abstract: A piezoelectric transducer, comprised of electroded and active pad PZT layer atop a backing PZT layer and protected with an acoustic matching layer, and operating under a pulse-echo technique for longitudinal ultrasonic imaging, acts as both source and detector. Ultrasonic transducer stacks (modules), which had failed or passed during pulse-echo sensitivity testing, were received from Consortium X. With limited background information on these stacks, the central theme was to determine the origin(s) of failure via the use of thermal and physicochemical characterization techniques. The optical and scanning electron microscopy revealed that contact electrode layers are discontinuous in all samples, while delaminations between electrodes and pad layer were observed in failed samples. The X-ray diffraction data on the pad PZT revealed an overall c/a ratio of 1.022 ratio and morphotropic boundary composition, with significant variations of the Zr to Ti ratio within a sample and between samples. Electron probe microanalysis confirmed that the overall Zr to Ti ratio of the pad PZT was 52/48, and higher amounts of excess PbO in failed samples, whereas, inductively coupled plasma mass spectrometry revealed the presence of Mn, Al, and Sb (dopants) and presence of Cu (sintering aid) in in this hard (pad) PZT. Additionally, three exothermic peaks during thermal analysis was indicative of incomplete calcination of pad PZT. Moreover, transmission electron microscopy and scanning transmission electron microscopy revealed the presence of parylene at the Ag-pad PZT interface and within the pores of pad PZT (in failed samples subjected to electric fields). This further dilutes the electrical, mechanical, and electromechanical properties of the pad PZT, which in turn detrimentally influences the pulse echo sensitivity. / Dissertation/Thesis / Masters Thesis Materials Science and Engineering 2018

The dissertation consists of the following three sections: 1. Hydroxyapatite (HA) coatings. In this work, we deposited HA precursor films from weak basic electrolytic solution (pH= 8-9) via an electrochemical approach; the deposits were changed into crystallite coatings of hydroxyapatite by sintering at specific temperatures (600-800 ºC). The formed coatings were mainly characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). XRD patterns show well-defined peaks of HA when sintered under vacuum conditions. FTIR measurements indicate the existence of hydroxyl groups, which were confirmed by the characteristic intensity of the stretching and bending bands at ~3575 and ~630 cm-1, respectively. The SEM shows an adhesive, crack free morphology for the double-layer coating surface of the samples sintered in a vacuum furnace. 2. Silver/polymer/clay nanocomposites. Silver nanoparticles were prepared in layered clay mineral (montmorillonite)/polymer (PVP: poly (vinyl pyrrolidone)) suspension by an electrochemical approach. The silver particles formed in the bulk suspension were stabilized by the PVP and partially exfoliated clay platelets, which acted as protective colloids to prevent coagulation of silver nanoparticles together. The synthesized silver nanoparticles/montmorillonite/PVP composite was characterized and identified by XRD, SEM, and TEM (transmission electron microscopy) measurements. 3. Ce-doped lead zirconate titanate (PZT) thin films. In this study, we fabricated cerium-doped PZT films (molar ratio of Zr/Ti:: 0.5:0.5) via cathodic electrodeposition on the indium tin oxide ( ITO) coated glass substrate. In the preparation process, the PZT films were modified by adding a small amount of cerium dopants, which led to the formation of Ce-doped PZT films after sintering at high temperatures. The fabricated PZT films on the ITO coated glass substrate may be used as electro-optic devices in the industrial application.

No description available.

No description available.

