Search

Purpose The purpose of this study is the design, fabrication and evaluation of a miniature ozone generator using the principle of electric discharge are presented. Design/methodology/approach The device was fabricated using a low-temperature co-fired ceramics (LTCC) technology, by which a multilayered ceramic structure with integrated electrodes, buried channels and cavities in micro and millimeter scales was realized. Findings The developed ozone generator with the dimensions of 63.6 × 41.8 × 1.3 mm produces approximately 1 vol. % of ozone in oxygen flow of 15 ml/min, at an applied voltage of 7 kV. Originality/value A miniature ozone generator, manufactured in LTCC technology, produces high amount of ozone and more than it is described in the available references or in datasheets of commercial devices of similar size.

Recent findings of a large electrocaloric (EC) effect in in polymeric and inorganic ferroelectric materials made this effect an attractive possibility in development of cooling or heating devices of new generation, which would be more environmentally friendly. We report a significant electrocaloric effect near the ferroelectric phase transition in substrate-free [Pb(Mg1/3Nb2/3)O3]1-x[PbTiO3]x (PMN-xPT) with x = 0.30 thick ceramic films on a platinum layer. A method and analysis of direct measurements of the large EC effect are presented. Results confirm that besides the large electrostrictive response already reported in similar self-standing films, the large EC effect of similar magnitude as found in bulk PMN-0.30PT ceramics exists in substrate-free thick films.

Pb(Mg1/3Nb2/3)O3-PbTiO3 is used as a model system of perovskite solid solutions with very high piezoelectric response at tailored morphotropic phase boundaries to demonstrate the processing of textured ceramics by ceramic-only technology. A novel homogeneous templated grain growth approach that uses conventional ceramic procedures and a single-source nanocrystalline powder for the matrix and also for obtaining the templates is described. Two batches of (100) faceted cube-shaped microcrystals with average sizes of 27 and 10 μm were successfully used as templates, and aligned by tape casting for the processing of -textured Pb(Mg 1/3Nb2/3)O3-PbTiO3 piezoelectric ceramics. Materials with effective piezoelectric coefficients up to 1000 pC/N and ferroelectric properties approaching those of single crystals are obtained. © 2013 The American Ceramic Society., Funded by: MICINN (now MINECO). Grant Number: MAT2011-23709; Slovenian Research Agency. Grant Number: J2-3633 and CoE NAMASTE.

PurposeIn this manuscript the purpose is to present and evaluate the developed non‐destructive method for analysing the phase composition of LTCC Du Pont “Green Tape 951” material fired in the temperature range from 800 to 1,000°C using X‐ray powder diffraction and Rietveld refinement.Design/methodology/approachThe method uses the crystalline Al2O3 which is already present in the material as an internal standard since its mass fraction was previously found to be constant in the described temperature range.FindingsThe results of the non‐destructive analyses and the classical destructive analyses are comparable and the estimated error of the destructive phase analyses and the calculated errors for the non‐destructive phase analyses are of the same order.Practical implicationsThe described method can be used also for analysing another type of LTCC material. In this case it is necessary to check whether the mass fraction of any crystalline phase present in the sample is constant in the given temperature range, because only in this case can it be used as an internal standard for a determination of the phase composition.Originality/valueThe non‐destructive method is a fast and easy approach for analysing the fired samples and is also suitable for controlling the phase composition of LTCC materials on 3D complex structures without destroying them, just by using the X‐ray diffraction patterns collected from their surface.

The present work is a systematic study of the influence of the sintering conditions on the structural and electrical properties of 0.57Pb(Sc 1/2 Nb 1/2 )O 3 –0.43PbTiO 3 ceramics prepared from mechanochemically activated powder. The ceramics were sintered at various temperatures and for a range of times. Three or even more contributions competed for influence on the functional properties of the ceramics, i.e., the density, the grain size and the phase composition. However, all these contributions combined in such a way that the best functional properties were obtained for the ceramics sintered at 1000 °C for 8 h.

