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High sensitivity novel piezoceramics for advanced applications - textured, thick films and multilayer structures

Deliverables

For textured ceramics which are composed at least of two piezoelectric phases, homogenisation models have been developed to simulate all the effective parameters of such piezoelectric materials considered as composites. With the electroelastic moduli of each phase, effective parameters as a function of single crystal volume fraction are calculated. The model is based on a generalisation of series and parallel connections (2-2 connectivity) with a matrix method. The materials can be completely represented by a unit cubic cell in which the single crystal phase is represented by a single inclusion, and the rest of the volume represents the other piezoelectric phase. This representation is applicable to different connectivities by changing the shape of the inclusion in the unit cell. Several connectivities (0-3, 3-3, 3-0) have been studied in order to optimise the effective properties of the textured ceramics according to the spatial arrangement of the phases. The choice of the phase and corresponding properties have also been studied by an optimisation process.
PMN-PT powder, (x PbMg1/3Nb2/3O3 + (1-x) PbTiO3), with x ranging from 0.1 to 0.6 have been investigated by the mixed-oxide route. The process consists to synthesis of the columbite phase in the first step, followed by a second step in which the columbite is reacted with PbO and TiO2 (and possibly various additives) to form the PMN-PT phase. This method allows preventing the formation of pyrochlore phases, which have a deleterious effect on the performances of the ferroelectric phase. Micometer grain size was obtained by mixed oxide routes and nano powders were obtained either by continuous attrition milling. Batch of 200g to 500g was prepared.
Textured PMN-PT ceramics were synthesized by homo-template grain growth (HTGG) using PMN-PT nano-particles and cubic single crystal templates - PMN-PT:Mn doped powders prepared by solid state reaction were milled using micro beads to reduce the grain size. Nano powders were obtained directly after high energy milling. - Seeds of PMN-PT ranging from 50 to 100 mm were obtained by flux method. Perfect cubic crystals of 50x50x50 mm were selected as templates. - Nano particles of PMN-PT: Mn and few wt.% of templates were mixed with organic binder to obtain homogenous slurry. Two percent excess of PbO was added in certain compositions. The mixture was tape cast using the doctor blade technique to obtain tapes of 100-150mm thick. Green tapes were dried, cut and laminated into samples of 0.5 to 3mm thickness. - Tape stacks were sintered between 1150 and 1200°C for different durations in PbO controlled atmosphere. Textured Tape Cast Ceramics display quasi complete (001) texture (f=0.99) in the cubic phase. The (111) pole figure reveals (001) fiber texture in accordance with optical observation. The texture was obtained in all the volume and only small orientation distribution (<6°) was observed. Smart Raman imaging shows that the final composition is very close to that of the matrix. Piezoelectric properties measured at low level using RIE method show that coupling efficiency of tape cast textured ceramics (kp =0.69, d33= 600pC/N) are about twice of tape cast random ceramics and ~20% better than random optimised disk ceramic.
The thick films on the porous PZT substrate appear to be a good solution for transducer fabrication due to a relatively high attenuation that limits the required backing thickness and high acoustical impedance, very close to the thick-film acoustical impedance, which increases the transducer bandwidth. The high value of thickness coupling factor allows a high transducer sensitivity to be obtained. The almost identical chemical composition of the thick film and substrate minimise chemical and physical interactions during processing of active PZT layer on the substrate.
Two types of reference devices are being manufactured and characterised for medical imaging, a high frequency and high sensitivity linear array transducer i.e. 20 MHz, and a multilayer linear array transducer, i.e. 6MHz. For high frequency ceramic samples, high fragility was observed during the manufacturing stage. However, electrical impedance measurements show intrinsic performance comparable to that of reference products. Amongst the multilayered samples delivered to Vermon, the composition 70/30 PMN-PT exhibits better performance and lets expect exciting perspective in further development steps: - Demonstrator using multilayer material has been built based on the reference design for imaging product; characteristics are promising with the exception of sensitivity level as compared to reference device. - On the other hand, thick film and more particularly multilayered ceramics would certainly need a suitable fabrication method combined with further material development stages that will take into account their intrinsic parameters (fragility, acoustic and electrical matching, etc.) in order to reveal their performance potential and outperform single layer designs in high end applications. - Scientific Publications: -- High frequency piezo-composite transducer array designed for ultrasound scanning applications, IEEE UFFC Symposium 1996. -- 20MHz ultrasound array for medical imaging from design to image evaluation, IEEE UFFC Symposium 2001.
