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1
Oates, William Sumner. "Fracture of Ferroelectric Materials." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4769.
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Ferroelectric materials continue to find increasing use in actuator, sensor and transducer design. Questions regarding lifetime and reliability remain a concern due to the inherent low fracture toughness and complex material behavior. The poling procedure required for use in actuator and sensing devices introduces anisotropy in elastic and dielectric coefficients as well as piezoelectric coupling between the mechanical and electrical fields. This introduces complex fracture behavior which necessitates advanced analytical techniques and fracture characterization.
In this dissertation, fracture mechanics of ferroelectric materials is evaluated by employing different analytical techniques and experimental methodology. The theoretical work has focused on linear piezoelectric coupling that accounts for the influence of anisotropy and heterogeneity on fracture. A new orthotropic rescaling technique is presented that explicitly solves the anisotropic linear elastic piezoelectric crack problem in terms of material coefficients. The effects of heterogeneities on electric field induced microfracture are analyzed by implementing a crack at the edge of a heterogeneous piezoelectric inclusion. A positive, flaw-localized driving force is realized when permeable crack face boundary conditions are considered.
The experimental portion of the work evaluates fracture behavior in the ferroelectric ceramic, lead zirconate titanate (PZT), and the ferroelectric relaxor single crystal PZN-4.5%PT. Relative humidity and electric boundary conditions are shown to have significant effects on crack kinetics in PZT. Fracture anisotropy in single crystal PZN-4.5%PT is characterized using the Single-Edge V-notch Beam (SEVNB) method and Vickers indentations. Scanning electron micrographs are used to determine the crack profile which leads to a prediction of crack tip toughness and local energy release rate. A weak cleavage plane is identified in the single crystal relaxor which contains a significantly lower toughness in comparison to the ferroelectric ceramic PZT.
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Rivollet, Benoit. "Constitutive models for ferroelectric materials." Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/16463.
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Buchacher, Till. "Polarisation dynamics in ferroelectric materials." Thesis, University of Surrey, 2017. http://epubs.surrey.ac.uk/841383/.
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Ferroelectric materials have established themselves as indispensable in key applications such as piezoelectric transducers and energy storage devices. While the use of ferroelectrics in these fields dates back more than 50 years, little progress has been made to extend applications of ferroelectrics into new fields. To a large extend the observed slow progress is not caused by a lack of potential applications, but to by the inherent complexity associated with a structural phase transition, combined with strong coupling of polarisation, strain and temperature, and the strong modification of the phenomena by material defects. This thesis takes a look at prospective applications in energy storage for pulse power applications, solid state cooling and non-volatile random access memory and identifies key issues that need to be resolved. The thesis delivers time-domain based approaches to determine ferroelectric switching behaviour of bulk materials and thin films down to sub-ns time scales. The approach permitted study of how information written to a ferroelectric memory decays as a result of multiple non-destructive read operations. Furthermore simultaneous direct measurements of temperature and ferroelectric switching established a direct link between the retarded switching phenomenon observed in ferroelectrics and temperature changes brought by the electrocaloric effect. By comparison with analytical models and numerical simulation a large localised temperature change on the scale of individual domains is postulated. It implies a much larger coupling between switching and local temperature than has been previously considered. In extension of the model the frequency dependence of polarisation fatigue under bipolar conditions is explained by the occurrence of large temperature gradients in the material.
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Song, Yicheng. "The behavior and properties of ferroelectric single crystals and ferroelectric nano-composites." Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/HKUTO/record/B3955806X.
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Song, Yicheng, and 宋亦誠. "The behavior and properties of ferroelectric single crystals and ferroelectric nano-composites." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B3955806X.
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Nonnenmann, Stephen Sommers Spanier Jonathan. "Integrated non-planar ferroelectric nanostructures /." Philadelphia, Pa. : Drexel University, 2010. http://hdl.handle.net/1860/3260.
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Wang, Jie. "Phase field simulations of ferroelectric materials /." View abstract or full-text, 2006. http://library.ust.hk/cgi/db/thesis.pl?MECH%202006%20WANGJ.
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Gough, Neil. "Smectic C materials for ferroelectric applications." Thesis, University of Hull, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.419091.
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Hilton, Andrew David. "TEM studies of relaxor ferroelectric materials." Thesis, University of Essex, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328755.
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Yang, Mingmin. "Photoelectric processes in ferroelectric/multiferroic materials." Thesis, University of Warwick, 2018. http://wrap.warwick.ac.uk/105580/.
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Photoferroelectrics, which is defined as the interaction of ferroelectric materials with light, has attracted renewed attention recently and emerged as a topic of both fundamental interest and technological importance. It not only provides potential applications in sensors and photovoltaic devices but also offers a fertile playground to gain insight into the physics of ferroelectricity. As a prominent example, the bulk photovoltaic effect manifested in the ferroelectric materials under illumination gives rise to an anomalous open-circuit photovoltage exceeding the bandgap as well as a light polarisation-dependent photocurrent, offering an alternative approach to boost the solar energy conversion efficiency. Although it has been established for decades, the field is still in its fancy and many fundamental issues remain to be resolved to fully exploit its potential. In the first part of this thesis, we focus on the photoelectric processes in the bulk photovoltaic effect of bismuth ferrite to unravel respectively the essential role of the sub-bandgap levels, its correlation with ferroelectric polarization and role of domain walls in conduction of photovoltaic current. Results demonstrate the sub-bandgap levels is at the electronic origin of the bulk photovoltaic effect in bismuth ferrite. The activity of the sub-bandgap levels in the photoelectric processes can be effectively utilized to tailor the ferroelectric photovoltaic performance. Also, contrary to the common intuition, we prove the independence of the bulk photovoltaic effect on the ferroelectric polarization. We also found that the ferroelectric domain walls can facilitate the conduction and collection of the photocurrent originated in the bulk photovoltaic effect despite its adverse effect on the photovoltage. Inspired by the abundant phenomena in the photoferroelectric field, we explored the light-induced reversible manipulation of the ferroelectric polarization in a deterministic way. This interesting issue is successfully addressed in this thesis by utilizing a combination of the bulk photovoltaic effect and a nanoscale electrode. The collection of photocurrent by an atomic force microscope tip generates a giant electric field locally, enabling ferroelectric switching. By tuning the direction of the photocurrent via either illumination areas or light polarization, the ferroelectric polarization can be reversibly controlled. At the last part of the thesis, we creatively generalised the bulk photovoltaic effect, which was originally constrained to the non-centrosymmetric materials, to a universal effect allowed in all the semiconductors irrespective of their symmetry by the mediation of the flexoelectric effect. This new photovoltaic effect, termed as flexo-photovoltaic effect, may offer a new mechanism to enhance solar cell efficiency. The research works studied in this thesis not only provide fundamental insights into the interactions of ferroelectrics with light but also largely expand the scope of photoferroelectrics into centrosymmetric materials.
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Makhort, Anatolii. "Tuning photovoltaic properties in ferroelectric materials." Thesis, Strasbourg, 2020. http://www.theses.fr/2020STRAE031.
