Increase In Dielectric Permittivity Research Articles

Fabrication and characterization of Ni0.3Zn0.7Fe2.0O4-BaTiO3 ceramic composites

The ceramic composites containing 1-25 vol% BaTiO 3 in a ferrite matrix phase of Ni 0.3 Zn 0.7 Fe 2 O 4 were fabricated by sintering at 1250°C in air. The sintered composites indicated a steep increase in dielectric permittivity in a small BaTi0 3 ratio up to 5 vol%. In a limited BaTiO 3 ratio of 3-15 vol%, a reaction between Ni 0.3 Zn 0.7 Fe 2 O 4 and BaTi0 3 resulted in the production of a liquid phase during sintering, which caused correspondingly the formation of secondary phases of BaFe 2 O 4 ss and hexagonal BaTi0 3 ss. These solid phase and microstructure changes, however, brought about little contribution to the increasing permittivity of the composites. Electrical property evaluations combined with compositional analysis revealed that the remarkably increasing permittivity could be predominantly attributed to the electron hopping between Fe 2+ and Fe 3+ in the ferrite matrix, which was caused by the incorporation of a small amount of Ti 4+ into the spinel sublattice.

Improvement of fatigue resistance on La modified BiFeO3 thin films

Abstract The effect of lanthanum (La) addition in BiFeO 3 (BFO) thin films deposited on Pt(1 1 1)/Ti/SiO 2 /Si(1 0 0) substrates prepared by soft chemical method was explained. Increasing La concentration promotes changes on structure, microstructure and dielectric/ferroelectric response of films. X-ray diffraction reveals that the films are free of preferred orientations and structural distortion. La addition promotes an increase in dielectric permittivity. The polarization switching and the fatigue behavior of the BFO films were significantly enhanced by the La concentration.

A comparative analysis of dielectric, rheological and thermophysical behaviour of ethylene vinyl acetate/BaTiO3 composites

Dielectric, rheological and thermal behaviours of ethylene vinyl acetate/barium titanate sphere (EVA/BaTiO3) composite materials were investigated in this work. Several composites were prepared for different volume concentrations (from 5% to 49%) and for two types of spheres sizes d: d = 9 µm and d = 105 µm. We show that the use of larger particles allows an increase of dielectric permittivity and thermal conductivity, particularly at high filler concentrations. A comparison between the thermal, dielectric and rheological behaviours of the composites is also reported in this paper. A linear dependence of the relative variation of thermal conductivity and dielectric permittivity, on the one hand, and thermal conductivity and Newtonian viscosity, on the other, was shown.

Dc-bias-field-induced dielectric relaxation and ac conduction in CaCu3Ti4O12 ceramics

The dielectric relaxation and ac conduction of CaCu3Ti4O12 (CCTO) ceramics were investigated at different temperatures under a dc bias. The dc bias gives rise to space charge accumulation, i.e. an electrode response, resulting in the significant increase of dielectric permittivity and dielectric loss tangent. Two Debye-like relaxations, arising from electrode and grain boundary responses, are present at low frequency with an increase of the dc bias. The electrode and grain boundary relaxations are distinguished according to the impedance spectroscopy and the frequency-dependent ac conductivity. The relaxation times of electrode and grain boundary relaxation are 0.955 ms and 0.026 ms, respectively, with a dc bias of 10 V at 328 K.

Synthesis and Electrorheological Properties of LTNO-PS Composites

Core-shell structural Li and Ti co-doped NiO/polystyrene samples (LTNO/PS) were synthesized by a sol-gel method and studied by TEM, X-ray diffraction, IR spectroscopy and LCR meter. It was found that the core-shell LTNO/PS particles are nearly smooth spheres with an average size of around 4.0 m, while the LTNO particles alone have a size of around 3.5 m. The electrorheological activity of LTNO particles with PS coating is larger than that of the bare ones with the same components. This research reveals that the high dielectric constant and corresponding dielectric loss of the LTNO is related to the Li and Ti contents. The increase of electrorheological activity of LTNO particles with PS coating is caused by the increase of dielectric permittivity, the surface structural change, and the reduction of leakage current of PS-coated samples due to the high resistivity and soft contacting of PS shell. By the preparation of core/shell structural materials and taking the advantage of the shell to reduce the leakage current between the particles, the electrorheological effect can be effectively increased.