For the fabrication of complex, micro-electromechanical systems (MEMS) devices based on low-temperature co-fired ceramic (LTCC), higher firing temperatures and longer times than those proposed by the LTCC producer are needed. These changes to the thermal budget may influence the material properties and consequently its functional properties. The effect of the firing conditions on the LTCC DuPont 951 and thus on the phase composition, that is, the alumina/anorthite ratio and porosity, on the mechanical properties is presented. The samples fired at low temperatures (800°C) had a high porosity (7%), which significantly contributed to the low elastic modulus (100 GPa) and the low mechanical strength of the LTCC (140 MPa). The samples fired at 850°C, which had only 1% of porosity, resulted in an elastic modulus of 122 GPa and a flexural strength of 224 MPa. A further increase in the temperature contributed to a slight decrease in the elastic modulus, while no significant difference in the flexural strength could be observed. The enhancement of the flexural strength with an increasing firing temperature was mainly related to a decrease in the porosity and to a lesser extent to the different ratio of the alumina/anorthite phases. The effect of firing time on the phase composition at selected temperatures (i.e., 100 h at 700 and 800°C) is also discussed.

Advanced micro- or macro-systems are in some cases made with multilayer ceramic technology. Low-Temperature Co-fired Ceramic (LTCC) technology is considered as one of the more suitable technologies for the fabrication of ceramic micro-systems that integrate screen-printed, thick-film electronic components as well as three-dimensional buried structures, for example, cavities and channels. One of the applications is a ceramic combustor. The chemical energy of the fuel is converted into thermal energy in a chemical micro-combustor through a burning process, while the accompanying high temperatures and, frequently, high pressures impose harsh conditions on the combustor structure. Therefore, the combustor must be carefully designed not only from the functional, thermal and chemical points of view, but also with respect to the mechanical strength. The combustor device was prepared by laminating of Du Pont 951PX LTCC green tapes. The fabricated 3D LTCC structures with buried cavities and channels including two inlets (for fuel and air), the evaporator for the fuel, the mixing system of the channels (for mixing the evaporated fuel and air), the distribution channels and eight microburners were realized. The main parts are eight micro-burners realized as buried cavities. In the burners a platinum-based catalyst was deposited to assist the oxidation, i.e., the burning, of the methanol with the air. Thickfilm, platinum-based heaters and temperature sensors are incorporated within the structure. The device was tested with different flow rates of liquid methanol (1 ml/h to 5 ml/h) and air (7 l/h to 15 l/h). The obtained temperatures were between 250°C and 450°C.

Low-temperature co-fired ceramic (LTCC) is an important material in the production of ceramic multilayer structures. Large and complex multilayer structures are usually fired at higher temperatures and/or longer firing times compared to the relatively thin LTCC tapes. The firing conditions of LTCC determine the phase composition and the microstructure, which both influence the physical characteristics, such as the mechanical and thermal properties. In this work the effect of the phase composition on the biaxial flexural strength and the temperature coefficient of expansion of the DuPont 951 LTCC is presented. The samples were fired at different temperatures and times to obtain different phase compositions. The phase composition, especially the mass fraction of anorthite, was correlated with the biaxial flexural strength and the thermal coefficient of expansion (TCE). A very long firing time, i.e., 100h at 800 °C, yields, apart from crystalline anorthite, the cristobalite phase. The anorthite that crystalizes from the glass phase in a dense LTCC material changes the crack-propagation mechanism and improves the biaxial flexural strength of the material. The major change in the biaxial flexural strength is observed when the anorthite phase appeared. The increasing mass fraction of anorthite does improve the biaxial flexural strength less drastically. With the increasing mass fraction of the anorthite, decreases of the TCE of the material and a small decrease of the density of the LTCC material occur.

The combination of the quantitative texture analysis and Rietveld methods is used to study the preferential orientation of morphotropic phase boundary (MPB) Pb(Mg1/3Nb2/3)O3-PbTiO3 ceramics obtained by homogeneous Templated Grain Growth. Their complex structure, with the coexistence of several polymorphs, and the presence of texture that is required to take advantage of their excellent piezoelectric properties, raise serious problems for a precise characterization of these materials. Conventional methods of texture analysis, although simple, are limited, and the information obtained, if not studied with care, may be misleading. The use of linear detectors and χ-scan are more appropriate for the study of diffraction peaks with several contributions as it is the case for MPB compositions. This work shows the simultaneous determination of structural and texture parameters through the application of the so-called combined method, already used for the analysis of similar problems in a range of polycrystalline materials, to this specific case.

