systems.

Observation of Time-Reversal Invariant Helical Edge-Modes in Bilayer Graphene/WSe2 Heterostructure

Topological insulators, along with Chern insulators and quantum Hall insulator phases, are considered as paradigms for symmetry protected topological phases of matter. This article reports the experimental realization of the time-reversal invariant helical edge-modes in bilayer graphene/monolayer WSe2-based heterostructures-a phase generally considered as a precursor to the field of generic topological insulators. Our observation of this elusive phase depended crucially on our ability to create mesoscopic devices comprising both a moiré superlattice potential and strong spin-orbit coupling; this resulted in materials whose electronic band structure could be tuned from trivial to topological by an external displacement field. We find that the topological phase is characterized by a bulk bandgap and by helical edge-modes with electrical conductance quantized exactly to 2e2/h in zero external magnetic field. We put the helical edge-modes on firm ground through supporting experiments, including the verification of predictions of the Landauer-Büttiker model for quantum transport in multiterminal mesoscopic devices. Our nonlocal transport properties measurements show that the helical edge-modes are dissipationless and equilibrate at the contact probes. We achieved the tunability of the different topological phases with electric and magnetic fields, which allowed us to achieve topological phase transitions between trivial and multiple, distinct topological phases. We also present results of a theoretical study of a realistic model which, in addition to replicating our experimental results, explains the origin of the topological insulating bulk and helical edge-modes. Our experimental and theoretical results establish a viable route to realizing the time-reversal invariant topological phase of matter.

The transport properties of iron-based superconductors

There are a variety of order states in iron-based pnictides, such as electronic nematic phase, spin density wave, and so on, which leads to plenty of novel physical phenomena. The measurements of transport properties can provide extremely useful information for understanding of the low-energy excitations of iron-based superconductors. Due to the multi-band electronic structure in iron-based pnictides, the temperature dependence of resistivity and Hall coefficient varies with different systems, however, there are no evidence for the pseudo-gap opening in the normal state which is a common feature in underdoped high-<inline-formula><tex-math id="M2">\begin{document}$T_{\rm{c}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20201836_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20201836_M2.png"/></alternatives></inline-formula> cuprates. In the hole-doped iron-based superconductors, the Hall coefficient changes its sign in low temperatures, and meanwhile the resistivity shows a broad hump in the same temperature range. Such a behavior is proposed as a crossover from incoherent to coherent transport. The Seebeck coefficients of iron-based superconductors also show remarkable differences from the cuprates. In iron-based superconductors, the absolute value of Seebeck coefficients in the normal state becomes the largest at the optimally doping point with highest <inline-formula><tex-math id="M3">\begin{document}$T_{\rm{c}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20201836_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20201836_M3.png"/></alternatives></inline-formula>, which is probably related to the strong inter-band scattering. The Nernst effect in the normal state of iron-based superconductors indicates that superconducting phase fluctuations is not obvious above <inline-formula><tex-math id="M4">\begin{document}$T_{\rm{c}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20201836_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20201836_M4.png"/></alternatives></inline-formula>, which is also significantly different from the cuprates. These unusual thermoelectric properties observed in iron-based superconductors have not been observed in the nickel-based pnictide superconductors with the analogous structure, i.e., LaNiAsO, and the nickel-based superconductors behave more like a usual metal. All these results above illustrate that these unusual transport properties of iron-based superconductors are inherently associated with their high temperature superconductivity, and these factors should be taken into account in the theory on its superconducting mechanism.

