Improvement of electrical conductivity in Pb0.96-yMn0.04SnyTe alloys for high temperature thermoelectric applications

Lead-tin-telluride is a well-known thermoelectric material in the temperature range 350-750 K. Here, this alloy doped with manganese (Pb0.96-yMn0.04SnyTe) was prepared for different amounts of tin. X-ray diffraction showed a decrease of the lattice constant with increasing tin content, which indicated solid solution formation. Microstructural analysis showed a wide distribution of grain sizes from <1 mu m to 10 mm and the presence of a SnTe rich phase. All the transport properties were measured in the range of 300-720 K. The Seebeck coefficient showed that all the samples were p-type indicating holes as dominant carriers in the measurement range. The magnitude increased systematically on reduction of the Sn content due to possible decreasing hole concentration. Electrical conductivity showed the degenerate nature of the samples. Large values of the electrical conductivity could have possibly resulted from a large hole concentration due to a high Sn content and secondly, due to increased mobility by sp-d orbital interaction between the Pb1-ySnyTe sublattice and the Mn2+ ions. High thermal conductivity was observed due to higher electronic contribution, which decreased systematically with decreasing Sn content. The highest zT = 0.82 at 720 K was obtained for the alloy with the lowest Sn content (y = 0.56) due to the optimum doping level.

High pressure studies on the electrical resistivity of Ge-Te-Tl glasses

The variation of electrical resistivity in the system of glasses Ge17Te83-xTlx, with (1 <= x <= 13), has been studied as a function of high pressure for pressures up to 10 GPa. It is found that the normalized electrical resistivity decreases continuously with the increase in pressure and shows a sudden drop at a particular pressure (transition pressure), indicating the presence of a transition from semiconductor to near-metallic at these pressures which are in the range 3.0-5.0 GPa. This transition pressure is seen to decrease with the increase in the percentage content of thallium due to increasing metallicity of the thallium. The transition is reversible under application of pressure and X-ray diffraction of samples recovered after pressurization show that they remain amorphous after undergoing a pressurization decompression cycle.

A Continuous Electrical Conductivity Model for Monolayer Graphene From Near Intrinsic to Far Extrinsic Region

We present a closed-form continuous model for the electrical conductivity of a single layer graphene (SLG) sheet in the presence of short-range impurities, long-range screened impurities, and acoustic phonons. The validity of the model extends from very low doping levels (chemical potential close to the Dirac cone vertex) to very high doping levels. We demonstrate complete functional relations of the chemical potential, polarization function, and conductivity with respect to both doping level and temperature (T), which were otherwise developed for SLG sheet only in the very low and very high doping levels. The advantage of the continuous conductivity model reported in this paper lies in its simple form which depends only on three adjustable parameters: the short-range impurity density, the long-range screened impurity density, and temperature T. The proposed theoretical model was successfully used to correlate various experiments in the midtemperature and moderate density regimes.

Frequency and Temperature-Independent Electrical Transport Properties of 2BaO-0.5Na(2)O-2.5Nb(2)O(5)-4.5B(2)O(3) Glass-Ceramics

The temperature (300-973K) and frequency (100Hz-10MHz) response of the dielectric and impedance characteristics of 2BaO-0.5Na(2)O-2.5Nb(2)O(5)-4.5B(2)O(3) glasses and glass nanocrystal composites were studied. The dielectric constant of the glass was found to be almost independent of frequency (100Hz-10MHz) and temperature (300-600K). The temperature coefficient of dielectric constant was 8 +/- 3ppm/K in the 300-600K temperature range. The relaxation and conduction phenomena were rationalized using modulus formalism and universal AC conductivity exponential power law, respectively. The observed relaxation behavior was found to be thermally activated. The complex impedance data were fitted using the least square method. Dispersion of Barium Sodium Niobate (BNN) phase at nanoscale in a glass matrix resulted in the formation of space charge around crystal-glass interface, leading to a high value of effective dielectric constant especially for the samples heat-treated at higher temperatures. The fabricated glass nanocrystal composites exhibited P versus E hysteresis loops at room temperature and the remnant polarization (P-r) increased with the increase in crystallite size.

