Small Electrical Conductivity Research Articles

Three-dimensional carbon-coating silicon nanoparticles welded on carbon nanotubes composites for high-stability lithium-ion battery anodes

Although silicon (Si) is regarded as one of promising anode materials in next-generation lithium-ion batteries (LIBs) due to the high specific capacity, commercial application is stifled by the large volume effect and small electric conductivity. Using rice husk (RH) biomass as nano Si source (RH-Nano Si), here we designed and fabricated the three-dimensional (3D) carbon-hybridized nano-Si hierarchical architecture composite (RH-Nano Si@C/CNT) via assembling Si with CNT by the self-electrostatic route, reinforcing by hydrothermal treating in a glucose solution, and calcination in Ar. In RH-Nano Si@C/CNT, the Si nanoparticles are anchored on the 3D conductive CNT network by the glucose-derived carbon through welding and coating, thus providing enhanced electrical contact and high structural integrity. As anode materials, RH-Nano Si@C/CNT exhibits improved rate capability and prolonged cycling stability compared to Si and CNT self-electrostatic sample. Boasting a high reversible capacity of 989.5 mAh g−1 at 0.5C (1C = 4.2 A g−1) and 345 mAh g−1 at 3C as well as low capacity decay of 0.035% per cycles after 1000 cycles, RH-Nano Si@C/CNT produced by this technique is promising as anodes in LIBs.

Dyshidrosis is associated with reduced amplitudes in electrically evoked pain-related potentials in women with Fabry disease

ObjectiveTo investigate A-delta fiber conduction in mild to moderate Fabry disease (FD) patients using pain-related evoked potentials (PREP). MethodsIn this case-control study we prospectively investigated 58 patients with mild to moderate FD and compared data with those of healthy controls. Small fiber function (quantitative sensory testing, QST and sympathetic skin response, SSR), morphology (intraepidermal nerve fiber density, IENFD), and electrical conduction (PREP) were assessed and correlated with sweating as major autonomic function disturbed in FD. Patients were further stratified for gender, disease severity as reflected by renal and cardiac function, and genetics. ResultsAn- or hypohidrosis (i.e. dyshidrosis) was reported by 7/32 (22%) women and 15/26 (58%) men with FD (p < 0.01). QST showed small fiber impairment in female and male patients regardless of clinical symptoms, while SSR was obtained in all patients except one man with hypohidrosis. IENFD was reduced in 50% of FD patients, with no differences between groups with and without autonomic symptoms. However, PREP amplitudes were reduced independent of the stimulation site only in female patients with dyshidrosis (p < 0.01). Genetics had no influence on PREP parameters. ConclusionA-delta fiber conduction investigated using PREP is impaired in mild to moderately affected female FD patients with clinical signs of hypohidrosis. SignificanceSmall fiber assessment in FD is of diagnostic value already in mild to moderate stages of disease.

Ohmic graphite-metal contacts on oxygen-terminated lightly boron-doped CVD monocrystalline diamond

A process to obtain ohmic contacts on oxygen-terminated lightly boron-doped CVD monocrystalline diamond films was developed. Samples were contacted by Ti/Au metallic pads in the transmission line model (TLM) configuration. The electric contacts were placed onto a mesa structure produced on the CVD boron-doped layer. One of the samples was additionally implanted with helium ions at 10 keV in order to induce the formation of a graphitic layer underneath the diamond surface before contacting so as to improve electrical conduction. The electrical performance of both devices was characterized by the TLM method and compared. As a result, the sample with metallic electrodes exhibited a small and non-linear electrical conduction, while the graphitic/metallic contacts showed an ohmic behaviour with an estimated specific contact resistance as low as 3.3 × 10−4 Ω·cm2 for a doping level of a few 1017 cm−3. This approach opens the way to more efficient ohmic contacts on intrinsic or low-doped diamond that are crucial for the development of electronic devices and detectors.

