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Abstract: Compatibility of Bi‐based piezoelectric ceramic and copper electrodes is demonstrated by co‐firing 0.88Bi1/2Na1/2TiO3–0.08Bi1/2K1/2TiO3–0.04BaTiO3 (BNKBT88) with copper. A combination of Bi2O3, CuO, ZnO, Li2CO3, and B2O3 are used as additives to reduce firing temperature to 900°C with minimal effect on the electromechanical properties compared to sintering at 1150°C without additives. Co‐firing with copper electrodes requires controlled oxygen sintering at low temperature. The atmosphere is controlled using carbon dioxide and hydrogen gas to maintain an oxygen partial pressure of 6.1 × 10−8 atm, which is necessary for the coexistence of Cu metal and Bi2O3. The thermodynamic activity of bismuth oxide in BNKBT88 is calculated to be 0.38. BNKBT88 ceramics were successfully co‐fired with internal as well as surface Cu metal electrodes. The copper co‐fired ceramics were successfully polarized and the dielectric and piezoelectric properties are evaluated. [ABSTRACT FROM AUTHOR]

The article discusses the challenges and advancements in the field of piezoelectric composites. It explains that combining ceramics and polymers to create composites has been effective in improving the performance of piezoelectric materials. However, achieving a balance between mechanical compliance and piezoelectric properties has been difficult. The researchers propose a new approach involving a composite with 3-3-3 connectivity patterns, which significantly enhances the piezoelectric performance while maintaining flexibility. This breakthrough has implications for flexible piezoelectric materials, smart devices, and soft robotics. [Extracted from the article]

To address the persistent challenge of balancing flexibility and piezoelectricity in polymer composites, Tang I et al i . put forth an innovative approach involving a composite with 3-3-3 connectivity patterns. The study of piezoelectric composites traces its origins back to the 1970s, when the concept of combining ceramics and polymers to introduce self-connectivity was first proposed [[1], [3]]. Conversely, polymer composites filled with interconnected ceramic scaffolds, such as composites with 1-3 or 3-3 connectivity patterns, can yield much higher piezoelectric coefficients. [Extracted from the article]

Abstract: Gel casting is a suitable near net shape-forming technique based on the solidification of aqueous suspensions for the production of green parts with interesting economic and environmental benefits. In the present work, PZT-5 suspensions in aqueous media were successfully prepared using ammonium polyacrylate (PAA-NH4) as the dispersing agent. The gelation of the 46–48vol.% PZT suspensions in aqueous media based on agarose was studied by measuring the height of the samples before and after demoulding. The study found that the suitable amount condition for development of the green parts made was achieved at 0.082–0.19wt.% agarose (based on dry solid). The density of the green body produced at the optimum content of agarose was determined. A very uniform part with green density of 52% and 55% before and after drying, respectively, was developed. Small shrinkage was measured after drying and heat treating at 550°C. Sintered samples at 1250 and 1285°C showed a theoretical density of 99% with an even smaller shrinkage of 16.2%. The dielectric constant and longitudinal piezoelectric charge coefficients, d 33, of the selected samples were 2550 and 680pC/N, respectively. [Copyright &y& Elsevier]

We present a new type of actuator named bilayer piezoelectric/electrostrictive dome unimorph (BIPEDU), fabricated by attaching a piezoelectric-electrostrictive monolithic bilayer composites (PE-MBLC) to a metal plate. Various ratios of piezoelectric/electrostrictive (P/E) volume percent were used to form PE-MBLC. It was found that d33eff and Keff in PE-MBLC follow the series 2-2 composite mixing rule. However, the measured results were slightly lower than those of the calculated values because of a large difference in dielectric displacement between piezoelectric and electrostrictive layers and because the electrostrictor acts as the resistor that impedes the domain switching in piezoelectric layer during poling. In addition, we have investigated the field-induced displacement in PE-MBLC and BIPEDU actuators. In comparison, the displacement of BIPEDU actuators was much higher than that of PE-MBLC actuators. This was attributed to the good quality of bonding between ceramic and metal, which contributed to the proper stress/force transfer, as well as the metal sheet, which acted as a fiextentional structure for PE-MBLC to generate more axial displacement in BIPEDU actuators. The load dependence of displacement in BIPEDU was obtained. In addition, the BIPEDU showed high reliability during the displacement cyclic testing. [ABSTRACT FROM AUTHOR]

