Dissertations / Theses on the topic 'Piezoelectric ceramics'

This research covers the fabrication of piezoelectric ceramics using a sol gel method. Commercial high temperature transducers are typically fabricated by a milled oxide method. The sol gel method presented here produced purer samples that can be prepared at lower temperatures than conventional milled oxide preparations. The performance of the samples as piezoelectric transducers was also investigated, with the samples produced by sol gel method exceeding the piezoelectric response of the commercial samples.

The foundations of this project lay in the authors research into the xBiFeO3-(1-x)(K0.5Bi0.5)TiO3 ceramic system. A broad pseudocubic region was identified where x = 0.4-0.3, these compositions produced large electric-field induced strains (>0.3%) due to the presence of polar nanoregions that are easily switched by an applied electric field, however, these return to a random order upon removal of the field. Positive-up negative-down (PUND) showed that ferroelectric switching was reduced in the pseudocubic region and synchrotron studies with an applied electric-field in-situ demonstrated predominantly reversible domain switching. Solid-solutions based upon the (1-x-y)BiFeO3-x(K0.5Bi0.5)TiO3-yPbTiO3 ternary system have been fabricated by conventional mixed oxide processing, this system is the primary focus of this thesis. Structural analysis using XRD established that long-range crystallographic order was present above a critical PbTiO3 concentration, in addition a broad mixed symmetry region was identified comprised of tetragonal and rhombohedral symmetries. The ferroelectric Curie temperature was between 410-590 ºC. Conventional ferroelectric and piezoelectric ordering was observed with the use of strain and polarization-field measurements. Rayleigh analysis was used to quantify the intrinsic and extrinsic contributions, a critical c/a ratio was identified at 1.045 with domain switching limited above this. Synchrotron x-rays with ex-situ electric-fields allowed for a more detailed structural analysis, selected compositions demonstrated significant phase changing behaviour. The room temperature tetragonal c/a ratio across the mixed symmetry region, Curie temperature, and piezoelectric d33 were found to correlate strongly with the PbTiO3 concentration in a number of compositions. This work demonstrates a number of important results that have wider implications. Ternary and pseudo-quaternary systems have recently been subject to large amounts of research as many of the possible binary systems have been exhausted. This has led to a raft of materials with reported high electric-field induced strains, these are often electrostrictive or have limited operating temperatures. The partial substitution of PbTiO3 promotes long-range non-centrosymmetric order, which leads to increased piezoelectric activity and TC.

Thesis Presented for the Degree of Magister Technologiae in the Department of Electrical Engineering Cape Peninsula University of Technology 2006
Because of the nature of piezoelectric ceramics and the physical construction pf high power piezoelectric transducers, such devices are inherently non-linear and become unpredictable when driven at high power. To drive an ultrasonic transducer or an array thereof efficiently, specific resonant points are used. These poin~s are characterised by the devices' mechanical modes of oscillation. At high electrical power levels, the resonance points of PZT transducers vary. The movement of the resonances points in the frequency domain, coupled with the transducers high Q, is severe enough to seriously hamper the devices' efficiency. The problem is specifically apparent when multiple transducer arrays are driven at power. The electrical fluctuations and interactions of the characteristics of separate transducers cause arrays to be driven efficiently at a single resonance point. To efficiently drive an array of PZT transducers it is necessary to employ a .suitable technique. Although several methods exist in the literature, each is designed for a specific configuration of transducers and dedicated matching circuitry. The fundamental flaw in most methods is that they are conceived with the assumption all PZT transducers are identical and can be driven as such. Inherent nonlinearities caused by poling and construction methods, result in each transducer to be slightly different causing a superposition of resonance frequencies for each transducer array. Existing methods cannot be used to efficiently drive generic transducer arrays and a novel approach has been adopted to accommodate transducer nonlinearities. This novel approach can be described as a culmination of two driving techniques and has been named, Swept Frequency Dwelling (SFD). This thesis examines five different driving techniques and quantifies their effectiveness by means of experimental evaluation proficiencies. The driving techniques are grouped into two categories - straight driving techniques and frequency sweeping techniques - which are compared and evaluated. In conclusion, a novel method for driving ultrasonic transducer arrays was established with the aim of eliminating some detrimental effects of other driving techniques, while exploiting some of their positive attributes and was found to be effective.