The initial goal of this study for TUS was to increase the sound level (3dB minimum) of Barrel Stave transducer. That means: - Ceramics, which withstand more power; - Improved design of the shell to withstand more stress and vibration level. First, the design (material and shape) of the shell has been optimised. Two kind of shell has been manufactured. The new Ti and steel shell design allowed to withstand the increase of sound level and endurance tests (electrical power > 1200W) have been fulfilled only with steel shell because the Ti transducers has been broken (fall down on the ground). The new ceramics (PMN from TRT, PZ 21 and PZ 54) allowed to increase the sound pressure level: - 2 dB for the PZ 21 and PZ 54 from FERROPERM; - 5 dB for the PMN material from TRT. Moreover, the endurance tests showed than PZ 21 are not compliant with the specific requirements (8s of pulse duration and 20% of duty cycle). With hard stress excitation, the temperature raises and modifies the impedance of the transducer: Rp decreases. So with a standard (not controlled) power unit, the power increase, so the temperature raise more and it’s looped. Maybe, to decrease this effect, we have to optimise the design of the complete transducer to get a better thermal dissipation of the power coming from the Joule effect.
A new piezoelectric composition has been developed. Rather than the well-known PZT (i.e., Pb(Zr,Ti)O3) system, this composition belongs to a new system of the general form BiMe - PT (i.e., solid solution between BiMeO3 and PbTiO3, where Me signifies a metal ion or combination of metal ions with an effective valence of +3). In this system, a large part of the toxic heavy metal Pb is substituted by Bi, so these compositions have a lower environmental impact than PZT. With a proper choice of Me ion, this system furthermore shows very interesting properties, e.g. a high Curie point compared to the PZT system. A number of Me ions are accommodated by the general formula, but within PIRAMID an important criterion has been the cost of precursors, in order to avoid that the price itself should prevent the exploitation of the composition. Therefore, such exotic Me ions as Sc3+ (previously reported in the literature) have been avoided and a combination of the form (Me1(II)_1/2,Me2(IV)_1/2) has been chosen on the basis of a similar average ionic radius. A very high Curie point of approximately 600ºC has been obtained for the most promising composition, but a phase transition close to 375ºC (probably ferroelectric-ferroelectric) seems to limit the operating temperature of this one (depolarisation occurs at 300ºC). Other relevant properties of this new composition include piezoelectric coefficients d33 and d31 of 100pC/N and -25 pC/N, respectively, free relative permittivity epsilon_r3{sigma)? 830 and thickness coupling factor k_t 0.3. Although the BiMe?PT composition developed in PIRAMID is an example of an interesting new type of piezoceramic systems, the future exploitation will be limited by the competition on one side from the well-established doped PZT compositions and on the other side from Aurivillius compounds (Bi layer oxides). Since the piezoelectric properties of doped PZT are significantly higher (d_33 higher by a factor of 3 to 6, k_t higher by a factor of 1.5), the justification of the BiMe - PT composition (presently d_33 ?100 pC/N; k_t 0.3) should be an extended temperature range of operation compared to PZT, combined with enhanced properties in comparison with the Aurivillius compounds (d_33 < 20 pC/N, k_t = 0.2). As described above, however, the low-temperature phase transition at present makes it impossible to take advantage of the high Curie point. On the other hand, future work with dopants may make it possible to shift the former transition temperature to below room temperature. Such future development should be driven by a market demand for a new material filling in the gap between PZT and the Aurivillius compounds, and when this demand is sufficiently important, the experience gathered within PIRAMID will be very useful.
High frequency single-element transducers based on materials developed in the project are under development. The first fabrication uses PZT thick film processed by screen printing and firing on porous PZT substrate. The unpoled substrate fulfils both technological requirements for the screen-printing process as well as acoustical requirements allowing it to be used directly as a backing in a transducer. Moreover, the porosity allows to increase the attenuation in the substrate and thus to reduce its size. The centre frequency is around 20 MHZ and addition of a lens is planned. This allows to an integrated transducer with minimal number of fabrication steps. The second fabrication is made with a PMN-PT curved disk where the focusing is obtained by the geometry. The centre frequency is around 40 MHz.
