Polar Materials Research Articles

Electrical Resistivity And Induced Polarization Imaging For Refuse Dump Site

Contamination from landfills as a result of leaching from organic and inorganic waste poses a threat to the environment because, subsoil and groundwater are affected. The contamination is more serious in developing countries where waste management is inefficient. The aim of this study was to determine the extent of pollution at this site. Three profiles were surveyed: two in North-South direction and the third in Northeast-Southwest. 2D electrical resistivity and Time Domain Induced Polarization (TDIP) data sets have been acquired along the three profiles in Boadi Community. Electrical resistivity and induced polarization together with excavations were successful in mapping the extent of the leachate plume. The study demarcated clearly three main zones: the first, second and third zones indicated chargeabilities > 12.8 msec near the surface, > 6.4 msec and > 12.8 msec at the base respectively. Similarly, resistivities 192 Ωm for the first, second and third zones respectively were delineated. The relatively lower electrical resistivity areas were thought to be due to the presence of the leachate plume and the comparatively higher chargeability zones were interpreted as duricrust. The relatively lower chargeability represents absence of polarizable materials. The study also delineated the weathered basement granodiorites showing relatively higher resistivities. These TDIP and ERT results show that the methods have been successful in mapping the landfill leachate plume. The results from the resistivity and chargeability compare very well with the excavations.

Bio‐Derived Materials Achieving High Performance in Alkali Metal–Chalcogen Batteries

AbstractAlkali metal–chalcogen batteries (ACBs) have attracted significant attention as next‐generation energy storages because of high energy density and reasonable cost as compared to the up‐to‐date lithium‐ion batteries. Nevertheless, their practical applications are harshly inhibited by some drawbacks, such as shuttle effects resulting from dissolved polysulfides and polyselenides, chalcogen volume expansion, and dendrite growth on metal anodes. Functional components, such as chalcogen host, binder, and interlayer, using various polar materials have been introduced to address these issues. Among them, bio‐derived materials are regarded as novel eco‐friendly alternatives. In this report, the authors focus on the unique physical/chemical/environmental properties of bio‐derived materials used in ACBs, including active host materials, polymer binders, separators, and additives. The authors hope that the present report can provide some new insights and directions for future research on high‐performance ACBs.

A Design Principle for Polar Assemblies with C3‐Sym Bowl‐Shaped π‐Conjugated Molecules

AbstractPolar materials attract wide research interest due to their unique properties, such as ferroelectricity and the bulk photovoltaic effect (BPVE), which are not accessible with nonpolar materials. However, in general, rationally designing polar materials is difficult because nonpolar materials are more favorable in terms of dipole‐dipole interactions. Here, we report a rational strategy to form polar assemblies with bowl‐shaped π‐conjugated molecules and a molecular design principle for this strategy. We synthesized and thoroughly characterized 12 single crystals with the help of various theoretical calculations. Furthermore, we demonstrated that it can be possible to predict whether polar assemblies become more favorable or not by estimating their lattice energies. We believe that this study contributes to the development of organic polar materials and their related studies.

A Design Principle for Polar Assemblies with C3‐Sym Bowl‐Shaped π‐Conjugated Molecules

AbstractPolar materials attract wide research interest due to their unique properties, such as ferroelectricity and the bulk photovoltaic effect (BPVE), which are not accessible with nonpolar materials. However, in general, rationally designing polar materials is difficult because nonpolar materials are more favorable in terms of dipole‐dipole interactions. Here, we report a rational strategy to form polar assemblies with bowl‐shaped π‐conjugated molecules and a molecular design principle for this strategy. We synthesized and thoroughly characterized 12 single crystals with the help of various theoretical calculations. Furthermore, we demonstrated that it can be possible to predict whether polar assemblies become more favorable or not by estimating their lattice energies. We believe that this study contributes to the development of organic polar materials and their related studies.