Thesis (M.S.)--University of Akron, Dept. of Mechanical Engineering, 2009.
"May, 2009." Title from electronic thesis title page (viewed 8/2/2009) Advisor, Celal Batur; Co-advisor, Ali Sayir; Committee member, Jiang Zhe; Department Chair, Celal Batur; Dean of the College, George K. Haritos; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.

Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2003.
Includes bibliographical references (leaves 132-137). Also available in electronic version. Access restricted to campus users.

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.

This PhD project is focused on three lead-free ferroelectric solid solutions, which are specifically Na0.5Bi0.5TiO3-KNbO3(NBT-KN), Na0.5Bi0.5TiO3-NaNbO3(NBT-NN) and Na0.5Bi0.5TiO3-BaTiO3(NBT-BT), to evaluate the effects of composition, electric field and temperature on structural and electrical properties. Novel observations of both reversible and irreversible electric field-induced phase switching were made in both NBT-KN and NBT-NN ceramics. The NBT-KN solid solution is the primary focus of this thesis. All compositions were observed to be cubic in the as-sintered, unpoled state. However, a well-defined ferroelectric hysteresis P-E loop was obtained for compositions with low KN contents, indicating that an irreversible phase transition from a weak-polar relaxor ferroelectric (RF) to a long-range ordered metastable ferroelectric (FE) state had occurred during the measurement procedure. Both the unpoled and poled ceramic powders were examined using high resolution synchrotron XRD. For the poled state, a rhombohedral R3c structure was identified for compositions with low KN content, confirming the occurrence of the irreversible electric field-induced structural transformation from cubic to rhombohedral. In contrast, a cubic structure was retained for high KN contents, giving rise to reversible phase switching evidenced by constricted P-E hysteresis loops. Similar behaviour was observed for NBT-NN system. An 'in-situ' electric field poling experiment was conducted using high energy synchrotron XRD. In certain NBT-KN compositions the structural transformation, from cubic to mixed phase cubic+rhombohedral and finally single phase rhombohedral, occurred progressively with increasing cycles of a bipolar electric field. Similar behaviour was observed for NBT-NN compositions having low NN contents. Furthermore, the distributions of domain orientation and lattice strain over a range of orientations relative to the poling direction were determined for NBT-KN, NBT-NN and NBT-BT ceramics exhibiting the rhombohedral phase. By combining the structural information with the results of dielectric and ferroelectric measurements, a phase diagram was constructed to illustrate the influence of temperature and composition on the stability of the metastable ferroelectric and relaxor ferroelectric states for the NBT-KN system. Furthermore, the phase transition temperatures obtained from dielectric measurements were correlated with the ferroelectric and thermal depolarisation characteristics for each of the NBT-KN, NBT-NN and NBT-BT systems.

