The electrical conductivity of magnesium silicate MgSiO3 has been studied, using the framework of the first-principles density functional theory and the Boltzmann transport theory, under the thermodynamic conditions of the Earth's lower mantle. We find that the conductivity of pristine MgSiO3 depends strongly on the structural phase of the material, as well as on temperature and pressure. The conductivity of the perovskite phase increases with increasing pressure (depth of the lower mantle) up to 90 GPa, then decreases at higher pressures due to a change in the material's band gap transition from direct to indirect. Finally, the structural phase transition that MgSiO3 undergoes near the bottom of the lower mantle, from perovskite to post-perovskite, causes an increase in the conductivity of MgSiO3, which should contribute to the increase in the electrical conductivity of the Earth's mantle under the thermodynamic conditions of the Earth's D" layer.
We report lattice thermal conductivities of MgO and MgSiO3 in the perovskite and post-perovskite structures at conditions of the Earth's lower mantle, obtained from equilibrium molecular dynamics simulations. Using an advanced ionic interaction potential, the full conductivity tensor was calculated by means of the Green-Kubo method, and the conductivity of MgSiO3 post-perovskite was found to be significantly anisotropic. The thermal conductivities of all three phases were parameterized as a function of density and temperature. Assuming a Fe-free lower-mantle composition with mole fractions xMg…
Thermal conductivity ($κ$) of mantle minerals is a fundamental property in geodynamic modeling. It controls the style of mantle convection and the time scale of the mantle and core cooling. Cubic CaSiO$_3$ perovskite (CaPv) is the third most abundant mineral in the lower mantle (LM) (7 vol%). However, despite its importance, no theoretical or experimental estimate of CaPv's $κ$ exists. Theoretical investigations of its properties are challenging because of its strong anharmonicity. Experimental measurements at relevant high pressures and temperatures are equally challenging. Here we present $a…
Iron spin crossover in ferropericlase and its effect on lower-mantle thermal conductivity
Carnegie Institution for Science（卡内基科学机构）；Florida International University（佛罗里达国际大学）；University of Münster（明斯特大学）；The University of Texas at Austin（德克萨斯大学奥斯汀分校）；The University of Edinburgh（爱丁堡大学）；Deutsches Elektronen-Synchrotron (DESY)（德国电子同步辐射研究所）；Albert-Ludwigs Universität Freiburg（弗赖堡大学）；European XFEL（欧洲X射线自由电子激光设施）；Univ. Lille, CNRS, INRAE, Centrale Lille（里尔大学）；Sorbonne Université, Muséum National d’Histoire Naturelle（索邦大学，法国国家自然历史博物馆）；Helmholtz-Zentrum Dresden-Rossendorf（德累斯顿-罗斯多夫亥姆霍兹中心）；Université Grenoble Alpes（格勒诺布尔阿尔卑斯大学）
The ability of Earths mantle to conduct heat by radiation is determined by optical properties of mantle phases. Optical properties of mantle minerals at high pressure are accessible through diamond anvil cell experiments, but because of the extensive thermal radiation at T above 1000 K such studies are limited to lower temperatures. Particularly uncertain is the temperature-dependence of optical properties of lower mantle minerals across the spin transition as the spin state itself is a strong function of temperature. Here we use laser-heated DACs combined with a pulsed bright supercontinuum l…
Lattice thermal conductivity ($κ_{lat}$) of MgSiO$_3$ postperovskite (MgPPv) under the Earth's lower mantle high pressure-temperature conditions is studied using the phonon quasiparticle approach by combing \textit{ab initio} molecular dynamics and lattice dynamics simulations. Phonon lifetimes are extracted from the phonon quasiparticle calculations, and the phonon group velocities are computed from the anharmonic phonon dispersions, which in principle capture full anharmonicity. It is found that throughout the lowermost mantle, including the D" region, $κ_{lat}$ of MgPPv is ~25% larger than …
Earth/s lowermost mantle displays complex geological structures that likely result from heterogeneous thermal and electromagnetic interaction with the core. Geophysical models of the core-mantle boundary (CMB) region rely on the thermal and electrical conductivities of appropriate geomaterials which, however, have never been probed at representative pressure and temperature (P-T) conditions. Here we report on the opacity of single crystalline bridgmanite and ferropericlase, which is linked to both their radiative and electrical conductivity, measured in dynamically- and statically-heated diamo…
The electrical conductivity of melts of boron and its carbide (B4C), nitride (BN), and phosphide (BP) has been studied at pressures to 7.7 GPa and temperatures to 3500 K. It has been shown that these melts are good conductors with specific electrical conductivity values comparable with that of iron melt at ambient pressure.