Reduced phase space of heat-carrying acoustic phonons in single-crystalline InTe

Chalcogenide semiconductors and semimetals are a fertile class of efficient thermoelectric materials, which, in most cases, exhibit very low lattice thermal conductivity κph despite lacking a complex crystal structure such as the tetragonal binary compound InTe. Our measurements of κph(T) in single-crystalline InTe along the c axis show that κph exhibits a smooth temperature dependence upon cooling to about 50 K, the temperature below which a strong rise typical for dielectric compounds is observed. Using a combination of first-principles calculations, inelastic neutron scattering (INS), and low-temperature specific heat and transport properties measurements on single-crystalline InTe, we show that the phonon spectrum exhibits well-defined acoustic modes, the energy dispersions of which are constrained to low energies due to distributions of dispersionless, optical modes, which are responsible for a broad double peak structure in the low-temperature specific heat. The latter are assigned to the dynamics of In+ cations in tunnels formed by edge-sharing (In3+Te42−)− tetrahedra chains, the atomic thermal displacement parameters of which, probed as a function of temperature by means of single-crystal x-ray diffraction, suggest the existence of a complex energy potential. Indeed, the In+-weighted optical modes are not observed by INS, which is ascribed to the anharmonic broadening of their energy profiles. While the low κph value of 1.2Wm−1K−1 at 300 K originates from the limited energy range available for acoustic phonons, we show that the underlying mechanism is specific to InTe and argue that it is likely related to the presence of local disorder induced by the In+ site occupancy.

Thermal transport properties of Ni–Co-based superalloy

We report systematic measurements of thermal transport properties of a Ni–Co-based superalloy at temperatures ranging from room temperature to around 800 K. In this temperature range, the thermal diffusivity and conductivity of the superalloy monotonically increase with an increase in the temperature, while the specific heat capacity is almost temperature-independent. We found that the observed thermal conductivity of the Ni–Co-based superalloy is higher than the electronic thermal conductivity expected from the Wiedemann–Franz law, indicating the substantial contribution of phonon thermal conductivity. The temperature dependence of the phonon thermal conductivity for the Ni–Co-based superalloy was observed to be weaker than that for other Ni-based alloys, which can be qualitatively explained by enhanced phonon scattering due to small γ′-phase precipitates in the superalloy. This result suggests possible tuning of the thermal conductivity of the superalloy based on phonon transport engineering.

Electronic entropy contribution to the metal insulator transition in VO2

${\mathrm{VO}}_{2}$ experiences a metal-insulator transition at 340 K. Discontinuities in electronic transport properties, such as the Seebeck coefficient and the electronic conductivity, suggest that there is a significant change in the electronic structure upon metallization. However, the thermodynamic nature of this transformation remains difficult to describe using conventional computational and experimental methods. This has led to disagreement over the relative importance of the change in electronic entropy with respect to the overall transition entropy. A method is presented that links measurable electronic transport properties to the change in electronic state entropy of conduction electrons. The change in electronic entropy is calculated to be $9.2\ifmmode\pm\else\textpm\fi{}0.7$ J/mol K which accounts for 62%--67% of the total transition entropy. This compares favorably with some estimates of the vibrational entropy.

Effective Electronic and Ionic Conductivities of Dense EV-Designed NMC-Based Positive Electrodes using Fourier Based Numerical Simulations on FIB/SEM Volumes

Experimental conductivity measurements, obtained on NMC532-based electrodes with markedly different porosities and made with percolating and non-percolating CB/PVdF phase, are compared with full-field numerical predictions. These ones are based on segmented nanotomography images and phase bulk properties and contain no tunable parameter. A good agreement between the calculated and measured transport properties is observed. 3D current density fields give insights on the microstructure impacts on the current density distribution. Ionic transport is dominated by low tortuosity micrometric channels. Results also highlight the presence of “dead areas” in porosity that are crossed by a very low ionic current showing that, at high rate, the effective porosity may reduce to the micrometric pore network. For electronic conductivity, the CB/PVdF mixture percolation threshold is evaluated at 6%–7% in volume. Even below this key value threshold, CB/PVdF aggregates significantly improve electronic conductivity by forming gateways between NMC clusters thus minimising the constriction resistances between them. The size of the representative volume element relative to electronic and ionic conductivities is also investigated.

Synthesis of Semiconducting 2H-Phase WTe2 Nanosheets with Large Positive Magnetoresistance.