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Les cellules photovoltaïques conventionnelles approchent leur limite fondamentale. Bien que les matériaux électriquement polaires offrent une solution alternative, la compréhension de leurs propriétés photovoltaïques, ainsi que la rareté des composés efficaces constituent un défi important. Cette thèse été consacrée à la recherche d'un composé photovoltaïque dit modèle et optimisation de sa performance. En conséquence, les propriétés photovoltaïques ont été découvertes dans le complexe PMN–xPT. Il est démontré l'existence d'une non-linéarité dans le photo-courant dans l'état de polarisation saturée qui peut également entraîner un effet de mémoire optique. Les études de l'influence de la température et de la déformation sur l'effet photovoltaïque ont été également menées. Les résultats globaux obtenus suggèrent fortement la nature hautement sensible et réglable des effets photovoltaïques et ouvrent les perspectives pour augmenter l'efficacité des cellules photovoltaïques et au-delàConventional solar cells are ultimately approaching their fundamental limit. Although electrically polar materials provide an alternative solution, understanding their photovoltaic properties, as well as a scarcity of efficient compounds constitute an important challenge. Therefore, this thesis was devoted to finding a model photovoltaic compound and optimization of its performance. As a result, the photovoltaic properties were discovered in the PMN–xPT complex. It was shown a nonlinearity in the photocurrent in the saturated polarization state that also results in optical memory effect. The stress and temperature-dependent studies of the photovoltaicity were performed as well. The overall obtained results strongly suggest the highly tunable nature of photovoltaic effects and open the prospect for additional degrees of freedom to increase ferroelectric-based photovoltaic cells efficiency and beyond
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Meng, Nan. "Processing, structure and ferroelectric properties of PVDF-based ferroelectric polymers." Thesis, Queen Mary, University of London, 2017. http://qmro.qmul.ac.uk/xmlui/handle/123456789/25910.
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Polyvinylidene fluoride (PVDF) and its copolymer with trifluoethylene (PVDF-TrFE) have been widely investigated. This is largely attributed to their ferroelectric properties, which are present in a limited number of polymers. In comparison with the more widely used ferroelectric ceramics, the ease of their fabrication makes them attractive in flexible electronic devices. Despite many advances in their application, we are still lacking a complete fundamental understanding of the relationship between their structure and the functional properties. The melt-extrusion of PVDF revealed that the α-phase is predominantly formed in films. The ferroelectric β-phase PVDF was obtained by high temperature drawing of the α-phase of as-extruded films. It was observed that a minimum draw ratio of 3 is required to generate the β-phase. Chain mobility is crucial to the formation of β-phase. Too high chain mobility when drawing at temperatures above 100 °C can only orientate the pre-existing α-crystals without making the chain conformation change to form the β-crystals. Furthermore, the comparison between the produced α- and β-PVDF films is summarized. The α-PVDF films crystallized into spherulites with random orientation, while β-PVDF films displayed fibriliar structure showing preferred orientation of the polymer chains along the drawing direction. The overall crystallinity obtained from DSC data hardly varied, however, the drawn β-PVDF films had a lower melting temperature, which was also confirmed from the dielectric temperature spectra. The drawn β-PVDF films showed higher dielectric constant and larger remnant polarization compared with the as-extruded α-PVDF films, which is mainly ascribed to their higher β-phase content and preferred orientation. Highly aligned PVDF-TrFE films were processed using a melt extrusion processing route. Crystalline structure and orientation were optimized by controlling the melt extrusion conditions. XRD patterns suggested that there was nearly perfect alignment of the c-axis (polymer chain direction) along the extrusion direction in the optimized as-extruded films. SEM analysis confirmed the morphology of the crystalline phase, showing edge-on lamellae stacked perpendicular to the extrusion direction. DSC data indicated high crystallinity and well-ordered ferroelectric structure of the extruded films. FTIR spectroscopy revealed strong intermolecular dipole-dipole interaction in the extruded films. Accordingly, the optimized as-extruded PVDF-TrFE films exhibited a coercive field of 24 kV/mm, half of the commonly reported values for bulk films (~ 50 kV/mm) and a remnant polarization of 0.078 C/m2 which further increased to 0.099 C/m2 after annealing. This value is close to the theoretical limit (0.102 C/m2) assuming perfect in-plane c-axis orientation and 100% crystallinity. The typical limitations of PVDF - low crystallinity and indirect ferroelectric β-phase crystallization - and PVDF-TrFE - higher materials and processing costs and a low Curie point - are tackled by a simple and industrially viable melt blending approach. Despite the immiscible nature of PVDF and PVDF-TrFE, strong interactions exist between the two polymers when co-melt processed, which substantially affect the morphology and texture of the blends as well as their dielectric and ferroelectric properties. Surprisingly, minor amounts of PVDF-TrFE led to a significant increase in the β-phase content and preferred orientation of PVDF, well beyond the rule-of-mixtures. Moreover, the blends exhibited maximum increases in the dielectric constant of 80% and 30%, respectively compared with pure PVDF and PVDF-TrFE. The ferroelectric remnant polarization increased from 0.040 to 0.077 C/m2, while the coercive field decreased from 75 to 32 kV/mm with increasing PVDF-TrFE from 0 to 40 wt. %. The enhancement of properties is explained by the strong interactions at the interfaces between PVDF and PVDF-TrFE, which also suppresses the Curie transition of PVDF-TrFE, providing a potentially increased working temperature range for blended films, which is important in applications like non-volatile energy storage devices, ferroelectric field-effect transistors and touch sensors. Ferroelectric composites, integrating dielectric ceramic fillers with mechanically flexible polymers, are promising materials for flexible electronic applications. Numerous research works have demonstrated enhanced dielectric and ferroelectric properties of composite materials. However, the mechanisms responsible for these enhancements are not completely understood. Herein, PVDF and BaTiO3 (BTO) were used to study the effect of dielectric filler on the crystallization, phase transformation and dielectric properties of PVDF. The crystallization of α-PVDF was not affected by the presence of BTO particles, but small amounts of BTO (< 3 vol. %) made PVDF crystallize into larger spherulites. This is linked to crystallization kinetic studies, which showed that BTO acted as a nucleation agent for large full ring banded spherulites when its content was less than 1 vol. %. Furthermore, solid state drawing in the presence of BTO particles promoted the formation of β-PVDF with more pronounced crystalline orientation at high drawing temperatures (120 °C). The dielectric and ferroelectric properties were enhanced with BTO filling. The 100 °C oriented drawn PVDF tape exhibited a dielectric permittivity of 14 (100 Hz) and remnant polarization of 0.080 C/m2 (10 Hz), which increased to 20 and 0.095 C/m2, respectively, after filling with 5 vol. % BTO; neither resulting in high dielectric loss tangent (~ 0.02) nor obvious current leakage. Moreover, the coercive field decreased from 80 to 50 kV/mm with increasing BTO content from 0 to 5 vol. %.
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Mieth, Oliver. "Low Voltage Electron Emission from Ferroelectric Materials." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-62190.
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Electron emission from ferroelectric materials is initiated by a variation of the spontaneous polarization. It is the main focus of this work to develop ferroelectric cathodes, which are characterized by a significantly decreased excitation voltage required to initiate the electron emission process. Particular attention is paid to the impact of the polarization on the emission process. Two materials are investigated. Firstly, relaxor ferroelectric lead magnesium niobate - lead titanate (PMN-PT) single crystals are chosen because of their low intrinsic coercive field. Electron emission current densities up to 5 · 10^(−5) A/cm² are achieved for excitation voltages of 160 V. A strong enhancement of the emission current is revealed for the onset of a complete polarization reversal. Secondly, lead zirconate titanate (PZT) thin films are investigated. A new method to prepare top electrodes with sub-micrometer sized, regularly patterned apertures is introduced and a stable electron emission signal is measured from these structures for switching voltages < 20 V. Furthermore, a detailed analysis of the polarization switching process in the PMN-PT samples is given, revealing a spatial rotation of the polarization vector into crystallographic easy axes, as well as the nucleation of reversed nano-domains. Both processes are initiated at field strengths well below the coercive field. The dynamics of the polarization reversal are correlated to the electron emission measurements, thus making it possible to optimize the efficiency of the investigated cathodesDie Ursache für Elektronenemission aus ferroelektrischen Materialien ist eine Veränderung des Zustandes der spontanen Polarisation. Gegenstand der vorliegenden Arbeit ist eine Verringerung der dafür nötigen Anregungsspannung, wobei besonderes Augenmerk auf die Rolle der ferroelektrischen Polarisation innerhalb des Emissionsprozesses gelegt wird. Es werden zwei verschiedene Materialien untersucht. Das Relaxor-Ferroelektrikum Bleimagnesiumniobat - Bleititanat (PMN-PT) wurde aufgrund seines geringen Koerzitivfeldes ausgewählt. Es konnten Emissionsstromdichten von bis zu 5·10^(−5) A/cm² bei einer Anregungsspannung von 160 V erreicht werden. Bei Einsetzen eines vollständigen Umschaltens der Polarisation wurde eine deutliche Verstärkung des Emissionsstromes festgestellt. Desweiteren werden Untersuchungen an Bleizirkoniumtitanat (PZT) Dünnfilmen gezeigt. Eine neue Methode, eine Elektrode mit periodisch angeordneten Aperturen im Submikrometerbereich zu präparieren, wird vorgestellt. Diese Strukturen liefern ein stabiles Emissionssignal für Anregungsspannungen < 20 V. Eine detailierte Analyse des Schaltverhaltens der Polarisation der PMN-PT Proben zeigt sowohl eine Rotation des Polarisationsvektors als auch eine Nukleation umgeschaltener Nanodomänen. Beide Prozesse starten bei Feldstärken unterhalb des Koerzitivfeldes. Die ermittelte Zeitabhängigkeit des Schaltprozesses erlaubt Rückschlüsse auf den Emissionsprozess und erlaubt es, die Effizienz der untersuchten Kathoden weiter zu optimieren
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Malbec, Aurélien. "Domain formation and evolution in ferroelectric materials." Thesis, Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/15905.