Pb(Zr₀.₅₂Ti₀.₄₈)O₃ (PZT) thin films are of interest for their large dielectric permittivity, ferroelectric, and piezoelectric properties. The material has been widely studied for use in high frequency transducers, multi-layered capacitors, and ferroelectric random access memory. Copper foils are an inexpensive, flexible substrate with a low resistivity which makes them ideal for many transducer and capacitor applications. PZT thin films on copper foils were produced by RF sputtering and crystallized under reducing conditions. Causes and prevention of a cuprous oxide interlayer are discussed. The film structure was characterized by XRD, SEM, and AFM. The permittivity was low, but remanent polarization increased to as high as ~40 μC/cm² as film thickness and crystallization temperature increased. Residual stresses were measured by x-ray diffraction using the sin²ψ method. The relative permittivity of the PZT/Cu films was measured as a function of applied AC electric field. By performing a Rayleigh analysis on this data one can determine the relative contributions of the intrinsic, reversible, and irreversible components to the permittivity. The residual stress could be correlated to the reversible part of the permittivity. The first order reversal curves (FORCs), which characterize the ferroelectric switching, give indications of the defect state of the film. Cantilever energy harvesters were fabricated. Large electrodes were able to be evaporated onto the films after oxidizing pinholes and cracks on a hot plate. Devices were tested on a shaker table at < 100 Hz. A dynamic model based on Euler-Bernoulli beam equations was used to predict power output of the fabricated devices. The observed output was comparable to model predictions. Resonant frequency calculations were in line with observed first and second resonances at ~17 Hz and ~35 Hz which were also close to those predicted by the dynamic model. / Graduation date: 2013

No description available.

No description available.

Ferroelectric materials are characterized by a reversible spontaneous polarization in the absence of an electric field. The characteristic polarization response of a ferroelectric material to an applied electric field enables a binary state device in the form of a thin film ferroelectric capacitor that can be used to store digital information. This provides opportunities for the development of high speed, low cost and low power, nonvolatile memory devices. The development of commercial ferroelectric memory devices has however been hampered by (a) several reliability issues including fatigue, leakage current, aging, time dependent dielectric breakdown, retention and imprint and (b) processing problems including the development of a low temperature thin film deposition process and the development of a patterning technology. Lead zirconate titanate (PZT) is now widely considered as the most promising material for ferroelectric memory applications as a result of its excellent ferroelectric properties and wide operating temperature range. However, it is commonly found that metal electroded-PZT capacitors (e.g., Pt/PZT/Pt) show a loss of switchable polarization with cumulative switching cycles. This phenomenon is known as fatigue and is the one of the critical problems affecting the lifetime of ferroelectric memories. This research is primarily focused on the problem of fatigue. On the basis of a quantitative model, various guidelines to minimize the degradation problem have been derived. The model attributes fatigue to domain pinning by space charge that is caused by defect (e.g. oxygen vacancy) entrapment at various interface sites such as electrode-ferroelectric interface, domain boundaries and grain boundaries. Two different approaches to minimize the problem have been outlined : (a) control of the defect density and (b) control of the interface state. The control of interface state was achieved by replacing the metal electrodes with conducting oxide electrodes such as RuO₂. The oxide electrode/PZT capacitors were characterized for their diffusion barrier properties, perovskite phase formation, interface nature and ferroelectric properties. The results indicate that these oxide electroded PZT films are good candidates for nonvolatile memory applications. However, the leakage current levels at the operating voltages are far higher than the metal counterparts. Simultaneous minimization of fatigue and leakage current in PZT films was achieved by using multilayer metal/conducting oxide electrodes (e.g., Pt/RuO₂). The control of defect density was attained by (a) donor doping to compensate for the oxygen vacancies (e.g, Nb doping in PZT) and (b) utilizing ferroelectric materials that have a low intrinsic defect concentration. As a result of the latter approach, novel ferroelectric materials belonging to the layer-structure family of oxides have been identified as excellent candidates for fatigue free nonvolatile memory applications. Laser ablated SrBi₂(Ta_xNb_{1 - x})₂O₉ (0<x<1) films showed very good hysteresis characteristics (remnant polarization value of 11 µC/cm², coercive field of 60 kV/cm), no fatigue was observed up to 10⁹ switching cycles and very low leakage current densities. Furthermore, the formation and properties of these films were characterized. It was found grain size and orientation played a major role in determining the properties of these films. C-axis oriented films were found to exhibit almost no polarization. An additional objective of this research was to identify an etching technology (process integration issue) for patterning of the ferroelectric capacitors. The etching process should provide high etch rates, good etch anisotropy, high etch selectivity and minimal post etch residues. It has been shown that a reactive ion etch process with CCl₂F₂/O₂ as the etch gas mixture can meet these requirements. A detailed process study has been conducted to determine the mechanism of etching. / Ph. D.

