Li2CO3 is a promising additive to reduce the sintering temperature for (Ba0.85Ca0.15) (Zr0.1Ti0.9)O3 (BCZT) ce-ramics, however, the solubility of Li2CO3 in water and the high volatility of Li2O at elevated temperatures make the processing and densification of BCZT-Li2CO3 ceramics (known as BCZT-L) challenging. In our work, an optimized processing route was developed to obtain dense and flat BCZT-L ceramics made with 0-10 mol% of Li2CO3 and involving sintering at 1300 degrees C-1400 degrees C. The chemical and structural evolution of BCZT-L ceramics during sintering with and without a BCZT powder bed are comprehensively documented and the distribution of Li in the matrix has been observed through TOF-SIMS to explain the effects of Li doping on the piezoelectric properties. The d33 and kp of BCZT-L initially increased with Li content, but then decreased with excess Li. The decreased d33 and kp with excess Li is associated with Li aggregation in the BCZT matrix.

Microultrasound (mu US) linear arrays operating at frequencies over 25 MHz have applications in high resolution biomedical imaging. 1-3 connectively piezoceramic - polymer composite ("piezocomposite") material is attractive for fabrication of these devices due to its high effective electromechanical coupling coefficient and low acoustic impedance for better acoustic matching between transducer and tissue. However, a major concern with this type of material comes from interference between the fundamental thickness-mode resonance and spurious modes, which is usually generated by wave propagation and reflection within the repetitive and symmetrical structure of classical piezocomposite. In general, a fine spatial scale is required of the material structure to suppress the spurious modes; however, the fabrication process is challenging using standard dice-and-fill methods at the fine scales required for high frequencies. A promising way to overcome this challenge is to manipulate the lateral geometry and spacing of the piezoceramic pillars with a random distribution. In this work, gel casting in association with a micromoulding technique has been developed for manufacturing 1-3 randomised piezocomposite active material for mu US linear arrays. 48 vol% solid loading of piezoceramic powder with 30 wt% Hydantoin resin content was employed to prepare a low viscosity aqueous suspension. Through varying powder size, it was found that the suspension with 1.22 mu m powder had the highest viscosity, similar to 0.47 Pa.s, and a short gelation time, similar to 10 mins. However, all suspensions had viscosities less than 1 Pa.s at a shear rate of 100 s 1, indicating that they had good flowability. The green body samples showed mean flexural strength 49.7 +/- 2.49 MPa. After piezocomposite fabrication with randomised pillars, surface planarisation was used to obtain reliable edge definition of photolithographically-defined electrodes. 20-element arrays with 50-mu m element pitch were configured using a bilayer lift-off process. The 1-3 randomised piezocomposite demonstrated its capability to minimise the effects of spurious modes in the thickness mode frequency range, while the thickness resonances provided k33 = 0.67. Without a matching layer, the array produced a 6 dB bandwidth of 38.4%- and 20-dB pulse length of 0.26 mu s. These results show that 1-3 randomised piezocomposite fabricated from gel-casting associated with a micromoulding technique is feasible for fabrication of mu US linear arrays and may offer a route to small wafer-scale production.

Microultrasound (µUS) arrays with operating frequencies beyond 25 MHz are suitable for subsurface diagnosis, e.g., dermatology, ophthalmology, intravascular US, because they offer increased image resolution compared to conventional, lower frequency devices. Presently, arrays made with 1–3 piezocomposite active materials are becoming increasingly attractive over bulk piezoelectric materials due to their excellent electrical and acoustic properties. However, because of their repetitive pattern, diced 1–3 piezocomposites are prone to mechanical coupling between spurious modes and the desired thickness resonance, leading to performance degradation. These modes can be successfully separated from the operating frequency by a composite structure comprising either sufficiently fine pillars, with high thickness-to-width aspect ratio (AR), or with a random distribution of pillars and kerfs, namely with a randomised pattern. The promising method presented in this paper describes the use of a gel-casting method combined with micromoulding for fabrication of 1–3 randomised piezocomposites with irregular pillar sections in the range of 2 - 50 µm, The proposed composite is then used as the active material of a 27 MHz, 20-element µUS array. The material's potential in suppressing spurious modes is evaluated through impedance measurements of each channel of the array and through pulse-echo response of the prototype transducer, compared to arrays comprising diced composites.