The development of silicone rubber nanocomposite with electrical conductivity activated by temperature and self-healing capabilities has been reported. Silicon rubber (SR) filled with graphite nanoplatelets (GNPs) was synthesized via a liquid mixing method. The electrical conductivity of the SR/GNPs composite showed a transition from insulating to conducting state with increasing the temperature. The SR/GNPs composite can be healed by simple thermal annealing.
W-based granular metals have been prepared by electron beam induced deposition from the tungsten-hexacarbonyl W(CO)6 precursor. In situ electrical conductivity measurements have been performed to monitor the growth process and to investigate the behavior of the deposit under electron beam post irradiation and by exposure to air. During the first part of the growth process, the electrical conductivity grows non-linearly, independent of the electron beam parameters. This behavior is interpreted as the result of the increase of the W-particles diameter. Once the growth process is terminated, the …
Very recent measurements of the electrical conductivity of solid systems AgX - CdX$_2$ (where X$\equiv$Cl,Br) that form large areas of solid solutions, have shown that maximum conductivity occurs for a concentration around 20 mol\% of the cadmium halide. Here, we suggest a quantitative explanation of this phenomenon based on a model that was suggested (J. Appl. Phys. 103, 083552, (2008)) for estimating the compressibility of multiphased mixed crystals. In addition, explicit conditions are obtained which predict when such a conductivity maximum is expected to occur.
We study the consequences of identifying the 'electron density parameter' N of Miedema et al. as the accurate valence of metallic elements. The incorporation of these as valence in Pauling's scheme for the electronic structure of transition metals, predicts, for the first time, that the electrical conductivity of transition metals would decrease in the order σ_Ag > σ_Cu > σ_Au > σ_Rh > σ_others, as is experimentally observed.
The electrical conductivity of the switching channel of vanadium dioxide thin-film sandwich structures is studied over a wide temperature range (15-300 K). It is shown that the electrical resistance of the channel varies with temperature as R~exp(aT-b/T) in the high-temperature region (above 70 K). The experimental results are discussed from the viewpoint of the small polaron hopping conduction theory which takes into account the influence of thermal lattice vibrations onto the resonance integral.
We derive a new cross-property differential effective medium scheme for a composite material's thermal conductivity as a function of its electrical conductivity and vice versa. Our scheme assumes that one phase is embedded in the other as inclusions. The relations are independent of inclusion volume fraction, but depend on the aspect ratio of the inclusions. We show that the method successfully models published laboratory measurements on a copper-graphite composite, with the inferred aspect ratio matching the physical shape of the inclusions. This work complements earlier results on elastic-el…
Thin-film nanocomposites, consisting of silver nanoparticles embedded in a dielectric Teflon\textregistered AF matrix, were synthesized using vapor phase co-deposition. The electrical conductivity of these composites was measured in-situ as a function of film thickness at various metal concentrations. At low metal concentrations (<30%), dielectric behavior and very little change with film thickness was observed. At moderate to high silver loadings (30-80%) a large increase in electrical conductivity was observed as the films grew thicker. As the thickness increased further, the conductivity fl…
The use of oxide glasses is pervasive throughout everyday amenities and commodities. Such glasses are typically electrical insulators, and endowing them with electrical conductivity without changing their salutary mechanical properties, weight, or thermoformability enables new applications in multifunctional utensils, smart windows, and automotive parts. Previous strategies to impart electrical conductivity include modifying the glass composition or forming a solid-in-solid composite of the glass and a conductive phase. Here we demonstrate using the latter strategy the highest reported room-te…
We present a first-principles study of the structure and energetics of Bjerrum defects in ice Ih and compare the results to experimental electrical conductivity data. While the DFT result for the activation energy is in good agreement with experiment, we find that its two components have quite different values. Aside from providing new insight into the fundamental parameters of the microscopic electrical theory of ice, our results suggest the activity of traps in doped ice in the temperature regime typically assumed to be controlled by the free migration of L defects.