Selective removal of iron(III), lead(II) and copper(II) ions by polar crude phytochemicals recovered from ten South African plants: identification of plant phytochemicals

This work consists of gathering the leaves of ten different South African plants from the local reserve. Black and green tea were sourced commercially. The plants were air dried and polar crude material extracted using deionized water. These crude phytochemicals were used as green chelators to remove metal ions from an aqueous solution. Iron(III), lead(II) and copper(II) ions were competitively removed from an eight metal ion solution with iron(III) being removed at more than 80% followed by lead(II) with greater than 40% removal and copper(II) with removal values of more than 20%. Metal ion removal was shown to be affected by change in pH of the solution, indicating that removal took place via the pH-swing mechanism. As the pH is increased, iron(III) is first removed followed by lead(II) and then copper(II). Iron(III) and lead(II) were selectively removed even at a 10-fold dilution level compared to the other metal ions present. Loading tests showed that iron(III) removal does not change, but for lead(II) and copper(II) there is a noticeable increase in removal with an increase in the amount of crude. The phytochemicals in the crude were identified using Liquid chromatography-tandem mass spectrometry (LC-MS/MS). Some crudes had similar phytochemicals (quercetin) while others had unique compounds. Statement of novelty It is the first time that crude polar phytochemicals from South African plants are used as green chelators. These green chelators selectively remove iron(III), lead(II) and copper(II) from a mix of eight different base metal ions. Iron(III) can be selectively removed at pH as low as 3.00 and, when iron(III) and lead(II) are 10 times more dilute compared to the other metal ions, iron(III) and lead(II) are still selectively removed. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is used to identify some of the phytochemicals present in these plants.

Thermomechanical properties of honeycomb lattices from internal-coordinates potentials: the case of graphene and hexagonal boron nitride

Lattice dynamics in low-dimensional materials and, in particular, the quadratic behaviour of the flexural acoustic modes play a fundamental role in their thermomechanical properties. A first-principles evaluation of these can be very demanding, and can be affected by numerical noise that breaks translational or rotational invariance. In order to overcome these challenges, we study the Gartstein internal-coordinate potential and tune its 13 parameters on the first-principles interatomic force constants for graphene. We show that the resulting potential not only reproduces very well the phonon dispersions of graphene, but also those of carbon nanotubes of any diameter and chirality. The addition of a cubic term allows also to reproduce the dominant anharmonic terms, leading to a very good estimate of the lattice thermal conductivity. Finally, this potential form works very well also for boron nitride, provided it is fitted on the short-range (analytical) part of the interatomic force constants, and augmented thereafter with the long-range dielectric contribution. This consideration underscores how potentials based on short-ranged descriptors should be fit, in polar materials, to the short-range part of the first-principles interactions, and complemented by long-range analytical dielectric models parametrized on the same first-principles calculations.

Velocity-inverted Three-dimensional Distribution of the Gas Clouds in the Type 2 AGN NGC 1068

Abstract Spatially resolved velocity maps at high resolutions of 1–10 pc are becoming available for many nearby active galactic nuclei (AGNs) in both optical/infrared atomic emission lines and submillimeter molecular lines. For the former, it is known that a linear relationship appears to exist between the velocity of the ionized gas clouds and the distance from the nucleus in the inner ∼100 pc region, where these clouds are outflowing. Here we demonstrate that, in such a case, we can actually derive the three-dimensional (3D) geometrical distribution of the clouds directly from the velocity map. Revisiting such a velocity map taken by the Hubble Space Telescope for the prototypical Type 2 AGN NGC 1068, we implement the visualization of the 3D distribution derived from the map, and show that this inner narrow-line region has indeed a hollow-cone structure, consistent with previous modeling results. Quite possibly, this is the outer extended part of the polar elongated dusty material seen in the recent mid-infrared interferometry at parsec scale. Conversely, the latter small-scale geometry is inferred to have a hollow-cone outflowing structure as the inward extension of the derived 3D distribution above. The AGN obscuring “torus” is argued to be the inner optically thick part of this hollow-cone outflow, and its shadowed side would probably be associated with the molecular outflow seen in certain submillimeter lines. We discuss the nature of the linear velocity field, which could be from an episodic acceleration that occurred ∼105 yr ago.