Lead magnesium niobate PbMg1/3Nb2/3 (PMN) was synthesised from water suspension at control pH. Lead and niobium oxide and different magnesium raw material has been used for synthesis. High alkaline media was used during homogenisation of starting material. After homogenisation step powder was separated, dried and fired at temperature from 700 - 00 degrees Celsius. Pure lead magnesium niobate - PMN without undesirable pyrochlore phase was present in the syntehsised powder. Synthesis from suspension is one-step synthesis compare to the classic two-step columbite synthesis method from oxide precursors.
Several methods for preparation of lead magnesium niobate PbMg1/3Nb2/3 (PMN) solid solution with lead titanate PbTiO3 (PT) (PMN-PT) without undesirable pyrochlore phase have been developed. The formation of compounds by high energy milling at room temperature is desirable for PbO containing materials due to avoiding PbO evaporation. Piezoelectric PbMg1/3Nb2/3 - PbTiO3 (PMN-PT) powders have been prepared by direct mechanochemical activation of precursors. Very slow kinetics of formation of PMN-PT solution from oxide powders was found out in the case of PMN rich solid solutions and high loading mass. Due to this new two step process was introduce. In the first step PT was formed by high energy milling and in the second phase PT was milled with the remaining oxide. The solid solution x PMN-(1-x) PT in the range of x=0.6-0.8 without pyrochlore phase was successfully sythesised by high energy milling at high mass ratio.
Piezoelectric (1-x) Pb (Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) bulk ceramics with x=0.2, 0.3, 0.35 and 0.4 have been processed from perovskite phase nanopowders synthesised by direct mechanochemical activation of precursors. This procedure, unlike solid state reactions at high temperature, allows the one step synthesis of the perovskite phase from the constituent oxides, and provides high chemical homogeneity as compared with the widely used columbite route (two successive solid state reactions). Systematic studies of their sintering behaviour have been carried out at temperatures between 900 and 1250 degrees Celsius. Conventional sintering and hot pressing were explored. A PbO atmosphere was found to be necessary to limit lead oxide volatilisation and to avoid the formation of second phases at the surface when temperatures above 1000oC were used. PbZrO3 (PZ) and PMN-PT packing were tested for creating such atmosphere. Ceramics sintered at 1200 degrees Celsius with PZ packing presented densities of ~90% and a grain size of ~4mm. Decrease of the sintering temperature from 1200 to 1150oC resulted in a reduction of density and of grain size (from 4.0+/-1.0 to 2.6+/-1.0 microns for x=0.35). Increase to 1250 degrees Celsius caused a drastic decrease of density and the development of large cubic grains (15±5 microns, also for x=0.35). Use of PMN-PT instead of PZ for packing increased density at 1200 degrees Celsius up to ~95%, but decreased grain size. Hot pressing at 900 degrees Celsius and 25 MPa provided ceramics with hardly porosity and submicron (0.1-0.5 microns) grain size, and increase of the temperature to 1000oC resulted in the appearance of porosity and caused limited grain growth. Differences with x (composition) were not significant. Therefore, processing of series of PMN-PT ceramics with increasing x and similar microstructure, porosity and grain size, on which the effect of structure (composition) on properties can be isolated, from these powders was feasible and was achieved. Processing of series of PMN-PT ceramics with a given x and increasing grain size, on which the effect of crystal size on properties can be isolated, was also done. The electrical, mechanical and electromechanical properties of these two series have been described by using a number of techniques. These were the dielectric permittivity and losses as a function of temperature and frequency by conventional impedance analysis, ferroelectric hysteresis loops as a function of frequency, the low frequency Young´s modulus and mechanical losses as a function of temperature, amplitude and frequency by dynamical mechanical analysis in three points bending, the s11 and s12 mechanical compliances and d31 piezoelectric coefficient in complex form, and so losses, as a function of temperature by analysis of piezoelectric radial resonances, and direct measurement of deformation under high fields by a linear variable differential transducer. Main features of these ceramics are their high compositional homogeneity and crystallographic quality. They are then very suitable for fundamental studies in the PMN-PT system, such as the relaxor to ferroelectric phase transition and its dependence on composition and crystal size, the ferroelectric phases present across the solid solution and their relationship to the macroscopic electric, mechanical and electromechanical properties, and the behaviour of the mechanical and piezoelectric losses, which are associated with the dynamics of domains. As a matter of fact, these bulk ceramics from powders synthesised by mechanochemical activation presented better defined features associated with these phenomena than columbite samples reported in the literature. An article on this result was prepared and has been recently published (M. Algueró, C. Alemany, B. Jiménez, J. Holc, M. Kosec and L. Pardo, “Piezoelectric PMN-PT ceramics from mechanochemically activated precursors”. Journal of the European Ceramic Society 24:6 937-940 (2004)). A second article is in preparation, initially thought for Journal of the American Society (“Processing and properties of piezoelectric Pb (Mg1/3Nb2/3)O3-PbTiO3 ceramics from powders synthesised by mechanochemical activation”), and at least two more manuscripts, specifically dealing with properties, will be prepared in the next months.
