Search results for "Percolation"
showing 10 items of 87 documents
Nucleus-driven crystallization of amorphous Ge2Sb2Te5: A density functional study
2012
Early stages of nucleus-driven crystallization of the prototype phase change material Ge${}_{2}$Sb${}_{2}$Te${}_{5}$ have been studied by density functional/molecular dynamics simulations for amorphous samples (460 and 648 atoms) at 500, 600, and 700 K. All systems assumed a fixed cubic seed of 58 atoms and 6 vacancies. Crystallization occurs within 600 ps for the 460-atom system at 600 and 700 K, and signs of crystallization (nucleus growth, percolation) are present in the others. Crystallization is accompanied by an increase in the number of ``$ABAB$ squares'' ($A$: Ge, Sb, $B$: Te), and atoms of all elements move significantly. There is no evidence of cavity movement to the crystal-glass…
Polar phonons in relaxor ferroelectric 0.2PSN-0.4PMN-0.4PZN
2008
Relaxor ferroelectrics 0-2PbSc(1/2)Nb(1/2)O(3) - 0.4PbMg(1/3)Nb(2/3)O(3)-0.4PbZn(1/3)Nb(2/3)O(3) ceramics were studied by means of the Fourier transform infrared reflection and THz transmission spectroscopy in the temperature range of 20-500 K. On heating from low temperatures, the A(1) component of the strongly split TO1 mode softens towards the Burns temperature, but the softening ceases near 400 K, which could be a signature of polar cluster percolation temperature.
Far-infrared and THz spectroscopy of 0.4PMN–0.3PSN–0.3PZN relaxor ferroelectric ceramics
2007
Abstract Temperature dependence of the optic phonons in 0.4PbMg 1/3 Nb 2/3 O 3 –0.3PbSc 1/2 Nb 1/2 O 3 –0.3PbZn 1/3 Nb 2/3 O 3 (0.4PMN–0.3PSN–0.3PZN) ceramics were studied by means of FTIR reflection and THz transmission spectroscopy in the temperature range of −253.15 to 226.85 °C. On heating from low temperatures, the A 1 component of the strongly split TO 1 mode softens towards the Burns temperature, but the softening ceases near 126.85 °C which could be a signature of polar cluster percolation temperature. Surprisingly, the TO 2 mode also softens on heating and follows the Cochran law with extrapolated critical temperature close to the melting point.
Multifunctional properties of nanocomposites made by 1D and 2D graphene based fillers
2015
High aspect ratio graphene based fillers with different dimensionalities showed the ability to greatly modify rheological, mechanical, thermal and electrical properties of polymers at very low content. In this work, the effect of filler dimensionality on the multifunctional properties of an epoxy matrix reinforced by both carbon nanotubes (1D) and graphite nanoplatelets (2D) have been investigated across the percolation region. Keywords-- Carbon nanotube, Graphite nanoplatelet, nanocomposites, mechanical properties, ...
Electrical conductivity properties of expanded graphite-polycarbonatediol polyurethane composites
2014
Conductive polymer composites of segmented polycarbonatediol polyurethane and expanded graphite (EG) have been synthesized with different amounts of EG conductive filler (from 0 to 50 wt%). SEM, X-ray diffraction measurements, Fourier transform infrared and Raman spectroscopies demonstrated a homogeneous dispersion of the EG filler in the matrix. The dielectric permittivity of the composites showed an insulator to conductor percolation transition with increase in EG content. Significant changes in the dielectric permittivity take place when the weight fraction of EG is in the range 20–30 wt%. Special attention has been paid to the dependence of the conductivity on frequency, temperature and…
Transition to Reinforced State by Percolating Domains of Intercalated Brush-Modified Cellulose Nanocrystals and Poly(butadiene) in Cross-Linked Compo…
2013
The classic nanocomposite approach aims at percolation of low fraction of exfoliated individual reinforcing nanoscale elements within a polymeric matrix. By contrast, many of the mechanically excellent biological nanocomposites involve self-assembled and space-filled structures of hard reinforcing and soft toughening domains, with high weight fraction of reinforcements. Here we inspect a new concept toward mimicking such structures by studying whether percolation of intercalated domains consisting of alternating rigid and reinforcing, and soft rubbery domains could allow a transition to a reinforced state. Toward that, we present the functionalization of rigid native cellulose nanocrystals …
Electrochemical behaviour and electrical percolation in graphite-epoxy electrodes
1994
The electrochemical properties of mouldable graphite-epoxy composite electrodes have been studied as a function of graphite content. The shape of ferri-ferrocyanide voltammograms relates to the ratio of graphite and an adsorption process. The dielectric constant from spectroelectrochemical impedance measurement of this composite electrode is maximum when the proportion of graphite is ca. 60 wt%. An electrochemical equivalent circuit is proposed. The graphite-epoxy composite acts as a multi-microelectrode near this proportion.
Rheological Percolation Threshold in High-Viscosity Polymer/CNTs Nanocomposites
2017
AbstractPolystyrene (PS)/multi-walled carbon nanotubes (CNT) nanocomposites have been prepared through melt mixing processing aiming at obtaining a uniform and homogeneous dispersion of the used nanoparticles within the polymeric matrix. Optical and scanning electron microscopy has been employed to determine the dispersion and distribution of CNTs at different length scales. Furthermore, the linear viscoelastic behavior of formulated nanocomposites has been deeply investigated. As a result of CNTs added, the nanocomposites experience a transition from liquid-like to solid-like rheological behavior, and a disappearance of relaxation processes at low frequency can be noticed. By plotting G’ v…
Pore structural characteristics, size exclusion properties and column performance of two mesoporous amorphous silicas and their pseudomorphically tra…
2007
Highly ordered mesoporous silicas such as, mobile composition of matter, MCM-41, MCM-48, and the SBA-types of materials have helped to a large extent to understand the formation mechanisms of the pore structure of adsorbents and to improve the methods of pore structural characterization. It still remains an open question whether the high order, the regularity of the pore system, and the narrow pore size distribution of the materials will lead to a substantial benefit when these materials are employed in liquid phase separation processes. MCM-41 type 10 microm beads are synthesized following the route of pseudomorphic transformation of highly porous amorphous silicas. Highly porous silicas a…
Effect of the Content and Ordering of the sp2 Free Carbon Phase on the Charge Carrier Transport in Polymer-Derived Silicon Oxycarbides
2020
The present work elaborates on the correlation between the amount and ordering of the free carbon phase in silicon oxycarbides and their charge carrier transport behavior. Thus, silicon oxycarbides possessing free carbon contents from 0 to ca. 58 vol.% (SiOC/C) were synthesized and exposed to temperatures from 1100 to 1800 °