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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.

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.

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.

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.

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.

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.

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.

A single crystal of (Na, K, Li)(Nb, Ta)O 3 has been grown for the first time by the solid state crystal growth process. A seed crystal of 〈0 0 1〉-oriented KTaO 3 was embedded in a matrix of (Na, K, Li)(Nb, Ta)O 3 powder, which was then densified by hot-pressing. During annealing of the hot-pressed sample, a single crystal of (Na, K, Li)(Nb, Ta)O 3 of between 20 and 50 μm thickness grew on the KTaO 3 seed. The single crystal contained porosity incorporated from the matrix. Chemical analysis showed the single crystal to have the same composition as the matrix. A single crystal of constant thickness could be grown by adding a liquid phase sintering aid to the powder. The solid state crystal growth method is promising for the growth of single crystals of (Na, K, Li)(Nb, Ta)O 3 .

We have evaluated the use of a milling map in the mechanochemical synthesis of ceramic oxides. In order to do this we constructed a milling map for NaNbO3, mechanochemically synthesized from a powder mixture of Na2CO3 and Nb2O5. Based on the milling map, we determined the critical or minimum cumulative kinetic energy for the formation of NaNbO3. In addition, we made a comparison between several oxide systems by constructing the milling map on the basis of the experimental data found in the literature. It is shown that a milling map is essential for a comparison of the results of mechanochemical synthesis when different planetary mills and milling conditions are used.

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.

PZT thick films (PbZr 0.53 Ti 0.47 O 3 with the addition of 6% PbO and 2% Pb 5 Ge 3 O 11 ) with a low sintering temperature were printed and fired on LTCC substrates (951, Du Pont), covered with an alumina barrier layer. The electrical characteristics (remanent polarisation, coercive field, dielectric constant and dielectric loss) of these PZT thick films, together with sets prepared on “unprotected” LTCC substrates and on alumina substrates were compared. Whereas the electrical characteristics of the films on LTCC substrates deteriorated significantly due to interactions between the LTCC substrates and the PZT layers the values obtained for the LTCC/alumina barrier structures were comparable with those on ceramic alumina substrates.

The stability of the La 3.5 Ru 4 O 13 and La 2 RuO 5 compounds in the La–Ru–O system in various atmospheres and various temperature ranges was investigated by thermal analysis, X-ray diffraction analysis and electron microscopy. The La 3.5 Ru 4 O 13 compound is stable in oxidizing and neutral atmospheres (N 2 with 10 ppm O 2 ), while La 2 RuO 5 is partially reduced in a neutral atmosphere to form La 2 RuO 4.6 . In a reducing atmosphere both compounds decompose into metallic Ru and La 2 O 3 . The thermal expansion coefficients of La 2 RuO 5 and La 3.5 Ru 4 O 13 at 800 °C are 11.2 × 10 −6 K −1 and 9.3 × 10 −6 K −1 , respectively. The specific electrical resistivity for La 3.5 Ru 4 O 13 is relatively independent of temperature and is 2 × 10 −2 Ω cm at 800 °C, while for La 2 RuO 5 it decreases with increasing temperature and is 1 Ω cm at 800 °C.

In this contribution the effect of alkaline-earth (AE) dopants Mg2+, Ca2+, Sr2+ and Ba2+ on sinterability and functional response of KNN is studied. Ceramic powders with the general formula (K0.5Na0.5)1−2yAEyNbO3, y = 0.005 were prepared by classical ceramic processing. The values of 94–95% of theoretical density (TD) are obtained for stoichiometric KNN after sintering at 1115 °C for 2 h. Calcium and strontium doping promotes densification while magnesium doping inhibits it. In the case of Ba-doping a secondary phase forms. The dielectric constant and piezo d33 coefficient determined by Berlincourt piezo d33-meter of Ca and Sr-doped KNN ceramics are 500 and 95 pC/N, respectively, while the values for undoped KNN are slightly lower.

Piezoelectric Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 (PMN-PT) ceramics with 0.2 and 0.35 PT have been prepared from mechanochemically activated powders. Pressureless sintering in air and hot pressing were tested. PbZrO 3 packing was necessary to limit lead oxide losses and to avoid the formation of second phases at the surface when temperatures above 1000 °C were used. Ceramics sintered at 1200 °C presented densities of 90% and a grain size of 4 μm. Hot pressed ceramics hardly showed porosity and had submicron (0.1-0.5 μm) grain size, which make the mechanoactivated powders very suitable for templated grain growth matrices. Electrical and electromechanical characterisation was accomplished. The 0.2 PT composition combined relaxor dielectric behaviour with piezoelectricity after poling. The 0.35 PT ceramics presented a first order ferroelectric-paraelectric transition at 171 °C and a complex transverse piezoelectric coefficient of -(181.8-13.6) pC N -1 at room temperature.