0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 powder was prepared by a single-step, solid-state synthesis at 850°C. This was enabled by the controlled agglomeration of precursor particles by the change of pH in water suspensions. With the design of the contacts between the particles in the agglomerates, a phase-pure perovskite powder was synthesized from a suspension with a pH = 12.5. At the inherent pH = 11.4, the agglomerates that promote the pyrochlore formation were formed, resulting in a mixture of perovskite and pyrochlore phases after the calcination. The ceramics prepared from the suspension with pH = 12.5 were sintered to 96% of theoretical density at only 950°C, and exhibited electrical properties comparable to ceramics prepared by the columbite method, sintered at much higher temperatures. In contrast, the properties of the ceramics from the pH = 11.4 suspension were heavily deteriorated due to the presence of the pyrochlore phase and the high degree of porosity.

The electrocaloric effect (ECE) has recently become very attractive phenomenon due to its various potential applications, for example in heating or cooling devices of new generation which could be more efficient and environmentally friendly. Here a direct measurements of the ECE in thick films of 8/65/35 PLZT ceramics, and in the relaxor ferroelectric polymer composition P(VDF-TrFE-CFE)0.95-P(VDF-CTFE)0.05 near room temperature are presented. Our results are consistent with those obtained by indirect measurements. The maximum of the ECE responsivity ΔTEC/E in 8/65/35 PLZT thick films is achieved near the critical point, and in the terpolymer/copolymer blends it is shifted toward higher fields.

The electrocaloric (EC) effect attracted very recently considerable attention due to recent findings of the existence of a giant EC in polymeric and inorganic ferroelectric materials and because of its great potential in development of cooling or heating devices of new generation, which would be more environmentally friendly. A method and analysis of direct measurements of the large EC effect in self-standing [Pb(Mg1/3Nb2/3)O3]1-x[PbTiO3]x (PMN-xPT) with x = 0.35 thick ceramic films on a platinum layer are presented. Besides very large electrostrictive response already reported in these self-standing films, the experimental results confirm the existence of the large EC effect of similar magnitude as found in bulk PMN-0.35PT ceramics.

Presented in this paper of this special issue of Ferroelectrics, dedicated to Prof. Wolfgang Kleemann, is our recent study of thermal response near the dipolar glass to ferroelectric (G-F) transition studied by a high resolution calorimetry in relaxor ferroelectric 9/65/35 PLZT ceramics. By theoretical investigations based on spherical random bond random field (SRBRF) model it is predicted that the discontinuous electrocaloric change (EC) of temperature should be observed at the G-F transition line in an electric field–temperature (E-T) phase diagram. Experimental results confirm existence of such discontinuous EC jump in temperature in the canonical relaxor system 9/65/35 PLZT ceramics, thus confirming the existence of the first order G-F transition line in the E-T phase diagram of the perovskite relaxor ferroelectrics.

In this work the effect of firing temperature and firing time on the phase composition, microstructure, biaxial flexural strength, and temperature coefficient of expansion (TCE) of low-temperature cofired ceramic (LTCC) material is presented. At temperatures around 700°C the Al2O3 starts to dissolve in a low viscosity glass phase and this takes place up to 800°C, when 10 wt% of Al2O3 ceramic filler is dissolved in the glass phase forming the alumina-enriched area. This area is suitable for the crystallization of anorthite, which nucleates on the Al2O3 particles. The crystallization starts at 875°C and the mass fraction of anorthite increases with increasing temperature until it reaches a plateau value of around 22 wt% at higher temperatures or longer firing times. The biaxial flexural strength of the LTCC increases with increasing firing temperature from 135 MPa (at 800°C) to around 300 MPa (at 900°C). The major effect on the biaxial flexural strength of LTCC is that of porosity. The effect of the amount of anorthite on the LTCC biaxial flexural strength is minor. The TCE of the LTCC decreases from 5.6 × 10−6 to 5.0 × 10−6 K−1 with increasing firing temperatures or times and it is correlated with the anorthite mass fraction, which crystallizes at the expense of a decreasing amount of glass phase in the LTCC.