Recent progress in (K0.44,Na0.52,Li0.04) O3-based ceramics (KNN) with special emphasis on (K0.44,Na0.52,Li0.04) (Nb0.84,Ta0.10,Sb0.06))O3 (KNN-LT-LS) is reviewed concisely. The base KNN and its compositional derivatives are analyzed in terms of dopant-property relationships, which are then extended to the ternary derivatives. The effects of processing conditions such as humidity, precursor purity, and oxygen partial pressure during sintering are elaborated on from a phenomenological perspective. It is also shown that the spontaneous polarization is sensitive to the processing route chosen for synthesis (mixed oxide versus perovskie routes). Special attention is devoted to the discussion of the morphotropic phase boundary (MPB) dilemma in the KNN-LT-LS system, where it is shown that the origin of high piezoelectric activity is actually due to a polymorphic transition at room temperature. It is shown that prototype transducers based on pure and 1 mol% Ba2+ doped KNN-LT-LS exhibit performance metrics comparable to those fabricated using PZT-5H. Overall, KNN-LT-LS ceramics show great promise for lead-free applications, although issues such as temperature dependence of properties and strong sensitivity to processing conditions remain as the 2 major challenges. [ABSTRACT FROM AUTHOR]

Presents a study which examined the relation of the size of a PbTiO... to the nature of ferroelectricity arising from dipolar coupling. Experimental details; Results; Discussion.

3D printing (3DP) technologies have transformed the processing of advanced ceramics for small‐scale and custom designs during the past three decades. Simple and complex parts are designed and manufactured using 3DP technologies for structural, piezoelectric, and biomedical applications. Manufacturing simple or complex geometries or one‐of‐a‐kind components without part‐specific tooling saves significant time and creates new applications for advanced ceramic materials. Although development and innovations in 3DP of ceramics are far behind compared with metals or polymers, with the availability of different commercial machines in recent years for 3DP of ceramics, exponential growth is expected in this field in the coming decade. This article details various 3DP technologies for advanced ceramic materials, their advantages and challenges for manufacturing parts for various applications, and perspectives on future directions. We envision this work will be helpful to advanced ceramic researchers in industry and academia who are using different 3DP processes in the coming days. [ABSTRACT FROM AUTHOR]

The effect of Mn and Fe dopants on the electromechanical and electrochemical properties of 0.88[Bi0.5Na0.5]TiO3–0.08[Bi0.5K0.5]TiO3–0.04[Bi0.5Li0.5]TiO3 piezoceramic is investigated with particular emphasis on complex impedance in the temperature range from 450 to 600 °C. The impedance spectra have been simulated with equivalent circuits in order to extract bulk and grain boundary characteristics and to determine activation energies of conduction. Mn and Fe dopants considerably enhance the mechanical quality factor and decrease the dielectric loss compared to the undoped composition. Mn doping leads to dramatically higher resistivity in the bulk and a modest increase in the bulk activation energy. On the other hand, conductivity increases dramatically via Fe doping with a significant lowering of activation energy in the bulk and corresponding raising of the activation energy at grain boundaries in comparison to Mn-doped and undoped ceramic. The bulk conductivity of Fe-doped piezoceramic reaches as high as 0.01 S cm−1 at 600 °C. [ABSTRACT FROM AUTHOR]

