Search results for "Permittivity"
showing 10 items of 176 documents
Full band spectroscopic studies on the molecular mobility of diluted alcohols
1991
Abstract Static permittivity has been determinded for pure n-decanol and cyclohexanol and their solutions in cyclohexane up to very dilute solutions, the dipole moment is found to decrease with the increase in concentration to a minimum, then it increases continuously. At a certain concentration range, no effect of temperature on the measured dipole moments could be observed, within the observed temperature interval. The dielectric loss was measured in the frequency range from o.1 GHz to 670 GHz. The data are analysed in several Debye and Frohlich terms and the results are discussed.
Electric polarization of Onsager fluids
2002
The problem of correct determination of electrical and optical characteristics of molecules of dielectric fluids can actually be brought to problem of description of the effective internal field which consist of the field included by external sources and the cumulate electric field of molecules on the medium including intermolecular interactions. An attempt was made to modify the model Onsager theory. A polarizable molecular dipole enclosed in spherical cavity is substituted for a rigid one submerged in polarizable medium which fills the cavity. The local dielectric permittivity of the Heaviside type is replaced for the oscillating, rapidly damping function of Fresnel integral. The analytic…
Non-linear dielectric behaviour and glass phase in Sr1-xCaxTiO3(x= 0.002 andx= 0.003)
1999
This work reports a study of the temperature and electric field dependence of the dielectric constant of strontium calcium titanate. The first part of the paper is focused on the analysis of a mean-field model for the polar clusters generated by the random impurities of calcium. It is shown that the dipolar moments within each cluster can be represented by an equivalent quantum two-level system. General expressions for the temperature and field dependence of the Edward-Anderson order parameter and of the electrical polarization are given. Analytical solutions are also obtained in the limit of high temperatures and in the limit of high tunnelling frequencies. The second part of the work repo…
Structure and properties of epitaxial ferroelectric PbLu0.5Nb0.5O3thin films
2001
Abstract Epitaxial thin film heterostructures of PbLu0.5Nb0.5O3 (PLuN) and La0.5Sr0.5CoO3 (LSCO) were deposited by in situ pulsed laser ablation onto MgO and LaAlO3 (100) substrates. The formation of crystalline phases, epitaxy, film-electrode-substrate orientation relationships, crystal perfection and chemical order were studied by x-ray diffraction. The structural properties were found to depend on the deposition conditions and on the substrate. The perovskite PLuN films were pseudocubic and epitaxial, with (001) planes parallel to the substrate surface. At room temperature, Au/PLuN/LSCO capacitors exhibited ferroelectric behavior and zero-field dielectric permittivity about e ≅ 210–260, …
Structure and dynamic dielectric behaviour of ferroelectric [NH2(CH3)2]3Sb2Br9(DMABA)
2000
The crystal structure of DMABA has been determined at 293 and 180 K. It crystallizes in the monoclinic P21/c space group. The structure was refined to R1 = 0.0466 for 1269 independent reflections at 293 K and R1 = 0.038 for 1728 reflections at 180 K. DMABA is isomorphous with the chlorine analogue, DMACA. Its anionic sublattice forms corrugated two-dimensional layers in the bc plane. There are two crystallographically independent, disordered dimethylammonium cations in the crystal structure. One of them occupies cavities inside the polyanionic layers; the other is located between the layers. The temperature dependence of lattice parameters has been determined between 100 and 290 K. The pres…
The structure and phase transition of tris(n-propylammonium) enneachlorodiantimonate (III),
1996
The crystal structure of at 298 K has been determined (monoclinic, space group Cc, a = 19.464(2) ?, b = 17.736(2) ?, c = 8.116(2) ?, , Z = 4). The structure consists of one-dimensional polyanionic chains extended along the c-axis, and n-propylammonium cations located in elongated cavities formed by polyanions. The cations are connected to chlorine atoms by hydrogen bonds. Differential scanning calorimetry, the temperature dependence of the lattice parameters and static electric permittivity studies revealed a first-order phase transition at K of an `order - disorder' type. It is related to the ordering of n-propylammonium cations that occurs on decreasing the temperature. Debye-like dispers…
Influence of B-site chemical ordering on the dielectric response of the Pb(Sc1/2Nb1/2)O3relaxor
2001
The influence of chemical B-site ordering between Sc3+ and Nb5+ cations on the properties of the Pb(Sc1/2Nb1/2)O3 (PSN) relaxor has been investigated. Depending of the degree of ordering, PSN exhibits different behaviours. For a completely disordered material, a relaxor–ferroelectric phase transition is observed at 379 K by DSC. Ordering between Sc3+ and Nb5+ cations on the B-site of the perovskite structure leads to a non-homogeneous material constituted of two phases: ordered and disordered phases. The phase transition temperature of the ordered phase is confirmed to be lower (346 K) than that of the disordered phase. It appears that the phase transition of the disordered phase is shifted…
The Structural and Dielectric Properties of the Li0.005Na0.995NbO3Ceramics
2009
The sodium niobate-lithium niobate (Li x Na1 − x NbO3) compounds were synthesized using conventional solid-state processing. Phase analysis was performed by X-Ray diffraction, and microstructural morphology was assessed by scanning electron microscopy. The dielectric measurements were performed in heating and cooling processes without and under axial pressure up to 120 MPa. It has been stated, that the maximum of electric permittivity ϵ (T) becomes more diffused with the increase of axial pressure and the temperature of phase transition T0 decreases. The value of tanδ increases with the increase of axial pressure and its local maximum shifts towards lower temperatures.
Imprinting the complex dielectric permittivity of liquids into the spintronic terahertz emission
2021
We report an approach in time-domain terahertz (THz) spectroscopy for measuring the dielectric response of liquids based on inherent properties of spintronic THz emitters (STEs). The THz electric field radiated from the STE is inversely proportional to the sum of the complex refractive indices of the media surrounding the thin metallic stack of the STE and the stack's conductivity. We demonstrate that by bringing a liquid in contact with the emitter, its complex refractive index and accordingly its dielectric response are imprinted into the radiated electromagnetic field from the emitter. We use water as the test liquid and ascertain its dielectric loss and permittivity in the range of ∼0.…
Dielectric breakdown strength of epoxy bimodal-polymer-brush-grafted core functionalized silica nanocomposites
2014
The central goal of dielectric nanocomposite design is to create a large interfacial area between the matrix polymer and nanofillers and to use it to tailor the properties of the composite. The interface can create sites for trapping electrons leading to increased dielectric breakdown strength (DBS). Nanoparticles with a bimodal population of covalently anchored molecules were created using ligand engineering. Electrically active short molecules (oligothiophene or ferrocene) and matrix compatible long poly(glycidyl methacrylate) (PGMA) chains comprise the bimodal brush. The dielectric breakdown strength was evaluated from recessed samples and dielectric spectroscopy was used to study the di…