Tin-Incorporation Induced Changes in the Microstructural, Optical, and Electrical Behavior of Tungsten Oxide Nanocrystalline Thin Films Grown Via Spray Pyrolysis

Undoped and Sn-doped WO3 thin films were grown on cleaned glass substrates by chemical spray pyrolysis, using ammonium tungstate (NH4)(2)WO4 as the host precursor and tin chloride (SnCl4 center dot 5H(2)O) as the source of dopant. The XRD spectra confirm the monoclinic structure with a sharp narrow peak along (200) direction along with other peaks of low relative intensities for all the samples. On Sn doping, the films exhibit reduced crystallinity relative to the undoped film. The standard deviation for relative peak intensity with dopant concentration shows enhancement in heterogeneous nucleation growth. As evident from SEM images, on Sn doping, appearance of island-like structure (i.e., cluster of primary crystallites at few places) takes place. The transmittance has been found to decrease in all the Sn-doped films. The optical band gap has been calculated for both direct and indirect transitions. On Sn doping, the direct band gap shows a red shift and becomes 2.89 eV at 2 at.% doping. Two distinct peaks, one blue emission at 408 nm and other green emission at 533 nm, have been found in the PL spectra. Electrical conductivity has been found to increase with Sn doping.

Application of Qualitative Imaging Methods to Electrical Performance-Aware Package Board Design

Package-board co-design plays a crucial role in determining the performance of high-speed systems. Although there exist several commercial solutions for electromagnetic analysis and verification, lack of Computer Aided Design (CAD) tools for SI aware design and synthesis lead to longer design cycles and non-optimal package-board interconnect geometries. In this work, the functional similarities between package-board design and radio-frequency (RF) imaging are explored. Consequently, qualitative methods common to the imaging community, like Tikhonov Regularization (TR) and Landweber method are applied to solve multi-objective, multi-variable package design problems. In addition, a new hierarchical iterative piecewise linear algorithm is developed as a wrapper over LBP for an efficient solution in the design space.

Structural, Magnetic, and Electrical Properties of Microwave-Sintered Cr3+-Doped Sr Hexaferrites

SrCrxFe12-xO19 (x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9) hexaferrites were prepared by a microwave-hydrothermal method and subsequently sintered at 950 degrees C for 90 min using the microwave sintering method. The results show that, with increasing Cr3+ content, the lattice parameters changed anisotropically. The average grain sizes of sintered samples were in the range of 280 nm to 660 nm. The saturation magnetization systematically decreased with increasing Cr3+ doping, but the coercivity values increased. The electrical resistivity (log rho) decreased linearly with increasing temperature up to a certain temperature known as the transition temperature (T-c), and T-c decreased with further increase (x>0.5) of the Cr3+ content. This decrease in log rho and the activation energy (E-g) is due to electron hopping and occupancy of doped ions at different lattice sites. We found that the dielectric constant and dielectric loss for all the samples decreased with the Cr3+ content. The structural, magnetic, and electrical properties of Cr3+-doped SrFe12O19 hexaferrites have thus been investigated.

Study the effect of electrical and mechanical shock loading on liberation and milling characteristics of mineral materials

Milling is an energy intensive process and it is considered as one of the most energy inefficient processes. Electrical and mechanical shock loading can be used to develop a pre-treatment methodology to enhance energy efficiency of comminution and liberation of minerals. Coal and Banded Hematite Jasper (BHJ) Iron ores samples were taken for the study to know the effect of shock loading. These samples were exposed to 5 electric shocks of 300 kV using an electric shock loading device. A diaphragmless shock tube was used to produce 3 and 6 compressed air shocks of Mach number 2.12 to treat the coal and Iron ore samples. Microscopic, comminution and liberation studies were carried out to compare the effectiveness of these approaches. It was found that electric shock loading can comminute the coal samples more effectively and increases the yield of carbon by 40% at 1.6 gm/cc density over the untreated coal samples. Mechanical shock loading showed improved milling performance for both the materials and 12.90% and 8.1% reduction in the D-80 of the particles was observed during grinding for treated samples of coal and iron, respectively. Liberation of minerals in BHJ Iron ore was found unaffected due to low intensity of the mechanical shock waves and non conductivity of minerals. Compressed air based shock loading is easier to operate than electrical shock loading and it needs to be explored further to improve the energy efficacy of comminution. (C) 2014 Elsevier Ltd. All rights reserved.