The first chapter introduces the basic principles governing the phenomenon like ferroelectricity, piezoelectricity and pyroelectricity, which influences the material properties for its device applications. An effort is made to examine the present status of material issues, measurement techniques and applications pertaining to the lead based PZT type systems. This chapter also highlights the objectives and the scope of work. The second chapter deals with the various basic experimental techniques and principles adopted for the synthesis and characterizations of materials which include phase and quantitative analysis by X-ray diffraction, density measurements, microstructures by scanning electron microscopy, electrical properties such as dielectric permittivity, dielectric loss, and piezoelectricity by impedance analyzer and piezometer etc. The materials were synthesized via two step solid state reaction by adopting a low temperature calcinations route. Further, hot processing was employed for densification and better control of microstructure of the ceramics. In the third chapter PZT1-x –PZNx (x=0, 0.1, 0.2 & 0.3) compositions prepared by the single step low temperature calcination method have been described. It is seen that the pyrochlore free perovskite phase could be obtained up to x=0.2 compositions. The effect of additives like Li and Mn on the structure, sinterability, microstructure, density and dielectric properties has been investigated. The improvement in densification and ferroelectric properties were observed for Li addition favor tetragonal phase while Mn addition compositions were inclined to pseudocubic phase. Further, the addition of Mn led to the significant decrease in Tc than the parent compositions compared to Li added compositions. In the fourth chapter, the X-ray diffraction data on pbzrx Ti1-x O3 (PZT) for x=0.48 to 0.52 are presented. High resolution x-ray studies for composition x=0.5 show the MPB which consists of monoclinic Zr rich studies and tetragonal Ti rich phase at room temperature. The refined structural parameters for MPB compositions have been obtained using least square Rietveld refinement program, FULLPROF 2006. The evolutions of lattice parameters of the system were also studied with respect to the temperature. The phase transformation in the system has been analyzed by x-ray diffraction pattern and dielectric measurements. The monoclinic phase transforms to tetragonal phase at 270oC after which the tetragonal phase transforms to paraelectric cubic phase at 370DoC. Dielectric properties show signature of the phase transformation. Hence, it is concluded to pole the MPB samples below 270o C to gain the advantage of increased ease of polarization reorientation for monoclinic phase. The fifth chapter deals with the systematic structural investigation on PZT1-y-PNZy (PZT-PNZ) and PZT1-y-PMNy (PZT-PMN) systems. In this chapter, an effort has been made to determine quantitatively the MPB phase contents and variation in Zr/Ti ratio of PZT-PZN and PZT-PMN systems. High resolution XRD data has been used for quantitative phase analysis using FULLPROF 2006. The correlation between the width of MPB and grain size has also been discussed for these systems. It is found that the addition of PMN and PZN to PZT system shifts the MPB towards pbZrO3 (PZ). The MPB can be regained by tuning the Zr/Ti ratio in the system. Further, there exists an inverse relation between the grain size and coexistence region in the system. It is seen that the MPB range is from x=0.48 to 0.58 and x=0.44 to 0.58 for 10% and 20% PZN concentration respectively. Similar trend has been obtained for the PZT-PMN system. The MPB ranges from x=0.46 to 0.53 and x=0.42 to 0.50 for 10% and 20% PMN respectively. The broadening of coexistence width is attributed to the lower grain size of our samples synthesized by adopting low temperature calcinations route. The sixth chapter deals with the hot pressing technique employed (adopting low temperature calcinations) for the synthesis of various PZT-PMN compositions with an intention of obtaining highly dense piezoceramics with fine, homogeneous and uniform microstructure. It also describes the dielectric, pyroelecrtic and pi ezoelectric properties were enhanced by hot processing technique. Li and Mn addition further improved the properties of the system. The seventh chapter investigates various nominal compositions of PZT-(Li, Nb) compositions based on certain assumptions. The attempt was made to introduce Li at A site and B site of ABO3 perovskite lattice. The ball milled, calcined powders were densified at<1000oC using hot pressing technique to prevent Li and Pb loss. High density ceramics have been studied for structural, dielectric, piezoelectric and pyroelectric properties. Through the clear cut evidence for the identification of Li site in the PZT system could not be established but the system which were synthesized under the assumption that Li substitutes A-site of the perovskite, favored the tetragonal phase and led to the enhancement in the dielectric, pyroelectric and piezoelectric properties. Further, their transition temperature was higher compared to the compositions where Li was tried to substitute B-site, which makes them promising candidates for transducer applications. The key finding in this thesis has been carried out by the candidate as part of the ph. D. programme. She hopes that this would constitute a worthwhile contribution towards the understanding of the behavior of lead based perovskites and in tailoring the properties of these ceramics towards device applications by the introduction of suitable additives in the system.

