Search results for "Cole–Cole equation"
showing 10 items of 20 documents
Broadband dielectric spectroscopy of 0.4PMN-0.3PSN-0.3PZN ceramics
2007
In this paper, results of the broadband dielectric spectroscopy of 0.4PbMg1/3Nb2/3O3-0.3PbZn1/3Nb2/3O3-0.3PbSc1/2Nb1/2O3(0.4PMN-0.3PZN-0.3PSN) are presented. Dielectric spectra of these solutions were investigated in a broad frequency range from 20 Hz to 100 GHz. Very strong and broad dielectric relaxation was analyzed in terms of distribution of relaxations times, using Tichonov regularization method. It revealed slowing down of the longest relaxation and the mean relaxation times in the agreement with the Vogel-Fulcher law and the Arrhenius law, respectively.
Molecular association and dynamics in n-pentanol and 2-methyl-2-butanol
1985
Static dielectric constant, viscosity, density, ultrasonic and dielectric relaxation measurements are reported for two pentanol isomers (n-pentanol and 2-methyl-2-butanol) in a wide range of temperatures. The results show a different extent of H-bonds self-association in relation to the molecular geometry of the alcohol. The activation energies obtained from dielectric and ultrasonic studies are compared with those obtained from viscous flow. Such a comparison, together with the analysis of all the dielectric and ultrasonic relaxation data, show that in n-pentanol a correlation between viscosity and ultrasonic relaxation exists, while dielectric relaxation is not correlated with the other t…
High-field nuclear spin relaxation in liquids and solids
1990
The authors generalise the standard theory of nuclear spin relaxation to situations in which the Markovian approximation is not applicable. Expressions for generalised frequency-dependent spin relaxation functions are presented. They show that under high-field conditions the relaxation of longitudinal magnetisation is exponential independent of the particular time dependence of the correlation functions.
Dielectric Relaxation of a Polybutadiene Melt at a Crystalline Graphite Surface: Atomistic Molecular Dynamics Simulations
2014
Dielectric experiments are an indispensable tool to further our understanding of the relaxation behavior of polymers, not only in bulk samples but also in confined situations. A chemically realistic Molecular Dynamics simulation, in which all information about molecular motions is available, can shed light onto the questions of heterogeneity and anisotropy of the underlying molecular relaxation processes which lead to the ensemble averaged experimental dielectric signal. In this contribution, we present a careful analysis of the dielectric response of a weakly polar and confined polymer, 1,4-polybutadiene between graphite walls. The relaxation of the segmental dipole moments was obtained in…
Distribution of relaxation times in 0.5PMN-0.5PSN ceramics
2007
Dielectric properties of chemically ordered and disordered 0.5PbMg1/3Nb2/3O3-0.5 PbSc1/2Nb1/2O3 (0.5PMN-0.5PSN) ceramics were investigated in frequency range from 20 Hz to 3 GHz by dielectric spectroscopy. The broad dielectric dispersion, similar to this typically obtained for relaxor ferroelectrics (RFE), was observed in both ceramics below 350 K. The frequency dependence of dielectric permittivity of these ceramics were analyzed in terms of the distribution of relaxation times and showed the splitting into two components at lower temperatures. The longest relaxation times part slows down following Vogel-Fulcher law with lower freezing temperature compare with typical RFE like PbMg1/3Nb2/3…
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.
High frequency dielectric relaxation in BaTio3derived materials
1992
Abstract A systematic study of the dielectric relaxation phenomenon has been carried out for ceramics with compositions derived from barium titanate in the frequency and temperature ranges 1 MHz–1 GHz and 250–500 K, respectively. Whatever the composition may be, a minimum of the relaxation frequency and a maximum of the dielectric dispersion appears at each phase transition temperature. The dipole-type relaxation is correlated to coherent displacements of the ions in the octahedron sites ordered either along chains or in 3D-lattice.
Broad Distribution of Relaxation Times in 0.6PMN-0.4PZN Relaxor Ceramics
2007
In this paper dielectric spectra of 0.6PMN-0.4PZN ceramic obtained from broadband dielectric spectroscopy is presented. Measurements revealed an unusual relaxor like nature. Two different processes in the dielectric spectra have been observed. High frequency, or short relaxation times, behaviour is typical for ferroelectric crystals. Longest relaxation times do not follow Vogel—Fulcher dependence, which is unusual for relaxors.
Dielectric relaxation in crystals and ceramics derived from BaTiO3
1992
Abstract A dielectric relaxation is reported in a crystal of BaTiO3 and in ceramics with composition (Ba1-yCay)TiO3 (0≤y≤0.2) in the frequency and temperature ranges 106 to 109 Hz and 350 to 450 K, respectively. A minimum of the relaxation frequency occurs close to the ferroelectric Curie temperature. The relaxation is of dipolar-type.
Dipolar Glass-Like Perovskite Sr0.8Bi0.2TiO3Ceramic
2010
In this work lead-free Sr0.8Bi0.2TiO3 ceramic have been investigated in the frequency range from 20 Hz to 36 GHz. The obtained results show pronounced dispersion below room temperature. It looks more similar to the one observed in dipolar glasses as in relaxors. Calculated relaxation time distribution function broadens towards longest relaxation times with decreasing temperature. The obtained most probable relaxation time fulfills Vogel-Fulcher relationship with the following parameters: dipole activation energy EA/kB = 1718 K, freezing temperature T0 = 65 K, attempt relaxation time, referring to dipole relaxation at very high temperatures, τ0 = 5.5·10−14 s.