Search

Understanding aqueous dispersion, rheological properties and colloidal stabilisation mechanisms of hierarchically assembled ceramic powders is important for progress in the fields of catalysis, separation and/or adsorption. The present study was designed to evaluate the rheological and sedimentation behaviour of highly loaded aqueous suspensions (up to φA = 0.126) containing AlN-powder-hydrolysis-derived, micron-sized, mesoporous, gamma alumina (MA) particulates with a high surface area (∼180 m2/g) dispersed with sodium polyacrylate (NaPAA). The as-prepared suspensions were prone to sedimentation and segregation. However, when divalent cations (Mg2+, Ca2+) or cellulose nanofibers were added, the formation of interparticle association networks in the aqueous suspensions containing MA particles was triggered, facilitating their long-term resistance to sedimentation lasting more than 12 weeks.

For transducer design, it is essential to know the acoustic properties of the materials in their operating conditions. At frequencies over 15 MHz, standard methods are not well adapted because layers are very thin and backings have very high attenuation. In this article, we report on an original method for measuring the acoustic properties in the 15–25 MHz frequency range, corresponding to typical skin-imaging applications, using a backing/piezoelectric multilayer structure. Onto a porous Pb(Zr0.53Ti0.47O3 (PZT) substrate, a piezoelectric PZT-based layer with a thickness of $\sim 20~\mu \text{m}$ was deposited and directly used to excite an acoustic signal into water. Herein, the measured signal corresponds to the wave that is first reflected on a target in water, then propagates back to the multilayer structure, and is transmitted through the thick film and further to the rear face of the porous backing, where it is again reflected and returns to the piezoelectric thick film, thus avoiding overlap with the electrical excitation signal. Two types of PZT backings with similar porosity of ~20% and spherical pores with size of 1.5 and 10 $\mu \text{m}$ were processed. The ultrasound group velocities were measured at ~3500 m/s for both samples. The acoustic attenuation of the backings with pore size of 1.5 and 10 $\mu \text{m}$ were 12 and 33 dB/mm, respectively, measured at 19 MHz. This advanced measuring technique demonstrated potential for the simple measurements of acoustic properties of backing at high frequencies in operating conditions. Importantly, this method also enables rapid determination of the minimum required thickness of the backing to act as a semi-infinite medium, for high-frequency transducer applications.

International audience

We show how sintering in different atmospheres affects the structural, microstructural, and functional properties of ~30 μm thick films of K0.5Na0.5NbO3 (KNN) modified with 0.38 mol% K5.4Cu1.3Ta10O29 and 1 mol% CuO. The films were screen printed on platinized alumina substrates and sintered at 1100 °C in oxygen or in air with or without the packing powder (PP). The films have a preferential crystallographic orientation of the monoclinic perovskite phase in the [100] and [−101] directions. Sintering in the presence of PP contributes to obtaining phase-pure films, which is not the case for the films sintered without any PP notwithstanding the sintering atmosphere. The latter group is characterized by a slightly finer grain size, from 0.1 μm to ~2 μm, and lower porosity, ~6% compared with ~13%. Using piezoresponse force microscopy (PFM) and electron backscatter diffraction (EBSD) analysis of oxygen-sintered films, we found that the perovskite grains are composed of multiple domains which are preferentially oriented. Thick films sintered in oxygen exhibit a piezoelectric d33 coefficient of 64 pm/V and an effective thickness coupling coefficient kt of 43%, as well as very low mechanical losses of less than 0.5%, making them promising candidates for lead-free piezoelectric energy harvesting applications.

This study was designed to better understand the microstructural and phase evolution of lead-free sodium potassium niobate based piezoceramics with a nominal composition (K0.5Na0.5)0.99Sr0.005NbO3 (KNNSr) during pressure-less spark plasma sintering followed by post-annealing in oxygen. The as-sintered samples were dark-coloured and electrically conductive as a result of partial reduction of Nb5+ to Nb4+ and formation of oxygen vacancies confirmed by X-ray photoelectron and Raman spectroscopy. The Rietveld refinement analysis showed that the as-sintered samples contained two perovskite phases with monoclinic Pm unit cell and slightly different unit-cell parameters. The microstructure with sub-micrometre-sized grains unambiguously confirmed that rapid heating and short dwell time hindered the grain growth. We found that post-annealing the samples at 950 °C in oxygen led to improvement in functional properties. The samples became white-coloured, the both perovskite unit cells decreased as a result of re-oxidation, while the microstructure remained essentially unchanged. The KNNSr sintered at nominal sintering temperature of 1300 °C for 3 min and post-annealed possessed a relative density of 88% and dielectric and piezoelectric properties similar to those of the conventionally sintered samples. Our findings contribute to the understanding of pressure-less spark plasma sintering of sodium potassium niobate-based materials and suggest that arrested grain growth and minimisation of alkali evaporation not necessarily lead to dense ceramic.

Thermomechanically active shape-programmable elastomer microparticles are very promising for development of particulate composites with unique operational properties, which could be attractive for various applications, e.g., in 3D printing. Liquid crystal elastomers are one of the suitable candidate materials due to their remarkable spontaneous shape change response. Performed rheological and thermomechanical tests demonstrate that shear stress can be used to efficiently manipulate the nematic order-driven morphology of liquid crystal elastomer microparticles (μLCEs). Specifically, by exploiting the soft-elasticity character of the material through manipulation of shear amplitude time profile, the nematic director can be oriented along the flow, which results in alignment of microparticles. Using this method, a suspension of well-aligned, thermomechanically elongated monodomain μLCEs can be created by shear stress-assisted cooling. Although the alignment can be lost in absence of persistent flow, it is restored instantaneously on re-application of the flow. The reason for this is the preservation of particle elongation at room temperature in zero flow. This shape memory can be erased by heating the system to the isotropic phase. Our work represents an important step forward in the development of a new generation of shape-programmable materials, which are potentially suitable for additive manufacturing of artefacts with anisotropic physical properties.

