Search results for "dispersion"
showing 10 items of 1101 documents
Improved carbon nanotubes dispersion through polar dispersant agents in polyamide
2016
The potential enhancement of the nanocomposite properties, with respect to the neat matrix, is strictly related to uniform distribution and dispersion of the nanofillers in the host polymer. In this work, two dispersant agents, particularly a polar wax and a silanol polyhedral oligomeric silsesquioxanes POSS, have been used in order to improve the dispersion of bare and functionalized carbon nanotubes in polyamide matrix. To ensure a good compatibility between matrix and nanofillers, the dispersing agents having specific polarity have been chosen, in order to match that of the matrix. Significant alterations of the mechanical and rheological behaviour due to dispersion action of used additi…
Relaxor ferroelectric ceramics of LiTaO3-type
1992
Abstract A ferroelectric relaxation has been identified in Li1-xCax (Ta1-xZrx)O3(x = 0.15 and 0.20) ceramics with LiTaO3-type structure. The relaxation frequency fr is minimum and the dispersion step (ϵ′S - ϵ′∞) is maximum at TC. When x increases, a higher conductivity associated with a lower activation energy and a decrease of the magnitude of fr at Tc are observed, while the unit cell volume becomes larger, TC lower and the transition more diffuse.
Phonon Dispersion of Wurtzite CdSe: The Bond Charge Model
2000
The phonon dispersion of wurtzite CdSe is presented along the main directions of the Brillouin zone. The study has been performed by using a bond charge model for wurtzite-type semiconductors with only six adjustable parameters. The results are compared against neutron scattering data and ab initio calculations. The phonon eigenvectors corresponding to the vibrational modes at the Γ-point are in very good agreement with the ab initio calculations.
Broadband Dielectric Spectroscopy of PSN-Rich PMN-PSN Ceramics
2008
The broadband dielectric permittivity of ordered 0.1PMN-0.9PSN and disordered 0.2PMN-0.8PSN ceramics was investigated. The anomaly of dielectric permittivity is clearly seen in the region of 370 K for 0.1 PMN-0.9 PSN at all frequencies. 0.2 PMN-0.8 PSN shows relaxor behaviour with huge frequency dispersion below 350 K. Calculated distribution of relaxation times shows noticeable influence of polar nano regions to the total dielectric spectrum below 320 K with the longest relaxation times edge diverging according to the Vogel-Fulcher law. In 0.1 PMN-0.9 PSN two a little overlapped peaks present in the distribution of relaxation times, influenced by displacive lead motions at high frequencies…
Description of Relaxor State in Na1/2Bi1/2TiO3-SrTiO3-PbTiO3 System of Solid Solutions
2011
Vogel-Fulcher law, traditionally applied to describe dispersion of dielectric permittivity in relaxor ferroelectrics, requires introduction of two different relaxation mechanisms above and below freezing temperature correspondingly. Extending distribution function of relaxation times, previously known for low-temperature region, allows creating common description of relaxation in all range, where distribution function of relaxation times can be regarded as wide, without freezing at certain temperature.
ELECTRICAL PROPERTIES OF LEAD FERROTANTALATE CERAMICS
2009
ABSTRACT Perovskite structures with high dielectric constants and magnetic properties play an important role in micro- and optoelectronics and have numerous practical applications. Relaxor type ferroelectric ceramics PbFe1/2Ta1/2O3 with perovskite structure was subject of present studies. Pyrochlore free lead ferrotantalate ceramics were produced by solid state technology from oxides. Low- and infra-low frequency studies of dielectric properties of PbFe1/2Ta1/2O3 ceramics have revealed considerable infra-low frequency dispersion at temperatures above the temperature of maximum dielectric permittivity. The observed dispersion described by lemniscates is due to a considerable Maxwell-Wagner r…
A neutron scattering study of the magnetic properties of PrSn3
1988
The intermetallic compound PrSn3 has been studied by elastic and inelastic neutron scattering. The paramagnetic phase shows overdamped crystal field excitations and an anisotropic distribution of the diffuse magnetic intensity. The dispersion relation of the excitations of the antiferromagnetic phase has been determined. The results are analyzed in terms of an anisotropic exchange coupling.
Anomalous Broad Dielectric Dispersion of 0.4PZN-0.3PSN-0.3PZN Relaxor Ceramics at Lower Temperatures
2006
Dielectric properties of 0.4PbZn1/3Nb2/3O3-0.3PbSc1/2Nb1/2O3-0.3PbMg1/3Nb2/3O3- (0.4PZN- 0.3PSN-0.3PMN) ceramics are presented for 200 < T < 500 K and 20 Hz < ν < 1 MHz. Dielectric constant is very high (more 14000) in the vicinity of the peak. Anomalous broad dielectric relaxation have been observed near the temperature of the maximum permittivity, Tm (at 1 kHz). External bias field considerably lowers the value of dielectric losses at low frequencies due to decrease of polar nano regions contribution to the dielectric permittivity.
Lattice phonon modes of the high-pressure phase CuCl-IV
1999
Raman spectra of isotopically pure CuCl samples ${(}^{63}\mathrm{CuCl}$ and ${}^{65}\mathrm{CuCl})$ were measured under hydrostatic pressure up to 14 GPa at low temperature $(5 \mathrm{K}).$ Up to six Raman modes were resolved for the binary BC8-analog phase CuCl-IV in the range from 4.1 to 14 GPa. The phonon dispersion relations of this phase were calculated within a rigid ion model. Based on this calculation an assignment for the observed Raman-active modes is proposed. The calculated pressure dependences of mode frequencies reproduce the experimental results. Raman spectra support the existence of the phase CuCl-IIa in a narrow pressure range from 3.3 to 4.1 GPa.
Phonon dispersion in GaN/AlN non‐polar quantum wells: confinement and anisotropy
2007
We have calculated the phonon dispersion relations in a non-polar GaN/AlN quantum well within the dielectric continuum model and making use of Loudon's model of uniaxial crystals. Due to the strong in-plane anisotropy of this orientation, we have found that in general ordinary and extraordinary phonons are not decoupled. In this work we analyze the conditions for the occurrence of interface modes. In these novel heterostructures there is an added dependence of the phonon dispersion on the orientation of the in-plane phonon wavevector, which allows the existence of interface phonons at energies forbidden in the better known polar structures. Under particular circumstances the vibrations exci…