Recent progress in lead-free piezoelectric ceramics and thin films with special emphasis on alkaline niobatebased and bismuth sodium titanate-based systems is reviewed concisely. Modifications of potassium sodium niobate (KNN) ceramics are presented and subsequent improvements in the electrical properties are summarized. Special attention is devoted to the phase diagram of the KNN system when a solid solution is formed with other perovskite niobates and titanates. Impact of A-site and B-site dopants on the electromechanical properties of KNN ceramics are distinguished in view of transition temperatures. It is shown that the addition of most A-site and B-site dopants reduces the transition temperatures and improves the piezoactivity at room temperature. This is attributed to the shift of polymorphic transition from tetragonal to orthorhombic phase in the vicinity of room temperature. In contrast, formation of a solid solution of KNN with 18 mol% AgNbO3 revealed a significant enhancement of properties without a notable change in the transition temperatures. Also, a bismuth sodium titanate (BNT) composition is introduced with particular emphasis on its binary and ternary derivatives. Moderate piezoelectric properties reported at the morphotropic phase boundaries, formed in BNT-based solid solutions are also represented. Advances on thin films based on these two compositions are evaluated and challenges involved with development of stoichiometric thin films with low leakage current are discussed. [ABSTRACT FROM PUBLISHER]

We have studied the processing and electromechanical properties of Mn and Fe-doped 0.88[Bi0.5Na0.5TiO3]-0.08[Bi0.5K0.5TiO3]-0.04[Bi0.5Li0.5TiO3] piezoelectric ceramics prepared by the mixed oxide route. Different amounts of Mn (0.01, 0.014, 0.015, 0.016, 0.017, 0.02, 0.022) or Fe (0.0125, 0.015, 0.0175) were doped to this lead-free piezoelectric composition. Ceramics were sintered at different temperatures (1075°C-1150°C) to achieve the highest density and mechanical quality factor. Mn or Fe doping resulted in a considerable enhancement of Q m in both planar and thickness resonance modes. In 1.5 mol% Mn-doped ceramics sintered at 1100°C, a planar Q m of about 970 and tanδ of 0.88% were obtained. In Fe-doped ceramics, a planar Q m as high as 900 was achieved. Acceptor dopants also resulted in decreasing the coupling coefficients, the piezoelectric charge coefficient, and the dielectric constant. [ABSTRACT FROM AUTHOR]

We have studied the effect of deposition parameters on the microstructure, crystallinity, and ferroelectric properties of 0.88(Bi0.5Na0.5)TiO3-0.08(Bi0.5K0.5)TiO3?0.04BaTiO3 thin films grown on SrRuO3-coated SrTiO3 substrates by pulsed laser deposition. The parameters studied were the repetition rates, substrate temperatures, oxygen pressures, and laser energies. It was realized that the films prepared at 800°C, 10 Hz, 400 mtorr, and 1.2 Jcm-2 exhibited the highest ferroelectric properties. The measured remanent polarization, dielectric constant at 1 kHz, and coercive field for this film were about 30 μCcm-2, 645, and 85 kVcm-1, respectively. Increasing the oxygen pressure during deposition from 200 to 400 mtorr improved the crystallinity, microstructure, dielectric constant, and polarization of the films. The leakage current and dielectric loss were suppressed at 400 mtorr because of the lower concentration of oxygen vacancies and disappearing pinholes and surface undulations in the film deposited at this pressure. [ABSTRACT FROM AUTHOR]

This paper discusses the fabrication and characterization of a single-element ultrasonic transducer with a lead-free piezoelectric active element. A piezoelectric ceramic with composition of 0.88Bi0.5Na0.5TiO3–0.08Bi0.5K0.5TiO3– 0.04Bi0.5Li0.5TiO3 was chosen as the active element of the transducer. This composition exhibited a thickness coupling coefficient (kt) of 0.45, a dielectric constant of 440 (at 1 kHz), and a longitudinal piezoelectric coefficient (d33) of 84 pC?N–1. To make the transducer, the ceramic was sandwiched between an epoxy–tungsten backing layer and a silver epoxy matching layer. An epoxy lens was also incorporated into the transducer?s design to focus the ultrasound beam. The focused transducer with a center frequency of about 23 MHz demonstrated a –6-dB bandwidth of 55% and an insertion loss of –32 dB; the –20-dB pulsed length was measured to be 150 ns. A phantom made of copper wires (30 μm in diameter) was utilized to investigate the imaging capability of the transducer. The results indicated that the fabricated transducer, with a lateral resolution of 260 μm and a relatively high depolarization temperature, could be considered as a candidate for replacement of lead-based ultrasonic transducers. [ABSTRACT FROM PUBLISHER]