We have investigated the processing of lead-zirconate-titanate-based thick films by inkjet printing Pb(Zr0.53Ti0.47)0.98Nb0.02O3 with a 6 mol% excess of PbO nanosized powder dispersed in water. Different waveforms were employed to determine the optimum size and shape of the drops. A uniform, defect-free pattern with dimensions of 4 mm × 4 mm can be printed using 20 V and a drop spacing of 20 μm. The inkjet-printed films were heated to 400 °C to remove the organics and subsequently sintered at 750 and 850 °C. The correlations between the density, grain size and electromechanical properties of the thick films and bulk ceramics are qualitatively discussed. A thickness coupling factor of 46% was obtained for a 15-μm-thick film sintered at low temperature of 850 °C, which is comparable to the value of the bulk ceramic with an identical nominal chemical composition. Our results are important for the economic and environmental-benign printing of piezoelectric materials applicable in variety of electronic devices, such as sensors, actuators, transformers, piezoelectric energy harvesters and transducers.

Membranes used in separation processes are subjected to fouling which decreases the efficiency of the process and the membrane's lifespan. To reduce this fouling, vibrating membranes made from piezoelectrics, have recently been proposed. In this study we propose an innovative and flexible design where a conventional alumina membrane vibrates under the influence of electrically driven lead zirconate titanate (PZT) piezoelectrics, which are integrated outside the filtering area. This design makes it possible to isolate the piezoelectric and electrical interconnections from the fluid during the operation. The vibration system was analysed using “hard” and “soft” PZT compositions. Both the numerical model and the measurements of the membrane vibrations in air confirmed higher vibration amplitudes in the case of the “soft” PZT. We demonstrate that the vibration system with “soft” PZT actuators also resonates under water pressure, but at amplitudes lower than those measured in air. Filtration tests with humid acid showed that when the membrane is subjected to piezoelectric vibration, the decline in the flux was reduced by 59%, compared to the situation without the piezoelectric effect, suggesting that the novel vibration system with a built-in piezoelectric can be used in fluid-separation systems to minimise the fouling of ceramic membranes.

Synchrotron-based scanning photoelectron microscopy (SPEM) has opened unique opportunities for exploiting processes occurring at surfaces and interfaces, which control the properties of materials for electrochemical devices, where issues of chemical and morphological complexity at microscopic length scales should be faced and understood. The present article aims to demonstrate the present capabilities of SPEM to explore the surface composition of micro- and nano-structured materials, focusing on cases relevant to electrochemical technologies. We report and discuss a selection of recent results about three different systems, targeting hot topics in the fields of electrochemical energy storage and electrochemical fabrication: (i) an in-depth analysis of Ag-In electrodeposited alloys exhibiting dynamic pattern formation, (ii) the analysis of electrochemical processes at the electrodes of a self-driven solid oxide fuel cell and (iii) an operando characterization of a single-chamber solid oxide fuel cell. The last example has been performed at near-ambient pressure conditions using a unique specially designed setup which extends the traditional capabilities of scanning photoemission microscopes in the ultra-high and high-vacuum regimes to operating conditions that are closer to realistic ones, contributing to overcome the so-called “pressure gap”.

Electrocaloric (EC) cooling elements in the form of multilayers (MLs) were prepared. The elements consist of five layers of the relaxor-ferroelectric 0.9Pb(Mg 1/3 Nb 2/3 )O 3 –0.1PbTiO 3 , about 60 μm thick, with internal platinum electrodes and exhibiting a dense, uniform microstructure with a grain size of 1.7 μm. The largest temperature change Δ T EC of 2.26 K was achieved at an electric field ( E ) of 100 kV cm −1 and at 105 °C, measured by a high-resolution calorimeter. These results agree well with the indirect measurements. The EC coefficient, Δ T EC /Δ E, obtained for the MLs, is similar to the value obtained for bulk ceramics of the same composition. The Δ T EC values above 2 K over a broad temperature range from 75 to 105 °C make the ML elements suitable candidates for EC cooling devices at significantly lower voltages than bulk ceramic plates with comparable dimensions and mass.

Cordierite ceramics were produced from alumina with 5 and 0.65 μm particle sizes or AlOOH and talc, clays and feldspar, to determine the influence of the alumina particle size on the microstructure, coefficient of thermal expansion (CTE) and flexural strength (FS) of the ceramics. After sintering at 1300 °C the ceramics made from 5-μm-sized alumina consisted of cordierite, glass, quartz, mullite and alumina, and had the highest density, FS and CTE. The alumina grains act as inclusions, from which the trajectories of the cracks were deflected or terminated, which increases the FS and CTE. The ceramics from sub-micrometre-sized alumina or AlOOH contained a negligable amount and no alumina, respectively, together with other phases. This is reflected in the low CTE and FS. The cordierite ceramic with the lowest CTE of ∼2.0 × 10 −6 K −1 and a high FS of 100 MPa was prepared from the 0.65-μm-sized alumina particles.