Piezoelectric Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) has been found to be a competitive lead‐free piezoceramic candidate and was prepared by a sol–gel technique due to its small particle size and homogeneous particle size distribution, but the sintering temperature is still quite high in the previous reports. In the present paper, lithium carbonate (Li2CO3) was used as a sintering aid and dopant for the sol–gel‐derived piezoceramic powder, to facilitate the sintering process and adjust the densification, the microstructures and functional properties. With the addition of 0.5 wt% Li2CO3 sintered at 1300 °C, a high relative density 96% with piezoelectric coefficient d33 ~447 pC/N, planar coupling coefficient kp ~0.51, and Curie point TC ~98.7 °C was obtained. The way to properly define the critical changing points on temperature‐dependent dielectric curves were further discussed. By altering sintering temperature and the amount of dopant, the mutual influence between the microstructures and the functional properties was explained, to further guide shaping BCZT in more complexed connectivities.

Piezoelectric energy harvesters have become increasingly popular in the field of green energy because of the ability to convert low-frequency environmental vibrations into usable electricity. To fabricate high-performance energy harvesters, the key requirements are piezoelectric ceramics with a small grain size, of near-full density, the intended stoichiometric ratio and a high transduction coefficient. In this work, the effects of two-step sintering on the sinterability, microstructure, piezoelectric properties and energy harvesting performance of (K0.5Na0.5)NbO3 were systematically investigated. Compared with conventional single-step sintering, two-step sintering samples were of higher density, increasing from 91 % to 95 % of theoretical, reduced mean grain size, down from 17 mu m to 7.5 mu m, and decreased evaporation of the alkali metals. This translated into an improved piezoelectric performance (d(33) similar to 122 pC/N, k(p) similar to 36 % and Q(m) similar to 76), a higher transduction coefficient and energy conversion efficiency as well as a higher open-circuit voltage and power density. This demonstrates the potential of two-step sintering as a high through-put sintering technique for moderate-performance, pure KNN ceramics.

We report (Ba0.85Ca0.15)(Zr0.1Ti0.9)O-3 + x wt.% CeO2 lead free piezoelectric ceramics fabricated by conventional solid-state reaction routes. The phase structure, microstructure and functional properties have been systematically investigated. The morphotropic phase boundary was investigated in the range of x = 0 - 0.1%. A comparative study of their functional properties as a function of sintering temperature is presented. The study shows the important role of sintering temperature and grain size on the functional properties of these ceramics. Enhanced properties are observed for x = 0.07% at a sintering temperature 200 degrees C lower than for pure BCZT, in which, d(33) = 507 +/- 20 pC/N, k(p) = 51.8%, epsilon(r) = 4091 +/- 100, tan delta = 0.02, P-r = 16.32 mu m/cm(2), E-C = 2.13 kV/cm and T-C = 104.6 degrees C indicating that these ceramics are promising lead-free substitutes for the widely used lead-based ceramics.

Direct ink writing (DIW) has become a widespread additive manufacturing technique for material engineering, but its application in lead-free Ba0.85Ca0.15Zr0.1Ti0.9O3 piezoelectric ceramics from aqueous systems has not been reported so far to our knowledge. The main obstacle is the high extent of hydrolysis reactions undergone by the starting powders when dispersed in water, hindering the attainment of stable water-based colloidal suspensions. This paper reports on the preparation of stable aqueous inks from a deagglomerated and surface-treated powder synthesized by solid-state reaction and on DIW of macroporous lead-free piezoelectrics. Based on zeta potential and rheological measurements, the optimal amounts of processing additives (dispersant, binder, and coagulating agent) were selected to transform the initial fluid suspension to a viscoelastic paste with sufficient stiffness and stability for the printing process. Dielectric and piezoelectric properties of samples sintered under different temperatures were also investigated.

Microultrasound (μUS) arrays are needed for biomedical imaging, especially for high definition subsurface diagnosis. Challenges of μUS array development lie in ultrafine features of 1-3 piezocomposite structures and array elements to operate at 30 MHz. 1-3 piezocomposites with fine regular square and irregular pillars were fabricated using the dice-and-fill and gel-casting methods, respectively. Planar, parallel and smooth surfaces are required to achieve accurate size and good edge definition in photolithographically-defined array elements. Curing at elevated temperatures is also a consideration to provide environmental resistance for processing. After finishing to thickness, periodic thickness variation was found in the composites because of differences in the stiffnesses of ceramic and polymer. Average surface roughnesses of diced and randomised ceramic composite of 30 - 37 nm were achieved. Surface modification before electrode patterning was explored to promote good adhesion using plasma cleaning. The feasibility of patterning 20-element arrays with 50 μm pitch on polished surfaces of 1-3 composites by photolithography is demonstrated.