The incorporation of active piezoelectric elements and fluidic components into micro-electromechanical systems (MEMS) is of great interest for the development of sensors, actuators, and integrated systems used in microfluidics. Low temperature cofired ceramics (LTCC), widely used as electronic packaging materials, offer the possibility of manufacturing highly integrated microfluidic systems with complex 3-D features and various co-firable functional materials in a multilayer module. It would be desirable to integrate high performance lead zirconate titanate (PZT) based ceramics into LTCC-based MEMS using modern thick film and 3-D packaging technologies. The challenges for fabricating functional LTCC/PZT devices are: 1) formulating piezoelectric compositions which have similar sintering conditions to LTCC materials; 2) reducing elemental inter-diffusion between the LTCC package and PZT materials in co-firing process; and 3) developing active piezoelectric layers with desirable electric properties. The goal of present work was to develop low temperature fired PZT-based materials and compatible processing methods which enable integration of piezoelectric elements with LTCC materials and production of high performance integrated multilayer devices for microfluidics. First, the low temperature sintering behavior of piezoelectric ceramics in the solid solution of Pb(Zr0.53,Ti0.47)O3-Sr(K0.25, Nb0.75)O3 (PZT-SKN) with sintering aids has been investigated. 1 wt% LiBiO2 + 1 wt% CuO fluxed PZT-SKN ceramics sintered at 900oC for 1 h exhibited desirable piezoelectric and dielectric properties with a reduction of sintering temperature by 350oC. Next, the fluxed PZT-SKN tapes were successfully laminated and co-fired with LTCC materials to build the hybrid multilayer structures. HL2000/PZT-SKN multilayer ceramics co-fired at 900oC for 0.5 h exhibited the optimal properties with high field d33 piezoelectric coefficient of 356 pm/V. A potential application of the developed LTCC/PZT-SKN multilayer ceramics as a microbalance was demonstrated. The final research focus was the fabrication of an HL2000/PZT-SKN multilayer piezoelectric micropump and the characterization of pumping performance. The measured maximum flow rate and backpressure were 450 μl/min and 1.4 kPa respectively. Use of different microchannel geometries has been studied to improve the pumping performance. It is believed that the high performance multilayer piezoelectric devices implemented in this work will enable the development of highly integrated LTCC-based microfluidic systems for many future applications.

