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International audience; Lead–zirconate–titanate (PZT) thick films for high‐frequency ultrasound applications were fabricated using an electrophoretic deposition (EPD) process. The PZT powder was synthesized from constituent oxides at close‐to‐room temperature by mechanochemical activation followed by calcination at 700°C. Homogeneous PZT thick films with a thickness of ~30 μm and a density of ~80% were produced from ethanol‐based colloidal suspensions containing PZT and PbO particles that were deposited using a constant‐current mode on a platinized alumina substrate and were sintered in the presence of a liquid phase at temperatures compatible with thick‐film technology. The dielectric, mechanical, and piezoelectric parameters of the PZT thick films with a porosity of ~20% were measured and a thickness‐coupling factor of 48% was obtained. Considering that a PZT thick film is a composite structure consisting of PZT and pores, there are several methods that can be applied to calculate the effective parameters where the composite is considered as a piezoelectric homogeneous material. For this study, a matrix method based on a generalization of 2‐2 connectivity was used to deduce the parameters of a completely dense configuration. Our results confirmed that the EPD process is suitable for the fabrication of efficient, high‐frequency transducers operating at frequencies above 40 MHz.

In this investigation we show that the dielectric, ferroelectric and piezoelectric properties of stoichiometric 0.57Pb(Sc 1/2 Nb 1/2 )O 3 –0.43PbTiO 3 (0.57PSN–0.43PT) ceramics prepared by mechanochemical synthesis are comparable or even better than the properties of 0.57PSN–0.43PT ceramics with Nb doping, which was proposed to enhance the electrical properties. Here, the stoichiometric ceramic was sintered to 97% of theoretical density at a temperature of 1000 °C, which is 200–300 °C lower than previously reported. The dielectric constant ɛ , remnant polarization P r , piezoelectric coefficient d 33 , coupling coefficients k p and k t and mechanical quality factor Q m of the ceramics prepared by mechanochemical synthesis were 2200, 43 μC/cm 2 , 570 pC/N, 0.71, 0.56 and 38, respectively. The effects of the poling field on the structural and electrical properties of the 0.57PSN–0.43PT ceramics were investigated. The results show that the ratio of the monoclinic to the tetragonal phases is influenced by the application of the poling electric field. The non-poled ceramics contain 71% of the monoclinic phase and 29% of the tetragonal phase. The highest d 33 , k p and k t were measured for ceramics poled at an electric field of 3 kV/mm. For these poled ceramics a phase determination of 86% monoclinic phase and 14% tetragonal phase was obtained from Rietveld refinements.

International audience; Relaxor ferroelectrics are a prototypical example of ferroic systems in which interplay between atomic disorder and order parameters gives rise to emergence of unusual properties, including non-exponential relaxations, memory effects, polarization rotations, and broad spectrum of bias- and emperatureinduced phase transitions. Despite more than 40 years of extensive research following the original discovery of ferroelectric relaxors by the Smolensky group, the most basic aspect of these materials - the existence and nature of order parameter - has not been understood thoroughly. Using extensive imaging and spectroscopic studies by variable-temperature and time resolved piezoresponse force microscopy, we fi nd that the observed mesoscopic behavior is consistent with the presence of two effective order parameters describing dynamic and static parts of polarization, respectively. The static component gives rise to rich spatially ordered systems on the 100 nm length scales, and are only weakly responsive to electric fi eld. The surface of relaxors undergoes a mesoscopic symmetry breaking leading to the freezing of polarization fl uctuations and shift of corresponding transition temperature.

This paper deals with the transmission of acoustic waves through multilayered piezoelectric materials. It is modeled in an octet formalism via the hybrid matrix of the structure. The theoretical evolution with the angle and frequency of the transmission coefficients of ultrasonic plane waves propagating through a partially depoled PZT plate is compared to finite element calculations showing that both methods are in very good agreement. The model is then used to study a periodic stack of 0.65 PMN-0.35 PT/0.90 PMN-0.10 PT layers. The transmission spectra are interpreted in terms of a dispersive behavior of the critical angles of longitudinal and transverse waves, and band gap structures are analysed. Transmission measurements confirm the theoretical calculations and deliver an experimental validation of the model.

International audience; As a lead-free candidate for electronic application, Na0.5Bi0.5TiO3 (NBT) thin films were produced by a 2-methoxyethanol sol–gel route and CSD method. Thermal decomposition and crystallization pathway of the alkoxide-based precursor have been studied by thermal analysis and X-ray diffraction (XRD) techniques. No transitory nanocrystalline phase was detected during the crystallization process of NBT. As a consequence, the nucleation of the stable perovskite phase occurred at low temperature (