Recent reports of conductive-filler/polymer composites with large dielectric permittivity (K) make them potential candidates for flexible capacitors. Hence, an interesting question is how these high K composites behave under a strong electric field strength. In this letter, we use in-situ-reduced graphite oxide (rGO)/poly(vinylidene fluoride) (PVDF) nanocomposites as an example to study the energy storage behaviour of high K materials. We show the dielectric behaviour contrasts between weak and strong fields. High K materials inevitably become more lossy with increasing field strength. Simultaneously, we reveal that the in-situ reduction temperature can affect the energy storage performance. Improved energy storage performance is achieved for a nanocomposite reduced at a moderate temperature. When reduced at 160 °C, a device with an rGO volume fraction of 1.5 vol. % displayed a discharge energy density of 0.67 J/cm3 at 50 MV/m. This was 2.9 times greater than pure PVDF. We develop a model to explain this behaviour that proposes a reduced electrical contrast of the rGO/PVDF heterointerface minimising the recombination of localized charge carriers. Our results indicate, simultaneously, the potential and limitation of high K nanocomposites and shed light on the optimisation of the design and fabrication of high discharge energy density flexible capacitors for microelectronic devices.

Piezoelectric ceramics are widely used in sensors, actuators, and ultrasonic transducers due to their ability to achieve efficient conversion between electric and mechanical energy. There is a current drive toward lead-free material systems capable of achieving comparable piezoelectric performance to environmentally hazardous, but commonly used, lead-based materials such as lead zirconate titanate. This work constructs an accurate phase diagram for barium calcium titanate (Ba1-xCaxTiO3 or BCTO). The substitution of Ca2+ on the Ba-site of BCTO is of much interest due to electric property improvements compared to BaTiO3. In this work, Ba1-xCaxTiO3 (x=0-0.30) samples have been made by solid-state methods and, following initial characterization by X-ray diffraction (XRD), evaluation of changes in the Raman spectra has allowed accurate determination of the phase transition temperatures and the construction of a phase diagram.

The Smart X-ray Optics (SXO) Basic Technology project started in April 2006 and will end in October 2010. The aim is to develop new technologies in the field of X-ray focusing, in particular the application of active and adaptive optics. While very major advances have been made in active/adaptive astronomical optics for visible light, little was previously achieved for X-ray optics where the technological challenges differ because of the much shorter wavelengths involved. The field of X-ray astronomy has been characterized by the development and launch of ever larger observatories with the culmination in the European Space Agency’s XMM-Newton and NASA's Chandra missions which are currently operational. XMM-Newton uses a multi-nested structure to provide modest angular resolution (∼10 arcsec) but large effective area, while Chandra sacrifices effective area to achieve the optical stability necessary to provide sub-arc second resolution. Currently the European Space Agency (ESA) is engaged in studies of the next generation of X-ray space observatories, with the aim of producing telescopes with increased sensitivity and resolution. To achieve these aims several telescopes have been proposed, for example ESA and NASA’s combined International X-ray Observatory (IXO), aimed at spectroscopy, and NASA’s Generation-X. In the field of X-ray astronomy sub 0.2 arcsecond resolution with high efficiency would be very exciting. Such resolution is unlikely to be achieved by anything other than an active system. The benefits of a such a high resolution would be important for a range of astrophysics subjects, for example the potential angular resolution offered by active X-ray optics could provide unprecedented structural imaging detail of the Solar Wind bowshock interaction of comets, planets and similar objects and auroral phenomena throughout the Solar system using an observing platform in low Earth orbit. A major aim of the SXO project was to investigate the production of thin actively controlled grazing incident optics for the next generation of X-ray space telescopes. Currently telescope systems are limited in the resolution and sensitivity by the optical quality of the thin shell optics used. As part of its research programme an actively controlled prototype X-ray thin shell telescope optic of dimensions 30x10cm has been developed to bench test the technology. The design is based on thin nickel shells bonded to shaped piezo-electric unimorph actuators made from lead zirconate titanate (PZT).