Effect of Properties of Silver Nanoparticles Coated with Polar Material and the Antibacterial Activity on Marine Pathogenic Bacteria

Silver nanoparticles (Ag NPs) have become one of the current research hotspots and are used in many fields such as electrochemistry, energy, bioanalysis, and environmental monitoring, especially in the field of antibacterial research. In this study, we investigated the effect of properties of Ag NPs coated with polar materials. Ag NPs covered by a dispersant that was triethylene glycol monoethyl ether was stable and conquered the aggregation of Ag NPs. The effect of the dispersant on biocompatibility was explored through interaction experiments between Ag NPs and DNA sequence. The coated Ag NPs could adsorb DNA, and the fluorescence of FAM-DNA could be quenched by Ag NPs. The adsorption and desorption experiments of DNA showed that the order of DNA functional groups on the interaction process was phosphate>T>C>A>G. Moreover, we selected marine pathogenic bacteria to test the antibacterial effect of Ag NPs coated with a polar dispersant. The polar material had a certain inhibitory effect on the antibacterial activity of Ag NPs. However, small molecules such as bases could interact on the surface Ag NPs and release Ag+ to perform the antibacterial activity. The results could contribute to the further application of Ag NPs.

Trapping and catalytic conversion of polysulfides by kirkendall effect built hollow NiCo2S4 nano-prisms for advanced sulfur cathodes in Li–S battery

To address the problems of low active utilization and fast capacity decay in practical application of lithium–sulfur (Li–S) battery, an effective and widely used strategy is incorporating polar materials into sulfur cathode to tune the redox reaction of polysulfides in recent years. Herein, a hollow nano-prism structured bimetallic sulfide (NiCo2S4) built by kirkendall effect is proposed to trap and catalyze conversion of polysulfides. Beneficial from the strong interaction and super electrocatalytic effect for the intermediates of sulfur reduction, the NiCo2S4 incorporated in sulfur cathode can significantly ease the shuttle effect, decrease the activation energy and dynamically accelerates the transformation of the polysulfides. As expected, together with the high conductivity, hollow structure and compositional superiorities, the sulfur cathode with NiCo2S4 for Li–S battery exhibits apparently enhanced sulfur utilization and improved cycling performance that preserves super low capacity fading rate of 0.05% per cycle after 800 cycles at 1 C. This work has guiding significance in the design of a sulfur cathode for advanced Li–S battery.

Detectability of axion dark matter with phonon polaritons and magnons

Collective excitations in condensed matter systems, such as phonons and magnons, have recently been proposed as novel detection channels for light dark matter. We show that excitation of i) optical phonon polaritons in polar materials in an ${\mathcal O}$(1 T) magnetic field (via the axion-photon coupling), and ii) gapped magnons in magnetically ordered materials (via the axion wind coupling to the electron spin), can cover the difficult-to-reach ${\mathcal O}$(1-100) meV mass window of QCD axion dark matter with less than a kilogram-year exposure. Finding materials with a large number of optical phonon or magnon modes that can couple to the axion field is crucial, suggesting a program to search for a range of materials with different resonant energies and excitation selection rules; we outline the rules and discuss a few candidate targets, leaving a more exhaustive search for future work. Ongoing development of single photon, phonon and magnon detectors will provide the key for experimentally realizing the ideas presented here.