The main goal is to develop and manufacture the high efficiency ultrasonic transducer for liquid flow measuring, based on the piezoelectric ceramics. The transducer will be incorporated in the flow measuring cell of the heat meter. The main advantage and improvement upon the so far existing transducers are in the piston-like operation mode. This mode enhances the accuracy of the heat meter and reduces its sensitivity upon the flow perturbations. The calculations and simulations give the result that the optimal shape f the transducer is the multilayer structure with 5 interlayer electrodes. The so far executed measurements indicate the error of the meter close to its metrological requested limits. The demonstrator transducers have been manufactured and glued with epoxyde resin to the PES membrane. It was a sensing part of the flow measuring system. This system has been successfully connected and tuned to the electronic circuitry. The operating frequency is 2,1 MHz. The final measurements that should have proven the quality of the meter were metrological tests. We have measured the meter on the test line within the flow range from 35l/h to 3500l/h. The verification was successful, and showed for the order of magnitude better accuracy and stability compared to the reference meter.
A new piezoelectric composition has been developed with an unusual combination of high permittivity and coupling on one hand and low dielectric and mechanical losses on the other hand. The composition system chosen for this work is the relaxor-based Pb[(Ni_1/3 Nb_2/3 )_x Zr_y Ti_1-x-y ]O_3 system, commonly abbreviated PNNZT. Very high permittivities can be obtained in this system without sacrificing too much in terms of Curie point, and the novelty is that the dielectric and mechanical losses have been reduced by doping. Selected properties for the new compositions are: high free and clamped permittivities (2800 and 1400, respectively), dielectric loss tan delta of only 0.003, mechanical quality factor Q_m above 1500, Curie point T_C of 225ºC, high planar and thickness coupling factors (k_p = 0.59, k_t = 0.48) and high piezoelectric coefficients (e.g., d_33 ~ 500pC/N). The new composition is already being commercialised with the type number Pz54. The new material will find use in applications where a combination of the traditional soft and hard PZT properties is requested, namely high permittivity for electrical impedance matching and high sensitivity for good efficiency or signal/noise ratio as well as low dielectric and mechanical losses for high-power operation. An important example is the growing field of high-intensity focussed ultrasound (HIFU), and also underwater acoustics and medical diagnostics are very interesting application fields.
Nanomotion Ltd. produces ultrasonic piezo-ceramic motors based on proprietary materials and technology. These motors are commercialized in many application especially in precision motion applications. A growing activity is the implementation of the motors into mass markets applications. Within the PIRAMID project several objectives where set for the motors: - Motors for high precision motion application: -- Improve dynamic performance of the motors by using piezoelectric materials with enhanced properties. -- Stabilize performance over temperature & time (aging). -- Reduce nonlinear effect of electric field on Piezo properties. - Develop better capabilities for high volume consumer products: -- Develop methods for enabling the use of as sintered piezo elements for motors to reduce material costs. -- Proof feasibility for the use of Lead free material for Nanomotion ultrasonic motors. -- Reduce operation voltage by implementing multi-layer piezo elements in motors. Multi layer motors were already implemented and the main challege here is in cost reduction. Within the PIRAMID project material properties were specified, Nanomotion propriety modelling was used to simulate motor performance vs. material properties. A reference demonstrator was developed and tested. It is planned to prove by manufacturing of operational demonstrators improved motor performance, reduced sensitivity to temperature, aging and high electrical field. Also demonstrators of motors with multi-layers, piezo materials operating at low voltage will be demonstrated. Finally motors with lead free and low lead content will be demonstrated.
