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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 trimethylammonium cobalt chloride dihydrate was obtained by slow evaporation at room temperature. The behavior in accordance with temperature variation was sought. The Rietveld refinement of the X-ray powder diffraction pattern led to the formation of a pure phase which crystallizes in the orthorhombic system with the Pnma space group. Three endothermic peaks at T 1 =310 K, T 2 =349 K, and T 3 =358 K were evidenced by DSC measurements. In order to characterize the phase transitions and their nature, Raman spectra were recorded in the frequency range related to the vibrations of the cations and anions (10−3600 cm −1 ). The results obtained show the utility of the Raman spectra to probe the changes in T 1 and then the reconstruction of new anionic parts after T 2 transition. The analysis of the line width based on the order-disorder model was used to obtain information concerning the activation energy near the phase transition at T 1 . A comprehensive study of the dielectric and electric modulus properties of this compound was conducted using impedance spectroscopy in the frequency range of 100 Hz to 1.3 MHz and over the temperature range of 270 K to 335 K. The analysis of Nyquist plots revealed the presence of grains, grain boundaries and the electrode effects. The modulus plots were characterized by the presence of two peaks associated with grains and grain boundaries. The temperature dependence of the electrical conductivity (σ g ) and AC conductivity (σ ac ) confirmed the phase transition. The AC electrical conduction in the [(CH 3 ) 3 NH]CoCl 3 ·2H 2 O compound underwent two processes attributed to a hopping transport mechanism: the correlated barrier hopping model in region I and the non-overlapping small polaron tunneling model proposed as a closely good model for region II.

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.

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.

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.

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.

Materials of the LiTi2 − xZrx(PO4)3 series (0 ≤ x ≤ 2) were prepared and characterized by powder X-ray (XRD) and neutron diffraction (ND), 7Li and 31P Nuclear Magnetic Resonance (NMR) and Electric Impedance techniques. In samples with x

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.

Composites having ceramic LiSn2P3O12 particles, that are Li+ ion conductor, and Teflon, that is an insulating polymer and works as binder, have been prepared in a wide compositional range (from 8 to 74% by volume of LiSn2P3O12). Their microstructure, as followed by Scanning Electron Microscopy, has been analyzed to understand the aggregation process of the ceramic particles. For low LiSn2P3O12 contents (below 30% by volume) some particles lay isolated and some aggregated in clusters (isolated clusters) both being surrounded by Teflon. For higher LiSn2P3O12 contents the isolated clusters grow and transform into clusters that are developed along the composite bulk (extended clusters); the latter clusters accounts for the ionic conductivity, which is discussed in terms of a percolation model. The shape and size of both types of clusters are analyzed as the LiSn2P3O12 content increases. The aggregation process here described could work in other composites made from mixing and compacting particles of a ceramic and a polymer.

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 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.

The formation of polyurethane networks has been followed by measuring ultrasonic absorption and velocity as a function of time for discrete frequencies. In order to determine the relaxation spectra in the pre-gel phase, ultrasonic measurements were performed on quenched samples over the frequency range 5–1000 MHz. The data observed are discussed in terms of molecular motions and interactions.