Search results for "Permittivity"
showing 10 items of 176 documents
Permittivity Measurements of Lossy Liquids at Millimeter-Wave Frequencies
1983
A measurement system is described which allows the determination of the complex permittivity of high-loss liquids at millimeter waves. Basically, the setup consists of a waveguide interferometer whose unknown arm embodies a liquid holder irradiated by an open-ended rectangular waveguide. The sample thickness is varied by means of a piston driven by a micrometer screw. The bridge output then is read as a function of the liquid thickness. Best fitting between experimental and computed data through a suitable model of the system enables the permittivity to be determined. The system can operate, with high sensitivity, over the whole frequency range of the dominant mode propagating in the wavegu…
The physical mechanisms of relaxation times distribution in inorganic and organic disordered ferroelectrics
2007
Abstract We discuss the physical background for relaxation times distribution in organic and inorganic disordered ferroelectrics. We show that such background is a disorder which is believed to be a reason for relaxor behavior. Due to this disorder the internal electric and elastic fields are of a random nature being characterized by certain distribution function. Having the distribution function f ( E ) of random field E , we can obtain the distribution function of relaxation times F ( τ ) with the help of relation between τ and E . Latter relation can be obtained considering the dynamics of a single electric dipole in a random field created by the ensemble of defects and impurities in a s…
Anomalous Broad Distribution of Relaxation Times in Mixed PMN-PSN Ceramics
2007
Dielectric permittivity of 0.8PMN-0.2PSN ceramic was measured in the frequency range from 20 Hz to 3 GHz. The typical ferroelectrics relaxor dielectric dispersion was observed. From the frequency dependence of complex dielectric permittivity, the distribution of relaxation times was calculated. The low frequency limit of the distribution of relaxation times diverges according to the Vogel–Fulcher law with the freezing temperature T f = 226 K which is lower than in PMN ceramics, obtained previously. The comparison of distributions of relaxation times between 0.8PMN-0.2PSN and pure PMN tends to the conclusion about smaller polar nano regions in 0.8PMN-0.2PSN ceramic.
Indications of Two Separate Relaxators in the Subphonon Region of Tetragonal BaTiO 3
1994
Significant discrepancies were generally reported in the dynamics of BaTiO3 between results deduced from various experimental techniques. Here dielectric and quasi-elastic light scattering measurements are investigated on high-quality BaTiO3 crystals. We show that two relaxators have to be introduced below the soft-phonon frequency. A complete dielectric dispersion in a very wide frequency range is thus achieved which consistently relies the high-frequency dielectric results and the Raman data. There is also a qualitative agreement between our two-relaxator model and the dynamics which were deduced some time ago from EPR experiments.
The multimodal detection as a tool for molecular material-based gas sensing
2013
Abstract The adsorption of a target gas on a material induces a change in several physical characteristics, such as the dielectric constant, the work function or the conductivity. The use of different transducers sensitive to the variation of these parameters appears to be a relevant methodology worthy of investigation. In the field of sensors, molecular materials present interesting and potentially valuable features as sensing elements for real gas sensor applications. In this article, we review the different types of conductimetric transducers and also show how a molecular material-based microwave transducer can be used for gas sensing. Among conductimetric transducers, resistors have bee…
Spectral theory of a Neumann-Poincare-type operator and analysis of cloaking due to anomalous localized resonance
2011
The aim of this paper is to give a mathematical justification of cloaking due to anomalous localized resonance (CALR). We consider the dielectric problem with a source term in a structure with a layer of plasmonic material. Using layer potentials and symmetrization techniques, we give a necessary and sufficient condition on the fixed source term for electromagnetic power dissipation to blow up as the loss parameter of the plasmonic material goes to zero. This condition is written in terms of the Newtonian potential of the source term. In the case of concentric disks, we make the condition even more explicit. Using the condition, we are able to show that for any source supported outside a cr…
Uniaxial Pressure Effect on Electric Properties of PSN and 0.95PSN-0.05PLuN Ceramics
2006
The dielectric, pyroelectric and hysteresis loops measurements of PSN and 0.95PSN-0.05PLuN ceramics stress-free and under the stress (0–1.5 kbar) have been carried out. It was shown that axial pressure seems to change the partially ordered state to a disordered one, shifts the phase transformation and decreases the thermal hysteresis of the dielectric permittivity and the field-polarization hysteresis. These effects can be connected with change in domain structure, inter-ionic distances and defect density under the action of uniaxial pressure. The thermodynamic parameters of the phase transition were also determined.
Temperature and electric field dependence of the permittivity of Ba0.9Sr0.1TiO3 films epitaxially grown on cuprate electrodes
1999
Abstract Cuprate, high-temperature superconductors and perovskite ferroelectrics have similar crystal structures and chemical constituents and, therefore, it can be advantageous to deposit epitaxial trilayer capacitors with high-Tc electrodes and operate these at room temperature, well above the transition temperature Tc, in order to achieve a high dielectric constant, tunability, and relatively low microwave loss. Epitaxial heterostructures (200 nm)YBa2Cu3O7−δ/(600 nm)Ba0.9Sr0.1TiO3/(200 nm)YBa2Cu3O7−δ and (200 nm)NdBa2Cu3O7−δ/(600 nm)Ba0.9Sr0.1TiO3/(200 nm)NdBa2Cu3O7−δ were laser deposited on (100)LaAlO3 substrates. The relative dielectric permittivity e/e0 of Ba0.9Sr0.1TiO3 was in the ra…
SrTiO3and Pr Effects on Structural, Dielectric and Ferroelectric Properties of Na0.5Bi0.5TiO3Ceramic
2015
[(Na0.5Bi0.5TiO3)0.7Sr0.3]1-xPrxTiO3(NBTS30P) (0 ≤ x ≤ 0.025) ceramics were prepared by solid-state synthesis process. Their crystal structure, microstructure dielectric and ferroelectric properties were studied. XRD data show that all of the ceramics possess a single perovskite phase. SEM results confirm that the ceramics are well sintered and exhibit relative densities higher than 97%. The results also reveal that the microstructure of the different compositions do not show a significant variation. The praseodymium (Pr) substitution to NBTS30 results in a change of crystal structure from cubic to tetragonal at x = 0.025. At the same time, electric permittivity decreases, the maximum is br…
Dielectric properties of BaTiO3 based materials with addition of transition metal ions with variable valence
2013
Dielectric properties of BaTiO3(BT), BaTiO3+0.1wt.%MnO2(BTMn) and BaTiO3+0.1 wt.%Fe2O3 (BTFe) solid solution was investigated. The effects of substitution on the microstructure and on the electric properties of BaTiO3 samples were studied by performing X-ray diffraction and electric measurements. X-ray diffraction analysis of the samples shows the formation of single-phase compound with a tetragonal structure at room temperature. SEM microphotographs exhibit the uniform distribution of grains. The electric properties (a real part of electrical permittivity(e') and an imaginary part of electric modulus (M")) were investigated in the temperature range from 150K to 600K and in the frequency ra…