Sub-micrometre-sized, niobium-modified, lead-zirconate-titanate powder (PZTNb) was stabilised in water with polyethylenimine and de-agglomerated using a high-energy ultrasound tip. The ink was printed with drop-on-demand piezoelectric inkjet printer with a nozzle size of 21 μm on a metalized alumina substrate and the structures were heated at 400 and 850 °C. The electron microscopy analyses showed that the PZTNb structures printed using a waveform duration of 9 μs and a voltage amplitude of 30 V possessed a predefined geometry and a homogeneous structure after heating at 400 °C. After sintering at 850 °C the thicknesses of the three-printed layer structures decrease and resulted in ∼20 μm-thick film with relative dielectric permittivity of 1100 and dielectric losses of 0.057. Results indicate that the inkjet printing of aqueous PZTNb ink and the subsequent heating are suitable procedures for obtaining piezoelectric thick-film structures with a predefine geometry.

Vibrational energy harvesting is a very promising way to replace batteries in many types of application like industry, infrastructure, aeronautic or healthcare. Piezoelectric based energy harvesting are commonly employed to scavenge mechanical energy from environmental vibrations in which resonance frequencies are mostly below 200 Hz. Piezoelectric materials that are generally based on lead zirconate titanate (PZT)are increasingly prohibited in many areas in the world for their toxicity to human health and to the environment. A serious alternative to PZT is the sodium potassium niobate (KNN)which presents appropriate properties like its Curie temperature, its coupling coefficient and its density. In this paper we propose to integrate a KNNSr (strontium doped sodium potassium niobate)ceramic in a bimorph structure in a cantilever beam configuration to scavenge vibrational energy in the frequency range of 25 Hz (for medical application). A thinned bulk approach is chosen for the fabrication of the bimorph in order to maintain the good properties of the bulk ceramic. Vibrational measurements demonstrate a power density of 13μW/G2/ cm 3and a resonance frequency of 24 Hz which is highly compatible with external vibrations at low frequencies.

International audience; We studied the effect of porosity and pore morphology on the functional properties of Pb(Zr0.53Ti0.47)O3 (PZT) ceramics for application in high frequency ultrasound transducers. By sintering a powder mixture of PZT and polymethylmetacrylate spherical particles (1.5 and 10 μm) at 1080°C, we prepared ceramics with ∼30% porosity with interconnected micrometer sized pores and with predominantly ∼8 μm spherical pores. The acoustic impedance was ∼15 MRa for both samples, which was lower than for the dense PZT. The attenuation coefficient α (at 2.25 MHz) was higher for ceramics with ∼8 μm pores (0.96 dB mm− 1 MHz− 1), in comparison to the ceramic with smaller pores (0.56 dB mm− 1 MHz− 1). The high α value enables the miniaturisation of the transducer, which is crucial for medical imaging probes. The dielectric and piezoelectric coefficients, polarisation, and strain response decreased with increased porosity and decreased pore/grain size. We suggest a possible role of pore/grain size on the switching behaviour.

We studied the thickness uniformity and homogeneity of lead-zirconate-titanate thick films on gold-coated alumina substrates obtained by constant-current electrophoretic deposition from ethanol-based suspensions with different conductivities. Based on the geometry of the experimental set-up, a finite-element model was constructed. The numerical analyses predicted a non-uniform current-density distribution on the electrodes, which was higher at the edges. We expected a thicker deposit at the edges, which was confirmed by measuring the cross-sectional profile of the as-deposited layer. The thickness non-uniformity was more pronounced for shorter deposition times and when performing the deposition from highly conductive suspensions. In the latter case the rate of deposition was decreased and the homogeneity of the deposits was increased, as evidenced by the scanning electron microscopy images. A homogeneous and uniform layer with a thickness of about 40 μm was prepared from the ethanol-based suspension with a conductivity of 20 μS/cm after 120 s.

The chemical stability of a powder with the nominal composition Pb(Zr 0.53 Ti 0.47 )O 3 (PZT) in water at pH 3, 7, and 10 for 14 days was studied to evaluate the effect of the pH on the subsequent sintering and properties of the ceramic. The concentrations of the Pb, Zr and Ti ions were 5.4, 0.09 and 0.02 mol.%, respectively, measured in the supernatants at pH 3 by inductively coupled-plasma mass spectroscopy. The PZT powder dissolved incongruently in acidic pHs. After sintering the ceramic was porous and contained a perovskite phase as well as traces of ZrO 2 . At pH 7 and 10 the amounts of leached ions were 10,000-times lower than that at pH 3. After sintering the single-phase ceramic was dense, with piezoelectric properties similar to those of PZT ceramics prepared from the non-aged powder. This study reveals that the neutral and alkaline regions are suitable for suspension preparation and subsequent processing.

Processing of piezoelectric linear-array elements for high-frequency linear-array transducers by electrophoretic deposition (EPD) was investigated. Powders with the nominal composition Pb (Zr0.53Ti0.47)0.98Nb0.02O3(PZT Nb) and PbO were stabilised in ethanol by the addition of a polyelectrolyte and mixed together in a molar ratio 98:2. The suspensions of both powders consisted of particles with a median size of 0.2 μm and with a zeta potential of about-50 mV. They were deposited on alumina substrates with patterned gold electrodes at a constant current density. The deposits were sintered at 950°C in a PbO-rich atmosphere. The influence of the inter-electrode distance and the geometry of the counter electrode on the shape and dimensions of the thick films were studied. With the increasing inter-electrode distance the width of the elements decreased and the space between them (kerf) increased. A higher lateral resolution of the elements was obtained when using square-shaped counter-electrode compared to lined-shaped one. When depositing on a substrate with the electrode width of 1 mm and the kerf of 0.5 mm using an inter-electrode distance of 25 mm and a square counter electrode, 20 μm thick PZT Nb elements with a kerf of 360 μm and sharp edge were obtained. When the substrates with the electrode width and kerf of 150 μm were used, the 160 μm wide elements with a kerf of 144 μm were obtained at the same deposition conditions. The results demonstrated that EPD is a suitable technique to process aligned linear-array structures with an element width and a kerf in the order of a few tens of micrometres at optimised deposition conditions.