We propose a new type of flextensional actuator comprised of an electcomechanically active element which is a piezoelectric-electrostrictive monolithic bi-layer composite (PE-MBLC) capped by truncated thin brass sheets. The PE-MBLC contains equal amounts of 0.65 {Pb(Mg1/3Nb2/3) O3}-0.35PbTiO3 and 0.9{Pb(Mg1/3Nb2/3)O3}-0.1PhTiO3 by volume, and is obtained by a co-sintering process. With applied Emax = 10 kV/cm unipolac drive, the maximum axial displacement (u33) produced by the uncapped and capped PE-MBLC is 11 and 21 μm, empectively. The hysteresis in unipolar u33 at 0.5 Emax is 4.6% for the uncapped PE-MBLC, while that for the capped one is 11%. Under bipolar excitation, the maximum u33 for uncapped is 11.6 μm at +Emax and 6.6 μm at -Emax with as asymmetry factor (ξ) of 1.75 for which u33 < 0 for all E < 0. Under bipolar exsitation, the maximum u33 at +Emax for the capped PE-MBLC is 19 μm while that for -Emax is 8 μm with ξ = 2.4, for which u33 > 0 at -Emax but is smaller than the u33 at +Emax. The origins of the observed asymmetry in u33 are discussed in the context of symmetry superposition and deformation mechanics of the endcaps. [ABSTRACT FROM AUTHOR]

Epitaxial and (110) oriented paraelectric thin films of Ba0.60Sr0.40TiO3 were grown on (100) oriented NdGaO3 orthorhombic substrates, and the nonlinear dielectric properties were studied at 10 GHz along selected in-plane crystallographic directions in the film thickness range of 25–1200 nm. The measured dielectric properties show strong residual strain and in-plane directional dependence. For instance, the in-plane relative permittivity is found to vary from as much as 500 to 150 along [110] and [001], respectively, in the 600 nm film. Tunability was found to vary from as much as 54% to 20% in all films and directions. In a given film, the best tunability is observed along the compressed axis in a mixed strain state, 54% along [110] in the 600 nm film. It is shown that, by nanoscale manipulation of epitaxy and planar anisotropy, the return loss and phase shift in a paraelectric can be tuned over a rather wide range. The approach presented herein opens avenues for obtaining various degrees of phase shift on the same film, enabling one with an additional degree of freedom in device design and fabrication as well as multifunctionality. [ABSTRACT FROM AUTHOR]

A method for synthesis of high aspect ratio platelet seeds by growth of SrTiO3 on Sr3Ti2O7 core particles is reported. The aim of this study was to identify and control the morphology and size of SrTiO3 particles via molten salt synthesis. Platelet and tabular morphologies with rectangular faces were obtained using rutile and anatase, respectively. Platelet SrTiO3 particles with an edge length of 10–40 μm and a thickness of 1–4 μm were obtained. High aspect ratios (edge length to thickness) of 7–10 were measured for platelet particles as opposed to lower aspect ratios of 2–4 for tabular particles. Highly anisotropic platelets are suitable template candidates to achieve textured ceramics. [ABSTRACT FROM AUTHOR]

In the last 25 years, piezoelectric ceramicpolymer composites have been conceptualized, prototyped, fabricated, and implemented in an array of applications encompassing medical imaging and military missions, among others. A detailed snapshot of the materials used, and a detailed account of the major innovative methods developed in making various piezoelectric ceramic-polymer composites are presented. The salient aspects of processing of such composites are summarized, and structure-processing-property relations are described using connectivity as the unifying central concept. Computer-aided design (CAD)-based fabrication methods, which result in composites whose structural complexity surpass that of composites obtained with traditional methods, are described to introduce the reader to novel concepts in processing of piezocomposites. A brief survey of some recent advances made in modeling of (0-3), (1-3), and (2-2) composites also is provided. [ABSTRACT FROM AUTHOR]

Deals with a study on the development of a three-dimensional connectivity model that enables the understanding of the effect of fiber orientation, matrix-properties and inter-fiber contact on the effective piezoelectric properties of a composite.

