Transport Properties Of Materials Research Articles

Thermal management for gas lubricated, high-speed turbomachinery

High-speed turbomachinery is commonly designed to achieve high power densities. Limited space for active cooling results in a challenging thermal management. A thermal modeling approach leveraging modern declarative programming capabilities is presented, yielding an efficient dynamic model capable of real-time simulation while achieving accurate results. These properties enable the inclusion of thermal management strategies in an early stage of the design process. Further, the effect of varying thermal and transport properties of materials and fluids during transient conditions is included and is suggested to yield a high impact on thermal loads and heat evacuation capabilities. The often neglected fluid advection within the system is modeled by integrating a 1D fluid network from MatlabTM SimscapeTM to the thermal model, displaying a significant impact on the temperature estimation for critical parts. The accuracy of the presented model is verified against three gas-bearing supported high-speed turbomachinery experiments for stationary and transient operation.

Soft phonon modes lead to suppressed thermal conductivity in Ag-based chalcopyrites under high pressure.

Pressure is a powerful way to modulate physical properties. Understanding the effect of pressure on the thermal transport properties of thermoelectric materials is of great importance for the efficient design and optimization of thermoelectric performance. In this work, based on first-principles calculations and phonon Boltzmann transport theory, we find that the lattice thermal conductivities of Ag-based chalcopyrites AgXY2 (X = Al, Ga, and In; Y = S, Se, and Te) are dramatically suppressed by applying pressure. The inherent distorted tetrahedral configuration together with highly delocalized p-orbital electrons promotes the formation of metavalent bonding. The fact of metavalent bonding with a single bonding electron and small electron transfer between neighboring atoms leads to soft low-frequency optical phonons. With the increase of pressure, the softening of acoustic and low-frequency optical phonons induces enhanced anharmonicity and scattering channels. Such strong acoustic-optical phonon coupling results in larger phonon scattering rates and thus lowers the lattice thermal conductivity. These findings not only help unveil the underlying physical mechanisms for the anomalous thermal transport behaviors under high pressure, but also pave the way for the pressure tuning of high-performance Ag-based thermoelectric materials.

Experimental evidence for the significance of optical phonons in thermal transport of tin monosulfide

The understanding of the lattice dynamics is essential for engineering the thermal transport properties in quantum materials. Based on the canonical point of view, acoustic phonons are believed to be the principal thermal carriers in heat flow. Here, in this work, optical phonons are elucidated to play a pivotal role in determining the lattice thermal conductivity in thermoelectric material SnS by using the state-of-the-art inelastic neutron scattering technique combined with first-principles calculations. Additionally, in contrast to acoustic phonons, optical phonons are observed to exhibit pronounced softening and broadening with temperature. Our observations not only shed light on the significance of the optical phonons in thermal transport but also provide a vital clue to suppress the propagation of optical phonons to optimize the thermoelectric performance of SnS.

Impacts of defects on the mechanical and thermal properties of SiC and GeC monolayers.

Defect engineering has been considered as an effective way for controlling the heat transport properties of two-dimensional materials. In this work, the effects of point vacancies and grain boundaries on the mechanical and thermal performances of SiC and GeC monolayers are investigated systematically by molecular dynamics calculations. The failure strength in SiC and GeC is decreased by introducing vacancies at room temperature, and the stress-strain relationship can be tuned significantly by different kinds of vacancies. When the grain boundary of 21.78° is applied, the maximal fracture strengths can be as large as 27.56% for SiC and 23.56% for GeC. Also, the thermal properties of the two monolayers show a remarkable dependence on the vacancies and grain boundaries. The high vacancy density in SiC and GeC can induce disordered heat flow and the C/Ge point defect is crucial for thermal conductivity regulation for the Si/GeC monolayer. More importantly, the SiC and GeC monolayers with a grain boundary of 5.09° show excellent interfacial thermal conductance. Our findings are of great importance in understanding SiC and GeC monolayers and seeking their potential applications.

RECONSTRUCTION OF RANDOM FIBROUS POROUS MATERIAL AND NUMERICAL STUDY ON ITS TRANSPORT PROPERTIES BY FRACTAL MONTE CARLO METHOD

The microstructures and transport properties of fibrous porous material are significant for chemical catalysts, textile engineering, electronic devices, etc. In this paper, a fractal Monte Carlo method (FMCM) is developed to reconstruct the random microstructure of fibrous porous material based on the fractal scaling laws of fiber columns. And, the two-point correlation function of reconstructed fibrous material is calculated, which shows the effectiveness of the FMCM reconstruction. Also, the single-phase fluid flow through the reconstructed random fibrous porous material is simulated by the finite element method. The predicted permeability indicates good agreement with available empirical formulas. It has been found that the effective permeability of fibrous porous material decreases with the increase of fractal dimensions for fiber column. However, the fractal dimension of fiber column width has a greater influence on the effective permeability of fibrous porous material compared with that of fiber column length. The proposed numerical method provides an effective tool to reconstruct the irregular microstructure and understand the complex transport mechanisms of fibrous porous material.

