Browsing by Author "Whatmore, Roger W."
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Item Open Access Apparent Reduction in the Value of the d 33 Piezoelectric Coefficient in PZT Thick Films.(Taylor & Francis, 2002-01-01T00:00:00Z) Dorey, Robert A.; Whatmore, Roger W.Thick PZT films (1 - 20 m) have been prepared using a composite sol gel technique whereby PZT powder and a PZT producing sol are formed into a slurry and spin coated onto silicon wafers. The maximum relative permittivity obtained was approximately 80% of that exhibited by bulk PZT of comparable composition. However, the d 33, f and e 31, f [1] piezoelectric coefficients were shown to be significantly lower than that of bulk PZT. It has been proposed that the measured value of d 33, f is affected appreciably by particle-particle rotation and substrate clamping leading to reduced poling efficiency which may also greatly reduce the value of e 31, f observed. Samples with high levels of porosity have been shown to exhibit a reduced value of d 33 . This was attributed to 31 and 51 mode piezoelectrically generated charges caused by the bending and shearing of particle-particle bridges. The effect of substrate clamping, on d 33, f and poling, has been studied by monitoring the changes in position and intensity of the (200)/(002) X-ray diffraction (XRD) peaks of composite films. The presence of the substrate was found to introduce tensile stresses parallel to the film plane which distorted the unit cell. Subsequent permanent polarisation following poling was found to be reduced due to the presence of these stresses. The discrepancies between the values of d 33 measured on thick films and bulk ceramics were highlighted as being of particular importance if thick film materials are to be modelled for device applications. Thick film piezoelectric coefficients (i.e. those of the combined film-substrate structure) should not be used in place of material piezoelectric coefficients when attempting to model the behaviour of devices. Such actions would inevitably lead to erroneous results.Item Open Access Aqueous colloidal processing and green sheet properties of lead zirconate titanate (PZT) ceramics made by tape casting(Elsevier Science B.V., Amsterdam., 2004-01-01T00:00:00Z) Navarro, A.; Alcock, Jeffrey R.; Whatmore, Roger W.An aqueous system for tape casting PZT ceramics was developed using poly (vinyl alcohol) binder, poly (propylene glycol) plasticizer, D3021 dispersant and Surfynol SE-F wetting agent. Screening experiments were performed to assess the stability of the suspension in the presence of the dispersant by performing pH, conductivity and Zeta potential measurements. Viscosity measurements were used to find the optimum level of dispersant needed to produce a stable slip at pH 10.2. Subsequently, the rheological and mechanical characteristics were also investigated.Item Open Access Characterisation of PZT thin film micro-actuators using a silicon micro-force sensor(Elsevier, 2007-01-08) Duval, Fabrice F. C.; Wilson, Stephen A.; Ensell, Graham; Evanno, Nicolas M. P.; Cain, Markys G.; Whatmore, Roger W.This paper reports on the measurements of displacement and blocking force of piezoelectric micro-cantilevers. The free displacement was studied using a surface profiler and a laser vibrometer. The experimental data were compared with an analytical model which showed that the PZT thin film has a Young's modulus of 110 GPa and a piezoelectric coefficient d31,f of 30 pC/N. The blocking force was investigated by means of a micro-machined silicon force sensor based on the silicon piezoresistive effect. The generated force was detected by measuring a change in voltage within a piezoresistors bridge. The sensor was calibrated using a commercial nano-indenter as a force and displacement standard. Application of the method showed that a 700 μm long micro-cantilever showed a maximum displacement of 800 nm and a blocking force of 0.1 mN at an actuation voltage of 5 V, within experimental error of the theoretical predictions based on the known piezoelectric and elastic properties of the PZT film.Item Open Access Comparative studies of PST thin films as prepared by Sol-Gel, LDCVD and sputtering techniques(Taylor and Francis, 2002) Huang, Zhaorong; Donohue, P. P.; Zhang, Qi; Williams, D.; Anthony, C. J.; Todd, M. A.; Whatmore, Roger W.Lead