Electromechanical and biological evaluations of 0.94Bi0.5Na0.5TiO3–0.06BaTiO3 as a lead-free piezoceramic for implantable bioelectronics

Smart implantable electronic medical devices are being developed to deliver healthcare that is more connected, personalised, and precise. Many of these implantables rely on piezoceramics for sensing, communication, energy autonomy, and biological stimulation, but the piezoceramics with the strongest piezoelectric coefficients are almost exclusively lead-based. In this article, we evaluate the electromechanical and biological characteristics of a lead-free alternative, 0.94Bi0.5Na0.5TiO3–0.06BaTiO3 (BNT-6BT), manufactured via two synthesis routes: the conventional solid-state method (PIC700) and tape casting (TC-BNT-6BT). The BNT-6BT materials exhibited soft piezoelectric properties, with d33 piezoelectric coefficients that were inferior to commonly used PZT (PIC700: 116 pC/N; TC-BNT-6BT: 121 pC/N; PZT-5A: 400 pC/N). The material may be viable as a lead-free substitute for soft PZT where moderate performance losses up to 10 dB are tolerable, such as pressure sensing and pulse-echo measurement. No short-term harmful biological effects of BNT-6BT were detected and the material was conducive to the proliferation of MC3T3-E1 murine preosteoblasts. BNT-6BT could therefore be a viable material for electroactive implants and implantable electronics without the need for hermetic sealing

Fabrication of lead free and lead based 1-3 piezoelectric composites for high frequency ultrasound transducers

This thesis is concerned with the fabrication and characterisation of lead free piezocomposites and transducers for use in high frequency medical ultrasound imaging applications. A water based gel casting and micro moulding approach has been developed to fabricate 1-3 composites with a random pillar structure in the lead free and lead based piezoelectric material. High frequency transducers incorporating the random composites as the active components have been fabricated, characterised and demonstrated in real tissue imaging environments. A water based gel casting system has been used incorporating Hydantoin Epoxy resin, amine hardener (Bis (3-aminoproply) amine) and dispersant. Viscosities of the 50BCZT and PZT systems were minimised by the addition of 2.4 and 1 wt% of dispersant respectively. The highest values of piezoelectric and dielectric properties corresponded to 50BCZT samples fabricated with a gel casting slurry incorporating 30 wt% resin and sintered at 1425 °C, with d33 and kp values of 330 pC/N and 0.43, respectively. 1-3 composites were successfully fabricated from the BCZT and PZT bristle block structures and only one resonance peak corresponding to the thickness mode was observed. PZT composites offered generally higher thickness coupling coefficients than 50BCZT composites, where the highest value of 0.78 was measured for samples sintered at temperature 1425 °C. Focused PZT, focused 50BCZT, unfocussed PZT and unfocussed 50BCZT transducers were successfully fabricated using the composites with randomised structure, and have operating frequencies of 35, 40, 50 and 35 MHz respectively

Fabrication of Grain-oriented Lead-free Piezoceramics

富山県立大学平成29年

Vibrational energy harvesting using piezoelectric ceramics and free-standing thick-film structures

This thesis presents a series of broad but systematic and consecutive investigations on the topic of piezoelectric energy harvesting. These include material fabrication and characterisation, harvester fabrication and material parameter selection, electric output and dynamic behaviour tests of energy harvesters, and the feasibility of utilising lead-free piezoelectric materials for energy harvesting. Three lead-based and one lead-free perovskite solid-solutions compositions have been researched individually and compared to each other. In the form of bulk ceramics the lead-free composition is considered capable of replacing the lead-based compositions for vibrational energy harvesting at room temperature. Typical properties of ε$_r$≈4700, $P$$_r$≈9 μC/cm$^2$, $d$$_3$$_3$≈500 pC/N, $k$$_p$≈0.51 have been achieved for the lead-free and lead-based compositions respectively. Vibrational energy harvesting based on a novel structure of piezoelectric/silver multi-layer free-standing thick-film unimorph and bimorph cantilevers have been investigated using two of the lead-based compositions. A planar shrinkage difference of 3-6% between the silver and piezoelectric layers is suggested in order to ensure successful fabrication. When tested under harmonic vibration conditions, a comparison of unimorph individual harvesters suggests that higher piezoelectric voltage and electromechanical coupling coefficients may be preferred when selecting materials. Further optimisations involving bimorph devices with tip proof mass have demonstrated maximum harvester outputs (root mean square) of about 9 μW and 2.8 V with approximately 14% bandwidth under resonant vibrations (I 00-150 Hz, 0.5 - I.Og). In addition, the cantilevers have utilised to harvest wind energy with a modified spinning configuration, exhibiting 3.4 V average open-circuit output voltage in optimum wind conditions

Effect of Dispersant and Binder on Fabrication of BZT-0.5BCT Piezoelectric Wafers by Tape Casting Technique