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.

Electrocaloric effect (ECE), i.e., a reversibly change in the temperature of an electrocaloric material due to the adiabatically applied electric field, is very attractive phenomenon due to its applications, for example in electric refrigeration. The first observations of the giant ECE were based on indirect measurements of the electric polarization and not on direct measurements of the ECE itself. By using direct measurements of ECE we show existence of the giant ECE in PMN ceramics near the electric field-induced ferroelectric phase transition.

During firing the conductive phase based on CaRuO3 in lead-free thick-film resistors decomposes, presumably due to interactions with the silica-rich glass phase. Subsolidus equilibria in the CaO-poor part of the RuO2–CaO–SiO2 diagram were studied with the aim of investigating possible interactions between the conductive phase and silica-rich glasses in thick-film resistors. The tie lines are between CaRuO3 and CaSiO3, and between RuO2 and CaSiO3. This indicates that the calcium ruthenate is not stable in the presence of the silica-rich glass phase.

The giant electrocaloric (EC) effect is of great importance for application in cooling or heating devices of new generation, which would be friendlier for environment. Recent predictions of the existence of the giant EC effect in polymeric and inorganic ferroelectric relaxors are based solely on the indirect measurements of the electric polarization and not on a direct measurement of the EC effect itself. Here a method and analysis of direct measurements of the giant EC effect in various soft and solid ferroelectric materials in the form of thick and thin films is presented. The field dependence of the EC effect is shown for PbMg1/3Nb2/3O3 (PMN) ceramics and P(VDF-TrFE) (68/32 mol%) copolymers.

We report detailed dielectric investigations of Pr 1− x Ca x MnO 3 (PCMO, x =0.5) ceramics, a member of the perovskite manganite family that exhibits a colossal magnetoresistance. Analysis of the electrical conductivity and dielectric constant data revealed that in the low temperature phase, below 42 K, small polarons are responsible for the charge transport in the system. This provides a new understanding of the phase diagrams in PCMO systems

The paper presents investigation of four lead free thick film resistor pastes, developed at ITME, denoted R-100, R-1k, R-10k and R-100k with sheet resistivities of 0.1, 1, 10 and 100 kΩ/□, respectively. The resistors were based on RuO2 as the conductive phase. The aim of the work was to evaluate the influence of firing conditions of the resistive pastes on a sintering process. The pastes were screen printed onto alumina substrate with prefired AgPd lead-free terminations. They were fired at several temperatures from 750 to 950 °C for 10 min at peak temperature, as well as fired at the highest temperature for 6 h, in order to bring the sintering process into the equilibrium. The properties of the resistors, i.e , sheet resistivity and temperature coefficient of resistance (TCR), microstructure changes, glass crystallization upon firing, etc., were examined. Dried and fired resistor samples were evaluated by X-Ray diffraction analysis and by the scanning electron microscopy. The RuO2 conductive phase maintained the same crystal structure regardless of the firing conditions. No devitrification was observed in lead-free resistors glasses. The lattice constants of RuO2 were uniform after firing at temperatures over 800 °C. The resistors matched the desired resistivity and the TCR was the least temperature dependent at the firing temperatures around 850 °C.

The electrical and microstructural characteristics of 1 kΩ/sq. thick-film NTC thermistors (4993, EMCA Remex) fired either on LTCC (low-temperature cofired ceramic) substrates or buried within LTCC structures were evaluated. The thermistors were fired at different temperatures to study the influence of firing temperature on the electrical characteristics. The results were compared with the characteristics obtained on alumina substrates. The sheet resistivities were higher than the resistivities of thick-film thermistors on alumina substrates. The increase of the sheet resistivities was attributed to the diffusion of the glass phase from the rather glassy LTCC substrates into the NTC thermistors. This was confirmed by EDS analyses. However, the increase in the resistivity was linked to an increase of the beta factors. Therefore, the results show that the evaluated NTC thermistors on LTCC substrates can be used for temperature sensors in MCM-Cs as well as in MEMS LTCC structures. When the thermistors were buried in the LTCC substrates, the LTCC structures delaminated during firing, leading to high sheet resistivities and high noise indices. This delamination is attributed to the different sintering rates of the NTC and LTCC materials.