Ferroelectric ceramics are at the heart of numerous electronic devices that surround us; indeed, it would be difficult to imagine our lives without these versatile materials. Their outstanding properties are the result of scientific breakthroughs in ceramics research, which makes possible the production of multilayer capacitors, piezoelectric transducers, actuators, and so on. In this review we describe the powder-based processing of ferroelectric perovskite ceramics.

Solid-state (non-activated) and mechanochemical activation (activated) synthesis methods were used to produce Sm-modified BiFeO 3 ceramics of composition Bi 0.88 Sm 0.12 FeO 3 . The first part shows that the formation of Bi 0.88 Sm 0.12 FeO 3 using the two synthesis methods followed a different reaction pathway on annealing the powders. The non-activated ceramics reacted by forming two intermediate phases, isostructural to BiFeO 3 and SmFeO 3 , and then inter-diffusing, forming the final Bi 0.88 Sm 0.12 FeO 3 solid solution. Unlike the non-activated samples, the activated ceramic powders formed Bi 0.88 Sm 0.12 FeO 3 phase on annealing the powders, without apparent intermediate phases. As revealed by transmission electron microscopy, the non-activated reaction pathway caused the Pbam phase to form as chemical inhomogeneous (Sm-rich) isolated nano-sized grain inclusions in the final ceramics. Conversely, the activated reaction pathway caused the Pbam phase to form chemically homogeneous nano-regions within the R 3 c phase grains. The results demonstrate the important role of processing in the appearance of the frequently discussed anti-polar Pbam phase in this system. In the second part, the high electric-field-induced polarization and strain behaviors of these ceramics were studied by means of polarization–electric (P–E) and strain–electric field (S–E) hysteresis loops, and the S–E loops were compared with those of unmodified BiFeO 3 . Bipolar S–E loops of Bi 0.88 Sm 0.12 FeO 3 had a distinctive butterfly shape with less frequency dependence relative to BiFeO 3 at driving-field frequencies of 0.1–100 Hz. BiFeO 3 ceramics exhibite strong driving electric-field-frequency-dependent domain switching, the origins of which were previously attributed to a domain-wall pinning mechanism and “hardening” behavior. This study shows that Sm-modification induces a “hardening–softening” transition in BiFeO 3 ceramics.

In the contribution the design and the fabrication of two different types of ceramic packaging for PiezoMEMS devices is presented. The first ceramic packaging is designed for housing the piezoelectric energy harvester. This packaging is made using LTCC technology and in the final application will integrate piezoelectric device, electronic circuit, storage capacitor and other components into the complex microsystem. The second packaging is developed for piezoelectric vibrating device as a part of water-purification system. In this case, the thick-film technology is used for electrical interconnection of piezoelectric actuators and for the hermetic watertight insulation of the system.

International audience; An original method to measure the acoustic properties of porous Pb(Zr0.53Ti0.47)O3 (PZT) backings at high-frequencies (HF, i.e. between 15 and 25 MHz), was developed. To this end, a piezoelectric PZT-based thick film was deposited onto the porous ceramic backing and directly used to generate an acoustic signal in water. Here, the considered signal is the one that was generated in water, reflected on a target, back toward the multilayer structure, transmitted through the piezoelectric thick film and then to the rear face of the porous backing and finally back to the active film. This method avoids the overlap of the electrical excitation and the measured signal. In this study, two types of porous PZT backings with 1.5 and 10 micrometers pore sizes (volume fraction around 20%) were characterized. For both samples, group velocities were around 3500 m/s and for the 10 micrometers pores size sample, the measured acoustic attenuation coefficient was 1.7 dB/mm/MHz in the frequency range of the transducer bandwidth. Finally, this method is found to be an easy way to determine, in operating conditions, the minimum required thickness of the porous PZT to be used as a backing (in order to be considered as a semi-infinite medium) for HF transducer applications.

Micrometre-sized Pb(Zr 0.53 Ti 0.47 )O 3 (PZT) powder was dispersed in water, stabilized with the ammonium polyacrylate (PAANH 4 ) and milled to reduce the particle size. The influence of the pH, the amount of PAANH 4 , and the milling time on the zeta potential, the PZT particle size and the particle size distribution was studied. The agglomeration took place regardless the milling time at pH 3. The suspension, containing 5 vol.% of PZT and 5 wt.% of PAANH 4 , milled at pH 10 for 240 min, was stable and contained particles with a narrow, log-normal particle size distribution with the median size of 160 nm. The dissociated carboxyl groups from the PAANH 4 interacted with the PZT particles as evidenced by Fourier transform infrared spectroscopy and electrosterically stabilized the particles in water at pH 10. The PZT particle size and the stability of the suspension fitted the requirements for the ink, suitable for ink-jet printing.

Magneto-electric (ME) ceramic composites of cobalt ferrite (CoF) and lead zirconate titanate (PZT) were prepared by mechanical mixing of the constituent powders followed by cosintering. The cosintering conditions for nano-sized CoF and submicrometer-sized PZT powders were studied in detail. It was found that the CoF powder needs to be presintered at 700°C for 2 h to minimize the differences in the sintering kinetics of the constituent powders. Despite the low cosintering temperatures (900°C–1000°C) the interdiffusion of the cations from both phases was confirmed with energy-dispersive X-ray analysis and X-ray diffraction. Efforts were made to optimize the cosintering conditions to prepare dense ceramic ME composites, which showed the converse ME effect.