A guide for the characterization of organic electrochemical transistors and channel materials.

The organic electrochemical transistor (OECT) is one of the most versatile devices within the bioelectronics toolbox, with its compatibility with aqueous media and the ability to transduce and amplify ionic and biological signals into an electronic output. The OECT operation relies on the mixed (ionic and electronic charge) conduction properties of the material in its channel. With the increased popularity of OECTs in bioelectronics applications and to benchmark mixed conduction properties of channel materials, the characterization methods have broadened somewhat heterogeneously. We intend this review to be a guide for the characterization methods of the OECT and the channel materials used. Our review is composed of two main sections. First, we review techniques to fabricate the OECT, introduce different form factors and configurations, and describe the device operation principle. We then discuss the OECT performance figures of merit and detail the experimental procedures to obtain these characteristics. In the second section, we shed light on the characterization of mixed transport properties of channel materials and describe how to assess films' interactions with aqueous electrolytes. In particular, we introduce experimental methods to monitor ion motion and diffusion, charge carrier mobility, and water uptake in the films. We also discuss a few theoretical models describing ion-polymer interactions. We hope that the guidelines we bring together in this review will help researchers perform a more comprehensive and consistent comparison of new materials and device designs, and they will be used to identify advances and opportunities to improve the device performance, progressing the field of organic bioelectronics.

Enhancing the solubility of Mn in AgSbSe2 for high thermoelectric performance through entropy engineering

Point defects play an important role in regulating the electrical and thermal transport properties of thermoelectric materials, but they are always restricted by the solubility of dopants in the matrix.

Study of the diffusion properties of zeolite mixtures by combined gravimetric analysis, IR spectroscopy and inversion methods (IRIS).

We report the development of a new method of investigation of the mass transport properties of acidic zeolite-based materials aiming to overcome the limitations of classical approaches. It consists in hyphenating gravimetric analysis and infrared spectroscopy. The former allows assessing the diffusion from the gas phase to all the porosity, while IR allows for selective assessment of diffusion to the zeolite active sites located in the micropores. Furthermore, the data are processed by an original methodology allowing the recovery of the distribution of diffusion domains by inversion of the integral equations describing the uptake curves or the evolution of the infrared spectra. The combination of gravimetric analysis and IR spectroscopy makes it possible to monitor and distinguish diffusion within the various components of the material. The methodology has been applied to the isooctane uptake in the mechanical mixture of FAU and MFI zeolites. Analysis of both gravimetric uptake curves and evolving infrared spectra allows distinguishing and assigning diffusion domains to the H-FAU and H-MFI components of the mixture, with high and low effective diffusion rate constants, respectively. The advantages and limits of the methodology are discussed.

Phonon transport in two-dimensional carbon-boron material and heterointerfaces

Developing semiconducting materials with suitable band gap has attracted increasing attention for next-generation intelligent electronic devices. Recently, the newly synthesized monolayer carbon boron (C3B) material exhibits outstanding electronic properties and processes with indirect bandgap, which is considered as the promising alternatives of graphene. The heat conduction capability plays a critical role in the performance of C3B-based electronic devices and thermocatalysis applications. Herein, the thermal conductivity of monolayer C3B and graphene, and interfacial phonon transport across heterointerface are systematically investigated utilizing non-equilibrium molecular dynamics simulation. Compared with graphene, the reduced thermal conductivity of C3B sheet mainly stems from the decreased phonon group velocity and phonon relaxation time when the periodical boron atoms are introduced in C3B sheet based on the lattice dynamics and spectral phonon transmission analysis. Meanwhile, the influences of temperature and strain on the thermal conductivity of C3B are also discussed. Moreover, the thermal transport across the graphene|C3B heterointerface with different temperatures is analyzed. Interestingly, it is found that the larger interfacial thermal conductance of zigzag heterointerfaces mainly originates from the stronger phonon-phonon coupling between the out-of-plane vibrational modes of C3B and graphene. Our work would provide more insights for fundamental understanding the thermal transport properties of two-dimensional materials and be beneficial to the design of thermal management and thermoelectric materials.