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.

The rheological behavior and tape-casting performance of ethanol-based Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT) slurries is studied. A nanocrystalline powder obtained by mechanochemical activation was used. Suspensions were prepared up to solid contents of 32 vol%, significantly higher than those usually reported for nonaqueous systems. The feasibility of replacing toxic solvents commonly used for tape casting of functional ferroelectric materials, often toluene, with ethanol is demonstrated. The density, phases and microstructure of the green tapes and sintered ceramics are presented. Cube-shaped templates were successfully aligned during the tape casting for the processing of 〈001〉-textured PMN–PT ceramics by templated grain growth. An effect of the lamination of tape stacks on the template orientation is described.

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.

All-ceramic lead-free percolative composite, comprising RuO 2 with high electrical conductivity denoted as the conductive phase and ferroelectric (K, Na)NbO 3 ceramics, was developed. Structural analysis revealed a uniform distribution of conductive ceramic grains within the ceramic matrix. Consequently, the dielectric response in the (K, Na)NbO 3 –RuO 2 composite follows the predictions of the percolation theory. Thus, close to the percolation point exceptionally high values of the dielectric constant were obtained—values as high as 20,000 were detected at room temperature at 1 kHz. Fit of the data, obtained for samples of different compositions, revealed critical exponent and percolation point, which reasonably agree with the theoretically predicted values.

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.

This paper discusses the feasibility of a piezoelectric resonant pressure sensor made of lead-zirconate-titanate (PZT) thick films on a preprocessed 3D low-temperature co-fired ceramic structure with a deformable diaphragm. Numerical and experimental analyses were carried out. Two different thick-film PZT compositions were characterized. Using experimentally evaluated material properties, a finite-element analysis showed the trends and facilitated the decisions in the design phase of the sensor.

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...

We investigated the grain size effect on the high temperature behaviour of PMN-35PT ceramics around the tetragonal–cubic phase transition using second harmonic generation (SHG) and dielectric spectroscopy. Our data revealed coexistence of the first-order ferroelectric phase transition and relaxor behaviour in the coarse grain (grain size ∼4 µm) µ_PMN-35PT. The phase transition is hindered and relaxor features prevail in the fine grain (grain size ∼150 nm) n_PMN-35PT ceramics. Effect of the grain-size reduction on the SHG and dielectric response could be attributed to stabilisation of intermediate domain configurations between the frozen polar nanoclusters and large ferroelectric domains and to the enhanced stability of polar nanoclusters in the fine grain ceramics.

The feasibility of a novel homogeneous templated grain growth approach for the processing of 0.65Pb(Mg 1/3 Nb 2/3 )O 3 -0.35PbTiO 3 ceramics is studied. Novelty rests on the use of a nanocrystalline powder synthesized by mechanochemical activation for the matrix, and also for obtaining the templates via conventional sintering. Templates are (1 0 0) faceted cube-shaped microcrystals with an average size of 12 μm. The role of processing parameters such as the presence of PbO excess, and a hot-pressing step previous to the final thermal treatment is studied. Extensive growth of the templates and nearly full densification are demonstrated. The approach used here involves only conventional ceramic technology from a single source powder, and can be used as a means of obtaining larger crystals.

In this paper we present a novel approach to preparing large-displacement 65Pb(Mg1/3Nb2/3)O3–35PbTiO3/Pt (65/35 PMN–PT/Pt) bimorph actuators. These “substrate-free”, bending-type actuators were prepared by screen-printing the 65/35 PMN–PT and Pt thick-film pastes as the electrodes on alumina substrates. After this screen printing and the subsequent firing the 65/35 PMN–PT/Pt composites were peeled off from the substrates. Displacements of nearly 100 μm at 18 V were achieved for actuators with dimensions of 1.8 cm × 2.5 mm × 50 μm for the 65/35 PMN–PT layer. The normalized displacement (the displacement per unit length) was 40 μm/cm at 18 V. The experimental results together with a computation procedure were used to obtain the material parameters for a finite-element analysis of the 65/35 PMN–PT/Pt bimorph actuators.

