Dielectric characteristic of nanocrystalline Na0.5K0.5NbO3 ceramic green body

International audienceDielectric spectroscopy was applied to porous nanocrystalline Na0.5K0.5NbO3 (NKN) ceramic green body, wherein influences of percolation effect and water adsorption at pore surface of the ceramic green body on dielectric response were examined over wide temperature (150 to 450 K) and frequency (100 Hz to 1 MHz) ranges. Dielectric permittivity of the ceramic green body is about 2-3 orders of magnitude higher than that of pure NKN powder or NKN ceramic. Furthermore, the high dielectric permittivity and high humidity sensitivity of the ceramic green body can appear again with aging a period of time in air. The data from this investigation make potential applications for NKN as a giant dielectric material or a humidity sensing material

Les actionneurs piézoélectriques pour le contrôle dynamique des vibrations

National audienc

Comparaison de divers actionneurs piézoélectriques dans un système d'amortissement actif

National audienc

Improved Properties of Doped BaTiO 3 Piezoelectric Ceramics

International audienc

Influence of 1-3 piezocomposite fabrications on lateral modes

International audience—Properties of 1-3 piezocomposites with periodic structure were characterized. This material can be typically fabricated in using the " dice and fill " method (DFM) and two phases were used (PMN-34.5PT ceramic and epoxy resin). The corresponding numerical simulations allowed to study the influence of spurious lateral modes on electromechanical performance of the thickness mode. This was performed in calculating the bandwidth and the sensitivity of the piezocomposite in water (emission-reception) in the frequency range 1-5 MHz. Moreover, three ceramic volume fractions between 25% and 60% were used. Finally, a comparison of these results with those obtained with a pseudo-periodic 1-3 piezocomposite was made. This composite can be fabricated by a lamination technique (LMT) and the use of a pseudo-periodic structure leads to a minimized effect of the lateral modes (confirmed on the simulated electrical impedance). Thanks to these results an optimum structure was discussed

Super-Cell Piezoelectric Composite With 1–3 Connectivity

International audience— The standard fabrication method for 1–3 piezo-composites for ultrasound transducers is the " dice and fill " method (DFM) in which lateral periodicity is introduced. This contributes to the appearance of spurious modes that can drastically affect the performance of the device if they appear near its thickness mode frequency, thus limiting the effective frequency range. A new 1–3 piezocomposite fabricated with a super-cell structure [1–3 super cell (13SC)] was designed in order to overcome these limitations. It consists of the merging of several periodic cells with 47% PZT volume fraction and epoxy resin as the matrix. Two lateral periodicities in one direction are defined as well as two different kerfs. The chosen cell shape is composed of five nonaligned square section rods (1 × 1 mm 2). For comparison of performance, two regular 1–3 piezocomposites (the same materials and equivalent periodicities) were fabricated by DFM. Electroacoustic responses in water were measured for the three composites being considered as transducers. Successive regular thinnings (from 2.8 to 1.1 mm) were carried out for each sample to increase the operating frequency (from around 0.4 to 1.3 MHz) and study the evolution of the characteristics (bandwidth and sensitivity). The experimental results confirmed the behavior of those obtained with numerical simulations, showing that the 13SC composite can be used in this entire frequency range, unlike regular composites

Internal Electric Field in Co-Doped BaTiO 3 With Co 2+/3+ , Nb 5+ , Li + , and F − : Impact on Functional Properties and Charge Compensation With Niobium and Fluorine Ions

International audienc

Orthorhombic to tetragonal structural phase transition in Na0.5K0.5NbO3-based ceramics

International audienceWe report the temperature-dependent x-ray powder diffraction of the Na0.5K0.5NbO3 (NKN)-based piezoelectric ceramics in the range between 320 and 700 K. In the case of NKN we have detected the structural phase transition region from the orthorhombic phase to the tetragonal phase over a broad temperature range from 496 to 458 K. The region is enlarged and shifted to lower temperature by introducing trace impurity or second component. It is considered that the coexistence of orthorhombic and tetragonal phases in NKN-based ceramics observed near room temperature are essentially due to the shift and enlargement of the phase coexistence region induced by lattice chemical pressure

Complete Electroelastic Set of Co doped Barium Titanate for Transducer Applications

International audienceBaTiO 3 ceramic doped with cobalt and calcium (BTCaCo), processed by a conventional technique with a reduced sintering temperature, is characterized. Particular attention is paid to the delivery of complete and accurate set of elastic, dielectric, and piezoelectric constants. These databases are relatively rare in the literature but are essential for numerical simulations of new devices, integrating these materials. The processed piezoelectric material exhibits an electromechanical thickness coupling factor (k t) of 45% and a relative dielectric constant of 1180, at constant strain. A 1-3 piezo-composite is successfully fabricated to improve the performance (k t =47%). Finally, BTCaCo disc is used to fabricate a transducer with a center frequency at 4.3 MHz, showing competitive performance compared to a standard PZT-based transducer