Electronic and magnetic properties of the topological semimetal SmMg2Bi2

Dirac semimetals show nontrivial physical properties and can host exotic quantum states like Weyl semimetals and topological insulators under suitable external conditions. Here, by combining angle-resolved photoemission spectroscopy measurements (ARPES) and first-principle calculations, we demonstrate that the Zintl-phase compound ${\mathrm{SmMg}}_{2}{\mathrm{Bi}}_{2}$ is in close proximity to a topological Dirac semimetallic state. ARPES results show a Dirac-like band crossing at the zone center near the Fermi level (${E}_{\mathrm{F}}$), which is further confirmed by first-principle calculations. Theoretical studies also reveal that ${\mathrm{SmMg}}_{2}{\mathrm{Bi}}_{2}$ belongs to a ${Z}_{2}$ topological class and hosts spin-polarized states around the ${E}_{\mathrm{F}}$. Zintl's theory predicts that the valence state of Sm in this material should be ${\mathrm{Sm}}^{2+}$, however, we detect many Sm-$4f$ multiplet states (flat-bands) whose energy positions and relative intensities suggest the presence of both dominant ${\mathrm{Sm}}^{2+}$ and minor ${\mathrm{Sm}}^{3+}$. The small concentration (2.5%) of ${\mathrm{Sm}}^{3+}$ in the bulk of a crystal is inferred to arise from Sm vacancies in the crystal. It is also evident that these flat bands and other dispersive states are strongly hybridized when they cross each other. Due to the presence of ${\mathrm{Sm}}^{3+}$ ions, the temperature dependence of the magnetic susceptibility $\ensuremath{\chi}(T)$ shows a Curie-Weiss-like contribution in the low-temperature region, in addition to the Van Vleck-like behavior expected for the ${\mathrm{Sm}}^{2+}$ ions. The present study will help to better understand the electronic structure, magnetism, and transport properties of related materials.

TRACK: A python code for calculating the transport properties of correlated electron systems using Kubo formalism

Exploring the transport properties of different materials brings new avenue for basic understanding of emergent phenomena and practical applications in many different fields. Here, we report a program named as TRACK (TRAnsport properties for Correlated materials using Kubo formalism) which is written in Python 3 for calculating temperature dependent electrical conductivity, electronic part of thermal conductivity, Seebeck coefficient and Lorenz number. In this code, Kubo linear-response formalism is utilized for computing these parameters using both interacting and non-interacting electronic structure methods. The formula for transport coefficients is accordingly modified to obtain the transport parameters under relaxation time approximation using band-theory. The basic inputs of this program are the structural information, dense k-points sampling in the irreducible part of the Brillouin zone and the information of velocity matrix elements, which can be calculated using third-party ab-initio package. TRACK is expected to calculate the transport properties of different class of materials. The code has been benchmarked by performing calculation on three different types of materials namely Vanadium (V), FeSi and LaCoO3, which are metal, semiconductor and Mott insulator, respectively. The temperature dependent behaviour of the transport coefficients for these materials show fairly good agreement with the corresponding experimental data. Program summaryProgram Title: TRACKCPC Library link to program files:https://doi.org/10.17632/jdt9tfkt4v.1Developer's repository link:https://sourceforge.net/projects/track-code/files/TRACK.zip/downloadLicensing provisions: GPLv3Programming language: Python3External routines/libraries: NumPy, SciPy, TimeNature of problem: Calculating the transport parameters using the Kubo linear-response formalism.Solution method: We present a Python3 open source code for calculating transport coefficients using Kubo formalism. Both interacting and non-interacting electronic structure methodology are possible to be used for computing transport parameters.

Synergistic effects of CuI doping on enhancing thermoelectric performance for n-type Bi2O2Se fabricated by mechanical alloying

The extremely low electrical conductivity and time-consuming preparation methods limit potential practical applications for Bi2O2Se-based thermoelectric materials. To solve these problems, a fast preparation method of combining mechanical alloying (MA) with spark plasma sintering (SPS) has been successfully adopted to synthesize CuI-doped Bi2O2Se in this work. The electrical conductivity was largely improved from 3 S cm−1 to 296 S cm−1 at 823 K attributed to the optimized carrier concentration. Meanwhile, an extremely low lattice thermal conductivity value of 0.39 W m−1 K−1 at 823 K was achieved by intensive phonon scatterings from point defects and dense grain boundaries. Consequently, an enhanced ZT value reached 0.45 at 823 K, which resulted in ∼380% improvement over that of the pristine Bi2O2Se prepared by solid-state reaction (SSR). This work opens a new gate for synergistically optimizing electron and phonon transport properties for Bi2O2Se-based thermoelectric materials.