An ink consisting of Pb(Zr0.53Ti0.47)O3 (PZT) particles with a median size of 170 nm and a narrow size distribution, in a dispersion of water and glycerol, and with a low viscosity and surface tension, was used for the fabrication of thick films by piezoelectric ink-jet printing. This study reports the printing conditions, the subsequent thermal treatment of the as-deposited layers, and the properties of the sintered PZT thick film. The film, sintered at 1100°C, had a locally dense microstructure and consisted of grains that are a few 100 nm across, as revealed by scanning electron microscopy. A local piezoelectric response of 15 pm/V was measured in the ink-jet–printed PZT thick film by piezoresponse force microscopy.

International audience; Acoustic properties of porous PZT ceramics intended to be used as backing in high-frequency transducer applications are investigated using a novel method where an electroded piezoelectric thick film is deposited on the backing under test. Two backings with pore sizes 1.5 μm and 10 μm were obtained by sintering a mixture of ceramic powder and an organic template, their porosity was evaluated by scanning electron microscopy at 15%, leading to a density around 6.5 g/cm3. The electroacoustic impulse responses of these devices were measured considering the backing as a propagation medium, the initial thickness of which was chosen small enough to allow back-wall echoes to be detected and large enough to be able to separate the signals in time domain. Then the thickness of the backing was reduced (from around 2 mm to less than 1 mm) and the measurements were repeated. Acoustic properties were then deduced: attenuation coefficients reaching 4 dB/mm/MHz and group velocities around 3400 m/s were obtained, leading to an acoustic impedance around 22 MRa. Such combination of high attenuation and moderate acoustical impedance make these materials an interesting solution for high-resolution ultrasonic imaging transducers.

We present a general protocol for processing cost-beneficial, environmentally benign aqueous-type suspensions containing metal-oxide nanostructured particles, and their patterning with piezoelectric ink-jet printing technology. The critical issues relevant to ink-jet printing are the preparation and stabilization of nanosized particles in a fluid and adjusting its physical properties to the values appropriate for a particular ink-jet printer mechanism. We discuss and illustrate, on a model titania system, the processing of a highly stable, colloidal, water-based suspension containing particles not bigger than 570 nm, prepared by a ball-milling process. For the ink-jet printing experiments, the surface tension and the viscosity of the suspension were modified by the addition of a small amount of the appropriate non-ionic amphiphiles and glycerol. The formation of droplets, their positioning on the substrate, and the shape and uniformity of the dots on the substrate are discussed and correlated with the fluid properties via the inverse Ohnesorge number Z. It was shown successfully that uniform, regular-shaped TiO2 dots with a diameter of 30 μm and a good positioning accuracy on Si/SiO2 substrates could be obtained by jetting a fluid with Z values of 5 and 9 using a piezoelectric ink-jet printer with a nozzle diameter of 21 μm operating at an amplitude of 13 V and a frequency of 5 kHz.

A general approach to prepare aqueous suspensions of inorganic particles suitable for ink-jet printing was developed. Titanium dioxide was used as the model material. Stable colloidal suspensions of TiO2 particles in water were prepared by adjusting the pH. The milling conditions were optimized in order to effectively mill the starting micron-sized powder. After 280 min of milling, the particle size was decreased to dmean = 170 nm. The fluid properties of the suspensions, i.e. viscosity and surface tension, were optimized by increasing the solid load of TiO2 powder and by addition of the surfactant triton X-100. Additionally, glycerol was added to the suspensions to control the drying behavior. The patterns of TiO2 were successfully printed on glass substrates.

We developed a new, simple method to prepare pure perovskite Pb(Mg1/3Nb2/3)O3 (PMN) from an aqueous suspension in a single annealing step. In this synthesis it is crucial to suppress the reaction between PbO and Nb2O5, which leads to secondary pyrochlore PbxNbyOz phases. Our method is based on the designed arrangement of particles of the starting compounds. The self-assembly of the colloidal aggregates was governed by particle surface charge, which was adjusted by the suspension pH. At pH below 11.8 particle–particle interactions lead to close contacts between lead oxide and niobium oxide particles in the suspension as well as in the dried powders, whereas at pH above 11.8 close contacts between lead and niobium oxide particles are avoided. The suspensions of the starting powders were prepared at pH 10.0, 11.4, 12.5, and in acetone. After heating of the dried suspension with the pH set at 12.5 at 900°C, a pure perovskite PMN powder was obtained. On the contrary, the powders prepared from the pH 11.4, 10.0, and acetone suspensions still contained the detrimental pyrochlore phase after heating at 900°C. The properties of the ceramics prepared from the pH 12.5 suspension are superior in comparison with the other samples.

In2O3–ZnO two-dimensional (2D) structures were processed by ink-jet printing and heating at 150°C and 450°C with the aim for implementation in transparent electronics. The In–Zn-solution precursor, based on In-alkoxide and Zn-acetate in 2-methoxyethanol, was originally designed for chemical solution deposition of thin films. To adapt it for piezoelectric ink-jet printing, the viscosity and surface tension were adjusted by the addition of a more viscous 1,3-propanediol. The optimum values were obtained for the ink consisting of 55 vol% of 1,3-propanediol. The printing parameters including the temperatures of the cartridge and the substrate, and the drop spacing were adjusted to allow patterning with a 40 μm resolution on SiOx/Si and glass substrates. The ink-jet-printed 2D structures heated at 150°C were amorphous and according to infrared spectroscopy organics-free, and upon heating at 450°C they crystallized without any preferential orientation, similarly as the spin-coated thin films, which were studied as a reference.