scandium tantalate (PST) thin films for pyroelectric applications have been deposited by using liquid delivery chemical vaporise deposition (LDCVD), sputtering and sol-gel techniques. These films were annealed by using rapid thermal annealing to improve their electrical properties. Their microstructures and electrical properties such as permittivity εr, dielectric loss tanδ, pyroelectric coefficient p, and thermal detection figure of merit Fd were studied. It is suggested to use a combination of methods to depositing films and then use rapid thermal annealing to produce high quality PST thin films.Item Open Access Correlation of sintered microstructure with green density in thick film PZT(Trans Tech Publications, 2003-06-28T00:00:00Z) Mortara, L.; Navarro, A.; Whatmore, Roger W.; Alcock, Jeffrey R.High density and low grain size are essential for the production of thick-film ceramics, in order that they possess adequate strength for any subsequent processing steps. In this paper sintered density and grain size were studied as function of green density and firing temperature. Wafers possessing a higher green density showed a more homogeneous microstructure and a higher sintered density.Item Open Access Development aspects of an integrated pyroelectric array incorporating a thin PZT film and radiation collectors(Taylor and Francis, 2004) Shaw, Christopher P.; Landi, Spartaco; Whatmore, Roger W.; Kirby, Paul B.Abstract Work is being undertaken to produce an uncooled pyroelectric infra-red detector array which incorporates within its structure, an array of radiation collectors made by the bulk micro-machining of silicon. Development aspects of the processing route are presented here.Item Open Access Direct and converse magnetoelectic effect in laminate bonded Terfenol-D-PZT composites(Elsevier Science B.V., Amsterdam., 2007-09-20T00:00:00Z) Record, P. M.; Popov, C.; Fletcher, J.; Abraham, E.; Huang, Zhaorong; Chang, Harrison Hoon Seok; Whatmore, Roger W.Results from measurements of the direct and converse magnetoelectric (ME) effect on a three-layer, epoxy-bonded, laminate composite are presented. The laminae are a single transversely polarized piezoelectric elements (PZ29) sandwiched between two longitudinal-magnetic ally polarized magnetostrictive TD elements (Terfenol-D-TX GMM). The direct ME effect was determined by measuring laminate output with a Helmholtz-generated AC field (up to 7 Oe) in the range 50 Hz-100 kHz biased by a DC field (0-1000 Oe). Peak voltage output occurred at the sample's mechanical resonant frequency, its value depending on the strength and direction of the applied magnetic field. The peak output was 3061 mV at 3 Oe AC field and 1000 Oe bias, equivalent to 74.4 V cm(-1) Oe(-1). The peak output coefficient, however, was 93.6 V cm(-1) Oe(-1) at 0.1 Oe AC field and 1000 Oe DC bias. The reduction at higher drive amplitudes was attributed to increased Young's modulus of the TD phase. Anomalous peaks in the low frequency spectrum of sample's output are explained. The converse magnetoelectric effect was measured by recording the voltage induced in a solenoid encompassing the ME while exposed to a DC bias field and the PZ phase driven by a 10 VAC source. The peak output is shown to depend on the strength of the applied DC magnetic field and developed a maximum field of 15.4 Oe at the sample's mechanical resonant frequency. This equates to a converse magnetoelectric coefficient of 55 Oe cm kV (-1) (c) 2007 Elsevier B.V. All rights reserved.Item Open Access Direct and converse magnetoelectric effect at resonant frequency in laminar piezoelectric-magnetostrictive composite.(Springer Science Business Media, 2008-02-01T00:00:00Z) Popov, C.; Chang, Harrison Hoon Seok; Record, P. M.; Abraham, E.; Whatmore, Roger W.; Huang, ZhaorongLaminar piezoelectric-magnetostrictive composites using piezoelectric lead zirconate titanate ceramics and the giant magnetostrictive rare-earth-iron alloy Terfenol-D were prepared by epoxy bonding. The direct and converse magnetoelectric (ME) effects at and off the mechanical resonant frequency were characterized and compared to the theoretical modelling. The mechanical resonant frequency of the composites depended on the sample orientation and the magnetic DC bias field. In the longitudinal configuration, the resonant frequency shifted down monotonically