The sequence of reactions during the synthesis of sodium niobate, potassium niobate, and sodium potassium niobate from alkaline carbonates and niobium oxide has been studied by diffusion couples in the temperature range between 500° and 700°C for up to 48 h. The reactions proceed by coupled diffusion of alkaline and oxygen ions into niobium oxide. The first phase to form at the interface Na 2 CO 3 /Nb 2 O 5 is Na 2 Nb 4 O 11 at 500°C. The perovskite phase forms only after heating at 700°C at the boundary between Na 2 Nb 4 O 11 and Na 2 CO 3 . In the K 2 CO 3 /Nb 2 O 5 diffusion couple, the sequence of phases after heating at 600°C is Nb 2 O 5 /K 6 ,Nb 10.88 O 30 /K 4 Nb 6 O 17 /KNb03/ K 2 CO 3 . In the (K 2 CO 3 +Na 2 CO 3 )/Nb 2 O 5 diffusion couple the (K,Na)NbO 3 solid solution forms via the intermediate phase (K,Na) 2 Nb 4 O 11 at 600°C. The order of magnitude of the parabolic reaction rate constant for the diffusion-controlled reaction at 600°C is about 10 -15 m 2 /s for the (K 2 CO 3 +Na 2 CO 3 )/ Nb 2 O 5 and the K 2 CO 3 /Nb 2 O 5 systems, which is about one order of magnitude less than that for Na 2 CO 3 /Nb 2 O 5 (10 -14 m 2 /s). The reaction rate in the ternary system is determined by the diffusion of the slower species, i.e., the potassium ions.

We studied the mechanochemical synthesis of NaNbO3 from a starting-powder mixture of sodium carbonate and Nb2O5 using ball-impact energies of 15 and 370 mJ/hit. Based on the results of a quantitative phase analysis we propose a mechanism for the mechanochemical synthesis of NaNbO3. During milling a condition is established, where the amounts of perovskite, X-ray diffraction -amorphous phase and residual carbonate in the mixture do not change with increasing milling time. Similarly, the NaNbO3 crystallite size and the quantity of microstrains reach final values that are independent of the applied ball-impact energy.

Nanocrystalline powders synthesized by mechanochemical activation were successfully used to process high-density submicron- and nanostructured 0.8Pb(Mg 1/3 Nb 2/3 )O 3 –0.2PbTiO 3 perovskite phase ceramics by hot pressing, with average grain size ranging from 0.36 μm down to 88 nm. These materials are very suitable for studying the size dependence of the properties across the submicron range approaching the nanoscale. This is the first report of such a series of ceramic materials of a relaxor-based morphotropic phase boundary composition, and of its properties as a function of the grain size.

Lead zirconate titanate (PZT) is a piezoelectric material that can sense or respond to mechanical deformations and can be used in ceramic micro-electro-mechanical systems (C-MEMS). A thick-film paste was prepared from a pre-reacted PZT powder (PbZr0.53Ti0.47O3) and thick-film technology (screen-printing and firing) was used to deposit the PZT layers on LTCC tapes and on alumina substrates. The microstructural, electrical and piezoelectric characteristics of the thick PZT films on relatively inert alumina substrates and on LTCC tapes were studied. Preliminary experiments indicated that due to the interaction between the printed PZT layers and the LTCC substrates during firing the electrical characteristics deteriorate significantly. To minimise the influence of substrate-film interactions different electrode materials and the use of additional intermediate layers as a barrier were evaluated. The dielectric permittivities, dielectric losses, and piezoelectric coefficients (d 33) were measured. The dielectric permittivities of the thick films fired on LTCC substrates were lower (210 with gold electrodes and 430 with silver electrodes) than those measured on alumina substrates (500). The piezoelectric coefficients d33 were measured with a Berlincourt piezometer. The d 33 values measured on the LTCC substrates were relatively low (60–80 pC/N) compared with the values obtained for the alumina substrates (around 140 pC/N). The lower dielectric constants and piezoelectric coefficients d 33 of the films on LTCC substrates are attributed to the formation of phases with a lower permittivity. This was a result of the diffusion of SiO2 from the LTCC into the active PZT layer. The diffusion of silica was confirmed by the SEM and EDS analyses.