Heteroepitaxial Ba 0.6 Sr 0.4 TiO 3 thin films of varying thickness (∼22-270 nm) were deposited on (100) oriented LaAlO 3 single crystal substrates by pulsed laser deposition using a KrF excimer laser (λ = 248 nm). XRD and FESEM were used to determine the structural quality, while RBS was used to investigate the chemical composition and thickness. The stoichiometry was found to be ideal with a Ba:Sr ratio of 1.5. XRD omega-scans showed that all films were epitaxial with a FWHM of 0.40°. Interdigitated electrodes were used to measure the capacitance and Q-factor of the films in the range of 1 GHz to 20 GHz. The films exhibited a capacitance of 0.156 - 0.463 pF at room temperature, with Q-factors in the range of 4-20, depending on frequency. The tunability of BST was also measured at microwave frequencies and found to be up to 38% at 10 GHz, for the thickest sample. [ABSTRACT FROM AUTHOR]

Grain-oriented lead-metaniobate (PbNb 2 O 6 ; PN) components have been fabricated by fused deposition of ceramics (FDC) process using templated grain growth technique. Needle-shaped PN seeds were synthesized for the templates by molten salt method. About 5 wt% seed was mixed with fine equiaxed matrix PN powder and compounded with a thermoplastic binder to obtain 52 vol% solids loading. Filaments extruded from the compounded materials were fed into FDC liquefier with a fine nozzle to prototype PN components through layer-by-layer deposition. SEM observations in the components showed that the seeds were aligned parallel to the deposition direction, surviving without major damage. By sintering at 1300 °C, a highly oriented microstructure with orthorhombic phase was successfully obtained. [ABSTRACT FROM AUTHOR]

Presents a two-dimensional analytical model of a spiral-shaped lead zirconate titanate ceramic actuator. Description of composite flextensional actuators; Equivalence between the semicircular spiral and archimedes spiral; Discussion on finite element analysis of the spiral-shaped actuators.

This paper discusses the fabrication and characterization of 3.5-MHz single-element transducers for therapeutic applications in which the active elements are made of hard lead-free BNT-based and hard commercial PZT (PZT-841) piezoceramics. Composition of (BiNa0.88K0.08Li0.04)0.5(Ti0.985Mn0.015)O3 (BNKLT88-1.5Mn) was used to develop lead-free piezoelectric ceramic. Mn-doped samples exhibited high mechanical quality factor ( Qm ) of 970, thickness coupling coefficient ( kt ) of 0.48, a dielectric constant ( \varepsilon ^T33 ) of 310 (at 1 kHz), depolarization temperature ( Td ) of 200 °C, and coercive field ( Ec ) of 52.5 kV/cm. Two different unfocused single-element transducers using BNKLT88-1.5Mn and PZT-841 with the same center frequency of 3.5 MHz and similar aperture size of 10.7 and 10.5 mm were fabricated. Pulse-echo response, acoustic frequency spectrum, acoustic pressure field, and acoustic intensity field of transducers were characterized. The BNT-based transducer shows linear response up to the peak-to-peak voltage of 105 V in which the maximum rarefactional acoustic pressure of 1.1 MPa, and acoustic intensity of 43 W/cm2 were achieved. Natural focal point of this transducer was at 60 mm from the surface of the transducer. [ABSTRACT FROM PUBLISHER]

This study aims to develop a novel design of piezoelectric transducer with the optimized geometry that is targeted for energy harvesting in roadway under vehicular loading. The Bridge transducer with layered poling and electrode design is proposed to enhance energy output. Finite element analysis was conducted to predict energy output and stress concentration in the transducer. Multi-physics simulations were conducted to evaluate energy outputs using different lead zirconate titanate materials, loading magnitudes, transducer types, and geometry parameters. The optimum configuration of transducer geometry was evaluated considering the balance between energy harvesting performance and mechanical failure potential due to stress concentrations. The novel design of Bridge transducer with layered poling and electrodes produces much greater energy than the traditional bridge and Cymbal transducer. The results show that within the failure stress criteria, the optimized design of Bridge transducer produced an electrical potential of 556 V, which could result in 0.743 mJ of potential energy (open circuit condition) for a single transducer under the external stress of 0.7 MPa. Laboratory testing on energy harvester module showed that simulation results agreed well with the measured power. [ABSTRACT FROM AUTHOR]

