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Al doped BiFeO3-BaTiO3 (BFA-BT) systems with a defined composition were prepared by a conventional solid-state method. From SEM and XRD analyses, the high-density of the ceramics and the high lattice parameters ratio c T / a T traducing large distortions of the rhombohedral phase play a dominant role in the enhanced piezoelectric properties. The high polarization and large strain were achieved in the BF0.970A0.030-BT system. 57Fe M o ¨ ssbauer spectra revealed the large disorder of Fe3+ at B sites preferentially occupied by more Al3+ doping ions, forming the diffusive phase transition for dielectric behaviors in ceramics. Grain and grain-boundary effects were pointed out from the dielectric modulus and its related thermal evolution. AC capacitances indicated two relaxation processes marked by the grains and interfaces involved in the polycrystalline ceramics for highly doped systems.

The [(C 2 H 5 )NH 3 ] 2 ZnCl 4 hybrid material was prepared and their calorimetric study and electric properties were investigated at low temperature. Indeed, the X-ray powder diffraction confirms the purity of the synthesized compound and the differential scanning calorimetric show several phase transitions at 231 K, 234 K, 237 K, 247 K and 312 K, which are proven by the variation of σ p and σ dc as a function of temperature. The equivalent circuit based on the Z-View-software was proposed and the conduction mechanisms were determined. The alternative current (ac) electrical conduction in [(C 2 H 5 )NH 3 ] 2 ZnCl 4 is studied by two processes that can be attributed to a hopping transport mechanism. These processes are the correlated barrier hopping (CBH) model in regions I and IV and the overlapping large-polaron tunneling (OLPT) model in region III. The optical study was also investigated by UV–vis absorption. In fact, the insulating behaviour of the material is established by Tauc plot obtaining a large value of indirect optical band gap energy.

[N(CH3)3H]2ZnCl4 has been analyzed by X-ray powder diffraction patterns, differential scanning calorimetry and impedance spectroscopy. The [N(CH3)3H]2ZnCl4 hybrid compound is obtained by slow evaporation at room temperature and found to crystallize in the orthorhombic system with Pnma space group. Five-phase transitions at low temperature were detected by differential scanning calorimetry measurements. The analysis of Nyquist plots has revealed the contribution of three electrically active regions corresponding to the bulk mechanism, distribution of grain boundaries and electrode processes. The dielectric relaxation is described by a non-Debye model. The study of the dielectric constants ϵ′, ϵ″ and loss tangent tan (δ) with frequency exhibits a distribution of relaxation times. The complex modulus plots have confirmed the presence of grains and grain boundaries as well as a non-Debye type of relaxation in the material. Thermodynamic parameters such as the free energy for dipole relaxation ΔF, the enthalpy...

The [N(CH 3 ) 3 H] 2 CuCl 4 compound is obtained by slow evaporation at room temperature and is characterized by XRD. It is found to crystallize in the monoclinic system with P2 1 / C space group. Four phase transitions at low temperature are detected by differential scanning calorimetry. The material is characterized by impedance spectroscopy technique measured in the 10 −1 –10 6 Hz frequency and 203–313 K temperature ranges. The dielectric permittivity indicates a ferroelectric–paraelectric phase transition at 293 K. The analysis of Nyquist plots has revealed the contribution of three electrically active regions corresponding to the bulk mechanism, distribution of grain boundaries and electrode processes. The modulus plots are characterized by the presence of two peaks associated with the grain and grain boundaries. The temperature dependence of the electrical conductivity ( σ g ) and AC conductivity ( σ ac ) confirms the phase transitions at T 1 = 226 K, T 2 = 264 K and T 3 = 297 K.