Recently, piezoelectric wafers/substrates have opened new opportunities for nondestructive evaluation (NDE) of structures in defence, aerospace and industrial sectors. Such wafers can be easily made by tape casting of slurries where dispersants and binders play a critical role. Generally, lead zirconate titanate (PZT) based compositions are used for piezo wafers/substrates. However, recent concern about environmental pollution from lead-based materials has generated renewed interest in developing lead-free ferroelectrics like Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 [BZT-0.5BCT] having high dielectric constant (εr>3500) and piezoelectric properties (d33> 500pC/N). To date, there are no reports on the fabrication of BZT-0.5BCT wafers by tape casting and their electrical characterization. The objective of the thesis is to develop a dense warpage free BZT-0.5BCT wafer/substrate with suitable dielectric and piezoelectric property. The BZT-0.5BCT powder was synthesized by solid-state reaction route. BZT-0.5BCT tapes were fabricated by a non-aqueous tape casting method. Tape casting slurries of BZT-0.5BCT powder were prepared using methyl ethyl ketone-ethanol (MEK-EtOH) (solvent), phosphate ester / polyvinyl butyral (PVB) (dispersant), PVB (binder), polyethylene glycol (PEG) and butyl benzyl phathalate (BBP) (plasticizer). The optimum amount of dispersant was determined from the minimum in slurry viscosity and sedimentation height. The role of the two dispersants (phosphate ester and PVB) in making stable slurry of BZT-0.5BCT powder vis-a-vis the final properties of the fired wafers was studied. It was confirmed that 1 wt.% phosphate ester is sufficient for effective dispersion of BZT-0.5BCT to get stable slurry and the amount was 0.5 wt.% when PVB was used as dispersant in place of phosphate ester. The role of the binder (PVB) on the fabrication of wafer was also studied. Variation of PVB content shows that at least 3wt% PVB required to get the workable green tape. Up to 3.5 wt% PVB (binder) addition, solid loading can be maintained at 65%. Improved dielectric (εr =1750 at 1 kHz), ferroelectric (Pr = 6.3 µC/cm2), and piezoelectric property (d33 =174 pC/N) were observed for wafers made without phosphate ester

Filmes espessos de PZT para dispositivos electrónicos embutidos

Mestrado em Engenharia Cerâmica e do VidroPós de titanato zirconato de chumbo, com um tamanho de partícula de aproximadamente 300 nm, foram usados como material base para a deposição electroforética (EPD) de filmes espessos de PZT em substratos flexíveis de cobre. Foram preparadas, modificadas e aperfeiçoadas várias suspensões a fim de optimizar a etapa de deposição. Para diminuir a temperatura de sinterização dos filmes espessos, de forma a tornar a sua utilização compatível com o uso de substratos de cobre, recorreu-se à utilização de diferentes aditivos de sinterização, nomeadamente um vidro composto por SiO2, PbO, Al2O3, B2O3 e uma mistura de dois óxidos (B2O3 e PbO). Foram então depositados por EPD filmes de PZT sobre folhas de cobre em presença destes aditivos de sinterização; primeiramente com a adição de 5, 10 e 20 % em peso de vidro e, posteriormente, com a adição de 1 e 3 % em peso de uma mistura de diferentes proporções dos óxidos B2O3 e PbO (90/10, 80/20 e 50/50) e os filmes foram sinterizados a diferentes temperaturas, entre 800ºC e 900ºC e em atmosfera de baixa pressão parcial de oxigénio (pO2) (~ 5x10-5 e 8x10-7 atm). Verificou-se que a deposição em presença de pós de vidro origina filmes não uniformes, com superfícies irregulares e microestruturas porosas, o que se deve à dificuldade em obter suspensões desfloculadas e estáveis. A resposta dieléctrica dos vários filmes espessos de PZT sobre cobre foi analisada em função da frequência à temperatura ambiente. Verificou-se que a presença dos óxidos aditivos de sinterização melhorou a densificação dos filmes. A adição da mistura de 3 % em peso de 50%B2O3 + 50%PbO originou a melhor resposta dieléctrica de filmes sinterizados a 800 ºC e 850ºC (permitividade de ~1195 e perda dieléctrica de~0,02). Os resultados obtidos foram comparados com os da adição de uma mistura de V2O3 e PbO, previamente reportados. Foi então demonstrado que os filmes espessos de PZT aditivados com misturas de B2O3 e PbO e fabricados por deposição electroforética em substratos de cobre flexíveis são passíveis de serem usados como condensadores embutidos em circuitos da microelectrónica. ABSTRACT: Powders of lead zirconate titanate with a particle size of about 300 nm, were used as base material for the electrophoretic deposition (EPD) of PZT thick films on flexible copper substrates. With these powders, several suspensions were prepared, modified and improved in order to optimize the deposition step. To lower the sintering temperature of thick films to make its employment consistent with the use of copper substrates, different sintering additives, including a glass comprising of SiO2, PbO, Al2O3, and B2O3 and a mixture of two oxides (PbO and B2O3) were studied. Films were then deposited by EPD of PZT films on copper sheets in the presence of sintering additives, first with the addition of 5, 10 and 20% by weight of glass and, later, with the addition of 1 and 3% by weight of a mixture of PbO and B2O3 (90/10, 80/20 and 50/50) and the films were sintered at different temperatures between 800 º C and 900 º C in an atmosphere of low oxygen partial pressure (pO2) (~ 5x10-5 and 8x10-7 atm). It was found that the deposition in the presence of glass powder causes non-uniform films with rough surfaces and porous microstructures, which is due to the difficulty in obtaining deflocculated and stable suspensions. The dielectric response of the various PZT thick films on copper was examined as a function of frequency at room temperature. It was found that the presence of oxide sintering additives improved the densification of the films. The addition of mixing 3wt% of 50% B2O3 + 50% PbO led to an optimized dielectric response for the films sintered at 800 º C and 850 º C (permittivity ~1195 and losses ~0.02). The results were compared with PZT films prepared with the addition of a mixture of PbO and V2O3, previously reported. In conclusion, PZT thick films manufactured by EPD on copper flexible substrates and sintered in the presence of PbO and B2O3 (as sintering aid mixtures) can be used as embedded capacitors in microelectronic circuits

