Search results for "CONDUCTIVITY"
showing 10 items of 1988 documents
A three-dimensional grain boundary formulation for microstructural modeling of polycrystalline materials
2013
Abstract A three-dimensional grain boundary formulation is presented for the analysis of polycrystalline microstructures. The formulation is based on a boundary integral representation of the elastic problem for the single grains of the polycrystalline aggregate and it is expressed in terms of the intergranular fields, namely displacements and tractions, that play an important role in polycrystalline micromechanics. The artificial polycrystalline morphology is represented using the Hardcore Voronoi tessellation, which is simple to generate and able to embody the main statistical features of polycrystalline microstructures. The details of the microstructure generation and meshing, which invo…
A quantitative electron microscopic study of the crystallite structure of molecular weight fractions of linear polyethylene
1984
Utilizing thin-section techniques, transmission electron microscope studies were performed on a series of bulk-crystalized fractions of linear polyethylene covering the range M = 5 × 103−6 × 106. The crystallization conditions were varied from long-time isothermal to rapid quenching. Quantitative analysis could be carried out on such samples crystallized under controlled conditions. The crystallite thickness distributions and long periods are presented in terms of histograms. From these data the degree of crystallinity can be calculated and was found to compare favorably with that from other methods. The amorphous thickness increases significantly with molecular weight for all modes of crys…
Thermoelectric properties of p-type Bi2Sr2Co2O9 glass-ceramics
2014
In the oxide system of Bi–Sr–Co glass melts have been prepared by adding a small amount of glass formers. A crystallization leads to crystalline phases of Bi8Sr8Co4O25, BiSrCo2Ox and Bi2Sr2Co2O9 (BC-222) densely embedded into a residual glass phase. This work shows the possibility of obtaining microstructured bulk material with low thermal conductivity and relatively high electrical conductivity via such a glass ceramic approach. Furthermore the stability of these materials under thermal cycling for temperatures up to 700 °C is shown. A characterization of the thermoelectric properties leads to a figure of merit (ZT) between 0.008 and 0.018.
Hole-Transporting Materials for Perovskite Solar Cells Employing an Anthradithiophene Core
2021
A decade after the report of the first efficient perovskite-based solar cell, development of novel hole-transporting materials (HTMs) is still one of the main topics in this research field. Two of the main advance vectors of this topic lie in obtaining materials with enhanced hole-extracting capability and in easing their synthetic cost. The use of anthra[1,9-bc:5,10-b'c']dithiophene (ADT) as a flat π-conjugated frame for bearing arylamine electroactive moieties allows obtaining two novel highly efficient HTMs from very cheap precursors. The solar cells fabricated making use of the mixed composition (FAPbI3)0.85(MAPbBr3)0.15 perovskite and the novel ADT-based HTMs show power conversion effi…
Harmonic emission at microwave frequencies in YBa2Cu3O7 single crystals near Tc
1998
Abstract Nonlinear microwave emission by YBa 2 Cu 3 O 7 single crystals is investigated at temperatures close to T c . Second- and third-harmonic signals are studied as a function of the temperature and input power, for different values of the external magnetic field. The results are discussed in the framework of a phenomenological theory based on the two-fluid model which assumes that both the microwave and static fields perturb the partial concentrations of the normal and condensate fluids. It is suggested that, at temperatures very close to T c , this mechanism is the only one responsible for the harmonic emission by YBa 2 Cu 3 O 7 single crystals in the Meissner state. It is also effect…
Temperature Effects on the Phonon Spectrum in YBa2Cu3O7 Single Crystals and Thin Films
1989
We have performed a detailed investigation of the temperature dependence of the 385cm-1 phonon in single crystals and thin films of the YBa2Cu3O7 superconductor by means of Raman spectroscopy. In the single crystal the frequency of this phonon shows a downshift of about 5 cm-1 on passing the superconducting transition from above, which is referred to a strong electron-phonon interaction in the superconductor. The shift of the phonon in thin epitaxial films on MgO or SrTiO3 substrates is only about 2.5 cm-1. This difference may be a result of a structural transition in the single crystal which is possibly suppressed in the films because of the epitaxy. The electron-phonon interaction is also…
<title>Effects of light polarization and crystal orientation on the holographic recording efficiency in doped LiNbO<formula><inf>&l…
2008
The holographic recording efficiency in doped LiNbO3 crystals has been studied both experimentally and theoretically depending on the type of dope, on the recording geometry and on the polarizations of the recording and readout light.. The studied crystals can be arranged in the following order by their efficiency: LiNbO3:Cu, LiNbO3:Fe (yet having a smaller thickness and donor concentration than LiNbO3:Cu), LiNbO3:Fe+Cu, LiNbO3:Fe+Ti, LiNbO3:Ti. It was found that the recording geometry with the holographic grating vector along the optical axis is much more efficient than in the perpendicular configuration.This fact is in accordance with the photorefraction theory based on photogalvanic and …
Testing laboratory methods to determine the anisotropy of saturated hydraulic conductivity in a sandy–loam soil
2009
Abstract Anisotropy, a (the log of the ratio of horizontal to vertical conductivity, log 10 ( K h / K v )), of saturated soil hydraulic conductivity, K s , affects transport processes in soil but is not routinely measured, probably because practical and validated methods are lacking. The objective of this investigation was to determine the effects of different constant-head laboratory and sampling procedures on anisotropy of saturated hydraulic conductivity measurements. The sequence of K s measurements was varied (vertical conductivity, K v , first, then horizontal, K h , second and vice versa) for an experimental set-up considering five variables: 1) water ponding type (Mariotte or siphon…
Evaluation of a new Cr-free alloy as interconnect material for hydrogen production by high temperature water vapour electrolysis: Study in cathode at…
2012
International audience; For economic and ecological reasons, hydrogen is considered as a major energetic vector for the future. Hydrogen production via high temperature water vapour electrolysis (HTE) is a promising technology. A major technical difficulty related to high temperature water vapour electrolysis is the development of interconnects working efficiently for a long period. Working temperature of 800 degrees C enables the use of metallic materials as interconnects. High temperature corrosion behaviour and electrical conductivity of a new Cr-free Fe-Ni-Co alloy were tested in cathode atmosphere (H-2/H2O) at 800 degrees C. The alloy exhibits a poor oxidation resistance but an excelle…
Optimisation of metallic interconnects for hydrogen production by high temperature water vapour electrolysis
2012
For economical and environmental reasons, hydrogen is considered as a major energetic vector for the future. Hydrogen production via high temperature water vapour electrolysis (HTE) is a promising technology. A major technical difficulty related to high temperature water vapour electrolysis is the development of interconnects working efficiently for a long period. Working temperature of 800°C enables the use of metallic materials as interconnects. Chromia forming alloys are among the best candidates. The interconnect material chosen in the present study is a ferritic stainless steel with 18% chromium content. High temperature corrosion resistance and electrical conductivity of the alloy was…