We have investigated the processing of 0.65Pb(Mg 1/3 Nb 2/3 )O 3 –0.35PbTiO 3 (denoted PMN–PT) thick films using an electrophoretic deposition process (denoted EPD), with the PMN–PT particles suspended in an ethanol-based suspension. The zeta-potential and the viscosity were measured to identify the conditions for the preparation of a stable suspension suitable for the EPD. The applied voltage, the deposition time, the chemical composition of the suspension and the concentration of the powder were investigated in order to obtain a high-quality PMN–PT deposit with a target thickness of about 50 μm. The PMN–PT thick films prepared from stoichiometric and PbO-excess suspensions by sintering at 950 and 1100 °C were examined by X-ray powder-diffraction analysis and scanning electron microscopy. The highest functional response was obtained for a homogeneous, dense, crack-free PMN–PT thick film prepared from a PMN–PT suspension with excess PbO. The film was deposited at a constant voltage of 10 V and for a time of 120 s, followed by sintering at 1100 °C in a PbO-rich atmosphere. The film's properties were as follows: a dielectric permittivity ɛ of 20,250 at a T m of 172 °C, a remanent polarization of 17 μC/cm 2 and a coercive field of 5 kV/cm.

We have studied the influence of increasing the amount of β-spodumene (LiAlSi2O6), as a Li2O-containing flux, on the phase composition, the microstructure evolution and the physical properties of high-alumina porcelain. Quartz reacts with β-spodumene in the temperature range 1150–1250 °C, forming lithium aluminium silicates with a larger amount of SiO2. The presence of lithium minerals contributes to a lower CTE for the fired bodies. At 1300 °C an improved flexural strength is achieved with compositions containing 1.0 or 1.2 wt.% of Li2O, as a result of a more uniform microstructure. With increasing amounts of Li2O the overfiring effect is greatly enhanced. The most favourable characteristics from an industrial perspective with regard to flexural strength and deformation during firing were attained by using a high-alumina porcelain composition containing 1.0 wt.% Li2O.

We have studied the formation of lead–magnesium–niobate Pb(Mg1/3Nb2/3)O3 perovskite powder produced by high-energy milling of the constituent oxides. By applying a low ball-impact energy and a low ball-impact frequency we were able to identify the reaction sequences. The crystal structure and the amount of crystalline and amorphous phases in the powder were determined using a Rietveld refinement. The morphology, structure and chemical composition of the powder were investigated by transmission electron microscopy. The surface composition, possible contamination and the chemical states of the elements were analyzed by X-ray photoelectron spectroscopy. In the early stage of milling the constituent oxides comminute, refine to nanosize dimensions and become amorphous. In the second step the Pb(Mg1/3Nb2/3)O3 nucleates from the amorphous regions where the stoichiometry corresponds to the perovskite. The perovskite phase nucleates and subsequently grows over the course of the milling. Simultaneously, the pyrochlore phase nucleates from the Pb- and Nb-rich regions; however, its nucleation and recrystallization stop after a certain milling time. The powder mixture consists of nanosized Pb(Mg1/3Nb2/3)O3 particles and an amorphous phase when milled for 94 h. No traces of contamination from the milling media were detected.

We have studied the processing of lead-zirconate-titanate PbZr0.53Ti0.47O3 (denoted PZT) based thick films using an electrophoretic deposition (EPD) process in order to obtain the active film with desired thickness and porosity at low the sintering temperature. The colloidal suspensions were prepared by mixing the ceramic powder in ethanol with the controlled addition of a polyelectrolyte salt and an organic base. In order to optimise the deposition process, the stability of the PZT and Pb5Ge3O11 (denoted PGO) particles in ethanol-based suspensions was studied. The electrophoretic deposition of PZT-PGO was performed from a mixture of optimal PZT and PGO suspensions in an appropriate molar ratio. PZT and PGO acting as a sintering aid were deposited on an Al2O3/Au substrate at a constant applied current and sintered at 850 oC. The thickness of the deposit was controlled by the deposition time and the applied current. PZT-PGO thick films deposited at 1.2 mA for 60 seconds and sintered at 850oC for 8 hours exhibited a room-temperature dielectric permittivity of 1050, dielectric losses of 0.038, a remanent polarisation Pr of 29 C/cm2, a coercive field Ec of 21 kV/cm and a d33 of 97pC/N.

TiO2, TiO2−x and Ti3O5 thick-film structures on corundum Al2O3 substrates were prepared using screen-printing technology. The screen-printed deposits were sintered up to 1500 °C in oxidising and reducing atmospheres to vary the Ti4+/Ti3+ ratio and consequently water contact angle. The structure of the thick films was studied with an X-ray powder diffractometer (XRD). The microstructural characteristics and the chemical composition were checked with a scanning electron microscope, equipped with an energy-dispersive spectrometer (EDS). The Ti–O films, up to 55 μm thick, exhibited excellent adhesion to the substrate and had uniform grain- and pore-size distributions. Ti3O5 and Al2O3 were found to be compatible phases up to 1500 °C in a reducing atmosphere. However, rutile-type TiO2 and Al2O3 are not compatible compounds at temperatures up to 1400 °C, in either oxidising or reducing atmospheres. TiO2 and TiO2−x form two types of reaction products with Al2O3. These reaction products were found to have various Ti/Al ratios.