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.

Subsolidus equilibria in the RuO2–Bi2O3–SiO2 diagram were studied with the aim of investigating possible interactions between the bismuth-ruthenate- based conductive phase and the silica-rich glasses in thick-film resistors. The tie lines are between Bi2Ru2O7 and Bi12SiO20 (gamma phase), between Bi2Ru2O7 and Bi4Si3O12, and between RuO2 and Bi4Si3O12. This indicates that the bismuth ruthenate is not stable in the presence of the silica-rich glass phase.

Piezoelectric thick films based on Pb(Zr,Ti)O 3 (PZT) were prepared on two types of LTCC tapes (Du Pont 951 and Electro Science Labs. 41020) and on relatively inert alumina substrates. The results obtained with the alumina were used as a reference. The microstructures of the cross-sections of the resistors were investigated using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDS) analysis. The dielectric permittivities, dielectric losses, remanent polarisation, coercive field and piezoelectric constant d 33 were measured. The dielectric and piezoelectric characteristics of the PZT fired on the LTCC substrates deteriorated in comparison to the samples on alumina, due to interactions between the LTCC substrate and the PZT layer. Lower dielectric constants, remanent polarisations and piezoelectric constants indicate the formation of phases with a low permittivity. This was attributed to the diffusion of SiO 2 from the LTCC into the active PZT layer and to the diffusion of PbO from the PZT layer into the LTCC substrate. The diffusion was confirmed by the SEM and EDS analysis.

The piezoelectric, microstructural and electrical characteristics of thick PZT films on relatively inert alumina substrates and on two LTCC tapes, i.e., Du Pont 951 and Electro Science Labs 41020 were studied. A thick-film paste was prepared from the pre-reacted PZT powder (PbZr0.53Ti0.47O3) and printed and fired on LTCC tapes and on alumina substrates, respectively. Dielectric permittivities, dielectric losses, remnant polarizations and coercive fields were measured. The dielectric constants (100–150) of thick films fired on LTCC substrates are low. The piezoelectric coefficients d 33 were measured by different methods, i.e. Berlincourt piezometer, interferometry and piezoresponse force microscope (PFM). The d 33 values on LTCC substrates are low (30–70 pm/V) as compared with values obtained on alumina substrates (around 120 pm/V). Lower dielectric constants and piezoelectric coefficients d 33 of films on LTCC substrates are attributed to the formation of phases with a low permittivity due to the diffusion of silica from LTCC substrates into PZT films. The d 33 constants of samples with different thicknesses of PZT layers (from 20 to 160 μm) at first increase with the increasing thickness of PZT layers and then decrease for thicker films. As the cracks in the structure were not observed the reason for the decreasing d 33 values for thicker films is still unclear.

Single crystals of (K 0.5 Na 0.5 )NbO 3 have been grown for the first time by the solid state crystal growth process. A KTaO 3 seed crystal was embedded in a matrix of (K x Na 1− x )NbO 3 powder with a nominal composition of (K 0.5 Na 0.5 )NbO 3 . K 4 CuNb 8 O 23 was used as a liquid-phase sintering aid. During sintering a single crystal of (K 0.5 Na 0.5 )NbO 3 grew on the KTaO 3 seed. Scanning electron microscopy energy dispersive X-ray spectroscopy (SEM-EDS) showed that Ta did not migrate into the single crystal and that the single crystal had a composition very close to that of the nominal value. SEM-EDS showed that the single crystal and the matrix grains had the same composition within the limits of experimental error. Transmission electron microscopy (TEM) confirmed that the grown material was indeed single crystalline and had grown epitaxially on the seed crystal. The single crystal contained a considerable amount of porosity, which could be reduced by pre-densification of the matrix by hot pressing.