Electromechanical properties and high power characteristics of Pb-free hard piezoelectric ceramics in the (BiNa0.88K0.08Li0.04)0.5 (Ti1-xMnx)O3 (x = 0, 0.014, 0.015, and 0.016) system were studied. Mn doping resulted in a considerable enhancement of mechanical quality factor Qm and vibration velocity. The lowest mechanical and dielectric losses were achieved in 1.5 mol% Mn-doped ceramics with a planar Qm of about 970 and tanδ of 0.89%. The heat dissipation and resonance frequency shift under high drive condition were remarkably suppressed upon Mn doping. The maximum vibration velocity was increased from 0.28 m/s in undoped ceramic to 0.6 m/s in 1.5 mol% Mn-doped composition. The results of this study revealed that Mn-doped BNT-based piezoelectrics exhibited a superior high power performance compared to their lead-based counterparts such as PZT4 and PZT8 ceramics. [ABSTRACT FROM AUTHOR]

MO3 (M = Mo, W) or VI–VI binary compounds are important semiconducting oxides that show great promise for a variety of applications. In an effort to tune and enhance their properties in a systematic manner we have applied a designing strategy to deliberately introduce organic linker molecules in these perovskite-like crystal lattices. This approach has led to a wealth of new hybrid structures built on one-dimensional (1D) and two-dimensional (2D) VI–VI modules. The hybrid semiconductors exhibit a number of greatly improved properties and new functionality, including broad band gap tunability, negative thermal expansion, largely reduced thermal conductivity, and significantly enhanced dielectric constant compared to their MO3 parent phases. [ABSTRACT FROM AUTHOR]

Abstract: A major obstacle for a viable technological development of dye sensitized solar cells (DSSCs) is still the synthesis of a high performance iodide-conducting polymer electrolyte. Here we present a series of eight electrolytic complexes with formula PEG1000/(MgI2) x (I2) y (0.0038≤ x ≤0.5801, 0≤ y ≤0.0636). The synthesis involves the preparation of a disordered form of MgI2 by a metallorganic route, which enables us to dissolve high amounts of salt in the chosen polymer host. The thermal analysis of the resulting polymer electrolytes was performed using modulated differential scanning calorimetry measurements. Vibrational studies were carried out using medium FT-IR, far FT-IR and FT-Raman. The variation of the CO and OH stretching modes in the medium infrared, as a function of the mole-to-mole ratio n Mg/n O, was investigated by Gaussian decomposition to provide insight into the polymer–polymer and salt–polymer interactions in these materials. The FT-Raman spectra confirmed and complemented the vibrational assignment. The conductivity study of these systems was performed by electrical spectroscopy in the frequency interval 10 mHz–10MHz. The direct current conductivity (σ DC) profiles versus the reciprocal temperature exhibited a Vögel-Tamman-Fülcher (VTF) behavior. The best σ DC at 50°C was 5×10−5 Scm−1. The overall results indicate the presence of bivalent, monovalent and neutral species, Mg2+, [MgI]+ and MgI2, respectively, which participate in the conduction process. These results are consistent with what was previously observed in PEG400-based systems doped with δ-MgCl2. The presence of at least one Mg site containing a distribution in parameters was observed using 25Mg solid state magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. The site has been assigned to a Mg complex involving the coordination by oxygen atoms of the polymer backbone. [Copyright &y& Elsevier]

