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The present work aims to establish a correlation between the characteristics of YAG and Er:YAG commercial powders produced by two different synthesis routes and sintered ceramic microstructures and their optical aspect by taking into account the influence of pressure applied during the Spark Plasma Sintering (SPS) process. Physical and chemical characteristics of the powders were compared using various techniques such as SEM, XRD, laser diffraction and chemical analyses. Their behaviours were evaluated through a rheological study, compressibility tests and dilatometry cycles using SPS. This paper pinpoints the most important powder features which influence the optical quality of YAG and Er:YAG ceramics. The optical quality is mainly affected by the porosity, related to powder characteristics that affect particle rearrangement, densification and grain growth. The applied pressure induces microstructural heterogeneities depending on the starting material used and resulting in core-shell aspects of sintered ceramics.

International audience; CuO was used to reduce the sintering temperature of (Na0.52 K0.44)(Nb0.9 Sb0.06)O3 –0.04LiTaO3 (NKNSLT) piezoelectric ceramics. XRD analysis reveals the formation of single phase perovskite structure. SEM has been used to investigate the grain morphology of the material. Impedance plots have been used as a tool to analyze the electrical properties of the sample as a function of frequency and temperature. Detailed studies of dielectric properties of the compound as a function of temperature at different frequencies suggest that the compound has a dielectric anomaly of ferroelectric to paraelectric type at 360°C, and exhibits diffuse phase transition. The Nyquist plot (Z′′ vs Z′′) revealed the presence only of the grain boundary effect in the materials. Bulk resistance is observed to decrease with an increase in temperature showing a typical negative temperature coefficient of resistance (NTCR). The plot of normalized complex dielectric modulus a function of frequency exhibits both short and long-range conduction in the ceramics. The ac conductivity spectrum was found to obey Jonscher's universal power law.

CuO was used to reduce the sintering temperature of (Na 0 . 5 Bi 0 . 5 ) 0.94 –Ba 0.06 TiO 3 + 0.03 wt.%Sm 2 O 3 (named NBTS) piezoelectric ceramics. Structural/micro-structural, dielectric, and resistive properties of this composition have been studied using impedance spectroscopic method to get better understanding of (i) the electrical conduction and dielectric relaxation mechanism and (ii) microstructure-electrical properties relationship of the materials as a function of temperature and frequency. The XRD patterns reveal the presence of the morphotropic phase MPB (coexistence of tetragonal and rhombohedral phase) for different compositions. Dielectric and complex impedance spectroscopic studies were carried out in a wide frequency (i.e., 10 2 –10 6 Hz) and temperature (30–500 °C) range. The maximum of permittivity (at transition temperature) was found to decrease with increasing CuO amount in NBTS, but the diffuseness of dielectric peak increases. The nature of frequency dependence of AC conductivity of NBTS follows the Jonscher power law, and calculated DC conductivity follows Arrhenius behavior. The Nyquist plots suggest that the grains only are responsible for the conduction mechanism of the materials. The occurrence of single arc in the complex modulus spectrum of NBTS compositions confirms the single-phase characteristics, and also confirms the presence of non-Debye type of multiple relaxation in the material.

The main aim of this work is to enhance the conversion of mechanical energy into electrical energy by using direct piezoelectric effect. Under the assumption of the Euler–Bernoulli Beam Theory, a piezoelectric cantilever bending of 31-effect was developed. The equations of motion for the global system were established by using Hamilton's principle and solved by using the modal decomposition method. It provided the transfer functions model between the inputs (force) and the outputs (voltage) allowing the description of its dynamic behaviour for energy harvesting. The model was implemented by using Matlab software and will be able to integrate with the circuit model of energy storage. The results obtained show a good agreement with the experiments and other previous works. The model and the experiment indicate that the second mode of resonant frequency provides the voltage and the bandwidth much larger than the first mode. While the mass at the free end increases, the voltage obtained by the first mode increases. In contrast, the voltage obtained by the second mode decreases.

cited By 3; International audience; Piezoelectric composites of PU/PZT with 0–3 connectivity were prepared in the film form. Homogeneous dispersion of the ceramic PZT in polyurethane matrix has been obtained and has been verified by SEM analysis. Dielectric properties reveal that under an electrical field of 1000 V the remnant polarization increased from 1.9 to 4 µC/cm−2 when the volume fraction of PZT increased from 50 to 80 %. Modeling and vibratory energy harvesting tests has been realized. At very low frequency and deformation, and without application of any static electric field, 1.15 µW of power has been obtained. The results obtained in this work contribute to demonstrate the ability of the incorporation of PZT particles in the polymer matrix to improve the conversion efficiency of the vibratory energy into electrical energy for the development of µ-generators. © 2016, Springer Science+Business Media New York.