We developed a method for measuring dielectric and piezoelectric properties of thick films under large fields (comparable to coercive field). For measurements of the dielectric polarization, the system consists of a charge amplifier, a lock-in analyser, an oscilloscope and function generator with voltage amplifier. The voltage signal is applied on a sample and the resulting charge (proportional to polarization) is first amplified by the charge amplifier and then analysed by the lock in amplifier and displayed on the oscilloscope. The lock-in amplifier signal gives us possibility to analyse nonlinear properties by analysing different harmonics (usually the first free) while the oscilloscope gives the polarization response-driving signal hysteresis. For piezoelectric measurements, we use an ultra-low displacement laser interferometer. Measured strain signal is again analysed by the lock-in amplifier and displayed on the oscilloscope. The oscilloscope signal gives total strain-electric field hysteresis, whereas lock-in amplifier signal gives information on different harmonics. By comparing the results of the dielectric and piezoelectric measurements, done under identical driving field conditions, it is possible to draw conclusions on the different mechanisms responsible for the dielectric and piezoelectric nonlinearity and hysteresis. Besides scientific importance, these results are useful as a feed back to materials preparation and device designing tasks.
Invasive Doppler probes are used to assess blood flow in a wide range of applications (vascular surgery, cardiovascular surgery, neurosurgery, endoscopy). The probes used for these applications are single element high frequency (16MHz, 20MHz) transducers with high sensitivity. As probes are used invasively, they must be sterilized prior to use, preferably by steam sterilization methods. Gas (EO), Plasma or Formaldehyde sterilization methods are also widely used. Restrictions may apply for some fields of use. The probes are reusable due to their high price. Depending on the application, probes are needed in different sizes. Reference devices working at 16MHz with diameters of 1.0mm and 2.0mm, which are the most commonly used probes, were manufactured using PZT bulk ceramics. These reference devices were tested and characterized and in-vivo measurements were carried out. PiezoCAD simulation software was used for modelling the devices. Using doped PZT, PNNZT and PLZT, demonstrators were designed and fabricated in considerable quantity. The demonstrators were characterized and tested in-vitro and in-vivo using lab equipment and a commercially available Doppler device. Good to excellent results were obtained for 16MHz/2mm probes with all three types of piezoceramics. For 16MHz/1mm probes, good results could be obtained with doped PZT and PNNZT materials. With PLZT it was difficult to build good 16MHz/1mm probes. Probes made with doped PZT and PNNZT behaved well at temperatures up to 140°C. Probes made with PLZT were gradually destroyed at temperatures above 80°C. 16MHz/1mm probes built with PNNZT and 16MHz/2mm probes built with PNNZT and PLZT are still in use with good results in two hospitals. All types of demonstrators could be sterilized with gas (EO), low temperature Plasma or Formaldehyde more than 20 times without loosing quality. Probes made with doped PZT and PNNZT kept the quality for 5 cycles of steam sterilization then gradually started loosing sensitivity. Probes made with PLZT were destroyed after the first cycle of steam sterilization. Within a few weeks we will start manufacturing 16MHz probes using PNNZT materials. We find an increasing demand for invasive Doppler probes and we expect to increase production volume from two hundred probes per year to more than a thousand per year within the next two years. New fields of applications will be identified to further increase production quantity.
The major challenge in the preparation of piezoceramic thick films by screen printing is to obtain a dense film with sufficient piezoelectric properties, without damaging the substrate during sintering. Especially the commercially interesting substrate materials silicon and stainless steel are challenging, because they require a sintering temperature below 900ºC. This should be compared with typical sintering temperatures of PZT-based ceramics above 1150ºC. In order to obtain such low sintering temperatures, the most relevant solution is to add a sintering aid, and within PIRAMID a new low-sintering composition has been developed. This composition, which is based on Ferroperm¿s commercial Pz27, can be sintered to a good density at only 850ºC, and a thickness-coupling factor of 38% has been obtained on bulk discs. Thick films of this composition have been prepared by screen-printing, but the characterisation of these is still in progress.