Mestrado em Engenharia de Materiais
This work is about lead-free ceramic materials intended for electromechanical applications and candidates to replace lead-based electroceramics. One of the most widely used piezoelectric ceramics is lead zirconate titanate (PZT). However, it contains more than 60% of lead and it is toxic for humans and environment. In 2003, a directive from European Union has prohibited the use of potentially hazardous elements as lead. Due to the lack of competitive materials for PZT replacement an exception was created until a competitive alternative be found. Potassium and sodium niobate due to its high Curie temperature and moderate piezoelectric properties is currently one of the most promising lead-free materials for PZT substitution. However, its effective industrial adoption requires, among others, optimization of its properties. In this context, in this work we initially studied the effect of dopants, texturing and sintering temperature of KNN ceramics. For this purpose KNN ceramics doped with i) 1.5 mol% CuO + 2.0 mol% Li2O, ii) 1.5 mol% CuO + 4.0 mol% Li2O and iii) 1.5 mol% CuO + 0.5 mol% MnO using different sintering temperatures (1050, 1065 and 1080 °C) were prepared. In addition in order to maximize the preferential crystallographic orientation of the ceramic KNN (texturing), in this case in the direction (h00), KNN single crystals were produced. These crystals were used as seeds in the texturing process KNN ceramics. It was found that the composition doped with copper and manganese was the only single phase one of the studied compositions. Dense (> 95%) ceramics, textured and non-textured, and with a high Lotgering factor among the studied compositions (≈ 20%) were prepared. The dependence of the dielectric properties of the Lotgering factor was demonstrated. In the attempt to optimize the Lotgering factor to top up the piezoelectric properties, the effect of the quantity of added crystals, heating and cooling rate and duration of sintering cycle were studied for the composition doped with copper and manganese. To this end, KNN textured ceramics and doped with 1.5 mol% of CuO and 0.5 mol% MnO, using 2.5, 5.0 and 10.0 wt% of single crystals were processed. For the same composition the heating rate of 2 °C/min and 20 °C/min and sintering level between 4 and 24 h was varied. Dense single phase KNN ceramics with an increase in the Lotgering factor from ≈20% to ≈38% for KNN ceramics doped with 1.5 mol% of copper and 0.5 mol% of manganese, textured with 5 wt% crystals and sintered at 1065 °C for 24 h with a heating rate/cooling of 10 °C/min have been achieved. These ceramics exhibit a relative permittivity at room temperature ≈ 300 for a Curie temperature value which remained high (TC ≈ 400 °C). The piezoelectric coefficient increased (d33 = 65 pC/N) with increased texturing. Despite the value of the piezoelectric coefficient achieved is still modest, the obtained piezoelectric voltage constant revealed values (g33 = 23.9 * 10-3 Vm/N) comparable to the values reported for certain compositions of commercial PZT, showing clearly competitive opportunities in applications (such as piezoelectric sensors) for KNN ceramics. The results of this study definitely contribute to the knowledge in the field of lead-free piezoelectric materials.
Este trabalho é acerca de materiais cerâmicos isentos de chumbo destinados a aplicações electromecânicas e candidatos à substituição de electrocerâmicos à base de chumbo. O titanato zirconato de chumbo (PZT) é o cerâmico piezoeléctrico mais utilizado em todo o mundo. No entanto, contém mais de 60 wt% de chumbo que é um elemento tóxico para os seres humanos e para o ambiente. Em 2003, a União Europeia aprovou uma directiva proibindo e restringindo o uso de elementos potencialmente perigosos como o chumbo. Devido à inexistência de materiais aptos para a substituição do PZT, foi feita uma exceção até ser encontrado um material alternativo competitivo. O niobato de potássio e sódio (K0.5Na0.5NbO3, KNN), devido à sua elevada temperatura Curie e propriedades piezoeléctricas moderadas, é um dos materiais isentos de chumbo mais promissores para substituição do PZT. No entanto, a sua efetiva adopção industrial requer, entre outros aspectos, a optimização das suas propriedades. Neste contexto, estudou-se neste trabalho o efeito de dopantes, da temperatura de sinterização e da texturização em cerâmicos de KNN. Foram fabricados cerâmicos de KNN dopados com i) 1,5 mol% CuO + 2,0 mol% Li2O, ii) 1,5 mol%CuO + 4,0 mol% Li2O e iii) 1,5 mol% CuO + 0,5 mol% MnO e sinterizados a diferentes temperaturas (1050, 1065 e 1080 ºC). Complementarmente com o objectivo de maximizar a orientação cristalográfica preferencial dos cerâmicos de KNN (texturização), neste caso segundo a direcção (h00), foram produzidos monocristais de KNN. Estes cristais foram usados como sementes no processo de texturização de cerâmicos de KNN. Verificou-se que a composição dopada com cobre e manganês foi a única das composições estudadas que se apresentou monofásica. Foram conseguidos cerâmicos, texturizados e não texturizados, densos (> 95 %) e com factor de Lotgering mais elevado dentre as composições estudadas (≈ 20 %). Foi possível demonstrar a dependência das propriedades dieléctricas do factor de Lotgering. Na tentativa de optimizar o factor de Lotgering para majorar as propriedades piezoeléctricas, foi estudado, para a composição dopada com cobre e manganês, o efeito da quantidade de monocristais adicionada, da taxa de aquecimento e arrefecimento e da duração do patamar de sinterização. Para tal, foram processados cerâmicos de KNN texturizados e dopados com 1,5 mol% de CuO e 0,5 mol% MnO, usando 2,5 wt%, 5,0 wt% e 10,0 wt% de monocristais. Para a mesma composição foi variada a taxa de aquecimento entre 2 ºC/min e 20 ºC/min e o patamar de sinterização entre 4 e 24 h. Foram conseguidos cerâmicos densos e monofásicos e um incremento no factor de Lotgering de ≈20 % para ≈38 %, para cerâmicos de KNN dopados com 1.5 mol % de cobre e 0.5 mol % de manganês, texturizados com 5 wt% de monocristais e sinterizados a 1065 ºC por 24 h com uma taxa de aquecimento / arrefecimento de 10 ºC/min. Estes cerâmicos exibem uma permitividade relativa de ≈ 300 à temperatura ambiente, para um valor da temperatura de Curie que se manteve elevado (TC ≈ 400 ºC). O coeficiente piezoeléctrico aumentou (d33 = 65 pC/N) com o aumento de texturização. Apesar do valor do coeficiente piezoelétrico conseguido ser ainda modesto, a constante de voltagem piezoeléctrica destes cerâmicos revelou valores (g33 = 23.9*10-3 Vm/N) comparáveis com os valores apresentados por certas composições de PZT comercial, mostrando claramente oportunidades competitivas em aplicações (nomeadamente como sensores piezoeléctricos) de cerâmicos de KNN. Os resultados obtidos neste trabalho contribuem para o conhecimento na área dos materiais piezoeléctricos isentos de chumbo.