Video capsule endoscopy (VCE) has become a clinically accepted diagnostic modality in the last 20 years and has established a technological roadmap for other capsule endoscopy (CE) devices, incorporating microscale technology, a local power supply and wireless communication. However, VCE does not provide a therapeutic function and research in therapeutic capsule endoscopy (TCE) has been limited. This paper proposes a new route towards viable TCE based on multiple CE devices including essential nanoscale components. A first device is used for multimodal diagnosis, with quantitative microultrasound as a complement to video imaging. Ultrasound-enhanced fluorescent marking of sites of pathology allows follow-up with a second device for therapy. This is based on fluorescence imaging and ultrasound-mediated targeted drug delivery. Subsequent treatment verification and monitoring with a third device exploits the minimally invasive nature of CE. Clinical implementation of a complete patient pathway remains the subject of research but several key components have been prepared in early prototype form. These are described, along with gaps that remain to be filled.

The relatively low melting point of lead oxide (approx. 900 °C) has always presented an issue in the processing of lead zirconium titanate (PZT) piezoelectric ceramics. The loss of PbO at high sintering temperatures (up to 1300 °C) can cause undesirable changes in stoichiometry, phase composition and electrical properties of the final ceramic product. In high-volume production, the PbO loss per piece is low and, with a small excess of lead oxide in the initial powder composition, it is usually sufficient to sinter samples in enclosed crucibles. Small-scale lab processing requires better atmosphere control, usually implemented by surrounding the sample in a lead oxide-containing powder bed. Such control is required in order to prepare samples for detailed composition- microstructure-property studies. In this work, a typical industrial sintering program with slow heating rate and long dwell time was used to sinter hard PZT samples (NCE40 supplied by Noliac) at 1260 °C in a laboratory furnace. It was found that conventionally used powder beds such as PZT or PbZrO 3 mixed in different ratios with ZrO 2 were either difficult to separate from the crucible/samples or not able to sufficiently prevent the weight loss of the samples. Excessive PbO loss was indicated by the presence of ZrO 2 secondary phase in sintered samples. Weight loss of individual samples, and their resulting electrical properties, varied depending on the composition and particle size of the powder bed. An alternative powder bed consisting of ZrO 2 sand reacted with PbO was found to sufficiently reduce the PbO loss in the samples (no secondary phase detected) while being easily separated from both the samples and crucible after sintering, and maintaining good piezoelectric properties in the sintered samples.

We report on the fabrication of multiscale three-dimensional (3D) micropatterning of 0.5Ba(Zr0.2Ti0.8)O3−0.5(Ba0.7Ca0.3)TiO3 (BZT−BCT) electroceramic material using soft lithographic PDMS moulds. The ceramic microcomponents were successfully consolidated by Epoxy Gel Casting from stable aqueous suspension of BZT-BCT material. A successful aqueous processing of electroceramic material was employed with surface protection of powder particles against hydrolysis as considerably an important parameter to achieve high solid loading suspension with pseudoplastic behaviour suitable for casting in micro scale moulds. The process to obtain micro sized pattern of material was divided in two steps: (i) production of high quality SU-8 master moulds and the respective negative replicas in PDMS (soft mould) by photolithography and soft mould replication, respectively; (ii) casting the soft moulds by stable high solid loading BZT-BCT suspensions in presence of gelation agents followed by de-moulding, drying and sintering. The resulting green micropattern structures show interesting features, including complex structures with a periodic variations through their length and, multiscale array of hexagonal shaped pillars of different aspect ratios (AR) (max AR≈8 with approx ∼320μm of height and side length ∼40μm) with smooth side wall features along height. The green pillar arrays were further sintered to show the suitability of aqueous processing of material and proposed casting method.

Citation for published version (Harvard): Arifin, N, Button, T & Steinberger-Wilckens, R 2017, Carbon-Tolerant Ni/ScCeSZ Via Aqueous Tape Casting for ITSOFCs. in SC Singhal & T Kawada (eds), Proceedings of SOFC XV. 1 edn, vol. 78, ECS Transactions, no. 1, vol. 78, Electrochemical Society Inc., Pennington, pp. 1417-1426, 15th International Symposium on Solid Oxide Fuel Cells, SOFC, 2017, Hollywood, United States, 23/07/17.