Electret effect in intercalated crystals of the A^{III}B^{VI} group

Measurements of dielectric properties of Ni-intercalated GaSe and InSe have been performed. The present study is aimed at the investigation of the low-admixture region where the intercalation induced electret effect occurs. The effect exhibits pronounced peak-like concentration dependences and a non-monotonous temperature behaviour with maximum magnitudes at low temperatures. Intercalation leads to over tenfold increase of dielectric permittivity over the whole measured frequency range with up to several orders at low frequencies for GaSe. Temperature dependences of the permittivity demonstrate well-defined peaks with localizations and heights strongly depending on the concentration. A microscopic model of order-disorder type has been proposed that considers redistribution of intercalant atoms between non-polar octahedral and polar tetrahedral positions in the crystal van der Waals gaps. Such a redistribution can occur in the form of phase transition to the polar phase (corresponding to the electret effect) which is stabilized by the internal field. For the case of octahedral positions being more preferable, the model predicts a peak-like dependence of the crystal polarization on chemical potential due to passing through the interjacent polar phase in accordance with the measured behaviour of the electret effect. The calculated temperature dependences of dielectric susceptibility qualitatively reproduce experimental results for permittivity as well.

Structural study of NaNO2 embedded into porous glass

AbstractTemperature‐dependent Raman study of NaNO2 confined within porous glass with a pore size of 46 nm has been performed. It is demonstrated that the bandwidths and frequencies of the Raman bands as a function of temperature show similar behaviour, but not identical, as those observed for bulk NaNO2. This result indicates that the first‐order phase transition mechanism is only slightly modified by embedding NaNO2 into the porous glass. It seems that formation of “premelted state” is not significant in the studied material, at least up to 40‐50 K above Tc. At higher temperatures, however, a significant increase of bandwidth of the 1326 cm–1 band is observed, which could indicate appearance of “premelted” state. The dielectric measurements are consistent with this view since they show large increase of dielectric permittivity above 480 K, well below the NaNO2 melting temperature (554 K). (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Significantly enhanced low-frequency dielectric permittivity in the BaTiO3/poly(vinylidene fluoride) nanocomposite

To disclose an effect of ceramic particle size on dielectric properties of BaTiO3/ poly(vinylidene fluoride) (BT/PVDF) composites at low frequency, the dielectric properties of the BT/PVDF composites loaded with different diameter BT particles at the same volume concentration were studied at wide frequency ranges from 10−1to107Hz. A significant low-frequency dielectric permittivity increase in the BT/PVDF nanocomposite was noticed, which was not reported previously. The authors considered that the marked aggrandizement of interface and dipole polarization at low frequency is charged with the significant increase in dielectric permittivity.

The Effect of MRET Polymer Compound on SAR Values of RF Phones

This article is related to the proposed hypothesis and experimental data regarding the ability of defined polar polymer compound (MRETpolymer) applied to RF phones to increase the dielectric permittivity of water based solutions and to reduce the SAR (Specific Absorption Rate) values inside the “phantom head” filled with the jelly simulating muscle and brain tissues. Due to the high organizational state of fractal structures of MRET polymer compounds and the phenomenon of piezoelectricity, this polymer generates specific subtle, low frequency, non-coherent electromagnetic oscillations (optimal random field) that can affect the hydrogen lattice of the molecular structure of water and subsequently modify the electrodynamic properties of water. The increase of dielectric permittivity of water finally leads to the reduction of the absorption rate of the electromagnetic field by living tissue. The reduction of SAR values is confirmed by the research conducted in June-July of 2006 at RF Exposure Laboratory in Escondido, California. This test also confirmed that the application of MRET polymer to RF phones does not significantly affect the air measurements of RF phone signals, and subsequently does not lead to any significant distortion of transmitted RF signals.

Dielectric catastrophe at the magnetic field induced insulator to metal transition in Pr1-xCaxMnO3(x = 0.30, 0.37) crystals

The dielectric permittivity and resistivity have been measured simultaneously as a function of magnetic field in Pr1-xCaxMnO3 crystals with different doping. A huge increase of dielectric permittivity was detected near percolation threshold. The dielectric and conductive properties are found to be mutually correlated throughout insulator to metal transition evidencing the dielectric catastrophe phenomenon. Data are analyzed in a framework of Maxwell-Garnett theory and the Mott-Hubbard theory attributed to the role of strong Coulomb interactions.