Extremely strong four-phonon scattering and ultra-low lattice thermal conductivity due to quartic anharmonicity in fluoride perovskites XHgF3 (X = K, Rb)

Using high-throughput first-principles calculations, combined with self-consistent phonon theory and Boltzmann transport equations, the lattice thermal transport properties of fluoride perovskites XHgF3 (X = K, Rb) with strong anharmonicity are investigated. After considering the quartic anharmonic renormalization, the imaginary frequency in the phonon spectrum disappears and the low-lying modes soften, resulting in a low group velocity of the acoustic phonons. The strong quartic anharmonicity also causes extremely strong four-phonon scattering, which is even greater than three-phonon scattering in the low frequency phonon mode. The results show that the lattice thermal conductivity κL of XHgF3 (X = K, Rb) is ultra-low and the temperature dependence is unusually weak. The κL of KHgF3 at 300 K is only 0.18 Wm−1K−1, which is one-fifth of the classical low thermal conductivity material, quartz glass. Our study points the way to addressing the thermal transport properties of materials with strong anharmonicity and demonstrates that XHgF3 (X = K, Rb) can not only serve as a good thermal insulation material but also has potential applications in the thermoelectric field.

First-principles analysis of novel Mg-based group II-VI materials for advanced optoelectronics devices

Here, in this work, the structural, electronic, optical, and transport properties of Magnesium-based group II-VI materials are studied by employing the density functional theory calculations. The WC-GGA and EV-GGA generalized gradient approximations were employed to compute the structure parameters along with the electronic nature of the ternary-type materials. Our calculations confirmed the materials to be indirect band-type semiconductors with a bandgap value of 1.17 ​eV, and 0.51 ​eV, for the MgCdO2 and MgCdS2 materials respectively. Since Sulfur has a larger atomic radius than Oxygen, the bandgap value declines in going from MgCdO2 to MgCdS2 material. The computed total density of states for these materials displayed a sequential shift with increasing energy. The linear optical parameters like the real and imaginary parts of the dielectric function, the energy loss function, the absorption coefficient, the reflectivity, and the refractive index values are calculated and analyzed in detail. Moreover, the thermoelectric properties were also computed, and the results are presented in depth, suggesting all these materials to be efficient for thermoelectric device applications.

Utilizing nano-SiO2 for modifying the microstructure, strength and transport properties of sustainable cementitious materials with waste concrete powder

Using waste concrete powder as an alternative binder in green cementitious materials contributes to reduce the number of construction and demolition waste, and developing an effective method to modify the performance of waste concrete powder blended cementitious materials is necessary. The influences of nano-SiO2 at 0–3% dosage on cementitious materials containing waste concrete powder as partial cement replacement (0–50%), under a ratio of 1:2 for both water-to-binder and binder-to-sand, were investigated in this study with the aspects of micro-structure and macro-performance. The results illustrated that mixing waste concrete powder negatively impacted the hydration reaction and micro-structure of cement paste; however, the mix of nano-SiO2 promoted the secondary hydration reaction and refined pore diameter of waste concrete powder mixed paste. Mixing nano-SiO2 raised the drying shrinkage but reduced the water loss of paste including waste concrete powder. The replacement of cement by waste concrete powder caused the reduction in compressive strength of paste. But at a fixed substitution level of waste concrete powder in paste, the compressive strength rose with the increment of nano-SiO2 content up to 3%. The transport properties rose as waste concrete powder was incorporated in mortar, but the mix of nano-SiO2 significantly reduced the transport properties of waste concrete powder incorporated mortar. Particularly, the effects of nano-SiO2 addition on the decrease in water absorption became more distinct as high content of waste concrete powder was blended. Optimizing the content of waste concrete powder and nano-SiO2 can obtain green cementitious materials owning good strength and low transport properties.

Thermoelectric properties variation in antimony telluride nanofilm using molecular dynamics

In recent years, thermoelectric materials that have the advantage of directly converting heat into electricity, have become a hot research topic. In this study, we designed a series of Sb2Te3 nanofilms using molecular dynamics simulation to explore the effects of structural defects on the phonon transport properties of thermoelectric materials. We predicted that temperature variations and structural defects can greatly increase the transfer of energy invalid and decrease thermal conductivity. Designing thermoelectric materials as composite interfaces, multilayer films, and defect structures is an effective way to achieve this goal.