Les principaux objectifs de cette thèse de doctorat ont été de réaliser la synthèse et la caractérisation structurale et dieléctrique des échantillons céramiques ferroélectriques appartenants au système Pb1-xRxZr0,40Ti0,60O3 avec R = Ba et La et x entre 0,00 à 0,50. Ce système a été choisi car il est un matériel ferroélectrique qui a des propriétés physiques intéressantes, comme haute constante diélectrique et piézo-électrique, ce qui les rend candidats potentiels pour des applications telles que les condensateurs à haute densité d'énergie et les actionneurs. Afin d'évaluer le comportement relaxor, les études ont été effectuées avec la variation de la composition, du type de dopage (par des atomes de la même ou différente valence – La ou Ba) et de la taille des particules de céramique, dès l'échelle micrométrique à l'échelle nanométrique. Les échantillons céramiques micrométriques ont été préparées par la méthode de réaction de l'état solide et la frittage dans un four électrique conventionnel. Les données fournies par la technique de diffraction des rayons X de cettes échantillons ont montré une transition de une phase tétragonal pour une phase cubique avec l'augmentation de la concentration de cations substituants. Ces changements ont été attribués à une diminution de distorsion dans le maille cristallographique en raison de l'apparition de défauts causés par l'incorporation de dopage. Les mesures électriques ont été obtenues par spectroscopie d'impédance et ont montré un comportement électrique relaxor à partir de compositions avec plus de 12% at. La et de 30% at. Ba pour les systèmes PLZT et PBZT, respectivement. Les mesures électriques de l'échantillon avec 12%, 13% et 14% at. La et 30% at. Ba présentent un comportement qui, selon la littérature, est liée à une transition de phase spontanée d'un comportement relaxor et au comportement d'un matérial ferroélectrique normal. La technique de diffraction des rayons X a également été utilisé pour surveiller le processus de transition de phase en fonction de la température pour échantillons PLZT et PBZT. Il est possible de voir le changement de structure tétragonal de groupe d'espace P4mm en structure cubique de groupe d'espace Pm-3m. En ce qui concerne la structure locale, nous avons effectué des mesures expérimentales avec la technique de spectroscopie d'absorption des rayons X dans le spectre XANES aux seuils d'absorption de différents éléments pour les échantillons PLZT et PBZT. Dans les cas de seuil d'absorption K du titane, l'intégration de La et Ba atomes de la structure du PZT entraîne une diminution dans le désordre local dans le octaèdre TiO6, vérifié par la réduction du déplacement statique de atome Ti au centre de l'octaèdre TiO6. Cette évolution est plus faible pour les échantillons que montrent le comportement relaxor. Les spectres d'absorption EXAFS au seuil LIII du plomb et seuil K du zirconium ont été effectués aussi et ces mesures indiquent que la structure locale autour des atomes de plomb ou de zirconium est également affectée par l'introduction des atomes de La et Ba dans la structure. Le comportement relaxor a été aussi étudié en fonction de la taille de grain dans une échelle nanométrique. Ainsi les échantillons de compostions PZT, PLZT11 et PBZT10 ont eté préparés en utilisant la méthode de synthèse chimique de polymères précurseurs et le processus de frittage par spark plasma. La caractérisation de ces échantillons par diffraction de rayons X montrent que les paramétres de maille réduisent en comparison avec les échantillons de même composition et taille de grain micrométrique. Pour l'échantillon de composition PLZT11, il est possible de constater le comportement