Scaling of terahertz conductivity at the metal-insulator transition in doped manganites

Magnetic field and temperature dependence of the Terahertz conductivity and permittivity of the colossal magnetoresistance manganite Pr_{0.65}Ca_{0.28}Sr_{0.07}MnO_3 (PCSMO) is investigated approaching the metal-to-insulator transition (MIT) from the insulating side. In the charge-ordered state of PCSMO both conductivity and dielectric permittivity increase as function of magnetic field and temperature. Universal scaling relationships between the changes in permittivity and conductivity are observed in a broad range of temperatures and magnetic fields. Similar scaling is also seen in La_{1-x}Sr_xMnO_3 for different doping levels. The observed proportionality points towards the importance of pure ac-conductivity and phononic energy scale at MIT in manganites.

Dielectric spectroscopy studies on (PVP + PVA) polyblend film

The thermal behavior of (PVP + PVA) polyblend film have been examined using differential scanning calorimetry and scanning electron microscopy. Capacitance and loss tangent values of polyvinyl pyrrolidone (PVP) + polyvinyl alcohol (PVA) polyblend film were measured in the frequency range 1–100 kHz and temperature range 298–423 K. Dielectric permittivity of real part ( ε′) was obtained from capacitance data and dielectric permittivity of imaginary part ( ε″) was obtained from real part of dielectric permittivity and loss tangent values. The decrease in dielectric permittivity was observed with increasing frequency and also observed increase in dielectric permittivity with increasing temperature. The complex dielectric constant ( ε*) has been described by the electric modulus M* = (1/ ε*) = M′ + iM″. The data of M* has been analysed by the stretched exponential decay of the electric field, Φ( t) = exp−( t/ τ 0) β .

Surface contact measurement of electrical cell uncoupling in the mouse heart during ischemia

Electrical cell uncoupling via gap junction closure is assumed to cause characteristic changes of the passive dielectric spectrum of ischemic heart tissue. In order to find an independent evidence for this assumption, we analysed heart tissue during ischemia, measured the open state of gap junctions by means of dye transfer and correlated this parameter with the time course of the dielectric permittivity. The hearts were preischemically arrested by perfusion with Ringer solution containing 20 mmol/L of potassium (group KCL, n=10). This solution was also used with the addition of two gap junction blockers, either 3 mmol/L heptanol (group HEP, n=4) or 20 μmol/L palmitoleic acid (group PA, n=7). During subsequent ischemia at 21.0±0.5 °C, we monitored the passive dielectric permittivity spectrum and the spread of dye. After a sigmoidal increase the dielectric permittivity reached an upper plateau at 61±22 min of ischemia in KCL, at 45±7 min in PA, and already during perfusion at 2±1 min in group HEP. At the beginning of ischemia, dye migrated to neighbouring cells in groups KCL and PA but not in HEP. In KCL and PA, the intercellular diffusion of dye stopped after 64±26 and 40±11 min of ischemia, respectively. Our results suggest that the sigmoidal increase in dielectric permittivity and the reduction of dye diffusion depend on a common mechanism, namely gap junction closure.

Effect of mechanical milling on the structural, magnetic and dielectric properties of coprecipitated ultrafine zinc ferrite

Nanosized ZnFe 2O 4 particles containing traces of α-Fe 2O 3 by intent were produced by low temperature chemical coprecipitation methods. These particles were subjected to high-energy ball milling. These were then characterised using X-ray diffraction, magnetisation and dielectric studies. The effect of milling on zinc ferrite particles have been studied with a view to ascertaining the anomalous behaviour of these materials in the nanoregime. X-ray diffraction and magnetisation studies carried out show that these particles are associated with strains and it is the surface effects that contribute to the magnetisation. Hematite percentage, probably due to decomposition of zinc ferrite, increases with milling. Dielectric behaviour of these particles is due to interfacial polarisation as proposed by Koops. Also the defects caused by the milling produce traps in the surface layer contributes to dielectric permittivity via spin polarised electron tunnelling between grains. The ionic mechanism is enhanced in dielectrics with the rise in temperature which results in the increase of dielectric permittivity with temperature.