Tungsten ditelluride (WTe2) is provoking immense interest because of its unique electronic properties, but studies about its semiconducting hexagonal (2H) phase are quite rare. Herein, we report the synthesis of semiconducting 2H WTe2 nanosheets with large positive magnetoresistance, for the first time, by a simple lithium-intercalation-assisted exfoliation strategy. Systematic characterizations including high-resolution transmission electron microscopy, X-ray diffraction, and Raman and X-ray photoelectron spectroscopies provide clear evidence to distinguish the structure of 2H WTe2 nanosheets from the orthorhombic (Td) phase bulk counterpart. The corresponding electronic phase transition from metal to semiconductor is also confirmed by density of states calculation, optical absorption, and electrical transport property measurements. Besides, the 2H WTe2 nanosheets exhibit large positive magnetoresistance with values of up to 29.5% (10 K) and 16.2% (300 K) at 9 T. Overall, these findings open up a promising avenue into the exploration of WTe2-based materials in the semiconductor field.

Effects of the Stacking Faults on the Electrical Resistance of Highly Ordered Graphite Bulk Samples

High anisotropy and the existence of two-dimensional highly conducting interfaces at stacking faults parallel to the graphene planes of the graphite structure influence, in a non-simple way, the transport properties of highly oriented graphite. We report two related effects on the electrical resistance of highly oriented pyrolytic as well as of natural graphite bulk samples, measured with the four points method in the temperature range 300 K ≤T≤ 410 K. A qualitative and quantitative change in the temperature dependence of the resistance was obtained by simply enlarging the electrodes and contacting the edges of the internal interfaces on the same sample. Additionally, at temperatures T≳350 K the resistance can change with time. We show that this temperature-dependent annealing effect is related to the stacking faults and can irreversibly change the absolute value of the resistance and its temperature dependence. A partial recovery is obtained after leaving the sample at normal conditions for several days. The overall results stress the importance of the electrodes location on a bulk graphite sample, the contribution of the stacking faults in the interpretation of the measured transport properties and the need of systematic studies on the influence of high temperature annealing on the interfaces properties.

Measurement of thermal transport properties of selected superlattice and thin films using frequency-domain photothermal infrared radiometry

Thermal transport properties in multi-layered semiconductor samples are reported using modulated photothermal infrared radiometry (PTR). The cross-plane thermal conductivity and diffusivity of thin AlxGa(1-x)As layers and AlAs/GaAs superlattices were determined by fitting solutions of the heat equation for multi-layered systems to PTR data. The thermal conductivity of an AlxGa(1-x)As film with x = 0.5 was found to be lower than an AlxGa(1-x)As film with x = 0.33 which is expected as scattering from alloy disorder is maximized for x = 0.5. In addition, it was found that thermal conductivities of AlAs/GaAs superlattices decrease when the superlattice period is decreased for a constant total thickness which is expected since the number of AlAs/GaAs interfaces (which impede thermal transport) increases as the period decreases. The maximum PTR amplitude signal was found to occur when the diffusion length of the thermal wave is on other order of the thickness of the semiconductor layer. The accuracy and applicability of photothermal infrared radiometry to the study of semiconductor multilayer structures are further discussed in the paper.

Kinetics of densification/phase transformation and transport properties of Mg-Sn cubic/trigonal composites

The Mg-Sn materials are interesting because of useful semiconducting properties and particularly because of their earth abundant, environmentally friendly constituent elements. The cubic Mg2Sn phase appears in the equilibrium phase diagram and has been extensively studied, while the transport properties of the trigonal phase—that does not appear in the phase diagram—have not been reported. We produced dense composites composed of cubic (stable) and trigonal (metastable) phases using a combination of high energy ball milling and current activated pressure assisted densification (CAPAD). We present a kinetic study of the densification and cubic to trigonal phase transformation. In addition, we present transport property measurements of cubic/trigonal composites. We determine densification rates and observe distinct densification regimes, attributed to the cubic-to-tetragonal phase transformation as well as porosity removal. Transport property measurements reveal that altering the amount of metastable phase in the composites changes both the electrical and thermal properties. The electrical conductivity significantly increases with increasing trigonal phase fraction. The thermal conductivities are similar for all compositions, which is likely due to the nanocrystalline character of the composites.