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Franzbach, Daniel Jason. "Field Induced Phase Transitions in Ferroelectric Materials." Phd thesis, tuprints, 2014. https://tuprints.ulb.tu-darmstadt.de/4134/1/Daniel%20Franzbach%20Field%20Induced%20Phase%20Transitions%20in%20Ferroelectric%20Materials.pdf.
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The focus of this dissertation lies in the theoretical description of electrical field- and mechanical stress-induced phase transitions and their influence on the material behavior of ferroelectric single crystals, polycrystals and composite materials. Phase transitions are interesting phenomena that lead to improved properties of the ferroelectric material.
The motivation for this work is presented in the first Chapter. Chapter 2 gives a short introduction on the basic formalism of electrostatics and continuum mechanics, which are the foundations of material models of ferroelectrics. In addition, some fundamentals of crystallography will be discussed to understand the atomistic reason of the ferroelectric effect. In the first part of Chapter 3, a two dimensional Landau type model is presented, which is used to study electrical field-induced tetragonal to orthorhombic phase transitions in arbitrary ferroelectric single crystal materials. The Landau energy landscape was varied to examine the influence of the switching energies and the polarization rotation path on the predicted phase transition field. In the second part, the model is expanded to three dimensions. Landau parameters from literature were used to predict the tetragonal to orthorhombic phase transition behavior of BaTiO3. Large signal measurements on single crystalline BaTiO3 were performed to verify the model and to compare the predictive capabilities of the various Landau potentials. In Chapter 4, the Landau model is further expanded to describe polycrystalline ferroelectrics like Pb(Zr,Ti)O3 under uniaxial compressive strain and electric field. In contrast to micro-mechanical models, the Landau energy model intrinsically considers tetragonal to rhombohedral phase transitions. These induced transitions provide a good explanation for the exceptional switching strain of rhombohedral Pb(Zr,Ti)O3 compositions close to the MPB.
Chapter 5 and 6 elucidate a different type of field-induced phase transition. Novel lead free materials, such as BNT-6BT-2KNN, show exceptional unipolar usable strain values that are larger than Pb(Zr,Ti)O3. Without any applied field these materials show nearly no remanent polarization and strain. Internal mechanisms prohibit the development of long-range interactions between the unit cells, so that the system decays in a disordered nano-domain state. Unfortunately, the fields that are required to induce a phase transition to a polar phase are too high for most applications. A composite structure with a chemical compatible ferroelectric material is used to decrease the required electric field. Two models are proposed to predict the dielectric behavior of a composite from the behavior of both components. In Chapter 5 the composite is replaced by a series configuration of two nonlinear hysteretic capacitors. The model is verified by comparing the results to experimental data from composite samples, and used to identify optimal material parameter combination for future materials. In the second model that is presented in Chapter 6, a two dimensional phase field implementation is expanded by a material model for the high strain material. In contrast to the previous case, this model allows one to study the influence of the microstructure on the composite effect. The model is then applied to test cases to demonstrate its capabilities.
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Jeon, Hyung Min. "Compact Leaky Wave Antenna Using Ferroelectric Materials." Wright State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=wright1358023409.
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Josefson, Carl Elof. "Evaluation of ferroelectric materials for memory applications." Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA232112.
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Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, June 1990.Thesis Advisor(s): Panholzer, R. Second Reader: Neighbours, J.R. "June 1990." Description based on signature page. DTIC Identifiers(s): Nonvolitile memories, ferroelectric materials. Author(s) subject terms: Ferrorelectric, nonvolatile memory, radiation hard. Includes bibliographical references (p. 80-86). Also available online.
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Chen, Wei. "Nonlinear constitutive behavior and fracture of ferroelectric materials and structures." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/18996.
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Abdollahi, Amir. "Phase-field modeling of fracture in ferroelectric materials." Doctoral thesis, Universitat Politècnica de Catalunya, 2012. http://hdl.handle.net/10803/285833.
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The unique electro-mechanical coupling properties of ferroelectrics make them ideal materials for use in micro-devices as sensors, actuators and transducers. Nevertheless, because of the intrinsic brittleness of ferroelectrics, the optimal design of the electro-mechanical devices is strongly dependent on the understanding of the fracture behavior in these materials. Fracture processes in ferroelectrics are notoriously complex, mostly due to the interactions between the crack tip stress and electric fields and the localized switching phenomena in this zone (formation and evolution of domains of different crystallographic variants). Phase-field models are particularly interesting for such a complex problem, since a single partial differential equation governing the phase-field accomplishes at once (1) the tracking of the interfaces in a smeared way (cracks, domain walls) and (2) the modeling of the interfacial phenomena such as domain-wall energies or crack face boundary conditions. Such a model has no difficulty for instance in describing the nucleation of domains and cracks or the branching and merging of cracks. Furthermore, the variational nature of these models makes the coupling of multiple physics (electrical and mechanical fields in this case) very natural.