Enhanced Ferroelectric Properties of V-Doped BaBi4Ti4O15 Single Crystal

Single crystals of barium bismuth titanate (BaBi4Ti4O15) and BaBi4Ti4O15 partially substituted with V5+ and Ba2+ for Ti4+ and Bi3+ sites, respectively, at 5 at.% (Ba1.2Bi3.8Ti3.8V0.2O15), were grown using slow cooling. The incorporation of vanadium into the B-site of the layered pseudo-perovskite block resulted in a shift of the Curie point to a higher temperature, from 410°C to 425°C, and an increase in dielectric permittivity from 8000 to 9500 along the a(b)-axis direction and from 150 to 160 along the c-axis direction at 1 MHz and at their respective Curie points. The increase in Curie temperature brought about an increase in remanent polarization, and saturated remanent polarization was enhanced from 14.8 µC cm-2 to 15.5 µC cm-2.

The phase transition of (PMN)0.67(PT)0.33 single crystal

The dielectric properties and mechanical properties of (PMN)0.67(PT)0.33 single crystal were studied. A kink of dielectric permittivity was found around 70°C, which was induced by the rhombohedral to tetragonal phase transition. A sharp increase of dielectric permittivity and a modulus softening were observed around 130°C, which correspond to the spontaneous ferroelectric-relaxor phase transition. The dielectric properties in ferroelectric phase can be strongly influenced by the cooling rate during the phase transition, which can be attributed to the size effect of subdomains.

Dielectric properties and structure of water at room temperature. New experimental data in 5 Hz–13 Mhz frequency range

The dielectric permittivity of destilled water was measured in the frequency range of 5 Hz to 13 MHz with different thicknesses of the sample and for various oscillator levels. The two electrode method was used with plate condenser. A simple model, composed of a dipole liquid with domain structure is described. Basing on the model, we show possible ways of polarization. The present conclusions relate dielectric properties of water which result from the model. We propose a new conductivity model for dipole liquid with domain structure. Measurements of dielectric permittivity are consistent with the model. It is shown that experimental dielectric permittivity curves are a superposition two Debye's curves with different relaxation times and two different values of static dielectric constant. Debye's resonance for lower frequency is associated with oxygen's domain structure and for higher frequency with hydrogen's domain structure. We observe an increase of dielectric permittivity with time associated with ordering of the structure after filling. For thin samples we can observe damping of the Debye's resonance and interaction of the domains' structures.

Electro-Optic Effect and Influence of Bias Electric Field on the Goldstone Mode Dielectric Behavior in Smectic C* Phase and Cell Thickness Dependence of the Dielectric Permittivity of a Ferroelectric Liquid Crystal Mixture

Results reported here on the spontaneous polarization, switching time, rotational viscosity and Goldstone mode dielectric strength and relaxation frequency as a function of electric field in the SmC* phase of a Ferroelectric liquid crystal mixture. It has been observed that the spontaneous polarization and the rotational viscosity are almost independent of the amplitude of the applied field. The response time however depends on the applied field. The field required to unwound the helix is much larger than the structurally similar compounds. The dielectric strength of the Goldstone mode is found to decrease with the increase of bias electric field but the relaxation frequency of the Goldstone mode on the other hand increases with the increase of bias electric field. Results also show that the critical field EC, for unwinding the helical structure in SSMC* phase depends on the temperature. Rotational Viscosity of the Goldstone mode has also been determined under D.C bias field in the SmC* phase. Dielectric permittivity is found to increase with the increase of cell thickness. The increase of dielectric permittivity and the temperature of transition (TC *), in a thicker cell have also been explained considering theoretical relations developed earlier.

Phase transitions and properties of perovskite ferroelectric ceramics and films for certain applications

The structure-properties relationships and phase transitions in perovskite ceramics, and films of PLZT, PLZST, PST, PSN, PMNT compounds are discussed with regard to ordering, relaxor behaviour, pronounced ferroelectric, electromechanical and electrocaloric properties. The theoretical approach is extended to the time dependent Ginsburg-Landau model. The evolution of dielectric properties in relaxors after the change of temperature and electric field creating an increase of dielectric permittivity is found to follow a logarithmic law of decay. A strong electromechanical response is observed in a number of thin films of different compositions.

Evolution of dielectric properties in transparent PLZT 8.3/70/30 ceramics at the diffused phase transition

The time evolution of dielectric properties after a temporary change of temperature and electric field is investigated. It is found, that below the temperature of ˛' maximum Tm the change of temperature and electric field creates an increase of dielectric permittivity followed by logarithmic decay when the change of these parameters is finished. At every temperature the dielectric properties are characterized by a unique ˛'(t) independent on previous thermal history. If the applied electric field is E< Ec, the state of polarization is not affected. The dependence on dielectric constant of storage time under field as well as field intensity is determined.