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Abstract: The impact of small amounts of carboxyl-functionalized multi-walled carbon nanotubes (MWCNT-COOH) added into a polyether-based thermoplastic polyurethane elastomer (TPU) was studied considering mainly on the morphological, mechanical, electrical and electrostrictive properties. The electrostrictive properties were measured by the analysis of the deformation response occurring under external electric fields E applied on 50μm-thick films. Dielectric measurements were carried out in order to determine the percolation threshold fc , which was found near 1v% loading. This volume fraction leads to a very high dielectric permittivity up to ≈330, i.e. about 50 times higher than that of the pure TPU, where . The thickness strain SZ and apparent electrostrictive coefficient M were measured at low electric fields, E ⩽4V/μm, by low frequency of 0.1Hz. The maximum induced-compressive strain was obtained from an optimal volume fraction of 0.8v% which yielded to a high Sz =11.5%, corresponding to almost a threefold increase of M compared to the neat TPU. Beyond fc , the conductivity sharply raised up and thus the electrostrictive activity disappeared. [Copyright &y& Elsevier]

Abstract: The electrostrictive properties of a polyether-based polyurethane elastomer and its corresponding composites filled with conductive carbon black (CB) were studied by measuring the thickness strain SZ induced by external electric fields E. For films with thicknesses of approximately 50μm, the apparent electrostrictive coefficient M was measured at low electric fields, E ⩽4V/μm, and different CB contents (up to a volume fraction of 2%). Dielectric measurements in AC mode were performed in order to determine the percolation threshold fc , which was 1.25v%. This optimal volume fraction yielded a remarkable threefold increase in M, associated with an increase of the dielectric constant by a factor 7, in comparison with pure PU. This enhancement of the electric field-induced strain and apparent electrostriction was mainly triggered by an increase of the dielectric constant, even if the intrinsic electrostriction coefficient Q was decreased. The nanocomposites thus seem to be very attractive for low-frequency electromechanical applications. Above fc , their conductivity was raised and their electrostrictive activity lost. Finally, there is a good agreement between the experimentally determined dependence on the CB content of the M coefficient and the theoretical estimation calculated from dielectric and mechanical measurements. [Copyright &y& Elsevier]

Abstract: This paper discusses the electromechanical potential improvement of polyurethane (PU) composite films by incorporation of carbon nanopowder in the polymer matrix. The beneficial influence on the electric field-induced is firstly measured and discussed. The observed non-linear mechanical behaviour of both pure PU elastomer and carbon/PU composite is described using constitutive hyperelastic Ogden Model. Finite Element Modeling with hyperelastic elements confirm the validity of the chosen model, assuming that actuation pressure is only due to electrostatic (Coulomb) forces at the electrodes. It also allows to predict the strain and stress distributions in the polymer films and the influence of the electrode size. Finally, mechanical performances of pure PU and composite C/PU disk actuators are compared in terms of strain energy density and actuation pressure under quasistatic state (non-linear actuator behaviour). The C/PU actuator exhibits an output mechanical energy increased by 50% compared to pure PU. [Copyright &y& Elsevier]

Abstract: In this study, ac and dc conductivity measurements were performed under ambient atmosphere on doped lead zirconate titanate (PZT) ceramics in order to investigate the defect chemistry by identifying the predominant charge carriers. The considered compositions were acceptor (1%mol Mn or Mg) and donor (Nb or F) co-doped PZTs with [Donor]=1 or 2%mol. The influence of donor concentration on the conductivity was determined. From the conduction activation energy values calculated in the temperature range 200–700°C, the principal contributing charge carriers are doubly-ionized oxygen and lead vacancies V Pb. For Mg doped PZTs, neither Nb nor F co-doping strongly reduce both conductivity levels and the dominant conducting species . For Mn doped materials, both donor co-dopants niobium and fluorine reduce the conductivity but do not have the same effect on the conduction mechanism at low temperature. With 2% Nb doping, the dominant conducting species are whereas electrical conduction is controlled by electrons from the second-ionization of oxygen vacancies with 2% F doping. The difference of oxygen vacancies content in (Mn, F) and (Mn, Nb) co-doped PZTs may be at the origin of the two distinct conducting species and of the different conductivity levels. [Copyright &y& Elsevier]

Abstract: Harvesting systems capable of transforming dusty environmental energy into electrical energy have attracted considerable interest throughout the last decade. Several research efforts have focused on the transformation of mechanical vibration into electrical energy. Most of these research activities refer to classical piezoelectric ceramic materials, but more recently piezoelectric polymer materials have also been considered. The goal of this paper has been to develop of a model capable of predicting the electrostrictive coefficient of EPCs. The model was developed by using the vibration transmission theory of a Euler–Bernoulli cantilever beam. After validating the model, at the macroscopic level, an empirical relationship was established predicting the value of the electrostrictive coefficient from the dielectric constants and the compliance coefficient of the material. The final results indicated that the dielectric constant was the crucial parameter, for the energy harvesting. [Copyright &y& Elsevier]

Abstract: The main objective of the paper is to point out the influence of composition and of poling state (poled and unpoled samples) on the evolution of various parameters (ɛ r, dilatation coefficients, lattice parameters) at different scales (lattice, bulk) using X-ray diffraction (XRD), thermo-mechanical analysis (TMA) and dielectric methods. The transition temperatures have been determined from the above measurements and compared. The composition has an influence on the transition temperature and not on the dilatation coefficient value. The poling state influences only the macroscopic dilatation evolution and not the value of the transition temperature. A scale effect is only observed on majoritary tetragonal compositions which show different values of transition temperatures from microscopic and macroscopic methods. [Copyright &y& Elsevier]

Abstract: The formation of barium titanate powder by solid-state reaction and oxalate coprecipitation route is re-investigated by differential thermal analysis–thermo-gravimetry (DTA–TG) thermal analysis and high temperature X-ray diffraction (XRD). The temperature formation of the perovskite phase is lower for the chemical way than for the solid state one, and no intermediate product is detected. The obtained powder leads to ceramics with high dielectric and piezoelectric properties. For example the room temperature piezoelectric d 33 coefficient is 260pC/N (higher than the values usually published in the literature) and it shows a good stability under electrical solicitations. These properties make BaTiO3 (BT) a lead-free high performance material for piezoelectric applications. [Copyright &y& Elsevier]

Abstract: Relaxor ferroelectric 0.60Pb(Mg1/3Nb2/3)O3–0.40PbTiO3 single crystal was synthesized by Bridgman method. The segregation along the length of this crystal was observed by various physico-chemical characterization techniques. First, we note the evolution of the crystalline structure along the length of the as-grown crystals. The tetragonality factor c/a increases from 1.013 to 1.020. This evolution has been correlated with the Ti content determination by flame atomic absorption spectrometry, and it is shown that this is due to the evolution of Ti concentration along the crucible. Furthermore, a continuous increase of the fraction of tetragonal phase with increasing Ti content was observed. Hence, we could compare the experimental data with a standard segregation model and therefore calculate the effective segregation coefficient k eff for this composition. This coefficient was found to be equal to 0.849. The variation of the titanium content along the ingot causes an inevitable fluctuation of the dielectric and piezoelectric properties of the single crystal. Due to the increase of Ti concentration, the Curie point was 186°C at the bottom of the ingot and 222°C at the top. The piezoelectric coefficient of oriented and poled <001> samples varies from 1500 to 250pC/N. [Copyright &y& Elsevier]