In this paper we report an extensive neutron diffraction investigation at high temperature on the BaCe0.80Y0.20O2.9 proton conducting material. Our results precisely define the structural evolution of the compound as a function of temperature which is from a monoclinic (room temperature) to a cubic (800C) structure. Neutron data have been correlated to calorimetric measurements (TGA and DSC) and conductivity properties of the material.
The thermal conductivity of polycrystalline bulk PZT (lead-zirconate-titanate) has been investigated according to electrical boundary conditions and poling. The thermal conductivity of poled PZT was measured in the poling direction for open circuit and short circuit conditions. The short circuit thermal conductivity had the largest thermal conductivity. The relationship between these two thermal properties, the electrothermal coupling factor $k_{33}^κ$, was found to be similar to the electromechanical coupling factor $k_{33}$ relating elastic compliance under short circuit and open circuit con…
We present an ab initio calculation of the DC conductivity of amorphous silicon and hydrogenated amorphous silicon. The Kubo-Greenwood formula is used to obtain the DC conductivity, by thermal averaging over extended dynamical simulation. Its application to disordered solids is discussed. The conductivity is computed for a wide range of temperatures and doping is explored in a naive way by shifting the Fermi level. We observed the Meyer-Neldel rule for the electrical conductivity with E_MNR = 0.06 eV and a temperature coefficient of resistance, TCR ~ -2.0% K^-1 for a-Si:H. In general, experime…
The author reports an experimental study of electrical and thermal transport in reduced graphene oxide (RGO)/polystyrene (PS) composites. The electrical conductivity ($σ$) of RGO/PS composites with different RGO concentrations at room temperature shows a percolation behavior with the percolation threshold of ~ 0.25 vol.%. Their temperature-dependent electrical conductivity follows Efros-Shklovskii (ES) variable range hopping (VRH) conduction in the temperature range of 30 to 300 K. The thermal conductivity ($κ$) of composites is enhanced by ~ 90 % as the concentration is increased from 0 to 10…
Electrical conductivity (sigma_dc) of the cellular Si/SiC ceramic composites has been measured over a temperature range 25-1073 K while the thermoelectric power (S) has been measured over 25-300 K. Remarkably, these cellular compounds developed through biomimetic route - where the ceramic system grows within a plant bio-template retaining the structural intricacies of the native templates - are found to exhibit excellent mechanical, thermal, and electrical properties quite comparable to or even better than those of the systems prepared through conventional ceramic route. The electrical conduct…
Poly(3,4-ethylenedioxythiophene) : poly(styrene sulfonic acid (PEDOT:PSS), an optically transparent organic semi-conductor, constitutes a suspension of conducting PEDOT:PSS grains, shelled by an insulating layer of PSS. While a percolation network enhances dc conductivity, structural and electrical inhomogenity hinters electric charge flow giving rise to capacitance effects. In the present work, two distinct relaxation mechanisms are detected by Broadband Dielectric Spectroscopy (BDS). Double polarization mechamisms are predicted by bi-phase suspension dielectric theory. Within the frame of in…
Combination of electrical conductivity and optical transparency in the same material -- known to be a prerogative of only a few oxides of post-transition metals, such as In, Sn, Zn and Cd -- manifests itself in a distinctive band structure of the transparent conductor host. While the oxides of other elements with $s^2$ electronic configuration, for example, Mg, Ca, Sc and Al, also exhibit the desired optical and electronic features, they have not been considered as candidates for achieving good electrical conductivity because of the challenges of efficient carrier generation in these wide-band…
Hematite Fe$_2$O$_3$ seed layers are shown to constitute a pathway to prepare highly conductive transparent tin-doped indium oxide (ITO) thin films by room temperature magnetron sputtering. Conductivities of up to $σ= 3300\,{\rm S/cm}$ are observed. The improved conductivity is not restricted to the interface but related to an enhanced crystallization of the films, which proceeds in the rhombohedral phase.