In this work, a polystyrene/polyaniline powder of core-shell structure was prepared by chemical polymerization of aniline, using tartaric acid as a dopant and ammonium persulfate as an oxidizer in presence of polystyrene. The matrix effect on the electrical properties of pure polyaniline was studied by means of dielectric relaxation spectroscopy (DRS) and electron paramagnetic resonance (EPR) technique at room temperature. AC conductivity and dielectric permittivity of the polystyrene/polyaniline were investigated in the frequency range of 10−1 - 106 Hz. The doped polyaniline showed a DC conductivity of 10−5 S/cm. Its incorporation in a polystyrene matrix lowered the conductivity of the mixture up to 10−7 S/cm. This value remains acceptable for semi conductive applications. EPR characterization confirmed this behavior, it gave g-factor values equal to 2.0046 and 2.0093 for polyaniline and polystyrene/polyaniline respectively, close to the free electron g-factor value (2.0023), suggesting that the resonance comes from the delocalized electrons in the main chain of polyaniline. High dielectric constants were obtained for both polyaniline and polystyrene/polyaniline allowing their use as high k-dielectrics. The composite material showed two different relaxation processes. The first one may originate from the electrode polarization while the second is associated to the bulk relaxation of charge carriers.

Bismuth vanadate (BiVO 4 ) nanomaterials were synthesized by mechano-chemical ball milling method and complementary investigations were devoted to their structures, nanoparticle morphologies and electronic active centres. The dielectric and conductivity behaviour were analysed systematically in wide temperature and frequency ranges to correlate such physical responses with the peculiarities of the samples. Large interfacial polarisations favoured by high specific surfaces of nanoparticles account for a drastic enhancement of the dielectric function in the quasi-static regime. Exhaustive analyses of the dielectric experiments were achieved and account for the main features of dielectric functions and their related relaxation mechanisms. The electrical conductivity is thermally activated with energies in the range 0.1–0.6 eV depending on the sample features. DC conductivity up to 10 –3 S/cm was obtained in well crystallized nanoparticles. Vanadium ions reduction was revealed by EPR spectroscopy with higher concentrations of the active centres (V 4+ ) in more agglomerated and amorphous nanopowders. The EPR spectral parameters of V 4+ were determined and correlated with the local environments of reduced vanadium ions and the characteristics of their electronic configurations. An insight is also made on the role of active electronic centres (V 4+ ) on the conduction mechanism in nanostructured BiVO 4 .

Conducting polymer composite films based on different aliphatic polyamides (PA) (PA-6, PA-11 and PA-12) have been synthesized by in situ aniline polymerization inside a surface layer of the PA host matrix. Dielectric permittivity and dielectric loss of these films are explained in terms of the interfacial polarization. The real part of permittivity is found to be higher in the PA/polyaniline (PANI) composite films than in the virgin PA polymer matrix. Such behaviour is attributed to the interaction between PA and PANI molecular chains and to the conductivity increase after the aniline polymerization. The performed confocal Raman spectrometry and X-ray diffraction studies also confirmed the presence of interactions between PA and PANI molecular chains.

Summary: Composite polyurethane/polyaniline (PU/PANI) films have been chemically prepared by oxidative in-situ polymerization of aniline inside the previously swelled PU film. Swelling kinetic studies have shown that for PU films the swelling degree of aniline is 25 wt.%. The dielectric and electrical properties of the composite films were measured using dielectric relaxation spectroscopy and four-probe method. Dielectric measurements as a function of temperature and frequency revealed the presence of a relaxation process for the composite PU/PANI-HCl film. This relaxation was explained in terms of interfacial polarization due to the double-layered structure of the composite film. The activation energy values found by dielectric and electrical measurements are close and this result confirms the conducting character of the PANI containing layer.

Composite polyurethane/polyaniline and polyamide-6/polyaniline films were chemically prepared by oxidative in situ polymerization of aniline inside the previously swelled matrix film. Swelling kinetic studies had shown that for polyurethane and polyamide-6 films the swelling degree of aniline was 25 wt.% and 15 wt.%, respectively. The dielectric and electrical properties of the composite films were established using dielectric relaxation spectroscopy and four-probe method. Dielectric measurements as a function of temperature and frequency revealed the presence of relaxation processes influenced by the nature of the polymer matrix, i.e. one relaxation process for the polyurethane based composite film and two relaxation processes for polyamide-6 based composite film. These relaxations were explained in terms of interfacial polarization caused by the polyaniline organisation as it was revealed by atomic force microscopy. Activation energy values obtained by dielectric and electrical measurements are close and this result confirms the conducting character of the polyaniline containing layer.