Hydromagnetic Oscillatory Slip Flow of a Visco-elastic Fluid through a Porous Channel

An investigation is carried out to study the effects of suction/injection on the slip flow of oscillatory visco-elastic hydromagnetic flow through a vertical porous channel. It is considered that the fluid has small electrical conductivity and the electro-magnetic force produced is also very small. The flow is subjected to suction at the cold wall and injection at the heated wall. Under the Boussinesq’s approximation, the governing equations are solved using multiparameter perturbation technique. The effects of pertinent flow parameters on fluid velocity, temperature, shearing stress, the rate of heat transfer is obtained and illustrated graphically. This study plays an important role in physiological, industrial and hydrological problems under suitable conditions.

Experimental and theoretical investigations for describing pressure dependence of amplified spontaneous emission output energy, small signal gain and electrical conductivity in nitrogen lasers

An experimental arrangement consists of an oscillator amplifier (OSC-AMP) N2 laser system having electrodes of different lengths, lAMP, was used to measure the amplified spontaneous emission (ASE) output energy extracted from the AMP section at different gas pressure, pAMP, and also the AMP small signal gain, g0 at a constant pAMP. It was observed that the extracted ASE output energy with respect to operational gas pressure has a non-symmetrical character. For explaining the observed behavior two different models for numerical calculations were applied for the results to be compared with each other and also with the experimental observations. The first model, i.e. the model of geometrically dependent gain coefficient (GDGC) was found to explain the pressure dependencies the observed behaviors of threshold and saturation lengths. The second model, which is based on using rate equations for N2 lasers, coupled to the circuit electric discharge was used to calculate the pressure dependences of the ASE output energy and small signal gain. The results showed that ASE output energy versus gas pressure had a symmetrical behavior and within a limited range of gas pressure, small signal gain is a constant value. As geometrically the small signal gain and the electrical conductivity behave similarly, the model was also applied for predicting the pressure dependence of the electrical conductivity. Calculations of g0 vs. lAMP at pAMP = 90 Torr based on applying both models are comparable with the measurements. It is concluded that the GDGC model can be suitably used for predictions of small signal gain, threshold and saturation lengths provided that ASE experimental measurements are available. The modified rate equations, on the other hand, can give appropriate results in absence of experimental measurements.

Partial Element Equivalent Circuit Method Modeling of Silicon Interconnects

A new integral-equation-based formulation is presented enabling the modeling of lossy dielectrics, such as silicon, in the framework of the partial element equivalent circuit (PEEC) method, in the time domain. Due to the reduced value of conductivity of the lossy dielectric, charge is not restricted to its surface, e.g., the relaxation time is not as small as in standard conductors. This requires the PEEC method to be reformulated in order to consider both the conductivity of the dielectric material and the reduced value of the electrical conductivity, which prevents the charge to be located only on the surfaces. The proposed new PEEC model is validated through comparison with results available from the theory and commercial software. Then, the proposed method is used to analyze two silicon interconnects showing how the finite even small electrical conductivity of silicon may have a significant impact on the results compared with the ideal behavior of the dielectric.

Effect of calcination temperature on structure and thermoelectric properties of CuAlO2 powders

Copper aluminum oxide (CuAlO2) with delafossite phase was synthesized by the Pechini method using different calcination temperatures to evaluate its influence on the structure and thermoelectric material properties. X-ray diffraction and Raman spectroscopy confirm that delafossite phase was formed at 1100 °C with the presence of 2H-CuAlO2 and Al2O3 impurities, while at lower calcination temperatures (900 and 1000 °C), a mixture of CuO + CuAl2O4 (spinel phase) was observed. Energy-dispersive X-ray elemental maps display an even distribution of copper, aluminum and oxygen in the sample calcined at 1100 °C. Direct optical band gap, E g = 3.6 eV, was calculated from reflectance diffuse spectra by Kubelka–Munk and Tauc methods. An absorption band at 1.7 eV accounts for defect levels, masking the characteristic indirect transition. The thermoelectric properties, such as Seebeck coefficient, and thermal and electrical conductivities of the sample calcined at 1100 °C were measured at different temperatures. Hall voltage and positive values of the Seebeck coefficient (425.8–434.4 µV K−1) confirm the material’s p-type character. The independence of the Seebeck coefficient on the operation temperature indicates a small polaron electrical conduction mechanism. Thermal conductivity decreases exponentially with the temperature from 43.45 to 23.9 W m−1 K−1, where the principal contribution is due to phonons. Figure of merit ZT of sample calcined at 1100 °C between 100 and 800 °C increases from 1.42 × 10−8 to 4.94 × 10−4 in the order of the literature reports. From the Arrhenius plot ln(σT) versus 1000/T, an activation energy E a = 0.32 eV for the electrical conductivity was calculated.