The electrical conductivity of a CdS thin film, controlled by grain structures is essential to enhance its photoconductivity to be able to be fit as a window material in CdS/CdTe heterojunction solar cell. In order to characterize a thin film, electromagnetically, we employed an open cavity resonator with a sub-millimeter VNA (Vector Network Analyzer). Our technique is capable of measuring complex dielectric permittivity, $\tildeε$, of a photovoltaic film as thin as 0.1 $μ$m. We measured the real part of the complex dielectric permittivity, $ε_{re}$, and electrical conductivity, $σ_{re}$ (deri…
A compound with metallic electrical conductivity usually has a considerable total thermal conductivity because both electrons and photons contribute to thermal transport. Here, we show an exceptional example of iridium oxide, Bi3Ir3O11, that concurrently displays metallic electrical conductivity and ultralow thermal conductivity approaching 0.61 W m-1 K-1 at 300 K. The compound crystallizes into a cubic structural framework with space group Pn-3. The edge- and corner-sharing IrO6 octahedra with a mixed Ir4.33+ charge state favor metallic electrical transport. Bi3Ir3O11 exhibits an extremely lo…
We propose a non-perturbative $ab$ $initio$ approach to calculate the electrical conductivity of a liquid metal. Our approach is based on the Kubo formula and the theory of electron-phonon coupling (EPC), and unlike the conventional empirical approach based on the Kubo-Greenwood formula, fully takes into account the effect of coupling between electrons and moving ions. We show that the electrical conductivity at high temperature is determined by an EPC parameter $λ_{\mathrm{tr}}$, which can be inferred, non-perturbatively, from the correlation of electron scattering matrices induced by ions. T…
The electrical conductivity and dielectric properties of Ni1.5Fe1.5O4 ferrite has been controlled by varying the annealing temperature of the chemical routed samples. The frequency activated conductivity obeyed Jonschers power law and universal scaling suggested semiconductor nature. An unusual metal like state has been revealed in the measurement temperature scale in between two semiconductor states with different activation energy. The metal like state has been affected by thermal annealing of the material. The analysis of electrical impedance and modulus spectra has confirmed non-Debye diel…
The thermodynamics of CaSiO3 in Earth's lower mantle
École Polytechnique Fédérale de Lausanne（洛桑联邦理工学院）；National Centre for Computational Design and Discovery of Novel Materials (MARVEL)（新材料计算设计与发现国家中心）；Paul Scherrer Institut（保罗谢尔研究所）；Università di Roma Sapienza（罗马第一大学）
Patterned structures of LaAlO3/SrTiO3 that exhibit a decrease in their electrical conductivity below 30 K, recover their higher conductivity upon warming in a thermally activated process. Two dominant energy barriers $E_b$ are identified: $E_{b1}=0.224\pm0.003$ eV related to conductivity recovery near 70 K and $E_{b2}=0.44\pm0.015$ eV related to conductivity recovery near 160 K. We discuss possible linkage to structural defects such as dislocations and twin boundaries.
The first electrical conductivity measurements of monoatomic carbon chains are reported in this study. The chains were obtained by unraveling carbon atoms from graphene ribbons while an electrical current flowed through the ribbon and, successively, through the chain. The formation of the chains was accompanied by a characteristic drop in the electrical conductivity. The conductivity of carbon chains was much lower than previously predicted for ideal chains. First-principles calculations using both density functional and many-body perturbation theory show that strain in the chains determines t…
We derive a formula for the electrical conductivity of solids that includes relaxation, dissipation, and quantum coherence. The derivation is based on the Kubo formula, with a Mori memory function approach to include dissipation effects at all orders in the relaxation interaction. It offers a practical method to evaluate the conductivity with electronic-structure codes and avoids the complications and limitations of the Kubo formula in the thermodynamic limit. The derivation of our formula provides a method applicable to other transport coefficients and correlation functions.