The full set of mechanical compliances, dielectric permittivities and piezoelectric charge coefficients of Mn doped 0.65Pb(Mg1/3Nb2/3) O3-0.35PbTiO3 (0.65PMN-0.35PT:Mn) at the morphotropic phase boundary (MPB) has been obtained in complex form. A method based on the use of four piezoelectric resonances for three sample geometries has been used. These are length resonance of a bar poled and excited along its length, shear resonance of a plate poled across and excited along its thickness, thickness resonance of a disk poled and excited along its thickness and radial resonance of a disk poled and excited along its thickness. The procedure provides the real and imaginary parts of the coefficients, and therefore the different losses. Piezoelectric losses are responsible for heat generation and hysteresis in actuators. Bars and discs presented well defined single piezoelectric length, thickness and radial resonances, respectively, from which a number of coefficients was obtained. Plates presented double piezoelectric shear resonances. The methods of analysis of this resonance were modified for addressing these double resonances. Their physical origin was investigated and found to be associated with the presence of a perovskite phase gradient (tetragonal and rhombohedral) across the thickness of the plates originated during (side) poling. This gradient seems to be characteristic of the composition. The resonance associated with the well poled material was identified and analysed for obtaining the rest of coefficients. The full set is: s11E=13.5-i0.04 x10-12 m2 N-1, s12E=-4.8+i0.02 x10-12 m2 N-1, s13E=-5.6+i0.08 x10-12 m2 N-1, s33E=14.6-i0.14 x10-12 m2 N-1, s55E=31.0-i0.63 x10-12 m2 N-1, e11T=(3740-i38) eo, e33T=(4047-i41) eo, d33=488-i7 x10-12 C N-1, d31=-219+i2 x10-12 C N-1 and d15=554-i22 x10-12 C N-1. A number of coefficients were also obtained as a function of temperature up to 100oC. The set of coefficients for MPB PMN-PT:Mn can be compared with those of a Navy type II PZT based piezoelectric ceramic, which have been reported together with the description of the method (M. Algueró, C. Alemany, L. Pardo and A.M. González, “Method for obtaining the full set of linear electric, mechanical and electromechanical coefficients and all related losses of a piezoelectric ceramic”. Journal of the American Ceramic Society 87 209-215 (2004)). Results for MPB PMN-PT:Mn have already been partially published ((M. Algueró, B. Jiménez, C. Alemany and L. Pardo, “Temperature dependence of the electrical, mechanical and electromechanical properties of high sensitivity novel piezoceramics”. Boletín de la Sociedad Española de Cerámica y Vidrio 43:2 540-543 (2004)), and a second article enclosing the complete results have been submitted to to Journal of the American Ceramic Society (M. Algueró, C. Alemany, L. Pardo and M. Pham-Thi, “Piezoelectric resonances, linear coefficients and losses of morphotropic phase boundary Pb(Mg1/3Nb2/3)O3-PbTiO3 ceramics”). Full sets of coefficients for the available piezoelectric ceramics are required for exploiting all the possibilities of finite element analysis, both in fundamental research (mechanisms of degradation) and development (element design). This numerical technique is necessary to explore the countless shapes provided by solid free form fabrication technologies.
Inks have been optimised with different solid solutions of lead magnesium niobate - lead titanate: (1-x)Pb(Mg1/3Nb2/3)-xPbTiO3 (with x=0.1, 0.3, 0.35, 0.4, 0.5, 0.6) without sintering aids. They have been prepared from micro-powders synthesised by Ferroperm and one from nanopwders elaborated by Thales (only one composition 0.65Pb(Mg1/3Nb2/3)-0.35PbTiO3.). A sintering study have been carried out, at high temperature for pure composition of PMN-PT, to optimise the influence of heating rates, dwell temperature / time, atmosphere on the densification and the grain growth. Pyrochlore-free PMN and PMN-PT thick films were successfully obtained by screen printing. The best thick films densification was obtained with a heating rate of 9 to 12°C/min and a sintering temperature between 1170 and 1210°C. The choice of sintering temperature was chosen according to the PT content in the relaxor-ferroelectric. The maximum relative permittivity for PMN film was 11000, which is lower than in bulk ceramics (18000) prepared under the same conditions. For 0.65PMN-0.35PT, the maximum relative permittivity was around 15500 against 24000 in the bulk. Several parameters, which might be responsible for the lower permittivity, are discussed. Poled 0.65PMN-0.35PT thick films prepared from Ferroperm’s micropowder exhibit relatively large piezoelectric response (d33 up to 200pm/V) and unipolar strains approaching 0.1%, making these films of interest for various actuator and transducer applications.