Electrical Resistivity Measurements of Fe‐Si With Implications for the Early Lunar Dynamo

AbstractThe effect of impurities on the electrical resistivity of Fe at core conditions is controversial due to the challenges of measuring transport properties of Fe alloys under high‐pressure and high‐temperature conditions. In this study we describe an innovative technique to make wires of Fe‐Si samples initially in powder form for measuring electrical resistivity. The electrical resistivity of Fe‐2, Fe‐8.5, and Fe‐17 wt%Si was measured at 3, 4, and 5 GPa at temperatures into the liquid state and compared to results of Fe‐4.5 wt%Si and Fe from prior studies. Isothermal electrical resistivity increases linearly with increasing Si content. Yet the effect of Si content on the magnitude of the electrical resistivity compared to that of Fe diminished as temperature increased at all experimental pressures. This implies the contribution to the electrical resistivity due to Si impurities is dependent on temperature, in disagreement with Matthiessen's rule. Thermal conductivity of Fe‐Si alloys calculated using the Wiedemann‐Franz law indicates a nonnegligible influence of the Si content on the thermal conductive properties of Fe‐Si alloys. The results are used to calculate the adiabatic heat flux of an Fe‐Si lunar core and date the end of the high magnetic field intensity era of the lunar dynamo to be in the range 3.32–3.80 Ga.

Charge transport properties in CdZnTeSe semiconductor room-temperature γ-ray detectors

CdxZn1−xTeySe1−y (CZTS) has emerged as a next-generation compound semiconductor for high energy gamma-ray detection. In the present study, we report for the first time the hole transport property measurements in CZTS based gamma-ray detectors in the planar configuration. Current–voltage measurements revealed a bulk resistivity of ∼5 × 108 Ω cm and the fabricated detectors produced well-resolved 5486 keV alpha particle peaks, for both electrons and holes drifting alike, when pulse-height spectra (PHS) were recorded using a 241Am radiation source. The PHS measurements were enabled to measure the charge transport properties for both the charge carriers. The mobility–lifetime product (μτ) for electrons and holes was calculated to be 6.4 × 10−4 cm2 V−1 and 8.5 × 10−5 cm2 V−1, respectively, using a single polarity Hecht plot regression method. The pre-amplifier pulses were also recorded and processed digitally to obtain electron and hole drift mobilities of 692 cm2 V−1 s−1 and 55 cm2 V−1 s−1, respectively, using a time-of-flight method. The measured transport properties indicated the hole lifetime to be greater than the electron lifetime by a factor of ∼1.5. Gamma-ray PHS were recorded using fabricated detectors that showed tailing of the 662 keV photopeak due to hole trapping effects. Depth dependent PHS were digitally generated from 2D biparametric plots to reveal the effects of hole trapping on the gamma PHS at different detector depths. Digital correction procedures were applied to generate well-resolved PHS with an energy resolution of ∼2% for 662 keV γ-rays.

Tetrahedrite Sintering Conditions: The Cu11Mn1Sb4S13 Case

Manganese-doped tetrahedrites, with Cu11Mn1Sb4S13 composition and synthesized by the solid-state method, were hot-pressed at temperatures ranging between 788 K and 848 K. The structure, microstructure, phase purity and thermoelectric properties of the materials were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and density studies. According to the XRD analysis, all the hot-pressed materials presented a main tetrahedrite phase. However, very small amounts of chalcostibite (CuSbS2) were detected by SEM–EDS. While keeping the pressure constant at 60 MPa, an increase in density with hot-pressing temperature was observed, reaching a maximum relative density of 97% for the samples hot-pressed at 848 K. Measurements of the electrical transport properties indicated higher thermal conductivity, electrical conductivity and Seebeck coefficient for the denser samples, with a greater power factor leading to an increase of > 10% in the figure of merit ( $$zT$$ ) relative to the less dense materials.

Inductance of YBa$_{2}$Cu$_{3}$O$_{7-\delta }$ Thin-Films With and Without Superconducting Ground Planes

We experimentally measured and compared the sheet inductance of YBa $_{2}$ Cu $_{3}$ O $_{7-\delta }$ (YBCO) films with and without superconducting ground planes. Specifically, we fabricated several superconducting quantum interference devices from single and multilayer films with different geometries using a focused helium ion beam. Measurements of the device electrical transport properties were analyzed to determine the sheet inductance. Additionally, temperature dependent measurements of the inductance were used in order to separate the contributions from geometric and kinetic inductance. We found that the presence of a ground plane in our multilayer structure significantly reduces the contribution of the geometric inductance with no detectable change in the kinetic inductance.