scholarly journals Ionische dielektrische Relaxationsprozesse in Festkörpern, I / Ionic Dielectric Relaxation Processes in Solids, I

1973 ◽  
Vol 28 (11-12) ◽  
pp. 721-730 ◽  
Author(s):  
Günter Schön
Keyword(s):  
Activation Enthalpy ◽  
Low Frequency ◽  
Life Time ◽  
Relaxation Processes ◽  
Dielectric Measurements ◽  
Frequency Range ◽  
Kcal Mole ◽  
Type Layer ◽  
Frequency Relaxation ◽  
Cation Sites

Dielectric measurements have been made on single-crystals of mica-type layer silicates (vermiculites) in the frequency range between 30 Hz and 10 MHz. The migration of K+-and NH4+-interlayer cations by free cation sites causes a low-frequency relaxation. It is interpreted by the orientation of large dipoles they form with parent negative layer charges. For both ions the activation enthalpy of diffusion across the lattice is 11.94 kcal/mole. Additional N-H · · · O hydrogen bonds are formed by the NH4+ ions at low temperatures. There results a bond enthalpy of 1.3 kcal/mole and a life-time of 1.2 · 10-5 sec (at 40°C). A discussion of the different rate process equations yields the applicability of the Bauer equation.

Dielectric and mechanical alterations of snow properties near the melting temperature

2003 ◽  
Vol 81 (1-2) ◽  
pp. 233-239 ◽  
Author(s):  
I Takei ◽  
N Maeno
Keyword(s):  
Melting Temperature ◽  
Propagation Velocity ◽  
Low Frequency ◽  
Dielectric Measurements ◽  
Frequency Range ◽  
Temperature Range ◽  
Snow Properties ◽  
Response Method ◽  
Dielectric And Mechanical Properties ◽  
Snow Samples

The dielectric and mechanical properties of snow were investigated in the temperature range –15 to 0°C. Dielectric measurements were carried out in the frequency range 50 Hz – 5 MHz; the low-frequency conductivity (at 100 Hz) of snow samples shows a peak in the temperature range –3 to –0.3°C and the dielectric dispersion-strength also shows a minimum in this same range. The propagation velocity of an elastic wave through snow samples was measured with a vibration response method in the frequency range 10 Hz – 1 MHz; the propagation velocity shows an increase with the bond growth as a result of progressive sintering, and a significant decrease above –0.6°C. The temperature dependence of the low-frequency conductivity and the propagation velocity for snow samples show a hysteresis near the melting temperature. A boundary between ice particles in snow samples is discussed as a means for understanding these phenomena. PACS Nos.: 61.43Gt, 77.22Gm, 46.40-f, 73.25+i

Study of the Molecular Mobility of Polysaccharide Solid Thin Layers by Dielectric Relaxation Spectroscopy

1997 ◽  
Vol 500 ◽  
Author(s):  
K. Liedermann ◽  
L. Lapčík ◽  
S. Desmedt
Keyword(s):  
Dielectric Relaxation ◽  
Low Frequency ◽  
Thin Layers ◽  
Side Chain ◽  
Relaxation Processes ◽  
Dielectric Relaxation Spectroscopy ◽  
Frequency Range ◽  
Polar Groups ◽  
Calculated Activation Energy ◽  
Β Relaxation

ABSTRACTTemperature dependence of measured dielectric relaxation spectra (DRS) in the frequency range 20 Hz - 1 MHz of hydroxyethylcellulose (HEC) are in the temperature range 100 – 350 K. of Arrhenius character with one relaxation process at 150 – 250 K. This process reflects most probably β-relaxation of the side chain groups. Calculated activation energy of this process was 5730 kJ/mole. Four types of polysaccharides were studied at 293 K temperature: hyaluronic acid (HA), chondroitin sulfate (CHS), HEC and carboxymethylcellulose (CMC), in the low-frequency range 10−5 - 100 Hz. Measured dielectric spectra were interpreted as sum of one A.C. conductivity process and of up to two relaxation processes. The relaxation processes were described by means of the Havriliak-Negami formula and their parameters were related to the molecular structure of the polymers. The low value of a in CHS is related to its strong coupling due to the presence of two polar groups in its monomeric unit, whereas low values of α × β are interpreted as being due to the strong steric hindrances caused by long pendants present in HEC.

Low Frequency Relaxation Processes in a PDLC Film

1999 ◽  
Vol 331 (1) ◽  
pp. 627-634
Author(s):  
Oleksandr V. Kovalchuk ◽  
Viktor Yu. Reshetnyak ◽  
Viktor V. Yarmolenko ◽  
Oleg V. Yaroshchuk
Keyword(s):  
Low Frequency ◽  
Relaxation Processes ◽  
Frequency Relaxation

Nanocomposite Material, Liquid Crystal-Aerosil Particles: Dielectric and Photon Correlation Spectroscopy Investigations

1999 ◽  
Vol 581 ◽  
Author(s):  
F.M. Aliev ◽  
G.P. Sinha
Keyword(s):  
Liquid Crystal ◽  
Photon Correlation Spectroscopy ◽  
Low Frequency ◽  
Correlation Spectroscopy ◽  
Relaxation Processes ◽  
Photon Correlation ◽  
Optoelectronic Application ◽  
Broadband Dielectric Spectroscopy ◽  
Tumbling Motion ◽  
Frequency Relaxation