Towards MXPn‐Type Compounds in the Systems Ge‐I‐Pn (Pn = P, As) – New Insights in the Structures and Properties of Inverse Type I Clathrates

Two ternary systems, Ge‐I‐P and Ge‐I‐As were investigated for the existence of double helical GeIPn phases (Pn = P, As). However, experiments in the temperature range of 673–1073 K always led to the formation of inverse type I clathrates. Optimization of the synthesis parameters resulted in phase pure samples for both clathrates on a gram scale. We found slightly varying compositions than for clathrates reported before in the two systems. Structural characterization by means of single crystal analysis and Rietveld refinement showed a defect model for the guest structures in combination with a mixed site occupancy for the host lattice sites. Both compounds reveal promising thermal conductivities and Seebeck coefficients but only small overall electrical conductivities.

Preparation and dielectric properties of CaTaO2N and SrNbO2N ceramics

A new approach for the synthesis of perovskite oxynitride ceramics via ammonolysis of thin pellets of their corresponding oxide precursors is reported. Phase-pure CaTaO2N- and SrNbO2N-ceramics with relative densities up to 78% were obtained by ammonolysis of Ca2Ta2O7- and Sr2Nb2O7-pellets with ≈10% porosities at 950°C (SrNbO2N) and 1100°C (CaTaO2N). The oxynitride samples were investigated with respect to their optical, thermal and dielectric properties. Temperature- and frequency-dependent impedance measurements revealed that CaTaO2N is an insulator at room temperature with a relative permittivity in the order of 100. In contrast, SrNbO2N exhibits a high relative bulk permittivity of ε′=25000 and a comparatively high bulk conductivity of 1.6×10−4Scm−1 at room temperature. At elevated temperatures, the evolving small electrical conductivity of CaTaO2N can be assigned to the formation of thermally activated electron-hole pairs. For SrNbO2N two defect-dominated conduction paths can be distinguished and related to grain boundary and bulk conductivity, respectively.

Relating electrical resistivity to permeability using resistor networks

We use resistor network models to explore the relationship between electrical resistivity and permeability in fractures filled with an electrically conductive fluid. The fracture aperture distribution is determined by generating fracture surface pairs that are constructed based on characteristics measured on rock samples. We use these to generate and solve resistor networks with variable hydraulic and electrical resistance. The aperture is incrementally increased, to analyse the changes in both properties as a fault is opened. At small apertures, electrical conductivity and permeability increase moderately with aperture until the fault reaches its percolation threshold. Above this point, the permeability increases by four orders of magnitude over a change in mean aperture of less than 0.1 mm, while the resistivity decreases by up to a factor of 10. The permeability increases at a greater rate than the conductivity, and therefore the percolation threshold can be defined in terms of the matrix to fracture resistivity ratio, M. The value of M at the percolation threshold, MPT, varies with the ratio of rock to fluid resistivity, the fault spacing, and the fault offset but is always less than 10. Greater M values are associated with fractures above their percolation threshold and therefore open for fluid flow.