This paper presents the fabrication and characterization of single-element ultrasonic transducers whose active elements are made of lead-free piezoceramic, 1-3 PZT/polymer composite and PVDF film. The lead free piezoelectric KNN- LT-LS (K044Na052Li004)(Nb054Tao1oSboo6)03 powders and ceramics were prepared under controlled humidity and oxygen flow rate during sintering. Due to its moderate longitudinal piezoelectric charge coefficient (175 pC/N) and kt of 0.50, the KNN-LT-LS composition may be a good candidate for high-frequency transducer applications. PZT fibers with 25 μm diameter formed by the viscose suspension spinning process were incorporated into epoxy to fabricate 1-3 composites with the averaged kt = 0.64 and d33 = 400 pC/N. Using KNN-LS-LT ceramic, 1-3 PZT fiber composite, and PVDF film, 3 different unfocused single element transducers with center frequencies of 25 MHz were fabricated. The acoustic characterization of the transducers demonstrated that wideband and low insertion loss could be obtained employing KNN-LS-LT ceramic. The -6 dB bandwidth and insertion loss were 70% and -21 dB, respectively. In comparison, the insertion loss of the ceramic transducer was much smaller than those made with 1-3 composite and PVDF film. This was attributed to closer electrical impedance match to 50 Ω and higher thickness coupling coefficient of the ceramic transducer. [ABSTRACT FROM AUTHOR]

Lead-based piezoelectric ceramics are suitable materials for noninvasive applications of ultrasound to medicine. However, the embedded therapeutic and diagnostic procedures require the use of lead-free piezoelectric materials as active elements in transducers. With this goal to mind, we investigated the substitution of Ba2+ cations in a lead-free piezoelectric systems of K1/2Na1/2NbO3-LiTaO3- LiSbO3 (KNN-LT-LS) with perovskite structure. The Ba2+ was added to the system as an A-site dopant in the range of 0-2 mol% in increments of 0.5 mol%. The addition of Ba2+ improved the piezoelectric charge coefficient, d33.,and longitudinal coupling coefficient, k33. The composition with 1 mol% Ba2+ had 36% and 58% higher d33 and k33, respectively, than the undoped composition. It appeared that the addition of Ba+2 induced "soft" characteristics in this lead-free piezoelectric system. This was verified by the increase of remnant polarization along with the decline of coercive field. The Ba2+ behaved as a grain growth inhibitor and caused a drastic reduction in polarization level ( 60%) when the grain size became smaller than 1.5 μm. Incorporation of Ba2+ up to 1.5 mol% increased the bulk resistivity of the KNN-LT-LS system and then reduced it drastically at high dopant concentrations. The electron-hole compensation model fit well with the results obtained in this study and verified the A-site substitution of donor-doped barium. KNN-LT-LS ceramics with 0 mol% and 1 mol% Ba2+ were used to fabricate single-element ultrasonic transducers resonating at 5.5 MHz. The -6 dB fractional bandwidth and -20 dB pulse length of the probe made of doped ceramic were 50% and 1.68 μs, respectively. This indicated that this system could he considered as a candidate for invasive and/or embedded medical ultrasound applications. [ABSTRACT FROM AUTHOR]

Traditional flextensional transducers classified in seven groups based on their designs have been used extensively in 1–100 kHz range for mine hunting, fish finding, oil explorations, and biomedical applications. In this study, a new family of small, low cost underwater, and biomedical transducers has been developed. After the fabrication of transducers, finite-elements analysis (FEA) was used extensively in order to optimize these miniature versions of high-power, low-frequency flextensional transducer designs to achieve broad bandwidth for both transmitting and receiving, engineered vibration modes, and optimized acoustic directivity patterns. Transducer topologies with various shapes, cross sections, and symmetries can be fabricated through high-volume, low-cost ceramic and metal extrusion processes. Miniaturized transducers posses resonance frequencies in the range of above 1 MHz to below 10 kHz. Symmetry and design of the transducer, polling patterns, driving and receiving electrode geometries, and driving conditions have a strong effect on the vibration modes, resonance frequencies, and radiation patterns. This paper is devoted to small, multimode flextensional transducers with active shells, which combine the advantages of small size and low-cost manufacturing with control of the shape of the acoustic radiation/receive pattern. The performance of the transducers is emphasized. [ABSTRACT FROM AUTHOR]