We compute the thermal conductivity and electrical resistivity of solid hcp Fe to pressures and temperatures of Earth's core. We find significant contributions from electron-electron scattering, usually neglected at high temperatures in transition metals. Our calculations show a quasi-linear relation between electrical resistivity and temperature for hcp Fe at extreme high pressures. We obtain thermal and electrical conductivities that are consistent with experiments considering reasonable error. The predicted thermal conductivity is reduced from previous estimates that neglect electron-electr…
We report the structural, magnetic and electrical transport properties of Y$_2$Ir$_{2-x}$Cr$_x$O$_7$ pyrochlore iridates. The chemical doping leads to order of magnitude enhancement of electrical conductivity. The introduction of Cr3+ at Ir4+ site tends to distort the Ir-O6 octahedra and suppresses antiferromagnetic correlation. The X-ray photoemission spectroscopy measurements suggest the coexistence of Ir4+ and Ir5+ valence states in the Y$_2$Ir$_{2-x}$Cr$_x$O$_7$ compounds. The concentration of Ir5+ is enhanced with Cr doping, leading to weak ferromagnetism and enhanced electrical conductiv…
We compute the electrical conductivity for liquid hydrogen at high pressure using quantum Monte Carlo. The method uses Coupled Electron-Ion Monte Carlo to generate configurations of liquid hydrogen. For each configuration correlated sampling of electrons is performed in order to calculate a set of lowest many-body eigenstates and current-current correlation functions of the system, which are summed over in the many-body Kubo formula to give AC electrical conductivity directly. The extrapolated DC conductivity at 3000 K for several densities shows a liquid semiconductor to liquid-metal transiti…
We investigate the minimum conductivity of graphene within a quasiclassical approach taking into account electron-hole coherence effects which stem from the chiral nature of low energy excitations. Relying on an analytical solution of the kinetic equation in the electron-hole coherent and incoherent cases we study both the electrical and thermal conductivity whose relation fullfills Wiedemann-Franz law. We found that the most of the previous findings based on the Boltzmann equation are restricted to only high mobility samples where electron-hole coherence effects are not sufficient.
We have characterized the electrical conductivity of the composite which consists of multi-walled carbon nanotubes dispersed in SU8 epoxy resin. Depending on the processing conditions of the epoxy (ranging from non-polymerized to cross-linked) we obtained tunneling and percolating-like regimes of the electrical conductivity of the composites. We interpret the observed qualitative change of the conductivity behavior in terms of reduced separation between the nanotubes induced by polymerization of the epoxy matrix.
The next-nearest neighbor interaction (NNN) is included in a tight-binding calculation of the electronic spectrum and conductivity of doped graphene. As a result, we observe a wide variation of the conductivity behavior, since the Fermi energy and the resonance peak are not shifted by the same amount. Such effect can have a profound effect in the idea of explaining the minimal conductivity of graphene as a consequence of impurities or defects. Finally, we also estimate the mean free path and relaxation time due to resonant impurity scattering.
Carbon nanotubes (CTNs) with large aspect-ratios are extensively used to establish electrical connectedness in polymer melts at very low CNT loadings. However, the CNT size polydispersity and the quality of the dispersion are still not fully understood factors that can substantially alter the desired characteristics of CNT nanocomposites. Here we demonstrate that the electrical conductivity of polydisperse CNT-epoxy composites with purposely-tailored distributions of the nanotube length L is a quasiuniversal function of the first moment of L. This finding challenges the current understanding t…
In the present work, the morphology and the electrical and thermal conduction properties of co-continuous poly(vinylidene fluoride) (PVDF), maleated polypropylene (PPgMA) and multiwall carbon nanotubes (CNT) nanostructured blends are investigated. CNT preferentially locates in the PPgMA phase and clearly causes a refinement in the co-continuous structure. Electrical conductivity experiments show that nanocomposites are well above the percolation threshold and evidence for one order of magnitude enhancement in conductivity for the co-continuous nanocomposites compared to the monophasic nanocomp…
The electrical conductivity of PVC films prepared with a patented plasticizer of type "A" was measured with high precision automated setup, based on standard ring sell with a voltage range much less than breakdown voltage. Continual voltage-current measurements permit to take into account Debay relaxation process and clearly distinguish specific polymer film conductivity effects, connected with continuous current-stabilization behavior and transitions between two stable (long-living) states with several order magnitude different conductivities. Spontaneous reversible and non-destructive transi…
Theory of electrical spin injection from a ferromagnetic (FM) metal into a normal (N) conductor is presented. We show that tunnel contacts (T) can dramatically increase spin injection and solve the problem of the mismatch in the conductivities of a FM metal and a semiconductor microstructure. We also present explicit expressions for the spin-valve resistance of FM-T-N- and FM-T-N-T-FM-junctions with tunnel contacts at the interfaces and show that the resistance includes both positive and negative contributions (Kapitza resistance and injection conductivity, respectively).