The main contribution of this thesis is to propose a phase-field model for the coupled simulation of the microstructure formation and evolution, and the nucleation and propagation of cracks in single crystal ferroelectric materials. The model naturally couples two existing energetic phase-field approaches for brittle fracture and ferroelectric domain formation and evolution. The finite element implementation of the theory is described. Simulations show the interactions between the microstructure and the crack under mechanical and electro-mechanical loadings. Another objective of this thesis is to encode different crack face boundary conditions into the phase-field framework since these conditions strongly affect the fracture behavior of ferroelectrics. The smeared imposition of these conditions are discussed and the results are compared with that of sharp crack models to validate the proposed approaches. Simulations show the effects of different conditions, electro-mechanical loadings and media filling the crack gap on the crack propagation and the microstructure of the material. In a third step, the coupled model is modified by introducing a crack non-interpenetration condition in the variational approach to fracture accounting for the asymmetric behavior in tension and compression. The modified model makes it possible to explain anisotropic crack growth in ferroelectrics under Vickers indentation loading. This model is also employed for the fracture analysis of multilayer ferroelectric actuators, which shows the potential of the model for future application. The coupled phase-field model is also extended to polycrystals by introducing realistic polycrystalline microstructures in the model. Inter- and trans-granular crack propagation modes are observed in the simulations. Finally and for completeness, the phase-field theory is extended for the simulation of conducting cracks and some preliminary simulations are also performed in three dimensions. Salient features of the crack propagation phenomenon predicted by the simulations of this thesis are directly compared with experimental observations.Los materiales ferroeléctricos poseen únicas propiedades electro-mecánicas y por eso se utilizan para los micro-dispositivos como sensores, actuadores y transductores. No obstante, debido a la fragilidad intrínseca de los ferroeléctricos, el diseño óptimo de los dispositivos electro-mecánicos es altamente dependiente de la comprensión del comportamiento de fractura en estos materiales. Los procesos de fractura en ferroeléctricos son notoriamente complejos, sobre todo debido a las interacciones entre campos de tensión y eléctricos y los fenómenos localizados en zona de fractura (formación y evolución de los dominios de las diferentes variantes cristalográficas). Los modelos de campo de fase son particularmente útiles para un problema tan complejo, ya que una sola ecuación diferencial parcial que gobierna el campo de fase lleva a cabo a la vez (1) el seguimiento de las interfaces de una manera suave (grietas, paredes de dominio) y (2) la modelización de los fenómenos interfaciales como las energías de la pared de dominio o las condiciones de las caras de grieta. Tal modelo no tiene ninguna dificultad, por ejemplo en la descripción de la nucleación de los dominios y las grietas o la ramificación y la fusión de las grietas. Además, la naturaleza variacional de estos modelos facilita el acoplamiento de múltiples físicas (campos eléctricos y mecánicos en este caso). La principal aportación de esta tesis es la propuesta de un modelo campo de fase para la simulación de la formación y evolución de la microestructura y la nucleación y propagación de grietas en materiales ferroeléctricos. El modelo aúna dos modelos de campo de fase para la fractura frágil y para la formación de dominios ferroeléctricos. La aplicación de elementos finitos a la teoría es descrita. Las simulaciones muestran las interacciones entre la microestructura y la fractura del bajo cargas mecánicas y electro-mecánicas. Otro de los objetivos de esta tesis es la codificación de diferentes condiciones de contorno de grieta porque estas condiciones afectan en gran medida el comportamiento de la fractura de ferroeléctricos. La imposición de estas condiciones se discuten y se comparan con los resultados de modelos clasicos para validar los modelos propuestos. Las simulaciones muestran los efectos de diferentes condiciones, cargas electro-mecánicas y medios que llena el hueco de la grieta en la propagación de las fisuras y la microestructura del material. En un tercer paso, el modelo se modifica mediante la introducción de una condición que representa el comportamiento asimétrico en tensión y compresión. El modelo modificado hace posible explicar el crecimiento de la grieta anisotrópica en ferroeléctricos. Este modelo también se utiliza para el análisis de la fractura de los actuadores ferroeléctricos, lo que demuestra el potencial del modelo para su futura aplicación. El modelo se extiende también a policristales mediante la introducción de microestructuras policristalinas realistas en el modelo. Modos de fractura inter y trans-granulares de propagación se observan en las simulaciones. Por último y para completar, la teoría del campo de fase se extiende para la simulación de las grietas conductivas y algunas simulaciones preliminares también se realizan en tres dimensiones. Principales características del fenómeno de la propagación de la grieta predicho por las simulaciones de esta tesis se comparan directamente con las observaciones experimentales.
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Bhattacharya, Prodipta. "Solid state NMR studies of ferroelectric relaxor materials." Thesis, University of Warwick, 2005. http://wrap.warwick.ac.uk/66666/.
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Multi-nuclear solid state nuclear magnetic resonance has been used to investigate the local atomic structure of the relaxor ferroelectric materials, lead magnesium niobate titanate (PMN-PT) and sodium potassium bismuth titanate (NKBT). In addition to these two series of materials, numerous precursor and model niobate compounds have also been analysed in order to gain a insight into the structures and phases present in these materials. The PMN-PT series was investigated using 93Nb, 207Pb and 170 NMR techniques. A total of 14 PMN-PT samples, from pure PMN to PMN-90PT, were investigated in order to fully understand the transitions taking place over the entire compositional range. 9~b proved to be the most informative nucleus, owing to its high sensitivity to the changes occurring at the B-site of the perovskite structure. We discovered three distinct niobium environments. We then proposed a new randomsite random-layer model explaining the distribution of the cations among two different layers ß' and ß". The high level of correlation between the theoretical predictions and the experimental results suggests that there are actually two different ways that PMN-PT behaves, one for titanium concentrations less than 25% and the other for concentrations over 25%. This was also clearly visible in our PMN-PT spectra, as a sharp line present in titanium concentrations below 25%, that disappears in the concentrations above 25%. We have also tied in our results with the existing literature on PMN-PT to identify possible links to the dielectric response and phase transitions in the material. NKBT was investigated using both 23Na and 39K MAS NMR techniques. The 23Na data proved most informative and results were obtained at different fields and different spinning speeds. We were then able to extract calculated isotropic chemical shift values and quadrupolar parameters to understand the subtle changes taking place. The preliminary results hint that there are some interesting changes taking place around the morphotropic phase boundary in the material.
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Parsa, Nitin. "Non Linear Interaction of Microwaves with Ferroelectric Materials." University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1451999954.
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Yao, Jianjun. "Structural Investigations of Highly Strictive Materials." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/37669.
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Ferroelectric (piezoelectric) and ferromagnetic materials have extensively permeated in modern industry. (Na1/2Bi1/2)TiO3-BaTiO3 (NBT-x%BT) single crystals and K1/2Na1/2NbO3 (KNN) textured ceramics are top environment-friendly candidates which have potential to replace the commercial lead zirconate titanate or PZT. High magnetostrictive strain (up to 400 ppm) of Fe-xat.%Ga makes this alloys promising alternatives to existing magnetostrictive materials, which commonly either contain costly rare-earth elements or have undesirable mechanical properties for device applications. These systems have common characteristics: compositional/thermal/ electrical dependent structural heterogeneity and chemical disorder on sub-micron or nano scale, resulting in diverse local structures and different physical properties. In this work, I have investigated domain and local structures of NBT-x%BT crystals, KNN ceramics and Fe-xat.%Ga alloys under various conditions, mainly by scanning probe and electron transmission techniques.
In NBT-x%BT single crystals, polarized light, piezo-response force (PFM) and transmission electron (TEM) microscopies were used to study domain structures and oxygen octahedral tiltings. Hierarchical domain structures were found in NBT: a high-temperature tetragonal ferroelastic domain structure is elastically inherited into a lower temperature rhombohedral ferroelectric phase. Nanoscale domain engineering mechanism was found to still work in NBT-x%BT system and a modified phase diagram was proposed based on domain observations. An increased intensity of octahedral in-phase tilted reflections and a decrease in the anti-phase ones was observed, with increasing x as the morphotropic phase boundary (MPB) is approached. It was also found that Mn substituents favor the formation of long range ordered micro-sized ferroelectric domains and octahedral in-phase tilted regions near the MPB. Nano-size heterogeneous regions were observed within submicron domain structure, indicating that the nanoscale polarization dynamics are not confined by domain boundaries, and the high piezoelectricity of NBT-x%BT is due to a polarization dynamics with high sensitivity to electric field and a broadened relaxation time distribution.
In KNN textured ceramics, an aging effect was found to exist in the orthorhombic single phase field, not only in the orthorhombic and tetragonal two-phase field as previously reported. No variation of phase structure was revealed between before and after aging states. However, pronounced changes in domain morphology were observed by both PFM and TEM: more uniform and finer domain structures were then found with aging. These changes were even more pronounced after poling the aged state. A large number of sub-micron lamellar domains within micron-domains were observed: suggesting a domain origin for improved piezoelectric properties.
In Fe-xat.%Ga alloys, an underlying inhomogeneity from Ga atoms embedded into the α-Fe matrix was believed to be the origin of giant magneostrictive properties. I have systematically investigated the phase structure and nano-size heterogeneity of Fe-xat.%Ga alloys subjected to different thermal treatments using standard TEM and high resolution TEM for 10
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Whittle, Thomas Anthony. "A Structural Investigation of Perovskite and Tungsten Bronze Type Ferroic Materials." Thesis, The University of Sydney, 2015. http://hdl.handle.net/2123/14586.