Fundamentals, advances and perspectives of piezocatalysis: A marriage of solid-state physics and catalytic chemistry

Piezocatalysis, an evolving catalytic technology built on the piezoelectric properties of catalysts, breaks down the barrier between mechanical energy and chemical energy. The potential difference that arises from the mechanical deformation of a piezoelectric material is commonly termed ‘piezopotential’. Piezopotential has been demonstrated to facilitate the manipulation of band structure and/or charge carrier separation. Despite significant efforts to design materials and understand the mechanism of piezoelectrically enhanced chemistry through semiconductor physics, there remains an opportunity to review the relationships between catalytic performance and piezo/ferroelectric properties. Herein, we provide a comprehensive summary of the catalytic mechanisms and correlated piezo/ferroelectric physical mechanism in the field of piezocatalysis. A fundamental understanding of piezo/ferroelectric structural design based on solid-state physics can be used to shed light on the future development of piezocatalysis. In addition, the types of piezoelectric materials, the design strategies for catalysis efficiency enhancement, and the up-to-date applications in environment remediation, renewable energy conversion, biomedicine and biotechnology are discussed. Finally, future perspectives for designing and developing highly active piezocatalysts using the guidelines of physicochemical relationships are proposed

Die polaren Nanoregionen in Na1/2Bi1/2TiO3–BaTiO3 und ihre Dynamik: Eine Untersuchung mittels Neutronenstreuung