State-of-the-art neurosurgery intervention relies heavily on information from tissue imaging taken at a pre-operative stage. However, the data retrieved prior to performing an opening in the patient's skull may present inconsistencies with respect to the tissue position observed by the surgeon during intervention, due to both the pulsing vasculature and possible displacements of the brain. The consequent uncertainty of the actual tissue position during the insertion of surgical tools has resulted in great interest in real-time guidance techniques. Ultrasound guidance during neurosurgery is a promising method for imaging the tissue while inserting surgical tools, as it may provide high resolution images. Microfabrication techniques have enabled the miniaturisation of ultrasound arrays to fit needle gauges below 2 mm inner diameter. However, the integration of array transducers in surgical needles requires the development of advanced interconnection techniques that can provide an interface between the microscale array elements and the macroscale connectors to the driving electronics. This paper presents progress towards a novel packaging scheme that uses a thin flexible printed circuit board (PCB) wound inside a surgical needle. The flexible PCB is connected to a probe at the tip of the needle by means of magnetically aligned anisotropic conductive paste. This bonding technology offers higher compactness compared to conventional wire bonding, as the individual electrical connections are isolated from one another within the volume of the paste line, and applies a reduced thermal load compared to thermo-compression or eutectic packaging techniques. The reduction in the volume required for the interconnection allows for denser wiring of ultrasound probes within interventional tools. This allows the integration of arrays with higher element counts in confined packages, potentially enabling multi-modality imaging with Raman, OCT, and impediography. Promising experimental results and a prototype needle assembly are presented to demonstrate the viability of the proposed packaging scheme. The progress reported in this work are steps towards the production of fully-functional imaging-enabled needles that can be used as surgical guidance tools.

Lead-free piezoelectric compositions based on (Ba,Ca)(Zr,Ti)O 3 have been reported to exhibit many piezoelectric properties similar to the conventionally used Pb(Zr,Ti)O 3 materials, and have thus been attracting much attention as potential replacements for lead-based piezoceramics. However, there appears quite a wide variation in the reported piezoelectric properties of the BCZT ceramics, indicating that such properties may be sensitive to fabrication and processing methods. This paper reports an investigation of a wide range of processing factors, including composition (e.g. ratio of Ba(Zr,Ti)O 3 to (Ba,Ca)TiO 3 ), sintering conditions (temperature and cooling rate), particle size of the calcined ceramic powder, structure and microstructure (e.g. phase, lattice parameters, density and grain size), and their effect on the piezoelectric properties. For individual compositions, lattice constants and grain size, which are themselves dependent on the ceramic powder particle size and sintering conditions, have been shown to be very important in terms of optimising piezoelectric properties in these materials.

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This paper demonstrates the feasibility of fabricating energy harvesters based on piezoelectric cantilevers with a free-standing thick-film structure. Demonstrator devices have been designed, built and evaluated in a range of mechanical coupling configurations, in order to harvest energy from machinery vibrations and weak air flow. In terms of wideband vibration energy harvesters, arrays of the individual harvesters were assembled onto plastic test circuit boards integrated with diode bridge rectifiers. The harvesters were designed with different dimensions and various tip masses were attached on the tip of the cantilevers in order to individually tune the resonant frequencies. The assembled harvesters were tested under harmonic vibration conditions. Great potential of harvesting vibration energy and broadening working bandwidth has been exhibited. In terms of the harvester for weak air flow, two individual cantilever devices were assembled on the chassis of a free-spinning fan. Permanent magnets were fixed on the blades of the fan as well as the cantilevers. The device was tested in an open fluidic environments. The air flow has been successfully transferred to axial oscillations thus driving the cantilevers bending up and down. Possibilities of such devices being optimised to meet the requirements of real applications of self-powered wireless sensor networks can be foreseen.

This paper reports an investigation of (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 (50BCZT) piezoelectric ceramics doped with Bi0.5(Na0.82K0.18)0.5TiO3 (18BNKT). For compositions between 1–5 wt% 18BNKT, a perovskite phase was observed in the sintered ceramics, with d33 values of approximately 370 pC/N measured at room temperature, which is about 80 % of that of pure 50BCZT. Also, the doped materials exhibit a remanent polarization of 2–5 µC/cm2 at temperatures above the Curie temperature (> 90 °C) of the pure 50BCZT composition. This research shows a promising route to improve the working temperature range whilst maintain good piezoelectric properties of the 50BCZT ceramics.