The solid solutions of lead magnesium niobate [Pb(Mg1/3Nb2/3)O3], and lead titanate (PbTiO3) were used for optimisation of the curved tape processing. The innovative feature of the result was related to the forming of the discs. Tape casting process and forming by uniaxial pressure were used to obtain curved discs with different thickness (50 to 630mm), diameters of 0.5 to 4 cm and radius of curvature between 6 and 10 mm. The range of compositions of (1-x) Pb (Mg1/3Nb2/3)-xPbTiO3 : with x=0.1-0.3-0.35 and 0.6 was investigated, and the processing of piezoelectric layers was optimised in each case. The results are used for preparation of focused single-element transducer by directly using a curved piezoelectric disk. Moreover, for high frequency medical imaging applications (over 30 MHz), the thickness of the piezoelectric element must be lower than 100 micrometers.
The PZT is the “engine” for over product. The unique motion for Xaar printheads is to use shermode and there by make a very compact concept. The main part of PZT developers doesn’t optimise their products for shearmode use, instead they put the efforts into creating materials with higher activity in bulkmode. With this program Xaar hopes to get a more shearmode - optimised product, which will help us with better outgoing quality, higher yield, and in general more stable product.
The key factors for commercial success for new triaxial accelrometers are: - Lower weight; - Smaller size; - Cheaper; - Better performance. Not all of them need to be fulfilled at the same time but some of them should be significant better the commercial available products today. The application for this accelerometer is development and test of complicated structures in industries where price, time to market and performance are important. The application area is development of products including modalanalysis for development and multichannel data aquisition systems for test. The transducers will be components for new and existing systems already available on the market. The endusers are the car manufacturing and aircraft industries, who will benefit from new products in terms of products with lower weight, lower power comsumption and lower noise and lower pollution. Some of the suggested solutions are better than the state of art. The main outcome is a new design with fewer components and prepared for use of bulk or tape PE material and new materials with better performance or lead free. Due to the fewer components a more compact, low weight, better specifications or cheaper transducer can be expected. The market we address with this product is the R&D, test and engineering market that is 84 MUSD and an increasing part is 3 axial accelerometers. Due to multichannel systems with more channels a lower channel price can be expected. The critical factors are: - Further development of the new technology for tape casting of PE material with uniform and good properties. The dimensions after sintering are not veldefined and the electrode patterning must also be accurate. Further development of joining techniques. The few components must be glued or welded together and with precise screenprinting. Use of lead free welding is another issue do a higher welding temperature.
PMN-PT templates were synthesised by flux method. Raw oxides or perovskite and PbO flux were heated between 1150-1250°C in the Platinum crucible. The flux was removed in acid solution. Cubic templates of the grain sizes from 10 to 200um wereobtained.
A model has been developed and implemented, with a friendly graphic interface (using matlab) and a fitting method to measure all the parameters corresponding to the thickness mode (ie: thickness coupling factor, longitudinal wave velocity, relative dielectric constant at constant strain, mechanical and dielectric losses) of a single piezoelectric layer included in a multilayer structure. The model is based on an equivalent electrical circuit (K.L.M.) and its result is fitted to the characterisation of piezoelectric thick film made by screen printing on a substrate. This structure is generally composed of four layers (substrate, bottom electrode, piezoelectric thick film and top electrode). If the acoustic properties of the inert layers are known, the unknown parameters of the thick film are deduced.