The new perovskite compound La0.5Ba0.5FeO3-delta was prepared by the sol-gel method. The Rietveld refinement, from the X-ray diffraction pattern, proved that the sample presents single phase type cubic structure at room temperature. In addition, electrical properties were performed using complex impedance spectroscopy (CIS) technique as a function of frequency (100 Hz to 7 MHz) at various temperatures (278-573 K). As a matter of fact, impedance analysis was performed using the equivalent circuit model and it indicated the presence of a single semicircle arc. Furthermore, the obtained results of the AC conductivity have been discussed in terms of the non-overlapping small polaron tunneling (NSPT) model. Finally, it is worth mentioning that the conductivity of our investigated perovskite oxide was found to be sigma(573) = 1.23 x 10(-2) Omega(-1) cm(-1). These results confer to this material a potential application as a cathode material.

The CaCu3Ti4O12 (CCTO) compound shows an unusually high and almost temperature independent dielectric constant at low frequencies. CCTO powders have been synthesized by an organic gel-assisted citrate process. The ceramic microstructure was optimized for a given sintering process. Both the grain size and density are shown to be maximum when PVA is introduced in powder before the complete formation of CCTO. A correlated increase of the dielectric constant is evidenced by impedance spectroscopy measurements. Results support the IBLC model proposed to explain the high dielectric constant of CCTO.

The dielectric properties of conducting polymer composite films based on polyaniline located in a thin layer in the vicinity of the surface of different insulating polymer matrices (polyamide and poly(ethylene terephthalate)) have been studied using dielectric relaxation spectroscopy in a wide temperature and frequency range. Several relaxation processes related to the film surface conductivity and influenced by the nature of the polymer matrix have been found in these composites. The nature of the polymer matrix is found to influence the rate of aniline polymerization, the distribution of polyaniline clusters and the depth of aniline penetration as shown, respectively, by Conducting Probe AFM and Raman spectroscopy. These features are correlated to the dielectric behavior of the composite films.

International audience; The flexoelectric effect is simply defined as the coupling between the strain gradient and polarization in solid dielectrics. It may be seen as an alternative transduction mechanism to the piezoelectric effect to directly sense the curvature of bent flexible thin structures. In the case of large curvatures, flexible and compliant sensors are required and soft polar elastomers may be suitable for curvature sensing. In this study, we report the flexoelectric characterization of soft semi-crystalline polyurethane (PU) films with thicknesses ranging from 1.7 μm to 350 μm. Dynamic bending experiments have been performed on PU films deposited onto rigid steel substrates in the vicinity of the mechanical resonance frequency of the cantilever beams. Quasi-static flexoelectric coefficients of PU films could be obtained by using a classical oscillating model. A global large increase of μ′12 with the decreasing film thickness was found, especially for thicknesses lower than 25 μm. The variation of μ′12 is explained by the presence of a Young's Modulus gradient through the thickness of PU films. Besides, a concomitant uncommon dramatic decrease in the dielectric constant is observed. The combination of these two effects contributes to enhancing the flexocoupling “F” constant with the decreasing thickness. At last, the potential use of a 6.6 μm-thick soft PU film as a large curvature sensor has been experimentally demonstrated by subjecting a flexible Aluminum foil/Polyethylene terephthalate bilayered cantilever to large deflections. A curvature of about 80 m−1 (radius of curvature of ∼1.2 cm) could be sensed under low frequency (3 Hz) bending motion. These results may pave the way for the development of low cost and easy to implement soft flexoelectric elastomer-based large curvature sensors on highly flexible metallic structures.

The present work deals with the preparation of films from polymeric core-shell particles. Our approach is based on the chemical polymerization of a very thin layer of polyaniline (PANI) around particles of transparent polymers (polyamide and polystyrene). Films are then obtained by dissolving the two type synthesized core-shell powders in dichloromethane and m-Cresol respectively. Electrical properties were investigated using a dielectric relaxation spectrometer. Both composite films exhibited a percolative behaviour and a well established dc conductivity for high PANI concentration related to the conductive properties of the PANI spanning clusters. This property allows using such films in semi-conductive applications. For polyamide films, high dielectric constants were obtained at 5 wt. % of PANI allowing their use as high k-dielectrics compatibles with organic printed circuit boards.