ABSTRACTNematic liquid crystal filled with Aerosil particles prospective inorganic-organic nanocom-posite material for optoelectronic application has been investigated by broadband dielectric spectroscopy (BDS) and photon correlation spectroscopy (PCS). The aerosil particles of diameter ≈ 10 nm in filled nematic liquid crystals form a network structure with linear size of LC domains about 250 nm and with random distribution of the director orientation of each domain. This material has a very developed liquid crystal-solid particle interface that makes the role of the surface layers of LC important in the determination of the properties of the material. BDS provides information on reorientational motion of polar molecules of liquid crystal while PCS probes dynamics of collective modes associated with director fluctuations. We found that the properties of 5CB are considerably affected by the network. Two bulk-like dielectric modes due to the rotation of molecules around short axes and the tumbling motion were observed in filled 5CB. Additionally, a low frequency relaxation process and dispersion of dielectric permittivity due to conductivity were observed. The treatment of the surface of filling particles has strongest influence on the properties of the slow process and it is less important for molecular modes. PCS experiment shows that two new relaxation processes appear in filled 5CB in addition to the director fluctuations process in bulk.

Low Frequency Dielectric Relaxation and Charge Transport in Bi12TiO20 Photorefractive Sillenite Crystals

2017 ◽  
Vol 753 ◽  
pp. 163-167
Author(s):  
Rene Alejandro Castro ◽  
Nadezhda Ivanovna Anisimova ◽  
Liliya Ansafovna Nabiullina ◽  
Evgeny Borisovich Shadrin
Keyword(s):  
Charge Transport ◽  
Dielectric Relaxation ◽  
Transport Mechanism ◽  
Low Frequency ◽  
Frequency Range ◽  
Thermally Activated ◽  
Relaxation Polarization ◽  
Polarization Mechanism ◽  
Frequency Relaxation ◽  
Thermally Activated Process

Features of processes of a dielectric relaxation and charge transport in photorefractive sillenite crystals Bi12TiO20 at low frequency range are investigated. It was found that the dispersion of dielectric permittivity ε' in crystals Bi12TiO20 is characterized by its growth with lowering frequency and rising temperature. This behaviour may be related to existence of dipole-relaxation polarization mechanism. The frequency dependence of dielectric loss tgδ reveals the existence of low frequency relaxation peaks in the studied temperature range. From the conductivity dependence on the frequency and temperature it was found that conductivity σ increases as frequency increases in the low frequency range. The observed dependence σ(ω)≈Аωs indicates that transport mechanism is due to hopping of carriers via localized electron states. The charge transport is thermally activated process in which activation energy Ea = (0.82±0.03) eV.

Dielectric Studies on Liquid Crystals under High Pressure: VI. Low Frequency Relaxation Process in the Nematic and Smectic A Phase of 4-n-Octyl-4'-Cyanobiphenyl (8 CB)

1994 ◽  
Vol 49 (4-5) ◽  
pp. 552-558 ◽  
Author(s):  
S. Urban ◽  
T. Brückert ◽  
A. Würflinger
Keyword(s):  
Nematic Phase ◽  
Liquid Crystalline ◽  
Activation Volume ◽  
Activation Enthalpy ◽  
Low Frequency ◽  
Smectic A ◽  
Liquid Crystalline Phases ◽  
Smectic A Phase ◽  
Frequency Relaxation ◽  
Increasing Temperature

Abstract Dielectric relaxation studies of 4-n-octyl-4'-cyanobiphenyl (8 CB) were performed in the pressure range 0.1 -120 MPa, the frequency range 1 kHz -13 MHz and the temperature range 295-331 K. The dielectric behaviour of 8C B in the nematic phase is similar to that of 5 CB, 6 CB and 7 CB. In particular, the activation enthalpy decreases with increasing pressure and the activation volume decreases with increasing temperature in the nematic phase. In the smectic A phase of 8 CB both these parameters are markedly lower and show opposite pressure and temperature dependencies. We tentatively interpret these effects as a result of breaking of the dipole-dipole correlations which manifests itself differently in these liquid crystalline phases.

Collective and Molecular Dielectric Relaxation in Confined Liquid Crystals: Effect of Different Layer Thicknesses and Boundary Conditions

2003 ◽  
Vol 790 ◽  
Author(s):  
Fouad M. Aliev ◽  
Manuel Rivera Bengoechea
Keyword(s):  
Liquid Crystal ◽  
Boundary Conditions ◽  
Layer Thickness ◽  
High Frequency ◽  
Low Frequency ◽  
Pore Wall ◽  
Relaxation Processes ◽  
Short Axis ◽  
Librational Mode ◽  
Frequency Relaxation

ABSTRACTBroadband dielectric spectroscopy was used to study the influence of boundary conditions and layer thickness of liquid crystal (LC) confined to cylindrical pores on low frequency and high frequency relaxation processes. Low frequency measurements provided information on the relaxation of surface polarization that arose at LC – pore wall interface. The dynamics of molecular reorientations were investigated in high frequency experiments. In samples with axial orientation of molecules, the dielectric mode due to reorientation of molecules around their short axis was investigated. The homeotropic alignment of molecules facilitated the investigation of the librational mode. The behavior of this mode was different from the behavior observed in investigations of relaxation due to reorientation of molecules around their short axis. Broadening of the dielectric spectra was observed in confined LC. The broadening increases with decreasing liquid crystal layer thickness.

Low-frequency relaxation processes in Pb5Ge3O11 ferroelectric crystals

2004 ◽  
Vol 46 (9) ◽  
pp. 1722-1729 ◽  
Author(s):  
A. A. Bush ◽  
K. E. Kamentsev ◽  
M. V. Provotorov ◽  
T. N. Trushkova
Keyword(s):  
Low Frequency ◽  
Relaxation Processes ◽  
Ferroelectric Crystals ◽  
Frequency Relaxation
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