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This thesis set out to investigate lead free ferroic materials with perovskite and tungsten bronze type structures, primarily focussing on the relationship between composition, temperature and crystal structure. A combination of diffraction techniques were employed to investigate the crystal structures. Additionally, other techniques including XANES, SEM, TGA, DSC and ferroic peroperty measurements were also employed to further illuminate these compounds. The first system investigated was the defect perovskite Sr0.8Ti0.6-yZryNb0.4O3, 0.0 ≤ y ≤ 0.6. It was found that neutron powder diffraction data were essential for determining the phase boundary composition. Second order compositional and temperature phase transitions were observed. Increasing the zirconium content increased octahedral tilting and led to higher transition temperatures. Local ordering was determined to be highly probable and it was found that the presence of vacancies extended the range of the high symmetry phase. The second system investigated was the BaxSr3-xTi1-yZryNb4O15, 0.0 ≤ x ≤ 3.0, 0.0 ≤ y ≤ 1.0, tungsten bronze type system. Barium rich compositions were found to adopt a tetragonal structure, while strontium rich compositions adopted an orthorhombic structure. Increasing the zirconium content of samples was seen to make the orthorhombic phase persist further. A large focus was placed on determining the structure of Sr3TiNb4O15 as a model for all orthorhombic compounds. A new structural model was proposed for Sr3TiNb4O15 distinct from those previously published. All orthorhombic compositions were observed to undergo first order phase transitions to the tetragonal structure on heating. The barium and strontium atoms were found to order onto two crystallographically distinct A sites. It was found that the tungsten bronze tolerance factor could be used as a predictive tool for the crystal symmetry of these materials. All compounds in this system for which ferroelectric measurements were performed displayed ferroelectric hysteresis behaviour.
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Tsou, Nien-Ti. "Compatible domain structures in ferroelectric single crystals." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:2ef69e2d-ec5a-4e1b-814f-b573b1649a58.
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The aim of the current study is to develop an efficient model which can predict low-energy compatible microstructures in ferroelectric bulks and film devices and their dynamic behaviour. The results are expected to assist in the interpretation of microstructure observations and provide a knowledge of the possible domain arrangements that can be used to design future materials with optimum performance. Several recent models of ferroelectric crystals assume low energy domain configurations. They are mainly based on the idea of fine phase mixtures and average compatibility, and can require intensive computation resulting in complex domain configurations which rarely occur in nature. In this research, criteria for the exact compatibility of domain structure in the form of a periodic multi-rank laminate are developed. Exactly compatible structure is expected to be energetically favourable and does not require the concept of a fine mixture to eliminate incompatibilities. The resulting method is a rapid and systematic procedure for finding exactly compatible microstructures. This is then used to explore minimum rank compatible microstructure in various crystal systems and devices. The results reveal routes in polarization and strain spaces along which microstructure can continuously evolve, including poling paths for ferro- electric single crystals. Also, the method is capable to generate all possible exactly compatible laminate configurations for given boundary conditions. It is found that simple configurations are often energetically favourable in conditions where previous approaches would predict more complex domain patterns. Laminate domain patterns in ferroelectrics are classified and corre- lated with observations of domains in single crystals, showing good agreement. The evolution of microstructures under applied mechanical and electrical loads is studied. A variational method, which minimises the overall energy of the crystal is developed. A new concept of transitional “pivot states” is introduced which allows the model to capture the feature that the microstructure in ferroelectric crystal switches between possible domain patterns that are energetically favourable, rather than assuming one particular domain pattern throughout. This model is applied to study the hysteresis responses of barium titanate (BaTiO3) single crystals subjected to a variety of loads. The results have good agreement with experimental data in the literature. The relationship between domain patterns and ferroelectric hysteresis responses is discussed.
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Gupta, Shashaank. "High Performance Lead--free Piezoelectric Materials." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/50959.
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Piezoelectric materials find applications in number of devices requiring inter-conversion of mechanical and electrical energy. These devices include different types of sensors, actuators and energy harvesting devices. A number of lead-based perovskite compositions (PZT, PMN-PT, PZN-PT etc.) have dominated the field in last few decades owing to their giant piezoresponse and convenient application relevant tunability. With increasing environmental concerns, in the last one decade, focus has been shifted towards developing a better understanding of lead-free piezoelectric compositions in order to achieve an improved application relevant performance. Sodium potassium niobate (KxNa1-xNbO3, abbreviated as KNN) is one of the most interesting candidates in the class of lead-free piezoelectrics. Absence of any poisonous element makes it unique among all the other lead-free candidates having presence of bismuth. Curie temperature of 400"C, even higher than that of PZT is another advantage from the point of view of device applications.Present work focuses on the development of fundamental understanding of the crystallographic nature, domain structure and domain dynamics of KNN. Since compositions close to x = 0.5 are of primary interest because of their superior piezoelectric activity among other compositions (0 < x < 1), crystallographic and domain structure studies are focused on this region of the phase diagram. KNN random ceramic, textured ceramic and single crystals were synthesized, which in complement to each other help in understanding the behavior of KNN.
K0.5Na0.5NbO3 single crystals grown by the flux method were characterized for their ferroelectric and piezoelectric behavior and dynamical scaling analysis was performed to reveal the origin of their moderate piezoelectric performance. Optical birefringence technique used to reveal the macro level crystallographic nature of x = 0.4, 0.5 and 0.6 crystals suggested them to have monoclinic Mc, monoclinic MA/B and orthorhombic structures respectively. Contrary to that, pair distribution function analysis performed on same composition crystals implies them to belonging to monoclinic Mc structure at local scale. Linear birefringence and piezoresponse force microscopy (PFM) were used to reveal the domain structure at macro and micros scales respectively.
A noble sintering technique was developed to achieve > 99% density for KNN ceramics. These high density ceramics were characterized for their dielectric, ferroelectric and piezoelectric properties. A significant improvement in different piezoelectric coefficients of these ceramics validates the advantages of this sintering technique. Also lower defect levels in these high density ceramics lead to the superior ferroelectric fatigue behavior as well. To understand the role of seed crystals in switching behavior of textured ceramic, highly textured KNN ceramics (Lotgering factor ~ 88 %) were synthesized using TGG method. A sintering technique similar to one employed for random ceramics, was used to sinter textured KNN ceramics as well. Piezoresponse force microscopy (PFM) study suggested these textured ceramics to have about 6¼m domains as compared to 2¼m domain size for random ceramics. Local switching behavior studied using switching spectroscopy (SS-PFM) revealed about two and half time improvement of local piezoresponse as compared to random counterpart.
Ph. D.
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Rahmanizadeh, Kourosh [Verfasser]. "Ferroelectric materials with interfaces : first principles calculations / Kourosh Rahmanizadeh." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2011. http://d-nb.info/1019344776/34.
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Roscow, James. "Composite ferroelectric materials for energy harvesting and storage applications." Thesis, University of Bath, 2018. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.761037.