with the increasing bias field. When the sample was in the transverse configuration, the resonant frequency decreased with the increasing field at first. However, at higher bias, it shifted up with the increasing bias. A phenomenological model based on the à  E effect of magnetostrictive materials is proposed to explain the observed phenomenaItem Open Access Electric-field structuring of piezoelectric composite materials(Cranfield University, 1999-09) Wilson, Stephen A.; Whatmore, Roger W.Piezoelectric composite materials, consisting of a ferroelectric ceramic in an electrically-inactive polymer matrix, have been shown to greatly outperform single phase materials for certain applications. A new assembly technique, which electrically controls the spatial distribution of the ceramic within the polymer, promises to enhance the sensitivity of 0-3 type piezoelectric composites. The materials so-produced have a quasi 1-3 structure and it is intended that they will exhibit some of the advantages of 1- 3 piezoelectric composites, whilst retaining the simplicity of 0-3 manufacturing. The electric field structuring technique exploits the electrokinetic phenomenon of dielectrophoresis, which is responsible for the electrorheological effect. When a suspension of ceramic particles in an insulating fluid is exposed to a moderate AC electric field, the particles polarize and as a result they exhibit a mutually attractive force. Under suitable conditions the particles assemble into `pearl-chains', `fibrils' or columns, oriented parallel to the applied field. If the fluid is a resin pre-polymer, this can then be cured and the newly formed structures frozen into place to form a composite material with anisotropic properties. The key process parameters are explored and the implications of employing this method to produce technologically useful materials are discussed. It is demonstrated, for the first time, that dielectrophoresis can be used to induce anisotropic dielectric and piezoelectric properties in 55%vol. fraction ceramic / polymer composites. A model composite system of pure lead titanate in an epoxy resin is considered in basic detail. A method of producing a lead zirconate titanate (PZT) powder with a narrow particle size distribution, by flux growth, has been shown to be effective. New concepts in multiphase composites are introduced, whereby chains are formed within the confines of a second immiscible fluid or where particles of two different materials are mixed in a suspension, each material having its own `polarization signature'.Item Open Access Electrical properties of Sb and Cr-doped PbZrO3-PbTiO3-PbMg1/3Nb2/3O3 ceramics(Elsevier, 2003-04) Whatmore, Roger W.; Molter, O.; Shaw, Christopher P.The pyroelectric, dielectric and DC resistive properties of Sb and Cr-doped ceramics with a base composition of Pb(Mg1/3Nb2/3)0.025(Zr0.825Ti0.175)0.975O3 have been studied. Sb doping has been shown to produce a linear reduction in Curie temperature (TC=−22z+294 °C) with concentration (z) and to give an increase in pyroelectric coefficient from 250 to 310 μCm−2 K−1 for z increasing from 0 to 3 at.%. It also produces first a reduction and then an increase in both dielectric constant and loss, so that the 33 Hz pyroelectric figures of merit (FOM's) are as follows: FV peaks at 3.8×10−2 m2 C−1 and FD peaks at 1.2×10−5 Pa−1/2. The resistivity is increased substantially from 1.1×1011 to ca 6×1011 Ωm with 1 at.% Sb, thereafter changing little. The behaviour has been explained in terms of Sb acting as a donor ion, reducing oxygen vacancy concentrations up to 1 at.%, with conductivity dominated by hole hopping between traps (Ea=0.59±0.05 eV) that are not changed by the Sb doping. It is concluded that additions of higher levels of Sb do not produce electron-mediated hopping conduction. The Cr additions have no effect upon TC, but reduce dielectric constant and loss, pyroelectric coefficient and resistivity at doping levels up to 3 at.