Enhanced electrical transport properties of PbTe single crystal through Ga substitution synthesized by a Pb-flux method

As a promising thermoelectric material at the medium temperature range, PbTe has attracted much attention during the past several decades. In this study, Ga-doped PbTe single crystals were synthesized by a facile Pb-flux method. The electronic structure calculations reveal that Ga substitution can introduce impurity level in the bandgap, which can effectively modulate the carrier concentration and therefore optimize the electrical conductivity. Experimentally, the carrier concentration was modulated from 1.95 to 4.46 × 1019 cm−3 at 300 K. Accordingly, the electrical conductivity reaches a maximum of 1.5 × 105 S·m−1 at 300 K for the sample with x = 0.025. As a result, maximal thermoelectric power factor 3.07 × 10−3 W·m−1·K−2 is attained at 360 K for the aforementioned sample, 62% higher than that of the undoped sample (1.89 ×10−3 W·m−1·K−2). This work provides a viable method to synthetize high-quality single crystal and it also verifies that Ga substitution can significantly improve the electrical transport properties of single crystalline PbTe thermoelectric material.

Ion Correlations and Partial Ionicities in the Lamellar Phases of Block Copolymeric Ionic Liquids.

Recently, significant interest has arisen on the impact of dynamical ion correlations on the conductivity and transport properties of polymeric electrolyte materials. It has been hypothesized that confining ion motion to narrow channels may reduce such ion correlations and enhance the resulting ionic conductivity. Motivated by such considerations, in this study we used a multiscale simulation framework to study the dynamical ion correlations in the microphase-separated lamella phase of block copolymeric ionic liquids and compare with the corresponding results for homopolymeric systems. We probed the influence of ion correlations through the partial ionicity, Δ, which quantifies the ratio of true conductivity to the ideal, Nernst-Einstein conductivity for the anion-related contributions. Consistent with our original hypothesis, our results demonstrate that the partial ionicity relating to the mobile anions is much larger in the lamella phases of block copolymers compared to that in homopolymers. Analysis of the distinct conductivity contributions demonstrates that such results arise as a result of an intricate compensation among the nonideal dynamical correlations relating to anions in lamella phases. Together, our results suggest that self-assembled phases of block copolymers may provide an avenue to tune the dynamical ion correlations in polymer electrolyte systems.

(Invited) Small Polarons in Metal-Oxide Based Solar Absorber Materials

The key materials for photo-electrochemical (PEC) processes are the photoelectrocatalysts that are required to absorb sunlight, form electron-hole pairs, and transport the charge carriers efficiently towards the electrolyte-semiconductor interface. Metal-oxides are thought to be the most stable materials under intense interfacial reactive conditions. However, the overall efficiencies of these metal-oxide photoelectrocatalysts are not as high as expected, even for those with near-suitable bandgap energies required for efficient solar energy absorptions. One of the main reasons is attributed to the poor transport properties in metal-oxides with strongly correlated electrons. Typically, strongly correlated systems exhibit polaron conduction via electron-phonon interactions. Polarons act like a bottleneck for photoconductions in such metal-oxides. Recently, there have been significant efforts to characterize polaronic states and their effects on transport properties in photoactive materials. First-principles theoretical and computational studies can reveal the electronic origin of the polaron formation and, therefore, can suggest how to improve overall transport properties in such photoactive materials. In this presentation, representative metal-oxides photo-catalysts will be considered to demonstrate the small polaron formation mechanism. The polaronic states in metal-oxides will be depicted from detailed electronic structure calculations by density functional theory (DFT) based methods. We will show how these polaronic states affect the PEC cell's transport properties and photo-voltages. We will also discuss how these computational results compare with the recent experimental outcome. Some part of the work was funded by National Science Foundation, USA. Computations were performed at the Texas Advanced Computing Center (TACC).

Compressive strength, water and chloride transport properties of early CO2-cured Portland cement-fly ash-slag ternary mortars

Early CO2 curing is a promising technology for improving the strength and long-term durability of mortar and concrete as well as CO2 sequestration. However, the effects of supplementary cementitious materials (SCMs) such as fly ash and slag on the chloride transport properties of cement-based materials subjected to early CO2 curing are not clear. In this study, compressive strength, water and chloride transport behaviors of Portland cement-fly ash-slag ternary mortars subjected to early CO2 curing and subsequent lime water curing were determined. The obtained results indicated that the addition of fly ash and slag lowered the compressive strength, water and chloride ions penetration resistance of cement mortars at the late age. Regarding the mechanical and transport properties, the replacement level of fly ash and slag in early CO2-cured cement mortars should not exceed 25% when it exposure to chloride ions. Slag had less influence on the mechanical and transport properties of early CO2-cured cement mortars than fly ash due to finer particle size of the former.