The electric-field–temperature (E–T) phase diagram for lanthanum modified lead zirconate (PLZT) 6.5/65/35 hot-pressed ceramics was determined by measurements of the quasistatic field-cooled–field-heated (FC/FH) dielectric susceptibilities. Approximately linear dependence of the phase transition line between the ergodic relaxor and ferroelectric phases on the bias electric field was found. In zero electric bias field the incipient ferroelectricity is established at nonzero phase transition temperatures. From the field-cooled polarization measurements a quasistatic spontaneous polarization of 0.37 As/m2 was determined at 25 °C. Measurement of the frequency dependent, linear complex dielectric constant as a function of the bias electric field shows a significant change in its temperature dependence as well as in the temperature dependence of the characteristic relaxation time, indicating freezing of those sample regions dominated by the disordered nanocluster relaxor state, to the nonergodic glass-like relaxor state.

The linear and third harmonic nonlinear dielectric constants were measured in 6.5/65/35 PLZT hot-pressed ceramics. Linear dielectric data obtained on ooling show the transition from an ergodic to a nonergodic relaxor phase while, on heating, a ferroelectric to ergodic relaxor phase transition appears. The third harmonic di-electric response is reminiscent of an ergodic to nonergodic relaxor phase transition. Existence of the spontaneous polarization below the Vogel–Fulcher temperature at which the longest relaxation time diverges, indicates the possibility that the sample breaks up at low temperatures into relaxor glass-like and ferroelectric order dominated regions.

Thick-film resistors that were developed for firing on alumina substrates have been evaluated in terms of their compatibility with ZrO 2 . The characteristics of a number of 10 kohm/sq. resistors that were fired on 96% alumina and on tetragonal zirconia substrates were investigated. Possible interactions between the resistor material and the zirconia were studied with X-ray powder-diffraction analysis, with scanning electron microscopy and with energy-dispersive X-ray analysis. Sheet resistivities, temperature coefficients of resistivity, current noise and gauge factors were measured. The results indicate that the evaluated thick-film resistors are compatible with zirconia ceramics.

The compatibility between RuO 2 based electrodes and PZT films was investigated by firing mixtures of RuO 2 and PZT. The reaction resulted in the formation of Pb 2 Ru 2 O 6.5 pyrochlore. Subsolidus equilibria in air in the RuO 2 –PbO–ZrO 2 systems were studied with the aim of obtaining some information on interactions between the RuO 2 and PZT materials. No ternary compound was found in the system. The tie lines are between Pb 2 Ru 2 O 6.5 and ZrO 2 , and between Pb 2 Ru 2 O 6.5 and PbZrO 3 . The obtained results confirmed that RuO 2 reacts with PZT forming Pb 2 Ru 2 O 6.5 .

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.

PZT thick films with lead germanate as low temperature sintering aid were prepared on alumina substrates. The thickness of films after sintering procedures reached 50 μm. Chemical compatibility and microstructure of layers was studied by EDS/SEM analysis. A fit between theoretical and experimental electrical impedance of several samples as a function of frequency is used to determine the elastic, dielectric and piezoelectric properties in thickness mode of the ceramic layers. Results for different poling fields (3 and 12 kV/mm) and sintering temperatures are obtained. Finally, the KLM equivalent circuit is used to obtain simulations of transducers integrating these thick films and their performance for medical imaging applications is evaluated.

The processing and ferroelectric properties of lead lanthanum zirconate titanate (PLZT) thick films on Pt-coated Al 2 O 3 substrate were studied. The most critical processing issue is to prevent lead losses during heat treatment. Maintaining a high PbO vapour concentration during heat treatment of the layers maintains a liquid phase that enables densification also in constrained conditions, possibly because of relaxation of the shear stress originating from constrained sintering. Reaction of PbO-rich liquid phase at the platinum/alumina interface results in β-alumina crystals that deteriorate the contact between the platinum electrode and the substrate. Instead of platinum on Al 2 O 3 , a new Al 2 O 3 /PLZT/Pt structure was introduced taking advantage of the excellent mechanical stability of the Al 2 O 3 /PLZT and Pt/PLZT interfaces. PLZT thick films with ferroelectric properties equal to or better than those of hot pressed samples were obtained. Such a sintering and electrode strategy can be applied in processing of other lead-based thick films.