Physical and photoelectrochemical characterizations of the pyrochlore La1.9Ba0.1Sn2O7: Application to chromate reduction under solar light

Abstract The substituted pyrochlore La 1.9 Ba 0.1 Sn 2 O 7 was prepared by nitrate route and the physical and electrochemical characterizations were investigated. The optical gap is found to be 3.01 eV and the conductivity is characteristic of a semiconducting behavior with activation energy of 0.42 eV. The conduction band of La 1.9 Ba 0.1 Sn 2 O 7 (−2.64 V SCE ), predicted from electro negativities of the constituent atoms, is close to that determined experimentally (−2.99 V SCE ). The capacitance measurement (C −2 –V) exhibits a linear behavior, characteristic of p type conductivity, from which a flat band potential of −0.05 V SCE and hole density N D of 8.42 × 10 14 cm −3 were determined, in agreement with the small electrical conductivity (σ 300K ∼3 × 10 −6 Ω −1 cm −1 ). The Nyquist plot showed a semicircle which is a contribution of capacitance and resistance in parallel. A bulk resistance contribution (R b = 71 kΩ cm 2 ) and a low density of surface states are observed. The center of the arc is localized below the real axis with a depletion angle of 14° ascribed to a constant phase element (CPE). As application, chromate was successfully converted to Cr 3+ on the pyrochlore under sunlight. ∼1 h was necessary to reach the adsorption equilibrium for an initial chromate concentration of 10 −4 M. The conduction band is more cathodic than the potential of HCrO 4 − which is spontaneously reduced under solar light. The best performance is obtained at pH ∼ 3 with a catalyst dose of 1 mg/mL. 40% of chromate disappears with a quantum yield of 0.53% in less than 2 h. The process obeys to a first order kinetic with an apparent rate constant of 2.3 × 10 −3 min −1 .

Water sources for cyanobacteria below desert rocks in the Negev Desert determined by conductivity

We present year round meteorological and conductivity measurements of colonized hypolithic rocks in the Arava Valley, Negev Desert, Israel. The data indicate that while dew is common in the Negev it is not an important source of moisture for hypolithic organisms at this site. The dominance of cyanobacteria in the hypolithic community is consistent with predictions that cyanobacteria are confined to habitats supplied by rain. To monitor the presence of liquid water under the small Negev rocks we developed and tested a simple field conductivity system based on two wires placed about 0.5 cm apart. Based on 21 replicates recorded for one year in the Negev we conclude that in natural rains (0.25 mm to 6 mm) the variability between sensor readings is between 20 and 60% decreasing with increasing rain amount. We conclude that the simple small electrical conductivity system described here can be used effectively to monitor liquid water levels in lithic habitats. However, the natural variability of these sensors indicates that several replicates should be deployed. The results and method presented have use in arid desert reclamation programs.

Relating permeability and electrical resistivity in fractures using random resistor network models

AbstractWe use random resistor network models to explore the relationship between electrical resistivity and permeability in a fracture filled with an electrically conductive fluid. Fluid flow and current are controlled by both the distribution and the volume of pore space. Therefore, the aperture distribution of fractures must be accurately modeled in order to realistically represent their hydraulic and electrical properties. We have constructed fracture surface pairs based on characteristics measured on rock samples. We use these to construct resistor networks with variable hydraulic and electrical resistance in order to investigate the changes in both properties as a fault is opened. At small apertures, electrical conductivity and permeability increase moderately with aperture until the fault reaches its percolation threshold. Above this point, the permeability increases by 4 orders of magnitude over a change in mean aperture of less than 0.1 mm, while the resistivity decreases by up to a factor of 10 over this aperture change. Because permeability increases at a greater rate than matrix to fracture resistivity ratio, the percolation threshold can also be defined in terms of the matrix to fracture resistivity ratio, M. The value of M at the percolation threshold, MPT, varies with the ratio of rock to fluid resistivity, the fault spacing, and the fault offset. However, MPT is almost always less than 10. Greater M values are associated with fractures above their percolation threshold. Therefore, if such M values are observed over fluid‐filled fractures, it is likely that they are open for fluid flow.