Screening of hot electrons in the ferroelectric semiconductor In2Se3

In a conventional semiconductor, electrons $(e)$ scatter efficiently with longitudinal-optical phonons $(\mathrm{p}{\mathrm{h}}_{\mathrm{LO}})$ via the Fr\ohlich interaction, e.g., in polaron formation or hot-electron cooling. Recent studies on lead halide perovskites have suggested that the Fr\ohlich interaction may be sufficiently screened by the polar lattice. Here we show that hot-electron cooling in a layered ferroelectric semiconductor $\mathrm{I}{\mathrm{n}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ slows down by 50% as temperature is increased from 115 to 387 K; this decrease is about four times more than that predicted by the Fr\ohlich model. We suggest that screening of Fr\ohlich interaction by polar domains or fluctuations in the ferroelectric semiconductor may be responsible for the reduced $\mathrm{e}\text{\ensuremath{-}}\mathrm{p}{\mathrm{h}}_{\mathrm{LO}}$ scattering. Such enhanced screening in polar materials featuring anharmonic lattice instability may also reduce carrier scattering with other charge carriers or with charged defects, leading to improved optoelectronic properties.

Prediction of Intrinsic Ferroelectricity and Large Piezoelectricity in Monolayer Arsenic Chalcogenides.

Two-dimensional materials that exhibit spontaneous electric polarization are of notable interest for functional materials. However, despite the prediction of many two-dimensional polar materials, the number of experimentally confirmed two-dimensional ferroelectrics is far less than bulk ferroelectrics. We provide strong evidence that the Pmn21 phase of arsenic chalcogenides As2X3 (X = S, Se, and Te), which include the recently isolated monolayer orpiment, are intrinsic ferroelectrics and demonstrate strong in-plane piezoelectricity. We found the calculated energy barriers for collectively reversing the electric polarization or moving a 180° domain wall are reasonable compared to previously reported ferroelectrics. We propose a high-symmetry structure (with Pmmn space group) that transforms into the ferroelectric Pmn21 phase by a soft B2u phonon mode. By studying other soft modes of the high-symmetry Pmmn structure, we identify several undiscovered metastable polymorphs, including a polar phase (with a P21 space group) with sizable piezoelectricity.

Thermoelectric transport properties in chalcogenides ZnX (X=S, Se): From the role of electron-phonon couplings

Electron-phonon coupling (EPC) is a key factor for thermoelectric properties of materials. In this paper, the thermoelectric properties of zinc-blende chalcogenides (p-type) ZnS and ZnSe have been studied through full evaluation of EPC from first-principles, including the influences on both electrical and thermal transport. We find that the polar longitudinal optical phonon scattering is the dominant mechanism for electrical transport. Due to the triple degeneracy near the valence band maximum, the inter-band scattering also has detrimental contributions to the electrical conductivities. For phonon transport, it shows that the lattice thermal conductivity can be reduced by the electron-phonon scattering significantly at high carrier concentrations (e.g., at 300 K with 1021 cm−3 of hole, the reduction is ∼24.9% for ZnS and ∼28.4% for ZnSe, respectively). Finally, the p-type thermoelectric figure of merit (ZT) of two systems have been obtained, which are 0.129 for ZnS and 0.141 for ZnSe, at 700 K with their respective optimal hole concentrations. Our work provides a complete and in-depth study of thermoelectric properties in chalcogenides ZnX from the role of EPC. The results suggest EPC plays an important role on the thermoelectric properties and thus full evaluation of EPC is necessary especially for polar materials.

Thornber–Feynman carrier-optical-phonon scattering rates in wurtzite crystals

It is well known that the carrier-optical-phonon scattering rates dominate the carrier-acoustic-phonon scattering rates in many polar materials of interest in electronic and optoelectronic applications. Furthermore, it is known that the Fröhlich coupling constants for carrier-optical-phonon in many materials is close to or great than unity, calling into question the validity of scattering rates based on the Fermi golden rule. In a celebrated paper by Thornber and Feynman it was shown that that the large Fröhlich coupling constant in polar materials does indeed lead to substantial corrections to the Fermi golden rule scattering rates. These large corrections are due to the fact that for strong coupling constants, the first-order perturbative approach underlying the Fermi golden rule does not take into account the presence of many phonons interacting simultaneous with the carrier. In this paper, the Thornber–Feymnan scattering rates for carrier-optical-phonon interactions are derived for several technologically important wurtzite semiconductors—BN, ZnO, CdS, CdSe, ZnS, InN, and SiC- and it is shown that the commonly used Fermi golden rule scattering rates must be corrected by factors ranging up to an order-of-magnitude. The corrections to the Fermi golden rule reported herein have widespread impact on carrier transport for materials with large Fröhlich coupling constants.