%. The FOM FV peaks at 3.6×10−2 m2 C−1 and FD at 1.9×10−5 Pa−1/2. The behaviour of the electrical resistivity as a function of dopant level is shown to produce a linear ln(σo) vs z−1/3 dependence (σo=DC conductivity), as would be expected for hole hopping conduction between Cr3+ sites, with an Ea=0.38±0.03 eV.Item Open Access Fabrication of lead zirconate titanate ceramics for pyroelectric applications(Cranfield University, 2001-10) Navarro, A.; Whatmore, Roger W.; Alcock, Jeffrey R.The objective of this work was twofold, i.e. to develop an aqueous route for tape casting Lead Ziconate Titanate (PZT)ceramics for pyroelectric applications and to optimise the die-pressing route for reducing defect size and number in bulk Lead Zicronate Titanate ceramics (PZT).Item Open Access Flextensional ultrasonic motor using the contour mode of a square piezoelectric plate.(IEEE Institute of Electrical and Electronics, 2004-08-01T00:00:00Z) Leinvuo, Joni T.; Wilson, Stephen A.; Whatmore, Roger W.This paper presents the design, fabrication, and characterization of a new type of standing wave piezoelectric ultrasonic motor. The motor uses a metallic flextensional amplifier, or cymbal, to convert the contour mode vibrations of a square piezoelectric ceramic plate into flexural oscillations, which are further converted to produce rotary actuation by means of an elastic-fin friction drive. The motor operates on a single-phase electrical supply. A beryllium copper rotor design with three-fin configuration was adopted, and the geometry was varied to include different material thicknesses, fin lengths, and inclinations. The best stall torque and no load speed for a 25-mm square motor were 0.72 Nmm and 895 r/minute, respectively. The behavior of the stator structure was analyzed by ANSYS finite element software using harmonic and modal analyses. The vibration mode estimated by finite element modeling (FEM) was confirmed by laser Doppler vibration measurements.Item Open Access Flextensional ultrasonic piezoelectric micro-motor.(IEEE Institute of Electrical and Electronics, 2006-12-01T00:00:00Z) Leinvuo, Joni T.; Wilson, Stephen A.; Whatmore, Roger W.; Cain, Markys G.This paper presents the experimental design, construction, and operational characteristics of a new type of standing wave piezoelectric ultrasonic micro-motor. The motor uses a composite stator, consisting of a metallic flextensional mode converter, or "cymbal," bonded to a 2-mm-square piezoelectric plate. The cymbal converts contour-mode vibrations of the plate into oscillations in the cymbal, perpendicular to the stator plane. These are further converted into rotational movement in a rotor pressed against the cymbal by means of an elastic-fin friction drive to produce the required rotary actuation. The motor operates on a single-phase electrical supply, and direct control of the output speed and torque can be achieved by adjusting the amplitude and frequency of the supply voltage. Noncontact optical techniques were used to assess the performance of the developed micro-motor. The operational characteristics were developed from the acceleration and deceleration characteristics. No-load output speed (11 rev s-1) and stall torque (27 nNm) were derived using high-speed imaging and image analysis. Maximum efficiency was 0.6%Item Open Access Giant electrocaloric effect in the thin film relaxor ferroelectric 0.9 PbMg1/3Nb2/3O3–0.1 PbTiO3 near room temperature.(American Institute of Physics, 2006-12) Mischenkoa, A. S.; Zhang, Qi; Whatmore, Roger W.; Scott, J. F.; Mathurb, N. D.We have recently observed a giant electrocaloric effect (12 K in 25 V) in 350 nm sol-gel PbZr0.95Ti0.05O3 films near the ferroelectric Curie temperature of 242oC. Here we demonstrate a giant electrocaloric effect (5 K in 25 V) in 260 nm sol-gel films of the relaxor ferroelectric 0.9 PbMg1/3Nb2/3O3 – 0.1 PbTiO3 near the Curie temperature of 60oC. This reduction in operating temperature widens the potential for applications in novel cooling systems.Item Open Access Investigation of the electrocaloric effect in a PbMg2/3Nb1/3O3-PbTiO3 relaxor thin film(American Institute of Physics, 2009-05) Correia, T. M.; Young, J. S.; Whatmore, Roger W.; Scott, J. F.; Mathur, N. D.; Zhang, QiPermittivity measurements of a 0.93PMN-0.07PT thin film show a broad maximum near 35 °C, and an anomaly at the depolarizing temperature Td = 18 °C on heating only, suggesting a dipolar glass-relaxor phase transition. No structural phase transition at 18 °C is apparent from ferroelectric hysteresis loops taken on field cooling and field heating. These loops show the thermal hysteresis expected for ferroelectric relaxors, which has not hitherto been experimentally verified in PbMg2/3Nb1/3O3-PbTiO3 