We have investigated the processing of 0.65Pb(Mg 1/3 Nb 2/3 )O 3 –0.35PbTiO 3 (PMN–PT) thick films on platinised alumina substrates. Nanosized PMN–PT powder with 2 mol% of excess PbO was prepared by high-energy milling and deposited on the substrate using screen-printing technology. The films were then sintered at 950 °C in a PbO-rich atmosphere. The influence of the sintering time and the amount of PbO-containing packing powder was studied and related to the structural, microstructural, dielectric and piezoelectric properties of the film. In order to obtain a homogeneous and dense thick film without any secondary phase, the PMN–PT films had to be sintered in the presence of a PbO-based liquid phase that had to be completely removed from the thick film during the final stage of the sintering. Under optimal sintering conditions we obtained a room temperature relative dielectric permittivity of 3600, dielectric losses of 0.036, a T m of 174 °C, a permittivity at the T m of 21,000 and a d 33 of 140 pC/N.

The fabrication of piezoelectric transducers for high resolution medical imaging applications requires a backing material to damp the piezoelectric resonance, resulting in a shorter time response, i.e. improved resolution, but lower sensitivity. Thus, the choice of such a substrate must be made according to its acoustical properties, namely the ratio of acoustic impedance of the backing material and the piezoelectric layer. Moreover, this backing material must have a relatively high attenuation, and provide good surface properties such as a low roughness and diffusion potential. Finally, the substrate material must have a good mechanical behavior at high temperature (around 900°C for the sintering of the piezoelectric thick film). In this context a review of available materials is first given, and the corresponding list is found to be quite limited. Several PZT/PGO piezoelectric thick films deposited by screen-printing have been fabricated on dense alumina [1] and have delivered good electromechanical per...

Solidly mounted integrated transducers with a Bragg cell inserted between the piezoelectric film and the substrate are investigated for high frequency ultrasonic applications. A numerically stable recursive one dimensional transmission/reflection model was used to analyze the behavior of the periodic structure. This theoretical analysis includes the study of the influence of the acoustic properties of the constitutive layer, the effect of the number of cells and their arrangement. A 35 MHz integrated transducer consisting in a PZT ceramic laid down on a Au/PZT Bragg cell deposited on a porous substrate was fabricated and characterized. Both theoretical and experimental results highlight the interest of using a periodic structure for high frequency ultrasonic applications.

Ceramics from the titanium–oxygen system were prepared by sintering TiO2 and Ti2O3 powders at 1400 °C in air or in Ar/H2 (7%). The surface compositions of the TiO2, the non-stoichiometric TiO2−x and the Ti2O3 ceramics, studied with X-ray photoelectron spectroscopy, are discussed in terms of their chemical composition, with particular emphasis on the valence state of the titanium ions. The correlation between the valence state of the titanium ions at the surface and the water-contact angle was examined. The presence of Ti3+, which can be introduced at the titanium–oxygen ceramic surface by sintering the ceramic in lower oxygen partial pressure, is related to a significant decrease in the water-contact angle. TiO2 ceramics with just Ti4+ at the interface had a water-contact angle of 67°; however, the non-stoichiometric TiO2−x and Ti2O3/Ti3O5 with Ti3+ at the interface had lower water-contact angles, i.e., 26° and 18°, respectively. The wettability of ceramics in the Ti–O system can be improved by introducing Ti3+ at the ceramic interface.

Structure–property relationship has been performed in the lanthanum-modified lead–zirconate–titanate (PLZT) with a lanthanum content of 6 and 10 at.% and a Zr/Ti ratio of 90/10 as a function of A- and B-compensation model. The X-ray powder-diffraction analysis, electron microscopy, energy-dispersive spectroscopy, density measurements and sintering behavior have evidently demonstrated that it is possible to tailor the microstructural properties of PLZT with using selected type of the compensation. The densification of B-site compensated PLZT occurs at lower temperatures and leads to higher density when compared to A-site compensated PLZT. A presence of PbO at the grain boundaries in B-site compensated PLZT and the lack of it in A-site compensated PLZT leads to different sintering mechanism. The dielectric response characteristics of A- and B-site compensation model do not vary significantly.

The phase composition, microstructure and electrical properties of thick-film structures based on 0.65Pb(Mg 1/3 Nb 2/3 )O 3 –0.35PbTiO 3 (PMN–PT) were studied. PMN–PT powder with 2 mol% of excess PbO was prepared by high-energy milling from the constituent oxides. A high yield of perovskite PMN–PT with nano-sized particles was obtained after the synthesis. A paste was prepared from the obtained powder, screen printed on platinised alumina substrates and sintered at 850, 900 and 950 °C. Single-phase PMN–PT thick-film structures without any pyrochlore phase were obtained after the sintering. The dense PMN–PT layers had good dielectric, piezoelectric and ferroelectric properties. The relative dielectric permittivity of 4100 and the peak value of 41,000 for the film sintered at 950 °C compare well with bulk ceramics sintered at much higher temperatures. The d 33 value of the film was 170 pC/N. The obtained values for the dielectric properties demonstrate the good chemical homogeneity of material synthesized by high-energy milling.

We have investigated the synthesis of lead-magnesium-niobate–lead-titanate perovskite powder using high-energy milling of the constituent oxides. The compositions of the crystalline and amorphous phases as a function of milling time were determined with X-ray powder diffraction using a Rietveld refinement. The perovskite can be formed by two reaction routes. In the initial stage of milling, it is formed directly from the highly activated nano-sized constituent oxides, and after a certain milling time it is mainly formed from a pyrochlore phase. The obtained as-milled powder consists of crystalline perovskite and an amorphous phase that crystallizes into the perovskite after heating at 800°C.