Diese Arbeit beschäftigt sich mit der atomaren Struktur und Dynamik des bleifreien Relaxor-Ferroelektrikums 0,964Na1/2Bi1/2TiO3–0,036BaTiO3 (NBT-3,6BT). Ein besonderer Fokus liegt dabei auf den Verkippungen der Sauerstoffoktaeder, die eng mit den polaren Nanoregionen zusammenhängen. Zunächst wird die Temperaturabhängigkeit der Oktaederverkippungsordnung mithilfe elastisch diffuser Neutronenstreuung an einem NBT-3,6BT-Einkristall untersucht. Um die Volumenanteile der verschiedenen Oktaederverkippungssysteme zu bestimmen, wird die Intensität der zugehörigen Überstrukturreflexe herangezogen. Die Phasenanteile der rhomboedrischen, tetragonalen und kubischen Komponenten hängen stark von der Temperatur ab: Nahe bei Raumtemperatur dominiert die rhomboedrische Phase, der Phasenanteil nimmt jedoch mit zunehmender Temperatur ab. Die tetragonale Phase dominiert im mittleren Temperaturbereich bis etwa 700 K. Da die Abnahme des tetragonalen Phasenanteils bei hoher Temperatur nicht sehr ausgeprägt ist, enthält die makroskopisch kubische Phase 200 K über dem Phasenübergang von tetragonal zu kubisch immer noch über 30 % der tetragonalen Phase. Weiterhin werden die Korrelationslängen der rhomboedrischen und tetragonalen Domänen aus den Profilen der Überstrukturreflexe ermittelt. Hierfür ist es notwendig, unterhalb von 480 K zwei Komponenten der rhomboedrischen Überstrukturreflexe in das Verfeinerungsmodell einzubeziehen, sodass sich zwei Korrelationslängen auf unterschiedlichen Längenskalen ergeben. Die Korrelationslängen der rhomboedrischen Domänen liegen bei 310 K über 10 Å bzw. 100 Å und nehmen mit zunehmender Temperatur kontinuierlich ab. Die Größe der tetragonalen Domänen ändert sich nur geringfügig zwischen 6 Å und 15 Å. Sie bleibt durchgehend kleiner als die der rhomboedrischen Domänen. Bemerkenswert ist, dass die Korrelationslänge der tetragonalen Domänen dieselbe Temperaturabhängigkeit zeigt wie der tetragonale Phasenanteil. Aus diesen Ergebnissen folgt, dass in eine rhomboedrische Matrix eingebettete, tetragonale Plättchen bei Raumtemperatur ein wesentliches Merkmal der Mikrostruktur sind. Diese tetragonalen Plättchen werden durch die lokale A-Kationenordnung chemisch festgehalten und sind häufig von einer kubischen Übergangsphase umgeben. Die Dicke der tetragonalen Plättchen ändert sich mit der Temperatur. Die Dicke der kubischen Zwischenlagen nimmt oberhalb des makroskopischen Phasenübergangs von rhomboedrisch zu tetragonal zu und führt zum Zusammenwachsen der kubischen Regionen bei hoher Temperatur, wenn die kubische Phase die Hauptkomponente der Matrix ist. Darüber hinaus findet sich eine klare Korrelation zwischen der quadratischen Dicke der tetragonalen Plättchen und der dielektrischen Permittivität. Diese Korrelation wird als Hinweis auf eine erhöhte Polarisierbarkeit des gedehnten und verzerrten Gitters im Zentrum der tetragonalen Plättchen interpretiert. Aufgrund des Zusammenhangs zwischen Verkippungsordnung und A-Kationenordnung könnte dies ein Ansatzpunkt sein, um die dielektrischen Eigenschaften von Na1/2Bi1/2TiO3–BaTiO3 über die chemische Ordnung gezielt einzustellen. Die lokale Dynamik von NBT-3,6BT steht im Mittelpunkt des zweiten Teils der Studie. Um sie näher zu beleuchten, werden Messungen der quasielastischen Neutronenstreuung (QENS) an demselben Einkristall durchgeführt. Die Daten werden anschließend zusammen mit Ab-initio-Molekulardynamik-Simulationen von reinem Na1/2Bi1/2TiO3 (NBT) mit 001- und 111-Kationenordnung ausgewertet. Der quasielastische Anteil der Neutronenstreudaten wird mit einer Linearkombination von berechneten Spektren reproduziert. Die Temperaturskala muss dafür hauptsächlich aufgrund des starken Einflusses der Bariumdotierung angepasst werden. Das 001-geordnete NBT wird aufgrund der bevorzugten c+-Verkippung als Modellsystem für die tetragonalen Plättchen in NBT-3,6BT herangezogen. Analog dazu wird 111-geordnetes NBT, das a–a–a–-Verkippungen bevorzugt, als Modellsystem für die rhomboedrische Matrix verwendet. Für die Reproduktion der gemessenen QENS-Spektren ist ein bemerkenswert hoher Anteil von 001-geordnetem NBT erforderlich. Dies zeigt, dass die Relaxationsdynamik in NBT-3,6BT in den tetragonalen Plättchen konzentriert ist. Die genauere Analyse der Ab-initio-Molekulardynamik-Trajektorien bestätigt eine Korrelation der Bismut- und Sauerstoffdynamik. Als Ordnungsparameter für gleichphasige und gegenphasige Verkippungen werden die Strukturfaktoren der Überstrukturreflexe 1/2(310) und 1/2(311) herangezogen. Mithilfe dieser Ordnungsparameter werden die verschiedenen Abschnitte charakterisiert, die innerhalb der Ab-initio-Molekulardynamik-Simulationen beobachtet werden. Dabei werden grundlegende Unterschiede zwischen quasistabilen und chaotischen Abschnitten aufgezeigt. Chaotische Abschnitte auf der Zeitskala mehrerer Pikosekunden, während derer sich die lokale Verkippungsordnung ständig ändert, liefern den größten Beitrag zur quasielastischen Intensität. Sie werden als angeregter Zustand der tetragonalen Plättchen interpretiert, deren Relaxation zurück in einen quasistabilen Zustand die Frequenzabhängigkeit der dielektrischen Eigenschaften von NBT-3,6BT im Bereich von 100 GHz bis einigen Terahertz verursacht. Das paraelektrische Verhalten von NBT-3,6BT bei Temperaturen oberhalb von etwa 540 K ergibt sich dann aus der Abwesenheit von quasistabilen Abschnitten, die bei niedrigeren Temperaturen den Zerfall der induzierten Polarisation verhindern. Somit führt auch die Untersuchung der atomaren Dynamik von NBT-3,6BT zu dem Ergebnis, dass die Relaxoreigenschaften von den tetragonalen Plättchen ausgehen