thin films. Our data suggest the intriguing possibility of a giant electrocaloric effect (ΔT = 9 K, ΔE = 720 kV cm−1) at and near room temperature.Item Open Access Kinetics of phase transformations in lead scandium tantalate thin films(Taylor and Francis, 2004) Battat, J.; Huang, Zhaorong; Donohue, P. P.; Todd, M. A.; Whatmore, Roger W.The phase transformations from amorphous to pyrochlore to perovskite in lead scandium tantalate (PST) thin films during rapid thermal annealing process (RTA) have been studied. Volume fractions for pyrochlore and perovskite were obtained from their respective X-ray diffraction intensities. Two models assuming the starting phase being pure amorphous or pyrochlore were analysed in detail. Equations have been derived and numerical calculation used to simulate the volume fractions for each phase as functions of annealing time. Transformation parameters k and n were obtained by comparing experiment with simulation using a least-squares curve fitting technique.Item Open Access Low fatigue lead zirconate titanate-based capacitors modified by manganese for nonvolatile memories(Elsevier, 2004-06-15) Zhang, Qi; Whatmore, Roger W.We have investigated the effects of Mn doping on the ferroelectric properties of Pb(Zr0.3Ti0.7)O3 (PZT) thin films on substrates Pt/Ti/SiO2/Si. Small amount of Mn-doped (≤1 mol%) PZT (PMZT) showed almost no hysteretic fatigue up to 1010 switching bipolar pulse cycles, coupled with excellent retention properties. We present evidence that while a low permittivity interfacial layer forms between the Pt electrode and PZT films, this does not occur in PMZT. We propose that Mn dopants are able to reduce oxygen vacancy mobility in PZT films and Mn2+ ions consume the oxygen vacancies generated during repeated switching, forming Mn4+ ions. These mechanisms are probably responsible for their low observed fatigue characteristics.Item Open Access A model of phase transition kinetics in lead scandium tantalate thin films(Taylor and Francis, 2003) Battat, J.; Huang, Zhaorong; Donohue, P. P.; Whatmore, Roger W.The phase transformations from amorphous to pyrochlore to perovskite in lead scandium tantalate (PST) thin films during rapid thermal annealing process (RTA) have been studied by X-ray diffraction (XRD) techniques. The growth and decay of the pyrochlore phase, the growth of the perosvkite PST were analysed using the Avrami model. Integral equations have been derived and numerical calculation been used to simulate the volume fractions for pyrochlore and perovskite as functions of annealing time. Transformation parameters k and n were obtained by comparing the simulated to the experimental intensities using a least-squares curve fitting technique. Activation energies for perovskite formation were calculated. The results indicate that the phase transitions are diffusion-limited. TEM, SEM, and EDS were employed to study the lead loss and other factors affecting phase transitions.Item Open Access Modified bismuth titanate piezoelectric ceramics(2003-12) Sanson, Alessandra; Whatmore, Roger W.Bismuth compounds are considered the most suitable alternatives to lead-based systems for ferroelectric and piezoelectric applications. Nevertheless little has been done to systematically study the relationships that link the two main classes of ferroelectric bismuth compounds: perovskite and bismuth layer compounds (Aurivillius compounds). The knowledge of these relationships could be a key to improve the performances of the bismuth compounds and could help to better tailor their properties for specific applications. The objective of this project was twofold: 1. To understand the structural and electrical relationships between perovskite and Aurivillius compounds within the Na^Bi^TiO^-Bi^Ti^O^-BaTiCb (NBT-BIT-BT) system; 2. To explore the possibility of obtaining a new perovskite of formula Bi2MgTiOô. A study of 83 different compositions allowed us to sketch the possible phase diagram of the NBT-BIT-BT system. XRD structural characterisation highlighted the importance of low angle analysis in the study of layered compounds. The presence of monophasic regions in the phase diagram stressed the flexibility of this class of compounds that are able to withstand high percentage of vacancies before collapsing. It was shown that, after taking into account some electronic