Effect of Line Defects on the Electrical Transport Properties of Monolayer MoS2 Sheet

We present a computational study on the impact of line defects on the electronic properties of monolayer MoS2. Four different kinds of line defects with Mo and S as the bridging atoms, consistent with recent theoretical and experimental observations, are considered herein. We employ the density functional tight-binding (DFTB) method with a Slater-Koster-type DFTB-CP2K basis set for evaluating the material properties of perfect and the various defective MoS2 sheets. The transmission spectra are computed with a DFTB-non-equilibrium Green's function formalism. We also perform a detailed analysis of the carrier transmission pathways under a small bias and investigate the phase of the transmission eigenstates of the defective MoS2 sheets. Our simulations show a two to four fold decrease in carrier conductance of MoS2 sheets in the presence of line defects as compared to that for the perfect sheet.

Growth and electrical transport properties of InGaN/GaN heterostructures grown by PAMBE

InGaN epitaxial films were grown on GaN template by plasma-assisted molecular beam epitaxy. The composition of indium incorporation in single phase InGaN film was found to be 23%. The band gap energy of single phase InGaN was found to be similar to 2.48 eV: The current-voltage (I-V) characteristic of InGaN/GaN heterojunction was found to be rectifying behavior which shows the presence of Schottky barrier at the interface. Log-log plot of the I-V characteristics under forward bias indicates the current conduction mechanism is dominated by space charge limited current mechanism at higher applied voltage, which is usually caused due to the presence of trapping centers. The room temperature barrier height and the ideality factor of the Schottky junction were found to 0.76 eV and 4.9 respectively. The non-ideality of the Schottky junction may be due to the presence of high pit density and dislocation density in InGaN film. (C) 2014 Elsevier Ltd. All rights reserved.

Role of electrical resistance of electrodes in modeling of discharging and charging of flooded lead-acid batteries

Electrical resistance of both the electrodes of a lead-acid battery increases during discharge due to formation of lead sulfate, an insulator. Work of Metzendorf 1] shows that resistance increases sharply at about 65% conversion of active materials, and battery stops discharging once this critical conversion is reached. However, these aspects are not incorporated into existing mathematical models. Present work uses the results of Metzendorf 1], and develops a model that includes the effect of variable resistance. Further, it uses a reasonable expression to account for the decrease in active area during discharge instead of the empirical equations of previous work. The model's predictions are compared with observations of Cugnet et al. 2]. The model is as successful as the non-mechanistic models existing in literature. Inclusion of variation in resistance of electrodes in the model is important if one of the electrodes is a limiting reactant. If active materials are stoichiometrically balanced, resistance of electrodes can be very large at the end of discharge but has only a minor effect on charging of batteries. The model points to the significance of electrical conductivity of electrodes in the charging of deep discharged batteries. (C) 2014 Elsevier B.V. All rights reserved.

Domain size correlated magnetic properties and electrical impedance of size dependent nickel ferrite nanoparticles

We report here the investigations on the size dependent variation of magnetic properties of nickel ferrite nanoparticles. Nickel ferrite nanoparticles of different sizes (14 to 22 nm) were prepared by the sol-gel route at different annealing temperatures. They are characterized by TGA-DTA, XRD, SEM, TEM and Raman spectroscopy techniques for the confirmation of the temperature of phase formation, thermal stability, crystallinity, morphology and structural status of the nickel ferrite nanoparticles. The magnetization studies revealed that the saturation magnetization (M-s), retentivity (M-r) increase, while coercivity (H-c) and anisotropy (K-eff) decrease as the particle size increases. The observed value of M-s is found to be relatively higher for a particle size of 22 nm. In addition, we have estimated the magnetic domain size using magnetic data and correlated to the average particle size. The calculated magnetic domain size is closely matching with the particle size estimated from XRD. Impedance spectroscopy was employed to study the samples in an equivalent circuit to understand their transport phenomena. It shows that nickel ferrite nanoparticles exhibit a non-Debye behavior with increasing particle size due to the influence of increasing disorders, surface effects, grain size and grain boundaries, etc. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