Strong Electron–Phonon Interaction in 2D Vertical Homovalent III–V Singularities

Highly polar materials are usually preferred over weakly polar ones to study strong electron-phonon interactions and its fascinating properties. Here, we report on the achievement of simultaneous confinement of charge carriers and phonons at the vicinity of a 2D vertical homovalent singularity (antiphase boundary, APB) in an (In,Ga)P/SiGe/Si sample. The impact of the electron-phonon interaction on the photoluminescence processes is then clarified by combining transmission electron microscopy, X-ray diffraction, ab initio calculations, Raman spectroscopy, and photoluminescence experiments. 2D localization and layer group symmetry properties of homovalent electronic states and phonons are studied by first-principles methods, leading to the prediction of a type-II band alignment between the APB and the surrounding semiconductor matrix. A Huang-Rhys factor of 8 is finally experimentally determined for the APB emission line, underlining that a large and unusually strong electron-phonon coupling can be achieved by 2D vertical quantum confinement in an undoped III-V semiconductor. This work extends the concept of an electron-phonon interaction to 2D vertically buried III-V homovalent nano-objects and therefore provides different approaches for material designs, vertical carrier transport, heterostructure design on silicon, and device applications with weakly polar semiconductors.

Long-range quadrupole electron-phonon interaction from first principles

Lattice vibrations in materials induce perturbations on the electron dynamics in the form of long-range (dipole and quadrupole) and short-range (octopole and higher) potentials. The dipole Fr\"ohlich term can be included in current first-principles electron-phonon ($e$-ph) calculations and is present only in polar materials. The quadrupole $e$-ph interaction is present in both polar and nonpolar materials, but currently it cannot be computed from first principles. Here we show an approach to compute the quadrupole $e$-ph interaction and include it in ab initio calculations of $e$-ph matrix elements. The accuracy of the approach is demonstrated by comparing with direct density functional perturbation theory calculations. We apply our method to silicon as a case of a nonpolar semiconductor and tetragonal PbTiO$_3$ as a case of a polar piezoelectric material. In both materials we find that the quadrupole term strongly impacts the $e$-ph matrix elements. Analysis of $e$-ph interactions for different phonon modes reveals that the quadrupole term mainly affects optical modes in silicon and acoustic modes in PbTiO$_3$, although the quadrupole term is needed for all modes to achieve quantitative accuracy. The effect of the quadrupole $e$-ph interaction on electron scattering processes and transport is shown to be important. Our approach enables accurate studies of $e$-ph interactions in broad classes of nonpolar, polar and piezoelectric materials.

Piezoelectric Electron-Phonon Interaction from AbInitio Dynamical Quadrupoles: Impact on Charge Transport in Wurtzite GaN.

First-principles calculations of e-ph interactions are becoming a pillar of electronic structure theory. However, the current approach is incomplete. The piezoelectric (PE) e-ph interaction, a long-range scattering mechanism due to acoustic phonons in noncentrosymmetric polar materials, is not accurately described at present. Current calculations include short-range e-ph interactions (obtained by interpolation) and the dipolelike Frölich long-range coupling in polar materials, but lack important quadrupole effects for acoustic modes and PE materials. Here we derive and compute the long-range e-ph interaction due to dynamical quadrupoles, and apply this framework to investigate e-ph interactions and the carrier mobility in the PE material wurtzite GaN. We show that the quadrupole contribution is essential to obtain accurate e-ph matrix elements for acoustic modes and to compute PE scattering. Our work resolves the outstanding problem of correctly computing e-ph interactions for acoustic modes from first principles, and enables studies of e-ph coupling and charge transport in PE materials.