An anomaly in the magnetic susceptibility has been observed at and below the paraelectric – ferroelectric transition in polycrystalline Pb(Fe1/2Nb1/2)O3. The results are indicative of magnetoelectric coupling of the form P2M2. The non-linear relation between the induced magnetization and the applied magnetic field demonstrates the presence of large superparamagnetic clusters embedded in a paramagnetic medium over the whole ferroelectric phase, i.e. far above the antiferromagnetic transition temperature T N .

Porous ceramics are of interest for ultrasonic transducer applications. Porosity allows to decrease acoustical impedance, thus improving transfer of acoustical energy to water or biological tissues. For underwater applications, the dhgh figure of merit can also be improved as compared to dense materials. In the case of high frequency transducers, namely for high resolution medical imaging, thick film technology can be used. The active films are generally porous and this porosity must be controlled. An unpoled porous PZT substrate is also shown to be an interesting solution since it can be used in a screen-printing process and as a backing for the transducer. This paper describes the fabrication process to obtain such materials, presents microstructure analysis as well as functional properties of materials. Modelling is also performed and results are compared to measurements. Finally, transducer issues are addressed through modelling and design of several configurations. The key parameters are identified and their effect on transducer performance is discussed. A comparison with dense materials is performed and results are discussed to highlight in which cases porous piezoceramics can improve transducer performance, and improvements are quantified.

Laminated 3D structures made using low-temperature co-fired ceramic (LTCC) technology are practical for ceramic micro-electro-mechanical systems (C-MEMS). The sensors for mechanical quantities, and/or actuators, are fundamental parts of MEMS. Thick-film resistors can be used to sense the mechanical deformations, and thick-film piezoelectric materials can be used as electro-mechanical transducers in a C-MEMS structure. The integration of these thick-film materials on LTCC substrates is in some cases difficult to realise due to interactions with the rather glassy LTCC substrates. The subject of our work is an investigation of thick-film materials for electro-mechanical transducers (sensors and actuators) and their compatibility with LTCC substrates. Resistors made with commercial thick-film resistor materials for use as sensors on LTCC substrates have been investigated and evaluated. Ferroelectric ceramic materials based on solid solutions of lead zirconate titanate (PZT) with low firing temperatures around 850°C were developed for thick-film technology and evaluated on LTCC substrates.

International audience; We have studied the mechanochemical synthesis of NaNbO3, prepared from a powder mixture of Na2CO3 and Nb2O5. The formation of NaNbO3 during milling was followed using thermal analysis and X-ray diffraction. According to the thermogravimetric analysis, after 20 and 40 h of milling there was still some residual carbonate, while the X-ray diffraction shows NaNbO3 as the major crystalline phase present in the mixture. Based on the quantitative XRD phase analysis, the residual reactants were amorphous and as such undetectable with the X-ray diffraction. Furthermore, an X-ray line-broadening analysis was used to determine the NaNbO3 crystallite size and the microstrain. A decrease in the NaNbO3 crystallite size coupled with an increase in the amount of microstrains was found from 10 to 40 h of mechanochemical treatment. Finally, the TEM analysis confirmed the NaNbO3 crystallite size determined by the X-ray line-broadening analysis.

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.

Lanthanum lead zirconate titanate with 5 at.% of La (5/65/35 PLZT) hot-pressed ceramics have been studied in order to explore its dielectric properties below Burns temperature. Previous measurements of 6.5/65/35 hot-pressed PLZT ceramics revealed relaxor-ferroelectric behavior, i.e. coexisting ferroelectric and relaxor dielectric response. Similar relaxor behavior, though not so pronounced, was also expected at lower concentrations of La in 5/65/35 hot-pressed PLZT ceramics. We explored the possible duality of ferroelectric and glassy relaxor behavior in 5/65/35 hot-pressed PLZT ceramics with measurements of the complex linear dielectric susceptibility as a function of temperature and bias electric field. These experiments revealed no indications of prominent relaxor behavior. Results revealed solely a smeared relaxor to ferroelectric transition. Moreover, polarization hysteresis measurements below this transition confirmed existence of the ferroelectric phase in zero bias electric field in 5/65/35 hot-pressed PLZT ceramics without relaxor features like freezing process and frequency dependence.