This result relates to the fabrication of multilayer piezoelectric structures of the new materials developed in PIRAMID. By laminating green sheets of piezoelectric ceramics with printed metal electrodes between the layers, followed by binder burn-out and sintering, piezoelectric components with layered internal electrodes can easily be fabricated. Such components can be used for a multitude of applications as actuators and transducers, especially related to audible sound and ultrasound devices. The thin layers and internal electrodes reduce the driving voltage of the component compared to similar bulk components, thereby reducing the cost and weight of the devices and simplifying the signal processing. The innovative feature of the result is related to the new materials developed in the project. The new materials require new procedures for the various processing steps in order to obtain the desired phase and textural properties. The result will be used for preparation of industrial demonstrators in PIRAMID. After completion of the project it will contribute to the knowledge basis of SINTEF as a multidisciplinary technological contract research institute. It will be used in new projects with industrial clients in the future and thereby increase the competitiveness of European industry.
A new PLZT (i.e., (Pb,La)(Zr,Ti)O3) composition in the 'very soft' category has been developed. The composition has a rather high permittivity (free: 3270; clamped: 2350), useful for electrical impedance matching of medical ultrasonic arrays, and a thickness coupling factor of 0.37. The exploitation of this PLZT composition is limited by a somewhat low thickness coupling factor, and other high-permittivity compositions from different systems (PNNZT, PMN-PT) developed in PIRAMID will be preferred at present, also for the work on a low-loss variant with medium-high permittivity. Hopefully future development by Ferroperm Piezoceramics will lead to improved compositions in the PLZT system as well. Such further development is foreseen in the scope of the fp6-STREP project MINUET (NMP2-CT-2004-505657), where a number of composition systems will be considered and the PIRAMID results on PLZT will be useful.
To minimise lead losses and chemical reaction between substrate and thick film within processing at high temperature, a low-sintering-temperature composition was developed. It consists of PZT and lead germanates - Pb5Ge3O11. A liquid phase above 710 degrees Celsius enable densification at low temperatures under constrained conditions. Up to 4 wt.% od lead germanate was added to PZT powder during preparation of thick film paste. Sintering temperature of PZT powder of such a mixture is 750 – 850oC.
Two inks of (1-x)Pb(Mg1/3Nb2/3)-xPbTiO3 previously optimised for alumina substrate, have been used for deposition on silicon wafers. Inks with sintering aids (Li2CO3) have been optimised for low-temperature processing (800-900°C) of relaxor-ferroelectric thick films by screen-printing (film thickness = 15 to 30µm) with different PT content (1-xPMN-xPT with x= 0.35, 0.4). They have been prepared from micro-powders synthesised by Ferroperm (for x= 0.4 and 0.3) and from nano-powders elaborated by Thales (for 0.35). To extend the low temperature process developed for thick films on alumina substrate to silicon substrates, and to optimise the heating treatment, the bottom electrode quality needed first to be improved. To avoid the electrode cleaving, an adhesion layer (TiO2, IrO2) was added between the substrate and the electrode. This layer was also helpful to prevent the lead diffusion into the substrate. In addition, a lower heating rate was necessary for processing of films deposited on silicon wafers. The dielectric properties of these films have been investigated and a maximum of relative permittivity for 0.65PMN-0.35PT thick films sintered at 890°C were 8200 and 6000 for films deposited respectively on alumina and silicon substrate.
This result is linked with the results in WP2 concerning new powder compositions. The new doped PMN-PT composition developed within PIRAMID has been upscaled by Ferroperm and is now ready for production in an industrial scale. The largest batch produced so far is 10 kg and the process used can yield batches up to 100 kg without further modifications. The preliminary results are quite promising, very high relative permittivities (free:5000) and low dielectric loss (tan delta < 0.01) and a thickness coupling coefficient k_t of - 0.46. When all the relevant properties of the doped PMN-PT produced in industrial scale have been measured and compared to those of similar materials (e.g., Pz54, the new doped PNNZT mentioned elsewhere), the commercial potential of this composition will be assessed in more detail. It is expected to become a useful alternative to Pz54 for a number of applications (ultrasonic transducers for high-intensity focussed ultrasound (HIFU), medical imaging and underwater acoustics etc.), especially those requiring very high permittivity and not too high Curie point. In case of sufficient customer interest, it will be marketed by Ferroperm Piezoceramics in the form of bulk ceramics parts.

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