Abstract: Organic–inorganic hybrid monoliths consisting of poly(methyl methacrylate) and SiO2 were synthesized by the sol–gel process. Three PMMA/TEOS ratios by weight were prepared, namely PMMA/TEOS=80/20, 50/50 and 20/80. The effects of the ratio of PMMA/TEOS on thermal stability, microstructure, morphology and optical properties were systematically studied. In particular, scanning electron microscopy (SEM) demonstrated morphological variation corresponding to the degree of miscibility between organic and inorganic components. Energy dispersive spectroscopy (EDS) clearly revealed that the SiO2 was more uniformly distributed in the hybrids with increasing PMMA content. The refractive index could be adjustable in the range of 1.474–1.486. The 80/20 monolith had the similar transparency to pure PMMA in the visible region and lower absorption than PMMA in the near infrared region, suggesting its potential applications for optical devices. [Copyright &y& Elsevier]

Highly grain-oriented lead metaniobate (PbNb2O6; PN) ceramics were prepared by a layered manufacturing (LM) process. This process has enabled us to obtain a net-shaped piezoelectric ceramic component with grain orientation of f∼89%, and improvement in electromechanical properties. The LM feedstock (filament) includes equiaxed (matrix; 90 vol%) and anisometric PN templates (10 vol%), both dispersed uniformly in a thermoplastic binder. The needle-like PN templates were synthesized by molten salt synthesis technique, while the equiaxed PN powder was prepared by conventional ceramic processing methods. The processing conditions were studied and optimized to obtain orthorhombic phase fine powder and anisometric templates. Samples were obtained through layer-by-layer deposition of the filament through a small diameter (500 μm) nozzle. After binder removal, the PN samples were sintered in a temperature range of 1150°–1300°C for 1 h. SEM observation revealed strong grain orientation perpendicular to the deposition direction. Relative permittivity at the Curie point ( Tc: 560°C) was 18 100 and 14 600 for the LM and random polycrystalline samples, respectively. Improved properties in piezoelectric figure of merit by 71%, d33 by 23%, and g33 by 31% were observed in the grain-oriented samples. Remnant polarization also showed about 80% improvement, increasing from 4.5 to 8.1 μC/cm2 for the grain-oriented LM samples. [ABSTRACT FROM AUTHOR]

Fused deposition of ceramics (FDC) is one of the developing solid freeform fabrication (SFF) techniques. The successful production of high performance ceramics by the FDC process requires that no defects exist in the green parts. However, build defects, such as missing roads, poorly bonded layers or sub-perimeter voids can be encountered in improperly built FDC parts. In this study, a method known as WIP''ing (warm isostatic pressing) was evaluated for its ability to eliminate existing defects in GS44 Si3N4 green FDC parts. Analogous to CIP''ing (cold isostatic pressing), the green FDC parts were rubber bagged and loaded into a pressure chamber filled with water soluble oil at different temperatures, ranging from 30 to 90°C, at pressures of up to 35 MPa. X-Ray radiography results indicated that at temperatures above 70°C, WIP''ing was effective in closing the gaps of the intentionally placed void defects in FDC parts. However, WIP''ing above 70°C was not effective in healing the defects completely. The fracture strengths of FDC parts with intentional added defects, WIP''ed above 70°C were substantially lower than control samples. [Copyright &y& Elsevier]

This paper presents the concept of a process signature for the use of online signature analysis and defect detection in the layered manufacturing (LM) of ceramic sensors and actuators. To achieve the high quality of parts built by the fused deposition of ceramics (FDC), an online process-monitoring system is implemented to detect the processing defects. Using a process signature extracted from the image of a layer captured by the monitoring system, an ideal image is created that is then compared to the original image to detect and identify the defects. Some results of signature analysis and defect detection for single-material and multi-material parts are also presented. [ABSTRACT FROM AUTHOR]

Examines a tool path-based deposition planning in fused deposition (FD) manufacturing processes. Use of constant deposition flow rate in FD technology; Achievement of high quality functional part; Utilization of a grouping and mapping algorithm.