considerations, a simple geometrical model can be use as “rule of thumb” to predict the stability of Aurivillius compounds. New unreported compounds were found in the system and a mechanism for the formation of the Aurivillius compounds is proposed. The dielectric and piezoelectric properties were linked to the fundamental layered structure of the Aurivillius phases showing that all these properties depend on the number of perovskite blocks present. The higher the number of perovskite blocks, higher the values of resistivity and relative permittivity.Item Open Access Nanostructured bottom electrodes for ferroelectric thin films(Cranfield University, 2001-09) Wilson, R.; Whatmore, Roger W.Lead zirconate titanate (PZT) is a oxide, which posseses a perovskite type structure. The material is ferroelectric making it technically useful for a diverse range of applications from thermal imaging to non-volatile integrated memory devices. Thin films of PZT are commonly deposited onto platinised-silicon (Pt(111)/Ti/SíOX/Si) bottom electrodes by chemical solution deposition (CSD). Depending on the conditions used a transient intermetallic phase Pt3Pb can form in-situ with a (111) preferred orientation during processing, which reduces the lattice mismatch between the desired perovskite phase and bottom electrode. Thereby, making it easier for the perovskite phase to both nucleate and take on a preferred (111) orientation. In the work presented experiments were conducted on modifying the surface of platinised-silicon to achieve a better lattice-match to Pb(Zr0_3Ti0_7)O3 (PZT30/70) through coating, alloying or reacting the platinum with silver (Ag), gold (Au) or lead (Pb). Single layer and multi-layer PZT thin fihns were deposited by a CSD method onto these modified bottom electrodes and plain platinised-silicon. Two precursor sols were used one that had 10% excess Pb added (PZT30/70) and one that had no excess Pb added (StoichPZT30/70). In general, two drying regimes prior to crystallisation were employed for the precursor fihns. i. Dried at 200°C for 3min ii. Dried at 300°C for 5min Crystallisation of the dried films was conducted i general at 480°C. The primary result of the work, showed that the presence of a lattice-matched surface is highly beneficial for nucleation of perovskite PZT and the subsequent transformation from amorphous precursor into perovskite PZT at low crystallisation temperatures <500°C. All the modified bottom electrodes performed well when used i conjunction with fihns dried at 300°C for 5min, which otherwise would not transform on plain platinised-silicon. It was found that the Au and Ag modified platinised-silicon behaved i a similar manner to plain platinised-silicon with respect to in-situ Pt3Pb, except that the Ag modified platinised-silicon appeared to impede its formation and promote its oxidation. I general the perovskite phase was detected by x-ray diffraction earlier on Ag modified platinised-silicon than on either Au modified or plain platinisedsilicon. The PZT30/70 thin films dried at 200°C for 3min on Au and Ag modified Abstract bottom electrodes appeared to have a higher crystallinity than similar than similar films deposited onto plain platinised-silicon. This was not observed for the StoichPZT30/70 sol as the crystallinity of these films, dried at 200°C for 3mjn were similar i value with all being greater than comparable PZT30/70 sol thin films. It was also proposed that the transformation rate from pyrochlore to perovskite could be affected by precursor sol Pb content and its distribution within the film during crystallisation. This was illustrated when bottom electrodes containing Pt3Pb before the film deposition (ex-situ) were used. PZT30/70 films dried at 200°C for 3min, provide conditions for forming in-situ Pt3Pb and this produced poor quality perovskite PZT thin films on ex-situ Pt3Pb. Implying that i the concentration of Pb is too high at the film/electrode, not only is the preferred orientation of the perovskite thin film compromised but also the degree of transformation from an amorphous to the perovskite phase will be compromised. However, StoichPZT30/70 films dried at 300°C for 5min do not form in-situ Pt3Pb on crystallisation but When crystallised on ex-situ Pt3Pb they appear to transform rapidly into the perovskite phase with a preferred (111) orientation.