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In this study composite ferroelectric materials have been investigated for their ability to harvest energy from mechanical vibrations via the piezoelectric effect, and store electrical energy as capacitor materials. A combination of modelling and experimental techniques have been used to understand the consequences of using multiphase materials for energy harvesting and storage applications, with particular focus on the significance of interactions between composite structure, electric field distributions and the effective material properties. A detailed investigation into the properties of ferroelectric ceramic-air composites, such as porous barium titanate, is presented. Introducing isotropic, randomly distributed porosity into barium titanate was found to increase the energy harvesting figure of merit from ~1.40 pm^2/N for the dense material to ~2.85 pm^2/N at 60 vol.% porosity. Finite element modelling was used to better understand the poling behaviour of barium titanate with different porous structures (uniform, porous sandwich layer and aligned), enabling the design of materials with improved energy harvesting capabilities. Complex porous structures were found to have enhanced energy harvesting figures of merit, with maximum values achieved of 3.74 pm^2/N and 3.79 pm^2/Nin barium titanate with a 60 vol.% porosity sandwich layer (overall porosity ~34 vol.%) and highly aligned freeze cast barium titanate with 45 vol.% porosity, respectively. Dense and porous barium titanate samples were mechanically excited and the derived electrical energy used to charge a capacitor. The porous barium titanate was found to charge the reference capacitor more effectively than the dense material, demonstrating the benefits of introducing porosity into ferroelectric materials for energy harvesting applications. Ferroelectric composites, in which either a conductive filler was added to a high permittivity ferroelectric matrix or a high permittivity ferroelectric phase was added to a low permittivity polymer matrix, were evaluated for their potential as a new generation of capacitor materials using finite element modelling. The studies suggested that the rise in effective permittivity due to the forming of composites is fundamentally linked to the rapid decline in dielectric breakdown strengths observed in composites, resulting in nearly all cases reported in the literature demonstrating a reduction in the energy storage figure of merit. It is concluded that future efforts into finding the next generation of energy storage materials should focus on single phase, or intrinsic, high permittivity materials rather than composite materials.
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Huang, Yi Ph D. Massachusetts Institute of Technology. "Electrically-tunable near-field heat transfer with ferroelectric materials." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/92139.
Full textAbstract:
Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 75-80).
Radiative heat transfer at small separations can be enhanced by orders of magnitude via the use of surface phonon polariton or plasmon polariton waves. This enhancement has potential applications in different devices, such as thermal emitters, thermal rectifiers, thermophotovoltaic and thermoelectric energy conversion systems. In this thesis, the author explores the tunable optical properties of ferroelectric materials to manipulate the near-field radiative heat transfer between two surfaces, aiming at the active control of near-field radiation heat transfer. Soft mode hardening of ferroelectric thin films induced by environmental changes, such as temperature and electric field, is widely used as a basis for tunable and switchable electrical and optical devices. However, this mechanism has not yet been examined for heat transfer applications. Using the fluctuation-dissipation theorem and the Dyadic Green's function method, the author shows via simulation that the magnitude and spectral characteristics of radiative heat transfer can be tuned via an externally applied electric field and temperature. Ways are explored to maximize the tuning contrast and discuss the trade-off between maximizing tunability and heat transfer. Our simulation results suggest that ferroelectrics can be used to develop new types of tunable nano-scale devices for thermal and energy conversion applications.
by Yi Huang.
S.M.
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Wei, Amanda Xin. "Design, Analysis, and Application of Architected Ferroelectric Lattice Materials." Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/101099.
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Ferroelectric materials have been an area of keen interest for researchers due to their useful electro-mechanical coupling properties for a range of modern applications, such as sensing, precision actuation, or energy harvesting. The distribution of the piezoelectric coefficients, which corresponds to the piezoelectric properties, in traditional crystalline ferroelectric materials are determined by their inherent crystalline structure. This restriction limits the tunability of their piezoelectric properties. In the present work, ferroelectric lattice materials capable of a wide range of rationally designed piezoelectric coefficients are achieved through lattice micro-architecture design. The piezoelectric coefficients of several lattice designs are analyzed and predicted using an analytical volume-averaging approach. Finite element models were used to verify the analytical predictions and strong agreement between the two sets of results were found. Select lattice designs were additively manufactured using projection microstereolithography from a PZT-polymer composite and their piezoelectric coefficients experimentally verified and also found to be in agreement with the analytical and numerical predictions. The results show that the use of lattice micro-architecture successfully decouples the dependency of the piezoelectric properties on the material's crystalline structure, giving the user a means to tune the piezoelectric properties of the lattice materials. Real-world application of a ferroelectric lattice structure is demonstrated through application as a multi-directional stress sensor.Master of Science
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Sui, Yongqiang. "Anisotropic organic materials ferroelectric crystals and spin-polarized radicals /." Diss., Columbia, Mo. : University of Missouri-Columbia, 2007. http://hdl.handle.net/10355/5933.
Full textAbstract:
Thesis (Ph. D.)--University of Missouri-Columbia, 2007.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed Mar. 13, 2009). Includes bibliographical references.
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YAU, CHIYAT BEN. "RAMAN, XRD AND POSITRON STUDY OF FERROELECTRIC FILMS." University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1155938071.
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Millar, Caroline Elizabeth. "The fabrication and properties of piezoceramic-polymer composites." Thesis, University of Leeds, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.278261.
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Illingsworth, J. S. "Investigation of the grain boundary layer characteristics of donor doped barium titanate ceramics." Thesis, Durham University, 1990. http://etheses.dur.ac.uk/1118/.
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Donor doped barium titanate ceramics are well known for their Positive Temperature Coefficient of Resistance (PTCR) characteristic above the crystallographic transition temperature, T° '130°C, where the material changes from the ferroelectric state to paraelectric. The shape and magnitude of the PTCR characteristic are known to be dependent on the composition and preparation of the ceramic, the presence of impurities, particularly donor dopant concentration and acceptor ions, and the sintering conditions. Thirty years ago Heywang proposed a model based on the presence of two-dimensional resistive grain boundary layers consisting of discrete electron traps located in energy between the conduction and valence bands, to explain the PTCR effect. Donor doped barium titanate samples were prepared in a number of different ways: the variation of donor concentration, the addition of impurity acceptor ions, reduction of the sintering temperature and variation of the sintering atmosphere. These samples were investigated by examining their microstructure and their electric and dielectric properties, both at room temperature and above the transition. Theoretical analysis of the experimental results, based on the Heywang model, was then performed to investigate the effects of preparation on the grain boundary layer characteristics. Resistivity - temperature measurements were carried out to find the effect of composition and sintering conditions on the PTCR characteristic and capacitance - temperature measurements demonstrated the effects of donor and acceptor incorporation on the dielectric properties of barium titanate. Grain boundary and grain bulk resistance were separated by means of a. c. impedance methods at room temperature, where the effects of composition and sintering on each were observed. Finally, current - voltage measurements between TT and the resistivity maximum were made for samples containing different donor concentrations, to examine the current conduction mechanism. Detailed analysis of the electric and dielectric measurements permitted the effects of composition and sintering on the grain boundary layer characteristics to be determined. Acceptor state densities were estimated using the resistivity - temperature measurements and capacitance - temperature results, between TT and the resistivity maximum. Resistivity - temperature measurements above the maximum enabled acceptor energies to be estimated. Analysis of the dielectric properties showed that neither the composition nor sintering atmosphere affected the dielectric properties of the grain boundary layers, which were found to obey the Curie-Weiss law above the transition temperature in the same way as the grain bulk. The observed effects of the changes in the preparative conditions to the electric and dielectric properties were explained in terms of the Heywang model and microstructural development, resulting from modifications to the grain boundary layers. The conduction mechanism was examined by means of current - voltage measurements above the transition temperature and below the resistivity maximum. In contrast to the prediction of Heywang. this was found to be predominantly diffusion limited.
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Johnston, Diane E. "Characterisation of lanthanum-doped barium titanate." Thesis, University of Aberdeen, 1993. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU554634.