relaxor par les mesures de la constante dieléctrique en fonction de la température. Les changements quand la taille de grain est dans une échelle nanométrique sont attribués à la limitation des frontières de grains, qui provoquent un systéme de tension, responsable de la diminuition des paramétres de maille, et provoquent l'apparition de domaines ferroélectriques nanométriques / The main objectives of this doctoral thesis were the synthesis and structural characterization of Pb1-xRxZr0.40Ti0.60O3 ferroelectric ceramic samples, with R = Ba and La and x between 0.00 to 0.50. This system was chosen because its interesting physical properties such as high dielectric and piezoelectric constant. These characteristics make it potential candidate for applications such as capacitors in high energy density and actuators. To evaluate the relaxor behavior, the studies were carried out with the change in the composition, type of doping (by atoms of the same or different valence – La or Ba) and the particle size of ceramics, from the micrometer to nanometer scale. Micrometric ceramic samples are prepared by the method of reaction of solid state and sintering in a conventional furnace. The characterization with X-ray diffraction technique of these samples showed a transition from tetragonal phase to a cubic phase with increase of the dopping cation concentration. These changes have been attributed to the appearance of defects caused by the incorporation of La or Ba cations. Electrical measurements were obtained by impedance spectroscopy and showed a electric relaxor behavior from compositions with more than 12 at. % of La and the 30 at. % of Ba for PLZT and PBZT systems, respectively. These measurements for the samples with 12 at. %, 13 at. % and 14 at. % of La and 30 at. % of Ba exhibit a behavior that, according to the literature, is related to a spontaneous phase transition from a relaxor behavior to a normal ferroelectric behsvior. The technique of X-ray diffraction also been used to monitor the phse transition phase as a function of the temperature for PLZT and PBZT samples. It is possible to note the change in a tetragonal structure with P4mm space group to a cubic structure with Pm-3m space group. Concerning the local structure, XANES spectra in the absorption edge of various elements in PLZT and PBZT samples were performed. In the cases of Ti K-edge absorption, the dopping of La and Ba atoms in the PZT structure leads to a decrease of the local disorder in the TiO6 octahedron and it is verified the reduction of static displacement of Ti atom in the center of the TiO6 octahedron. This displacement is lower for samples that show relaxor behavior. The EXAFS measurements in Pb LIII-edge and Zr K-edge were performed and also indicate that local structure around lead or zirconium atoms is also affected by the introduction of La and Ba atoms in the PZT structure. The relaxor behavior was also studied depending on the size of particle size in a nanometer scale. Thus samples PZT, PLZT11 and PBZT10 compositions were prepared using the synthesis method of precursor polymers and the process of sintering by spark plasma. Characterization of these samples by X-ray diffraction shows that the lattice parameters are reduced in comparison with samples of the same composition and micrometer particle size. For PLZT11 composition, it is possible to observe a relaxor behavior by measurement of the dielectric permittivity as a function of the temperature. These changes when the grain size is in a nanoscale are attributed to the grain boundaries, that are responsible for the decrease in the lattice parameters and the appearance of ferroelectric nanodomains