Study on Exploding Wire Compression for Evaluating Electrical Conductivity in Warm-Dense Diamond-Like-Carbon

To improve a coupling efficiency for the fast ignition scheme of the inertial confinement fusion, fast electron behaviors as a function of an electrical conductivity are required. To evaluate the electrical conductivity for low-Z materials as a diamond-like-carbon (DLC), we have proposed a concept to investigate the properties of warm dense matter (WDM) by using pulsed-power discharges. The concept of the evaluation of DLC for WDM is a shock compression driven by an exploding wire discharge with confined by a rigid capillary. The qualitatively evaluation of the electrical conductivity for the WDM DLC requires a small electrical conductivity of the exploding wire. To analyze the electrical conductivity of exploding wire, we have demonstrated an exploding wire discharge in water for gold. The results indicated that the electrical conductivity of WDM gold for 5000 K of temperature has an insulator regime. It means that the shock compression driven by the exploding wire discharge with confined by the rigid capillary is applied for the evaluation of electrical conductivity for WDM DLC.

Amplitudes of Pain-Related Evoked Potentials Are Useful to Detect Small Fiber Involvement in Painful Mixed Fiber Neuropathies in Addition to Quantitative Sensory Testing - An Electrophysiological Study.

To investigate the usefulness of pain-related evoked potentials (PREP) elicited by electrical stimulation for the identification of small fiber involvement in patients with mixed fiber neuropathy (MFN). Eleven MFN patients with clinical signs of large fiber impairment and neuropathic pain and ten healthy controls underwent clinical and electrophysiological evaluation. Small fiber function, electrical conductivity and morphology were examined by quantitative sensory testing (QST), PREP, and skin punch biopsy. MFN was diagnosed following clinical and electrophysiological examination (chronic inflammatory demyelinating neuropathy: n = 6; vasculitic neuropathy: n = 3; chronic axonal ­neuropathy: n = 2). The majority of patients with MFN characterized their pain by descriptors that mainly represent C-fiber-mediated pain. In QST, patients displayed elevated cold, warm, mechanical, and vibration detection thresholds and cold pain thresholds indicative of MFN. PREP amplitudes in patients correlated with cold (p < 0.05) and warm detection thresholds (p < 0.05). Burning pain and the presence of par-/dysesthesias correlated negatively with PREP amplitudes (p < 0.05). PREP amplitudes correlating with cold and warm detection thresholds, burning pain, and par-/dysesthesias support employing PREP amplitudes as an additional tool in conjunction with QST for detecting small fiber impairment in patients with MFN.

Giant Seebeck effect in pure fullerene thin films

The small thermal conductivity of molecular solids is beneficial for their thermoelectric applications. If Seebeck coefficients were sufficiently large to compensate for the relatively small electrical conductivity, these materials would be promising candidates for thermoelectric devices. In this work, the thermoelectric properties of C60 were studied by in situ measurements under ultrahigh vacuum after the deposition of a pure C60 thin film. An exceptionally large Seebeck coefficient of more than 150 mV/K was observed as a steady-state thermoelectromotive force. Even considering several extreme but realistic conditions, conventional semiclassical thermoelectric theories cannot explain this giant Seebeck effect.

Monitoring CO2 migration in a shallow sand aquifer using 3D crosshole electrical resistivity tomography