International audience; Metal core piezoelectric fibres (MCPFs) show strong potential for structural actuator applications. Unfortunately the development of such fibres is problematic because of their fabrication difficulties. In order to obtain the best properties, both aspect ratio and piezoceramic–metal core compatibility have to be considered. For those reasons, fabrication of such fibres by a multi-dip-coating process has been investigated on platinum wires. The multi-coating process is shown to be more versatile and allows to control the aspect ratio. It is shown that decreasing slurry temperature during the dip process is a suitable way to reduce the number of coating steps in order to achieve high aspect ratio. After sintering, coatings exhibit the same behaviour as bulk ceramics in terms of microstructure, crystallography and ferroelectric loops.

The Lead Zirconate titanate (PZT) ceramic is known by its piezoelectric feature, but also by its stiffness, the use of a composite based on a polyurethane (PU) matrix charged by a piezoelectric material, enable to generate a large deformation of the material, therefore harvesting more energy. This new material will provide a competitive alternative and low cost manufacturing technology of autonomous systems (smart clothes, car seat, boat sail, flag ...). A thin film of the PZT/PU composite was prepared using up to 80 vol. % of ceramic. Due to the dielectric nature of the PZT, inclusions of this one in a PU matrix raises the permittivity of the composite, on other hand this latter seems to decline at high frequencies.

International audience; The aim of this work was to efficiently convert the mechanical vibrations into electrical energy by using direct piezoelectric effect. Most mechanical vibrations occur at low frequencies varying from 50 to 120 Hz. As piezoelectric converters provide maximum energy conversion when their natural frequencies are close to the frequency of the mechanical source, it would be interesting to design piezoelectric converters operating at low resonance frequencies. For those reasons, a piezoelectric generator has been developed with multi-cantilever piezoceramics operating at low frequencies. The device was shaped using the tape casting technique followed by a laser cutting process. It was made of six piezoelectric cantilevers with different lengths and various masses at their free-ends. Its piezoelectric response was characterized and analysed. It was shown that it can operate at low and many resonant frequencies. Moreover the frequency bandwidth was widened up to 200% compared to the one obtained from a single cantilever beam. It allowed efficiently exploiting mechanical vibrations of sources exhibiting wide frequency spectrum.

ZnTiO3 nanopowders were obtained by sol-gel method. The nanopowders were characterised by means of TGA/DTA analysis, X-ray diffraction, TMA analysis and SEM characterisation. The results show that the crystalline structure of the sol-gel powders was obtained at 600?C, with crystallite sizes of 10 nm. SEM shows that most of the prepared ZnTiO3 nanopowders are agglomerated. Since agglomeration plays an important role in the sintering of the ZnTiO3 ceramics, different deagglomeration techniques (ultrasonication, pulverisation and attrition milling) were investigated. Dense ZnTiO3 structure was obtained from the attrition milled powder at 1050?C and its dielectric characteristics were also investigated (?r =25, t?= -26 ppm/?C and tg? < 10-3 at 1 MHz). The low sintering temperature and the good dielectric properties show promise for the manufacture of multilayered capacitors with internal copper electrodes.