International audience; Electrophoretic deposition (EPD) was used for the fabrication of piezoelectric [lead zirconate titanate (PZT)] thick films on alumina substrates. The EPD was performed in constant current mode from an ethanol based suspension consisting of PZT and PbO particles. The influence of addition of ethyl cellulose (EC) and sintering temperature on the thickness, density, homogeneity and functional response of PZT thick films is studied. Results show that the highest electromechanical performance is obtained for the PZT thick films sintered at 900 or 950°C, with a thickness coupling factor kt of 50%. The addition of EC influenced the thickness of the PZT thick films but had only minor effect on the porosity content for sintering temperatures over 900°C. Moreover, elastic constants of the thick films based on the suspension with EC were lower, which leads to lower acoustic impedance (15 MRa) while maintaining high (kt) value. In this last case, a better acoustic matching can be expected with propagation media such as water or biological tissues for ultrasound medical imaging applications.

The synthesis of Pb(Mg 1/3 Nb 2/3 )O 3 (PMN) with high-energy milling was studied by X-ray powder diffraction (XRD) using the Rietveld-refinement method. The results are discussed in terms of the qualitative and quantitative composition of the crystalline and amorphous phases as a function of milling time. The mechano-synthesis of PbO, Nb 2 O 5 , and MgO leads to the formation of perovskite PMN. In the initial stage of milling, particle size reduction and a high degree of amorphization were observed, together with the simultaneous formation of perovskite and pyrochlore-type structures. A mechanism for the formation of PMN by the mechano-synthesis route is proposed.

Thick film varistors based on the system ZnO–Bi 2 O 3 –Sb 2 O 3 have been prepared by screen printing technology on dense alumina substrates. Different processing strategies have been designed in order to control the excessive volatilization of Bi 2 O 3 in varistor films during the sintering, due to the high area–volume ratio, and as a means to improving their electrical response. Starting powders were selected and pre-treated in different ways to obtain different phases and control the Bi-rich liquid phase formation. Significant differences have been observed in the electrical properties which are related to the selection of the starting powders.

The paraelectric to ferroelectric phase transition in 9.5/65/35 lead lanthanum zirconate titanate-poly(vinylidene fluoride–trifluoro ethylene) ceramics–copolymer composite denoted as PLZT 0.24 [P(VDF 0.5 /TrFE 0.5 )] 0.76 has been studied by means of calorimetry and dielectric spectroscopy. Results were compared to those obtained in pure poly(vinylidene fluoride–trifluoro ethylene) [P(VDF 0.5 /TrFE 0.5 )] copolymer. Heat capacity measurements reveal that the weakly first order paraelectric to ferroelectric transition becomes broadened and the heat capacity anomaly is suppressed in the PLZT-P(VDF/TrFE) composite. The excess enthalpy slightly increases in the dc bias electric field as a consequence of the improved field-induced ferroelectric long range ordering. It is shown that the transition takes place approximately in the middle of the temperature range in which the dielectric constant exhibits a significant break. The dielectric constant anomaly in the PLZT-P(VDF/TrFE) composite is also slightly broadened, however its peak value is enhanced by about 40%. The enhancement of the dielectric constant could be reasonably explained within the simple Maxwell–Garnett effective-medium approach.

La 1-y Sr y Fe 1-x Al x O 3-δ perovskites were studied as potential materials for solid-oxide fuel cell (SOFC) cathodes. The phase relations in the LaFeO 3 -SrFeO 3-δ -LaAlO 3 system were investigated by X-ray powder diffraction analysis. The defect structure of the La 1-y Sr y Fe 1-x Al x O 3-δ perovskites was investigated by Mossbauer spectroscopy and weight-loss analysis. Relations between the nonstoichiometry and the conductivity of the La 1-y Sr y Fe 1-x Al x O 3-δ perovskites were investigated. The incorporation of aluminum (x) into LaFe 1-x Al x O 3 was found to have no influence on the defect structure but to decrease the conductivity. The incorporation of strontium (y) into La 1-y Sr y Fe 1-x Al x O 3-δ promotes the formation of anion vacancies and Fe 4+ that lead to higher conductivity.

The subsolidus phase relations in the La–Fe–Al–O system were investigated for solid oxide fuel cell (SOFC) applications. Five compounds, LaAlO3, LaAl11O18, LaFe12O19, AlFeO3, and LaFeO3, coexist in the La–Fe–Al–O system at 1380 °C in air. The microstructure and composition of the samples were studied by x-ray diffractometry and scanning electron microscopy. Based on experimental evidence, a phase diagram of the La2O3–Al2O3–Fe2O3 system has been proposed.

The chemical compatibility of a La 1– y Sr y Fe 1– x Al x O 3- δ cathode and an yttria-stabilised ZrO 2 electrolyte (YSZ) was studied for solid-oxide fuel cell (SOFC) applications. The Al addition to the LaFe 1– x Al x O 3 reduces the reactivity with the YSZ associated with increasing tolerance factor. The Sr addition to the LaFe 1– x Al x O 3 leads to Fe 4+ and anion-vacancy formation. The Sr addition hinders the formation of La 2 Zr 2 O 7 , but at y ⩾0.2 promotes the formation of SrZrO 3 at the La 1– y Sr y Fe 1– x Al x O 3– δ /YSZ interface. At low p(O 2 ) the formation of secondary phases is pronounced what could be related to the formation of anion vacancy.