Calcium Permeable AMPA Receptor-Dependent Long Lasting Plasticity of Intrinsic Excitability in Fast Spiking Interneurons of the Dentate Gyrus Decreases Inhibition in the Granule Cell Layer

The local fast-spiking interneurons (FSINs) are considered to be crucial for the generation, maintenance, and modulation of neuronal network oscillations especially in the gamma frequency band. Gamma frequency oscillations have been associated with different aspects of behavior. But the prolonged effects of gamma frequency synaptic activity on the FSINs remain elusive. Using whole cell current clamp patch recordings, we observed a sustained decrease of intrinsic excitability in the FSINs of the dentate gyrus (DG) following repetitive stimulations of the mossy fibers at 30 Hz (gamma bursts). Surprisingly, the granule cells (GCs) did not express intrinsic plastic changes upon similar synaptic excitation of their apical dendritic inputs. Interestingly, pairing the gamma bursts with membrane hyperpolarization accentuated the plasticity in FSINs following the induction protocol, while the plasticity attenuated following gamma bursts paired with membrane depolarization. Paired pulse ratio measurement of the synaptic responses did not show significant changes during the experiments. However, the induction protocols were accompanied with postsynaptic calcium rise in FSINs. Interestingly, the maximum and the minimum increase occurred during gamma bursts with membrane hyperpolarization and depolarization respectively. Including a selective blocker of calcium-permeable AMPA receptors (CP-AMPARs) in the bath; significantly attenuated the calcium rise and blocked the membrane potential dependence of the calcium rise in the FSINs, suggesting their involvement in the observed phenomenon. Chelation of intracellular calcium, blocking HCN channel conductance or blocking CP-AMPARs during the experiment forbade the long lasting expression of the plasticity. Simultaneous dual patch recordings from FSINs and synaptically connected putative GCs confirmed the decreased inhibition in the GCs accompanying the decreased intrinsic excitability in the FSINs. Experimentally constrained network simulations using NEURON predicted increased spiking in the GC owing to decreased input resistance in the FSIN. We hypothesize that the selective plasticity in the FSINs induced by local network activity may serve to increase information throughput into the downstream hippocampal subfields besides providing neuroprotection to the FSINs. (c) 2014 Wiley Periodicals, Inc.

Design and Testing of a Control System for Supply Side Electrical Load Management

India's energy demand is increasing rapidly with the intensive growth of economy. The electricity demand in India exceeded the availability, both in terms of base load energy and peak availability. The efficient use of energy source and its conversion and utilizations are the viable alternatives available to the utilities or industry. There are essentially two approaches to electrical energy management. First at the supply / utility end (Supply Side Management or SSM) and the other at the consumer end (Demand Side Management or DSM). This work is based on Supply Side Management (SSM) protocol and consists of design, fabrication and testing of a control device that will be able to automatically regulate the power flow to an individual consumer's premise. This control device can monitor the overuse of electricity (above the connected load or contracted demand) by the individual consumers. The present project work specially emphasizes on contract demand of every consumer and tries to reduce the use beyond the contract demand. This control unit design includes both software and hardware work and designed for 0.5 kW contract demand. The device is tested in laboratory and reveals its potential use in the field.

A Gold Sensors Array for Imaging The Real Tissue Phantom in Electrical Impedance Tomography

Surface electrodes in Electrical Impedance Tomography (EIT) phantoms usually reduce the SNR of the boundary potential data due to their design and development errors. A novel gold sensors array with high geometric precision is developed for EIT phantoms to improve the resistivity image quality. Gold thin films are deposited on a flexible FR4 sheet using electro-deposition process to make a sixteen electrode array with electrodes of identical geometry. A real tissue gold electrode phantom is developed with chicken tissue paste and the fat cylinders as the inhomogeneity. Boundary data are collected using a USB based high speed data acquisition system in a LabVIEW platform for different inhomogeneity positions. Resistivity images are reconstructed using EIDORS and compared with identical stainless steel electrode systems. Image contrast parameters are calculated from the resistivity matrix and the reconstructed images are evaluated for both the phantoms. Image contrast and image resolution of resistivity images are improved with gold electrode array.