Search results for "electric [charge]"
showing 10 items of 729 documents
Influence of thickness and interface on the low-temperature enhancement of the spin Seebeck effect in YIG films
2016
The temperature-dependent longitudinal spin Seebeck effect (LSSE) in heavy metal (HM)/Y_{3}Fe_{5}O_{12} (YIG) hybrid structures is investigated as a function of YIG film thickness, magnetic field strength, and different HM detection materials. The LSSE signal shows a large enhancement with reductions in temperature, leading to a pronounced peak at low temperatures. We find that the LSSE peak temperature strongly depends on the film thickness as well as on the magnetic field. Our result can be well explained in the framework of magnon-driven LSSE by taking into account the temperature-dependent effective propagation length of thermally excited magnons in the bulk of the material. We further …
Structural Principles and Thermoelectric Properties of Polytypic Group 14 Clathrate-II Frameworks
2013
We have investigated the structural principles and thermoelectric properties of polytypic group 14 clathrate-II frameworks using quantum chemical methods. The experimentally known cubic 3C polytype was found to be the energetically most favorable framework, but the studied hexagonal polytypes (2 H, 4 H, 6 H, 8 H, 10 H) lie energetically close to it. In the case of germanium, the energy difference between the 3C and 6H clathrate-II polytypes is ten times smaller than the difference between the experimentally known 3C-Ge (α-Ge) and 4H-Ge polytypes. The thermoelectric properties of guest-occupied clathrate-II structures were investigated for compositions Na-Rb-Ga-Ge and Ge-As-I. The clathrate-…
Field Induced Evolution of Nanoscale Structures in Relaxor PLZT Ceramics
2005
Abstract The kinetics of the nanoscale structures under application of bipolar and unipolar ac field was investigated by recording of the switching charge in wide temperature and field range in hot-pressed relaxor PLZT ceramics. Original analysis of the switching charge data was based on the consideration of the field induced transformation as an evolution of the nanoscale domain structure with nanoscale nonpolar inclusions. We have shown that the inhomogeneous depolarization field produced by the bound charges existing at the interphase boundaries play the key role in spontaneous backswitching effects.
Synthetic nanopores with fixed charges: An electrodiffusion model for ionic transport
2003
Synthetic nanopores with fixed charges exhibit ionic equilibrium and transport properties that resemble those displayed by biological ion channels. We present an electrodiffusion model based on the Nernst-Planck flux equations, which allows for a qualitative description of the steady state ionic transport through a nanopore when the membrane fixed charges and all mobile carriers (including the water ions) are properly taken into account. In particular, we study the current-voltage curve, the electrical conductance, the reversal potential (a measure of the nanopore ionic selectivity), as well as the flux inhibition by protons and divalent cations in the nanopore. The model clearly shows how …
Thermoelectric properties of spark plasma sintered composites based on TiNiSn half-Heusler alloys
2011
Half-Heusler (HH) and especially TiNiSn-based alloys have shown high potential as thermoelectric (TE) materials for power generation applications. The reported transport properties show, however, a significant spread of results, due mainly to the difficulty in fabricating single-phase HH samples in these multicomponent and multiphased systems. In particular, little attention has been paid to the influence of the various minority phases on the TE performance of these compounds. A clear understanding of these issues is mandatory for the design of improved and stable TE HH-based composites. This study examines the structural and compositional influence of the residual metallic (Sn) and interme…
Synthesis and thermoelectric properties of 2- and 2,8-substituted tetrathiotetracenes
2018
Reaction of elemental sulfur with 2-R1 and 2,8-R1,R2-substituted tetracenes (2) in refluxing DMF affords 5,6,11,12 tetrathiotetracenes (1) in good yields (74–99%) for a range of substituents where R1,R2 are: H,H (a); Me,H (b); MeO,H (c); Ph,H (d); Me,Me (e), iPr,Me (f, iPr = iso-propyl, CHMe2), Me,MeO (g); MeO,MeO (h). The reaction rate is limited only by the solubility of the tetracene (2); 2g–h being both the least soluble and slowest reacting. At partial conversion recovered single crystalline 2g led to its X-ray structure determination. Vacuum deposited (substrate deposition temperature 300 K, pressure 7 × 10−6 mbar, source temperature 500 K) thin films from 1 (of initial 88–99% purity)…
Thermal stability and enhanced thermoelectric properties of the tetragonal tungsten bronzes Nb8-xW9+xO47 (0 <x <5)
2017
Thermoelectric materials are believed to play a fundamental role in the energy field over the next years thanks to their ability of directly converting heat into usable electric energy. To increase their integration in the commercial markets, improvements of the efficiencies are needed. At the same time, cheap and non-toxic materials are required along with easily upscalable production cycles. Compounds of the tetragonal tungsten bronze (TTB) series Nb8-xW9+xO47 fulfill all these requirements and are promising materials. Their adaptive structure ensures glass-like values of the thermal conductivity, and the substitution on the cation side allows a controlled manipulation of the electronic p…
Optimization of the carrier concentration in phase-separated half-Heusler compounds
2014
Inspired by the promising thermoelectric properties of phase-separated half-Heusler materials, we investigated the influence of electron doping in the n-type Ti_(0.3−x)Zr_(0.35)Hf_(0.35)NiSn compound. The addition of Nb to this compound led to a significant increase in its electrical conductivity, and shifted the maximum Seebeck coefficient to higher temperatures owing to the suppression of intrinsic carriers. This resulted in an enhancement of both the power factor α^2σ and figure of merit, zT. The applicability of an average effective mass model revealed the optimized electron properties for samples containing Nb. There is evidence in the literature that the average effective mass model i…
Molecular dynamics of carrageenan composites reinforced with Cloisite Na+ montmorillonite nanoclay
2017
[EN] Nanocomposites comprising biodegradable carrageenan and glycerol(KCg) as the host polymer, with different contents of natural montmorillonite (MMT) as filler, were prepared by a solution casting process. Different techniques have been used to determine the interaction/behavior among the different components of the samples such as Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Transmission electron microscope (TEM) and, mainly, Dielectric relaxation spectroscopy (DRS). FTIR indicates hydrogen interaction between carrageenan matrix and silicate that is confirmed by the XRD data indicating some kind of carrageenan intercalation between the MMT layers. A rather ho…
Effect of Chitin Whiskers on the Molecular Dynamics of Carrageenan-Based Nanocomposites
2019
[EN] Films of carrageenan (KC) and glycerol (g) with different contents of chitin nanowhiskers (CHW) were prepared by a solution casting process. The molecular dynamics of pure carrageenan (KC), carrageenan/glycerol (KCg) and KCg with different quantities of CHWs as a filler was studied using dielectric relaxation spectroscopy. The analysis of the CHW effect on the molecular mobility at the glass transition, T-g, indicates that non-attractive intermolecular interactions between KCg and CHW occur. The fragility index increased upon CHW incorporation, due to a reduction in the polymer chains mobility produced by the CHW confinement of the KCg network. The apparent activation energy associated…