Three-dimensional (3D) crosshole electrical resistivity tomography (ERT) was used to monitor a pilot CO2 injection experiment at Vrøgum, western Denmark. The purpose was to evaluate the effectiveness of the ERT method for detection of small electrical conductivity (EC) changes during the first 2 days of CO2 injection in a shallow siliciclastic aquifer and to study the early-time behavior of a controlled small gaseous CO2 release. 45kg of CO2 was injected over a 50-h period at 9.85m depth. ERT data were collected using horizontal bipole-bipole (HBB) and vertical bipole-bipole (VBB) arrays. The combined HBB and VBB data sets were inverted using a difference inversion algorithm for cancellation of coherent noises and enhanced resolution of small changes. ERT detected the small bulk EC changes (<10%) from conductive dissolved CO2 and resistive gaseous CO2. The primary factors that control the migration of a CO2 plume consist of buoyancy of gaseous CO2, local heterogeneity, groundwater flow and external pressure exerted by the injector. The CO2 plume at the Vrøgum site migrated mostly upward due to buoyancy and it also skewed toward northeastern region by overcoming local groundwater flow. The conductive eastern part is more porous and becomes the preferential pathway for the CO2 plume, which was trapped within the slightly more porous glacial sand layer between 5m and 10m depths. The gaseous and dissolved CO2 plumes are collocated and grow in tandem for the first 24h and their opposite effects resulted in a small bulk EC increase. After raising the injection rate from 10g/min to 20g/min at the 24-h mark, the CO2 plume grew quickly. The bulk EC changes from ERT agreed partially with water sample EC and GPR data. The apparent disagreement between high CO2 gas saturation and prevailing positive bulk EC changes may be caused by limited and variable ERT resolution, low ERT sensitivity to resistive anomalies and uncalibrated CO2 gas saturation. ERT data show a broader CO2 plume while water sample EC had higher fine-scale variability. Our ERT electrode configuration can be optimized for more efficient data acquisition and better spatial resolution.

Magnetic properties of novel magnetic porous glass-based multiferroic nanocomposites

In this paper we report on the first experimental studies of the magnetic and electric properties of the ferroelectric materials incorporated in magnetic porous glasses with the controlled pore size. This new material exhibits very small electrical conductivity which allows us to examine the dielectric and magnetoelectric characteristics of these porous glasses concerning magnetite. The magnetic measurements of empty porous glasses and glasses with multiferroic nanocomposites demonstrate the Verwey transition in magnetite. Ferroelectric phase transitions were observed together with hysteresis loops as irrefutable proof of the ferroelectricity in multiferroic nanocomposites based on magnetic porous glasses. The observed exceptional electrical properties show large potential of this novel group of multiferroics for modern applications.

Eddy current pulsed phase thermography considering volumetric induction heating for delamination evaluation in carbon fiber reinforced polymers

Anisotropy and inhomogeneity of carbon fiber reinforced polymers (CFRPs) result in that many traditional non-destructive inspection techniques are inapplicable on the delamination evaluation. This letter introduces eddy current pulsed phase thermography (ECPPT) for CFRPs evaluation considering volumetric induction heating due to small electrical conductivity, abnormal thermal wave propagation, and Fourier analysis. The proposed methods were verified through experimental studies under transmission and reflection modes. Using ECPPT, the influence of the non-uniform heating effect and carbon fiber structures can be suppressed, and then delamination detectability can be improved dramatically over eddy current pulsed thermography.

Fabrication of LSM-SDC composite cathodes for intermediate-temperature solid oxide fuel cells

Microstructure, interfacial resistance, and activation energy for composite cathodes consisting of 50 wt% (La0.85Sr0.15)0.9MnO3-δ (LSM) and 50 wt% Sm0.2Ce0.8O1.90 (SDC) were studied for intermediate-temperature solid oxide fuel cells based on SDC electrolytes. Microstructure and interfacial resistance were greatly influenced by the characteristics of starting powder and temperatures sintering the electrodes. Optimum sintering temperatures were 1100 and 950 °C, respectively, for electrodes with SDC prepared using oxalate coprecipitation technique (OCP) and glycine-nitrate process (GNP). Area-specific resistances determined using impedance spectroscopy were 0.47 and 0.92 Ω cm2 at 800 °C for LSM-SDC/OCP and LSM-SDC/GNP, respectively. The high electrochemical performance is attributed to small grain size, high porosity, and high in-plane electrical conductivity of composite cathode, demonstrating the dramatic effects of microstructure on electrode performance. To increase the electrode performance, it is critical to enhance the diffusion rate of oxygen species.