Dielectric relaxation spectroscopy is applied for the study of α- and Maxwell–Wagner (MW) relaxations of polyurethane (PU) coating on steel and gold substrates during a water exposition. The evolution of the α-relaxation time of the PU coating in contact with water can be characterized by four stages: (1) Relaxation time increases with starting of the water penetration. The presence of water molecules in the coating leads to an increase in charge carriers at the metal/polymer double layer which influences the cooperative molecular motions in the polymer coating. (2) Relaxation time decreases because of the plasticizing effect of the water in the polymer. (3) Decreasing of the relaxation time and ionic conductivity associated with formation and growing of blisters. Appearance of blisters gives way to an interfacial dielectric relaxation (MW) in the low frequency region. (4) Overlapping of the α-relaxation peak by MW effect when the coating is completely displaced with water. The role of the metal/polymer interaction on these stages is discussed.

SiC nanopowders have been investigated by means of dielectric relaxation spectroscopy over the frequency range 0.1 Hz–1 GHz and sample temperature range 150–570 K. The relaxation processes and the electrical conductivity are analysed using the Havriliak–Negami dielectric response. The electrical and dielectric properties are interpreted taking into account the material composition, grain morphology and the nature of the interfaces. We have shown that the dielectric and electrical behaviour are influenced by interfacial polarisation in powders with high specific surfaces.

Quenched systems corresponding to different reaction extents of polyurethane (PU) network formation have been studied using broadband dielectric spectroscopy in order to apprehend the evolution of α-relaxation during gel formation. Three PU systems based on poly(oxypropylene) triol of molar mass 260, 700 and 6000 g/mol. have been investigated. While for the pure triols the distribution and temperature dependence of relaxation times are found to be similar, their evolution with connectivity in PU systems depends on molar mass of the triol used. This has been interpreted in terms of relative influence and transformation of active dipoles as a consequence of reaction and evidenced by the appearance of a new dynamic associated to new active dipoles.

The influence of metal–polymer interaction on dielectric relaxation properties of polyurethane (PU), prepared from poly(oxypropylene)diol and hexamethylendiisocyanate, was investigated by means of dielectric relaxation spectroscopy in the frequency domain on the dependence of the thickness of the PU layer and electrode material (gold and steel). Strong electrostatic part of an adhesion interaction between steel substrate and PU results in changes of the α -, β -, γ - and Maxwell–Wagner–Sillars relaxation of the PU, as compared to a gold substrate. The effect of the metal–polymer double layer results in the complication of the cooperative and local motions in the polymer. The influence of metal–polymer interaction on the relaxation parameters becomes pronounced at a thickness of less than 60 μm for the steel substrate. For the gold substrate the relaxation characteristics hardly depend on the thickness.

Dielectric Relaxation Spectroscopy (DRS) has been applied for the investigation of the influence of the metal/polymer interfacial interaction on the dielectric relaxation properties of polyurethane (PU), in the frequency range from 0,1 Hz to 10 MHz at temperatures from 223 to 423 K in the dependence of thickness of the PU layer (from 10 to 150 μm) and electrode material (gold and steel). Strong electrostatic interaction between steel substrate and the PU results in changing the dielectric relaxation properties of the latter, comparatively with gold substrate. The influence of metal/polymer electric double layer becomes significant at thickness less than 60 μm for the steel substrate. For the gold electrodes, the relaxation characteristics of the PU hardly depend on thickness.

The present work deals with the preparation of transparent antistatic films from an extreme dilution of an intrinsically conducting polymer (ICP) with not coloured polymers. Our approach is based on the chemical polymerization of a very thin layer of Polyaniline (PANI) around particles of an insulating polymer (PA12). Films were obtained by dissolving the synthesized core-shell particles in m-Cresol. The electric property and structure relationships were investigated by using dielectric relaxation spectroscopy, X-ray diffraction and micro-Raman spectroscopy. Composite films exhibited a well established dc conductivity over all the frequency range for 10 wt. % of PANI concentration related to the conductive properties of the PANI clusters. X-ray diffraction data show broader and lower intensity of PA12 peaks when increasing PANI content, probably due to the additional doping effect of m- cresol. The doping of PA12/PANI films with Dodecyl benzene sulfonic acid (DBSA) was unequivocally verified by Raman spectroscopy.