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One significant application of donor doped barium titanate (BaTiO3) is in the manufacture of Positive Temperature Coefficient of Resistance (PTCR) thermistors. Combined synthesis, phase diagram and electrical studies were undertaken on donor doped barium titanate with a view to understanding the factors responsible for PTCR phenomena. A range of materials, both commercial PTCR devices and in-house lanthanum-doped barium titanate samples, have been studied. All three commercial PTCR samples measured were found to be electrically inhomogeneous with two PTCR-exhibiting regions and a conductive grain core. The conductive core resistance had a characteristic temperature dependence, with a minimum occurring in the vicinity of the tetragonal to cubic phase transition (Tc) of barium titanate. The phase relations and electrical behaviour of two joins in the lanthanum-doped BaTiO3 system, join A (Ba4-4xLa4xTi4-xO12) and join B (Ba1-yLayTiO3+), were also studied. Compositions on joins A and B for 0x0.195 and 0y0.1 respectively, crystallised as single phase barium titanate. Charge compensation on both joins (at these concentrations) was achieved by a mixture of both titanium vacancies and free electrons. The electron compensation mechanism, Ba_1-yLa_yTi. 4+_1-yTi. 3+O_3, significantly complicates determination of phase relations in this system, since it occurs off the BaO-TiO_2-La_2O_3 ternary phase diagram. Ac impedance measurements indicated that samples on join A were electrically inhomogeneous resulting in the presence of different regions with variable Tx values; furthermore, the phase transitions in each region were themselves complex. The tetragonal to cubic phase transition was studied by a combination of x-ray diffraction, ac impedance and by varying dopant concentration. The resulting behaviour was complex, with both first order and continuous transitions occurring. There was also evidence of a two phase, (i.e. both cubic and tetragonal barium titanate) region associated with a distribution in particle size: small particles (&60 2m) were cubic; larger ones were tetragonal. It is apparent that the combined, complicating effects of grain size and segregation phenomena make it inappropriate to give an explanation for the phase relations and electrical behaviour of lanthanum-doped barium titanate in terms of classical phase equilibria and phase transition theories.
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Cui, Yongfei. "Ferroelectric barium titanate for semiconductor photocatalytic application." Thesis, Queen Mary, University of London, 2015. http://qmro.qmul.ac.uk/xmlui/handle/123456789/9530.
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Semiconductor photocatalysis has received extensive attention due to its wide applications in water and indoor air purification, solar fuel production, etc. Charge carrier separation is a crucial step in semiconductor photocatalysis and influences the overall efficiency. It has been demonstrated that internal depolarisiation field of ferroelectric materials can drive spatial separation of charge carriers, which results in spatial separation of reduction and oxidation reactions, and improved charge carrier separation. In this thesis, ferroelectric barium titanate was chosen and its photocatalytic performance in decolourisation of organic dye molecules was investigated. Photodeposition method was adopted to deposite silver nanoparticles on the surface of barium titanate. Silver modified barium titanate showed increased photodecolourisation rate compared with bare barium titanate due to its role of electron traps and hindered charge carrier recombination. A simple thermal treatment was used to alter the phase composition of the as-received barium titanate. Samples which contained more ferroelectric tetragonal phase were found to possess higher photocatalytic activity compared with non-ferroelectric samples. This was associated with stronger ferroelectricity after thermal treatment, which enhanced dye molecule adsorption and aid charge carrier separation. The mechanism and intermediates generated in photodegradation of Rhodamine B with silver modified ferroelectric barium titanate were studied. Cleavage of chromophore was demonstrated to dominate in the initial process. Benzoic acid was identified as the main intermediate and no siginificant discrepancy in intermediates distribution between ferroelectric photocatalytic system and non-ferroelectric system was observed. The influence of ferroelectric dipole of barium titanate on photocatalytic activity of heterostructured barium titanate/hematite was also studied. The synthesised heterostructured barium titanate/hematite showed higher photodcolourisation rate than both barium titanate and hematite. This phenomenon was attributed to the improved charge carrier separation and extended charge carrier lifetime arising from heterojunction and an interaction between the ferroelectric dipole and the carriers in the hematite.
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Xu, Ziguang. "Synthesis and characterization of magnetically ordered dielectric and ferroelectric materials." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0008/MQ61520.pdf.
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Young, Daniel James. "Synthesis and evaluation of some novel ferroelectric liquid crystal materials." Thesis, University of Hull, 1989. http://hydra.hull.ac.uk/resources/hull:3804.
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Colizzi, G. "Theory of hydrogen bonded ferroelectric materials : the case of KDP." Thesis, Queen's University Belfast, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.419559.
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Komandla, Srinivas Reddy. "The synthesis and evaluation of ferroelectric liquid crystal host materials." Thesis, University of Hull, 2015. http://hydra.hull.ac.uk/resources/hull:13091.
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This research is based on the synthesis and evaluation of liquid crystalline host materials for use in ferroelectric liquid crystal devices. The liquid crystal materials are synthesised by incorporating silane bulky end groups linked by an alkoxy spacer to a fluoroterphenyl molecular core. The main aim of the research is to improve the alignment quality with the ultimate aim of bookshelf alignment. Almost as important is the target of wide temperature range, high tilt, and low melting SmC phase materials, but maintaining the low rotational viscosity of the fluoroterphenyl core. The syntheses are reported of a series of silane compounds with bulky terminal groups attached to mono-, di-, and tri-fluoroterphenyl cores. The initial targets contain a pentamethyldisilane end group, but the route was unsuccessful so simpler targets with a butyldimethylsilane bulky end groups were prepared. The key part of the synthesis involves hydrosilylation, low temperature directed lithiation and Suzuki-Miyaura coupling reactions. The report discusses the syntheses and transition temperatures obtained from DSC and thermal polarising optical microscopy. The trends in the transition temperatures, and tilt angles of derived FLC materials, values are discussed and compared to literature compounds. An exemplar is the addition of a chiral dopant (BE8OF2N) to butyl(6-((4''-((10- (butyldimethylsilyl)decyl)oxy)-2',3'-difluoro-[1,1':4',1''-terphenyl]-4-yl)oxy)hexyl)dimethylsilane 30a produces a high SmC* tilt angle of around 45° which varies little with temperature and there is a step in Ps data. This example 30a is mixed in percentages up to 50% with a model difluoroterphenyl KC1020 substituted in the middle ring. The bulky end group suppresses the N and SmA phase when compared to the dialkyl mesogen. A marked reduction in crystallisation temperature shows eutectic behaviour which is promising for ferroelectric mixture formulation. The same example 30a mixed with KC1019, fluorinated on the end ring, has similar behaviour, but with more support of the SmC phase. Other silane materials are mixed with KC1020 only, and their phase behaviour is discussed. Selected 50% mixtures of 30a+KC1019, 30a+KC1020, and an end ring monofluoroterphenylbutyldimethylsilane 39+KC1020 are doped with 7% w/w of standard dopant BE8OF2N(-S) aimed at the ideal phase sequence I-N*-SmA*-SmC*-C. The SmC* tilt angles are close to the ideal value of 22.5° at room temperature but Ps values vary.
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Huang, Qianwei. "Effects of external stimuli on the microstructures of ferroelectric materials." Thesis, University of Sydney, 2020. https://hdl.handle.net/2123/23031.
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Ferroelectric materials are frequently used in electronic devices because of their excellent ferroelectric, piezoelectric and dielectric properties. These properties are closely related to the microstructures of materials. In practical terms, ferroelectric fatigue is a significant issue that impedes the extensive application of these materials in electronic devices and that is also relevant to their microstructures. To optimise the scientific design of ferroelectrics for next-generation electronic devices, a comprehensive understanding of how ferroelectric microstructures react to external stimuli is essential, as is an insight into the nature of ferroelectric fatigue. Until recently, it has been difficult to probe the microstructural evolution of materials as a result of the experimental challenges; however, using the state-of-the-art technique of in-situ transmission electron microscopy (TEM), it is now possible to study the microstructural evolution of ferroelectrics under electric and cyclic electric fields.
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Islam, Noor Ul. "Alignment structures in ferroelectric liquid crystals." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299465.
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Viola, Giuseppe. "Domain switching dynamics in ferroelastic and ferroelastic/ferroelectric perovskites." Thesis, Queen Mary, University of London, 2010. http://qmro.qmul.ac.uk/xmlui/handle/123456789/382.
