Search results for " Conductivity"

Metallic Conductivity Down to 2 K in a Polyoxometalate-Containing Radical Salt of BEDO-TTF

2004

Fabrication of soft-etched nanoporous polyimide membranes for ionic conduction and discrimination

2021

Abstract Ionic selectivity in nanopores is usually based either on steric or charge exclusion mechanisms. By simultaneously incorporating both mechanisms into a functionalized membrane, an improved control over selectivity can be achieved. We describe the fabrication and experimental characterization of alkali metal cation-selective nanopores in heavy ion-tracked polyimide (PI) membranes using the soft-etching (SE) technique. The latent ion tracks in the PI membrane are selectively dissolved by an organic solvent to form tiny pores without affecting the bulk material. The ionic transport properties of SE-PI membranes are characterized using different electrolyte solutions containing alkali …

Universal Transients in Polymer and Ionic Transition Metal Complex Light-Emitting Electrochemical Cells

2012

Two types of light-emitting electrochemical cells (LECs) are commonly distinguished, the polymer-based LEC (p-LEC) and the ionic transition metal complex-based LEC (iTMC-LEC). Apart from marked differences in the active layer constituents, these LEC types typically show operational time scales that can differ by many orders of magnitude at room temperature. Here, we demonstrate that despite these differences p-LECs and iTMC-LECs show current, light output, and efficacy transients that follow a universal shape. Moreover, we conclude that the turn-on time of both LEC types is dominated by the ion conductivity because the turn-on time exhibits the same activation energy as the ion conductivity…

Electrical conductivity and permittivity of water-AOT-n-heptane microemulsions

1995

Measurements of the electrical conductivity and of the complex permittivity of water-sodium bis(2-ethylhexyl) sulfosuccinate (AOT)-n-heptane microemulsions are reported. The experimental results are rationalized in terms of a hopping mechanism of AOT anions within clusters of reversed micelles. The dependence of the hopping rate and of the cluster dimensions upon the ratio [water]/[AOT] and temperature is discussed.

Electron-relaxation-mode interaction in BaTiO3:Nb.

1992

Dielectric relaxation was previously reported in ${\mathrm{BaTiO}}_{3}$ and ${\mathrm{BaTiO}}_{3}$:Fe single crystals at radio frequencies [M. Maglione et al., Phys. Rev. B 40, 11 441 (1989)]. We have measured the dielectric dispersion in four ${\mathrm{BaTiO}}_{3}$:Nb samples (${\mathit{x}}_{\mathrm{Nb}}$0.3 at. %) as a function of frequency (10f${10}^{9}$ Hz) and temperature (20T450 K). The electronic conductivity of ${\mathrm{BaTiO}}_{3}$:Nb enhances drastically the relaxation step at all temperatures. In the rhombohedral phase of ${\mathrm{BaTiO}}_{3}$:Nb (T180 K), an unusual slowing down of the relaxation motion is measured. The relaxation time increases to more than ${10}^{\mathrm{\en…

New conducting radical salts based upon Keggin-type polyoxometalates and perylene

2004

Three new radical salts, Per6[PMo12O40]·CH2Cl2 (1), Per6[PMo12O40]·CH3CN (2), and Per9(NBu4)4[SiW12O40]2 (3) (Per = perylene), have been synthesised and their electrical and magnetic properties characterised. These three salts are diamagnetic and they behave as semiconductors with room temperature conductivities of 69, 3.6 and 0.85 S cm−1. While salt 2 presents hole-type conduction and 3 exhibits electron-dominated electrical transport properties, salt 1 shows at 150 K an abrupt change in the thermal dependence of the electrical conductivity and the Seebeck coefficient suggesting a phase transition.

Conductivity and light-induced absorption in BaTiO3

1990

A charge transport model including deep and shallow traps explains both the nonlinear relation between photoconductivity and light intensity and the light-induced absorption in BaTiO3. A correlation between measurements of photoconductivity and light-induced absorption as a function of temperature yields parameters for the shallow center, among them thermal activation energy and generation rate.

Electrically conductive TCNQ complexes of aromatic ionenes

1995

New types of complex salts of 7,7',8,8'-tetracyanoquinodimethane with aromatic ionenes and their model compounds were prepared. The electrical conductivity and the activation energy were measured and discussed in relation to their structure. The effects of the nature of the aromatic unit, and the flexibility and rigidity of the polymer backbone were compared with the corresponding model compounds. The effects of frequency and temperature are discussed in terms of the molecular structure of the complex. The electroconductivity at room temperature of the 1 :1 polymer complex salts was found to be between 2 x 10 -4 and 7 x 10 -5 S/cm, while that of the model complex salts was between 1.3 x 10 …

Metallic Conductivity in a Polyoxovanadate Radical Salt of Bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF): Synthesis, Structure, and Physical Chara…

2004

Computational and theoretical studies on lattice thermal conductivity and thermal properties of silicon clathrates

2016

The lattice thermal conductivity is usually an intrinsic property in the study of thermoelectricity. In particular, relatively low lattice thermal conductivity is usually a desired feature when higher thermoelectric efficiency is pursued. The mechanisms which lower the lattice thermal conductivity are not known in sufficient detail and deeper understanding about the phenomena is needed and if such understanding is achieved it can be used to design more efficient thermoelectric materials. In this thesis, the lattice thermal conductivity and other thermal properties of several silicon clathrates, which are known to be promising candidates for the thermoelectric applications, are studied by theoreti…