Dielectric measurements are reported on the changes that occur in the nature of the dipole relaxation processes during cure of an epoxy-amine and a diisocyanate-triol system. The epoxy resin forms a vitrified solid in the final cured state, whereas the urethane retains its elastomeric properties. The initial behaviour for the epoxy resin is dominated by ionic conduction processes. Subtraction of the conductivity contribution reveals a dipolar relaxation process, which is analysed using the Havriliak-Negami (HN) equation. The characteristic exponent 1 - n of the HN equation changes in a similar manner to that found with other epoxy-amine systems. However, the dipolar process in the urethane occurs at very high frequency and a different form of the 1 - n dependence is observed. Sensitivity of the dielectric method for the detection of vitrification and gelation is critically assessed. If the vitrification is allowed to occur, then detection of a gel point may not necessarily be inferred from the dielectric data.

Dielectric, ultrasonic and 13C nuclear magnetic resonance relaxation measurements are reported on mixtures of t-butyl alcohol and water over the temperature range 278–308 K. Supporting measurements of the refractive index, density and viscosity are also presented. Deviations from ideal mixing behaviour are observed in the volumes of mixing, permittivities and adiabatic compressibilities of the mixtures. The location of the minima in the excess occurring at different compositions depend upon the method of measurement. Similarly the relaxation behaviour, as observed using different techniques, reveals different aspects of the motion of the molecules in the fluid. The various effects observed are rationalized in terms of a model in which it is assumed that t-butyl alcohol dimers and trimers and various hydrated forms play an important role in determining the structure of these mixtures.

The X-ray powder diffraction pattern shows that at room temperature, [N(CH3)3H]2ZnCl4 is crystallized in the orthorhombic system with Pnma space group. The phase transitions at T1 = 255 K, T2 = 282 K, T3 = 302 K, T4 = 320 K, and T5 = 346 K have been confirmed by the differential scanning calorimetry. The electrical technique was measured in the 10−1–107 Hz frequency range and 233–363 K temperature intervals. The temperature dependence of the dielectric constant at different temperatures proved that this compound is ferroelectric below 282 K. Besides, [N(CH3)3 H]2ZnCl4 shows classical ferroelectric behaviour near curie temperature. In order to characterize the phase transitions, Raman spectra have been recorded in the temperature range of 233–383 K and the frequency range related to the internal and external vibrations of the cations and anions (90–4000 cm−1). The temperature dependence of the Raman line shifts ν and the half-width Δν detects all phase transitions and confirms their nature, especially at 2...

An application of blocking layers between sample and electrodes permits to avoid the influence of electrode polarization and opens new opportunities in DRS investigations of the conductive systems, such as polysaccharides and proteins containing water and electrolytes. The proposed methodical approach is applied for plate capacitor type of the cell and for the one in coaxial lien for the measurements in the frequency region 0,1 Hz-10 MHz and 1 MHz-1GHz respectively, using Novocontorl GmbH equipment. The possibilities to investigate an evolution of the biological system in time and temperature scale avoiding the influence of electrode polarization are demonstrated.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A new approach to explain the interfacial polarization phenomenon in conducting composite films is proposed. HCl-doped poly(ethylene terephthalate) (PET) and polyamide-6 (PA-6) matrices with embedded polyaniline (PANI) particles as filler were investigated and analysed, combining dielectric spectroscopy and AFM electrical images with the effective medium theory analysis. Up to three relaxation peaks attributed to the interfacial polarization phenomena were detected in the studied frequency range (0.1 Hz–1 MHz). The AFM electrical images revealed that the doped PA-6/PANI composite can be modelled as a single-type particle medium and the PET/PANI one as a two-type particle medium. A simple dielectric loss expression was derived from the Maxwell–Wagner–Hanai mixture equation and was applied to the experimental data to identify the interfaces involved in each of the relaxation peaks. The parameter values (permittivity, conductivity, volume fraction of the PANI particles) were found to agree well with the measured one, hence validating the models.

The dielectric relaxation measurements on poly(ethylene-terephthalate) (PET) containing adsorbed aniline and polyaniline (PAni), prepared by polymerization into the PET matrix, have been performed between 173 and 403 K in the frequency range 1 to 107 Hz. The influence of aniline and PAni on the β-relaxation of PET and the effect of the presence of PAni on the α-relaxation of PET have been studied. For the films PET–PAni doped with HCl, two relaxation processes around 0.5–5 kHz and 0.2–1 MHz were observed.