The crystal structure, microstructure, dielectric and ferroelectric properties of (1 − x )Na 0.5 Bi 0.5 TiO 3 – x BaTiO 3 ceramics with x = 0, 0.03, 0.05, 0.07 and 0.1 are investigated. A structural variation according to the system composition was investigated by X-ray diffraction (XRD) analyses. The results revealed that the synthesis temperature for pure perovskite phase powder prepared by the present sol–gel process is much lower (800 °C), and a rhombohedral–tetragonal morphotropic phase boundary (MPB) is found for x = 0.07 composition which showing the highest remanent polarization value and the smallest coercive field. The optimum dielectric and piezoelectric properties were found with the 0.93Na 0.5 Bi 0.5 TiO 3 –0.07BaTiO 3 composition. The piezoelectric constant d 33 is 120 pC/N and good polarization behaviour was observed with remanent polarization ( P r ) of 12.18 pC/cm 2 , coercive field ( E c ) of 2.11 kV/mm, and enhanced dielectric properties ɛ r > 1500 at room temperature. The 0.93Na 0.5 Bi 0.5 TiO 3 –0.07BaTiO 3 -based ceramic is a promising lead-free piezoelectric candidate for applications in different devices.

The electrochemical performances of fluorinated graphite have been improved by coating a uniform carbon layer on commercial CFx (x = 1) powder used as cathode material in lithium battery. In comparison with the cell using un-coated CFx as cathode, the cell using carbon coated CFx cathode has a higher energy density and higher power density, particularly at higher discharge current rates (1C above). This is because the conductive carbon coating provides the exterior connectivity between particles for facile electron conduction, resulting in high rate performance.

The effects of various additives, namely ZnO-B 2 O 3 -SiO 2 (ZSB), B 2 O 3 and B 2 O 3 + LiF on the lowering of sintering temperature and dielectric properties of ZnTiO 3 based ceramics were investigated. From the dilatometric studies, it was shown that the sintering temperature is significantly lowered owing to the addition of 15 mol. % of ZSB or of the addition of 15 mol. % of B 2 O 3 : ZSB added sample can be sintered at 950 °C and B 2 O 3 added one at 1000 °C whereas pure compound hence can be sintered at 1100 °C. The most interesting result concerns the ZSB added sample sintered at 950 °C during 4 h which exhibits a density higher than 92% of the theoretical one, high dielectric constant (e r ≈ 25) and low dissipation factor (tan(δ) < 10 -3 ) in the range -60°C/160°C at 1 MHz. The temperature coefficient of the dielectric constant is also reasonable (τ e ≈ -150 ppm/°C) as well as the temperature coefficient of the resonant frequency (|τ f

( Bi 0.5 Na 0.5)0.94 Ba 0.06 TiO 3 + x% Ce 2 O 3 + y% La 2 O 3 + z% Y 2 O 3 compounds (named BNT–BT– x/y/z) were synthesized by a sol–gel technique, for (x,y,z) = (0,0,0), (0.25, 0.25, 0.25), (0.25, 0.5, 0.5), (0.5, 0.25, 0.25) and (0.5, 0.5, 0.25). The structural variation according to the different system compositions is investigated by X-ray diffraction analyses. The results shows that the addition of Ce2O3 , La2O3 or Y2O3 in BNT–BT system, do not modify the crystalline structure, and a rhombohedral–tetragonal morphotropic phase boundary is maintained for different dopant addition. The BNT–BT–x/y/z-based ceramics sintered at relatively low temperature (1100°C) exhibit a good densification ratio. The optimum dielectric and piezoelectric properties are obtained with the BNT–BT–0.5/0.25/0.25 composition. High dielectric properties at room temperature (εr > 1000) and low dielectric losses (tan δ < 4 × 10-2) are obtained for this composition. This compound exhibits a piezoelectric constant d33 of 95 pC/N, a good polarization behavior is observed with high remanent polarization Pr of 9.21 μC/cm2 and low value coercitive field Ec of 2.66 kV/mm.

Investigation using a variable angle spectroscopic ellipsometer revealed the influence of sample preparation conditions on sol-gel PbZr 0.52 Ti 0.48 O 3 (PZT 52/48) thin-film homogeneity that allows identification and further optimization of thin-film performance. Separate crystallization of the layers determined the optical gradient appearance, irrespective of the chemical solvents used in this work. A more refined analysis showed that a refractive index gradient was apparent in the samples in which lattice parameters strongly changed with thickness. For these films, energy-dispersive X-ray spectroscopy analysis showed significant variation in Pb and Zr. Additionally, complex dielectric functions for each PZT 52/48 thin film in the wide phonon energy (1.03-5.39 eV) range were evaluated.