Metal-organic frameworks (MOFs) derived carbon-coated NiS nanoparticles anchored on graphene layers for high-performance Li-S cathode material

Due to its high capacity (1675 mAh g−1), Li-S batteries have been considered as one of the ideal energy storage systems. The grand challenges of lithium-sulfur batteries are sulfur immobilization and improving electrical conductivity of cathode composite. The carbon-sulfur (C-S) composites and the polar materials (Ni(OH)2, TiO2, MnO2, TiS2, Co9S8, etc) integration have been proven to be two of the most effective routes to achieving good Li-S battery performance. However, each strategy has drawbacks: the C-S composites have low volume density and the polar materials are often lack of electrical conductivity. Therefore, the hybridization of carbon and polar materials shall provide synergistic effects achieving ideal sulfur cathode. Herein, a hybrid material with carbon-coated NiS nanoparticles grown on graphene sheets was synthesized through a hydrothermal reaction followed by two steps of annealing. The obtained composite has a well-balanced ratio between graphene and NiS. An optimized energy density was demonstrated in lithium-sulfur cells.

Natural frequency and bending analysis of heterogeneous polar orthotropic-faced sandwich panels in the existence of in-plane pre-stress

In this paper, the effects of plane pre-stresses on the free vibration and static analyses of circular and annular sandwich panels are examined based on an accurate formulation, as first time. It is assumed that initially pre-stresses consist of in-plane normal (tensile/compressive) and pure bending stresses. New first-order shear deformation theory together with a layerwise approach for sandwich panel is utilized. The sandwich panels are made up of either orthotropic or heterogeneous polar orthotropic materials. Furthermore, piecewise-defined linear local in-plane displacements are adopted based on zigzag theory. The governing partial differential equations are extracted by implementing principle of minimum total potential energy. A unified analytical solution procedure is developed based on power series method for the analysis of heterogeneous initially stressed annular and circular sandwich panels with arbitrary boundary conditions. The transverse shear stress is precisely calculated by considering three-dimensional theory of elasticity. To validate the proposed formulation, the obtained results are compared with those of finite element method. After numerically demonstrating the accuracy of the method, the effects of different geometrical and material parameters, boundary conditions and in-plane pre-stresses on the free vibration and static behavior of circular and annular sandwich panels are investigated.

Enhancing Graphene Plasmonic Device Performance via its Dielectric Environment

Graphene plasmons provide a compelling avenue toward chip-scale dynamic tuning of infrared light. Dynamic tunability emerges through controlled alterations in the optical properties of the system defining graphene's plasmonic dispersion. Typically, electrostatic induced alterations of the carrier concentration in graphene working in conjunction with mobility have been considered the primary factors dictating plasmonic tunability. We find here that the surrounding dielectric environment also plays a primary role, dictating not just the energy of the graphene plasmon but so too the magnitude of its tuning and spectral width. To arrive at this conclusion, poles in the imaginary component of the reflection coefficient are used to efficiently survey the effect of the surrounding dielectric on the tuning of the graphene plasmon. By investigating several common polar materials, optical phonons (i.e., the Reststrahlen band) of the dielectric substrate are shown to appreciably affect not only the plasmon's spectral location but its tunability, and its resonance shape as well. In particular, tunability is maximized when the resonances are spectrally distant from the Reststrahlen band, whereas sharp resonances (i.e., high-$Q$) are achievable at the band's edge. These observations both underscore the necessity of viewing the dielectric environment in aggregate when considering the plasmonic response derived from two-dimensional materials and provide heuristics to design dynamically tunable graphene-based infrared devices.