碩士
國立中央大學
光電科學研究所
92
Along with the invention of piezoelectric ceramic, there were many other small-sized but highly efficiency- transformed devices being researched and developed since then. In order to reduce the volume of power supplies and raise its efficiency simultaneously, researchers use piezoelectric transformers made by piezoelectric ceramic to serve their purpose. This thesis focuses in the piezoelectricity of piezoelectric ceramic, how to motivate a piezoelectric transformer, and how to use piezoelectric transformers to drive the backlight source.

A number of new lead-free electroceramics have been developed based on the known lead-free ferroelectric system Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3 (BNT-20BKT) at the morphotropic phase boundary by introducing small amounts of K0.5Na0.5NbO3-Bi0.5K0.5TiO3 (KNN-03BKT). With increasing KNN-03BKT content, the materials show a reduction in the ferroelectric and piezoelectric properties. At the same time, the achievable maximum electrostrain peaks at a KNN-03BKT concentration of 1 mol% with 0.46 % at 8 kV/mm. A matrix of 10 compositions surrounding the composition with the highest electrostrain at room temperature was created with 0, 1 and 2 % KNN-03BKT for BNT-19BKT, BNT-20BKT and BNT-21BKT as well as BNT-20BKT-0.5(KNN-03BKT). The large-strain temperature and frequency dependence of these compositions was investigated between room temperature and 200 °C and 50 mHz and 500 Hz. While 8 compositions show typical ferroelectric behaviour, BNT-20BKT-1(KNN-03BKT) and BNT-20BKT-2(KNN-03BKT) both show a high strain at room temperature but very low remanent polarisation and strain. They also both show lower frequency and temperature dependant variation in the large-field strain than the ferroelectric compositions.

Piezoelectric materials have shown large potential on hard tissue applications due to their ability to stimulate osteogeneses and osseointegration. Barium titanate (BT) is a well-known piezoelectric ceramic. This work reports the consequences of calcium acceptance in BT lattice without compromising the formation of piezoelectric tetragonal phase under physiological conditions. Analytical reagents CaCO3, BaCO3 and TiO2 were used to prepare, via solid state reaction, Ba(1-x)CaxTiO3 (BCT), 0 ≤ x ≤ 0.3 mixtures. Materials were sintered from 1150°C to 1450°C under air and N2 atmospheres. Composites were prepared from Ba(1-x)CaxTiO3 (0 ≤ x ≤ 0.15) and hydroxyapatite (HP) at 10/90 and 20/80 (HP/BCT wt%) proportions. Reagents and produced ceramics were characterized by DTA-TG, granulometry, X-ray diffraction, FTIR, Raman and SEM/EDS. Samples were polarized by corona poling at 110°C, 1 hour, tip potential -15kV and -2kV grid potential for subsequent bioactivity essays. The polarization was analysed by thermally stimulated depolarization currents. Calcium substitution up to 15 mol% deformed the known BaTiO3 lattice without compromising the tetragonal phase stability, maintaining Curie point between 123 °C and 125 °C. All materials tested were non cytotoxic. Corona poling was successfully done to BCT samples. Hydroxyapatite reacts with BCT while sintered at 1350 °C forming different phases, but materials original structures are partially maintained. Early stage bioactivity studies made after both polarized and unpolarized samples were immersed in SBF (simulated body fluid) for 7 days. Results from ICP-AES supported by SEM/EDS point to the materials enhanced ability while polarized to deposit calcium and phosphor ions on its surface.

碩士
南台科技大學
電子工程系
96
In this thesis,Pb(Zr,Ti)O3 and PbO was discussed for doping compositions characterization, the densities of low PbO-doping compositions increases with increasing of sintering temperature, and reach a maximum value nearly equally to 97.5% of theoretical value at 1200oC, then decrease with increasing of sintering temperature. But the densities of other high PbO doping compositions were nearly constant with the sintering temperature, but they are much lower than that of low PbO doping compositions. The PbO loss of high PbO doping compositions was much higher, and the loss percentage was increased with increasing of sintering temperature and PbO doping amount.