Conductive polymers or "organic metals" are highly engineered nanostructured materials made from organic building blocks. They are candidates as molecular wires for nanotechnology applications in molecular electronics. The conduction in these polymers is due to the presence of delocalized molecular orbitals. In this work, we present the synthesis of chloride doped polyaniline by bulk oxidative chemical polymerization using a solid aniline salt as a monomer instead of liquid aniline to diminish toxic hazards. The FTIR and UV-visible spectra confirmed the expected structure of the polymer. The e…
By using laboratory x-ray photoemission spectroscopy (XPS) and hard x-ray photoemission spectroscopy (HX-PES) at a synchrotron facility, we report an empirical semi-quantitative relationship between the valence/core-level x-ray photoemission spectral weight and electrical conductivity in La_{1-x}Sr_{x}MnO_{3} as a function of x. In the Mn 2p_{3/2} HX-PES spectra, we observed the shoulder structure due to the Mn^{3+} well-screened state. However, the intensity at x=0.8 was too small to explain its higher electrical conductivity than x=0.0, which confirms our recent analysis on the Mn 2p_{3/2} X…
CuI has been recently rediscovered as a p-type transparent conductor with a high figure of merit. Even though many metal iodides are hygroscopic, the effect of moisture on the electrical properties of CuI has not been clarified. In this work, we observe a two-fold increase in the conductivity of CuI after exposure to ambient humidity for 5 hours, followed by slight long-term degradation. Simultaneously, the work function of CuI decreases by almost 1 eV, which can explain the large spread in the previously reported work function values. The conductivity increase is partially reversible and is m…
Metal ion implantation into ceramics has been demonstrated to be an effective and controllable technique for tailoring the surface electrical conductivity of the ceramic piece, and this approach has been used in a number of applications. Importantly, it provides a method for grading the voltage drop across high voltage insulators, and thereby increasing the maximum operational voltage that can be applied across the insulator without surface flashover. However a concern for the use of the method is the long term stability of the implantation-induced conductivity, this especially so if the impla…
Cross-plane electrical and thermal transport in thin films of a conducting polymer (poly(3,4-ethylenedioxythiophene), PEDOT) stabilized with trifluoromethanesulfonate (OTf) is investigated in this study. We explore their electrical properties by conductive atomic force microscopy (C-AFM), which reveals the presence of highly conductive nano-domains. Thermal conductivity in cross-plane direction is measured with Null-Point scanning thermal microscopy (NP-SThM): PEDOT:OTf indeed demonstrates non-negligible electronic contribution to the thermal transport. We further investigate the correlation b…
We theoretically consider, comparing with the existing experimental literature, the electrical conductivity of gated monolayer graphene as a function of carrier density, temperature, and disorder in order to assess the prospects of accessing the Dirac point using transport studies in high-quality suspended graphene. We show that the temperature dependence of graphene conductivity around the charge neutrality point provides information about how close the system can approach the Dirac point although competition between long-range and short-range disorder as well as between diffusive and ballist…
We analyze a new family of carbon nanotube-based molecular wires, formed by encapsulating metallocene molecules inside the nanotubes. Our simulations, that are based on a combination of non-equilibrium Green function techniques and density functional theory, indicate that these wires can be engineered to exhibit desirable magnetotransport effects for use in spintronics devices. The proposed structures should also be resilient to room-temperature fluctuations, and are expected to have a high yield.