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A comprehensive study of domain switching process in different ferroelastic and ferroelastic/ferroelectric perovskite structured ceramics has been performed. The effects of thermal fluctuations on domain switching dynamics were investigated in the ferroelastic and in the ferroelectric case under static and dynamic electric and mechanical conditions. In the ferroelastic case, domain switching behaviour was investigated for different compositions, using different types of mechanical tests. Compression tests were carried out to characterize the ferroelastic properties, such as coercive stress, hysteresis loop and irreversible strain. Creep experiments were performed to study the domain switching time dependence at different stress levels. Domain switching kinetics during creep was characterized by implementing a rate model, based on thermal activation rate theory, which allowed the activation volume to be estimated. A Rayleigh-type analysis was performed to study the effects of stress amplitude, loading rate, temperature and composition on ferroelastic switching. Rayleigh-type relationships were proposed to fit the results and the rate model developed was applied to quantify the effect of the loading rate on the Rayleigh loops. Alternative methodologies were developed to assess the effects of rate and temperature on the coercive stress, providing original sets of data. A further application of the rate model provided an estimation of the activation parameters (volume and enthalpy). In PZT 5A at the coercive field the activation volume was calculated to be 2.44 nm3, with a reasonable consistency with the value obtained from creep tests (7.49 nm3). In the ferroelectric case, domain switching was studied by generating P-E and butterfly hysteresis loops and by analysing creep-relaxation curves. In creep experiments, the polarization and the strain were measured simultaneously, during the application of a constant electric field. An insight into the evolution of domain structure and on domain switching mechanisms was gained, highlighting analogies and differences with the ferroelastic case. Experiments at different frequencies, allowed the activation volume to be estimated at the coercive field (77 nm3). The relatively large value indicates small rate dependence and suggests a domain structure with broad and mobile domain walls, being the preferred sites for the nucleation.
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Randall, C. A. "A transmission electron microscopy study of normal and relaxor perovskite ferroelectric materials." Thesis, University of Essex, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376749.
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Reeve, William Francis. "Structural study of the ferroelectric materials PbNb₂O₆ and PbTa₂O₆." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301253.
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Chen, Chen. "Synthesis, structural and ferroelectric properties of perovskite-like layered structured materials." Thesis, Queen Mary, University of London, 2015. http://qmro.qmul.ac.uk/xmlui/handle/123456789/9526.
Full textAbstract:
Perovskite-like layered structured (PLS) compounds display a range of interesting physical and chemical properties, including photocatalysis, photoluminescence, ion conductivity, electrochemical stability, magnetic properties, ferroelectricity and piezoelectricity. There are mainly three homologous series of PLS compounds distinguished by their different BO6 octahedra orientation: the Dion-Jacobson phase (A'An-1BnO3n+1); the AnBnO3n+2 phase; and the hexagonal phase (AnBn-1O3n). Some of the 4-layer AnBnO3n+2 compounds, like La2Ti2O7 and Sr2Nb2O7, have been reported to be ferroelectrics with super high Curie point (above 1300 °C), but no ferroelectric properties have been reported for the 2-layer and 3-layer AnBnO3n+2 compounds, and also there are few reports on the ferroelectric properties of compounds with Dion-Jacobson structure and hexagonal structure. Consequently, in this work, the crystallographic structures, microstructures, dielectric, ferroelectric and piezoelectric properties of (AxLa1-x)Ti2O7 (A = Sm and Eu) solid solutions with 4-layer AnBnO3n+2 structure, Pr3Ti2TaO11 with 3-layer AnBnO3n+2 structure, LaTaO4 with 2-layer AnBnO3n+2 structure, ABiNb2O7 (A = Rb and Cs) with Dion-Jacobson structure and Sr6TiNb4O18 with hexagonal structure were studied. Spark plasma sintering (SPS) was used to sinter ceramics with high density and preferred orientation. X-ray diffraction refinement (XRD) and transmission electron microscopy (TEM) were used to study the crystallographic structures and microstructures of the layer structured compounds. The ferroelectricity was studied using the current-electric field and polarization-electric field hysteresis loops. The Curie point and phase transitions were studied using the temperature dependence of the dielectric constant and loss. Piezoresponse force microscopy (PFM) was also used to study the ferroelectric domain structure of some layer structured compounds. In the first part of this work, the piezoelectric constant of La2Ti2O7 was improved by doping Sm. The crystallographic structure of (Eu1-xLax) 2Ti2O7 and (Sm1-xLax) 2Ti2O7 solid solutions were well studied. (AxLa1-x)Ti2O7 solid solutions were isomorphous with La2Ti2O7 when x was less than 0.5 for (EuxLa1-x)Ti2O7 and 0.8 for (SmxLa1-x)Ti2O7. When x was above their solubility limit, a biphase was observed. The XRD and Raman data suggested that the biphase consisted of (AxLa1-x)2Ti2O7 perovskite-like layered structure and pure Sm2Ti2O7 pyrochlore structure. Ferroelectric domain switching was observed in the I-E and P-E hysteresis loops for textured (SmxLa1-x)Ti2O7 (x < 0.2). The highest d33 was 2.8 pC/N for (Sm0.1La0.9)Ti2O7. In the second part, The Pr3Ti2TaO11 compound was demonstrated to have a 3-layer type II AnBnO3n+2 PLS structure belonging to space group Pmc21 with unit cell parameters a = 3.8689(3) Å, b = 20.389(2) Å, c = 5.5046(5) Å, and its ferroelectric properties were investigated. Analysis of the XRD and TEM results showed that Pr3Ti2TaO11 ceramics have an n = 3 (type II) heteroblock structure consisting of alternating n = 2 and n = 4 octahedral oxide layers. High resolution electron microscopy revealed the layered structure to be highly disordered, with faulting of the heteroblock structure and the coexistence of a n = 4 phase on a fine scale (nm), which was evident as a broadening of the XRD peaks of the ceramics. Pr3Ti2TaO11 ceramic exhibits a super-high Curie point (1415±5 °C). A small, but measurable piezoelectric constant d33 between 0.1 and 0.2 pC/N was detected for the samples poled above 900 °C under an electric field of 100~200 V/cm. Pure LaTaO4 powders with orthorhombic phase were be prepared by co-precipitation method. The orthorhombic LaTaO4 powders have a 2-layer perovskite-like layered structure with space group A21am, which was refined using Rietveld method. The single phase O-LaTaO4 ceramic was prepared using SPS with a slow cooling rate (20 °C/min). A d33 of 0.3 pC/N was obtained from the electric field induced orthorhombic phase. In the second part of this work, the ferroelectricity and piezoelectricity of CsBiNb2O7 with Dion-Jacobson type PLS structure was successfully demonstrated for the first time. The ferroelectricity and piezoelectricity of RbBiNb2O7, which have similar structure with CsBiNb2O7, were also fully studied. Highly textured 2-layer Dion-Jacobson ceramics ABiNb2O7 (A = Rb and Cs) were prepared by one-step SPS. High resolution TEM showed well ordered (0 0 1) lattice planes. Striped ferroelectric domains were observed using PFM. The ferroelectricity and piezoelectricity of CsBiNb2O7 has been demonstrated for the first time. The Tc of RbBiNb2O7 and CsBiNb2O7 are 1098±5 and 1033±5 °C, respectively. The piezoelectric constant of RbBiNb2O7 and CsBiNb2O7 were approximately 5 and 8 pC/N. Thermal depoling studies confirmed the Curie point and the stability of the piezoelectricity. Sr6Nb4TiO18 ceramics with non-centrosymmetric structure were successfully prepared, but no obvious evidence was found to prove its ferroelectricity. The untextured and textured 6-layer Hexagonal compound Sr6Nb4TiO18 was prepared by solid state reaction and spark plasma sintering. Its Curie point was found to be greater than 1500 °C. No ferroelectric properties were observed by studying of I-E and P-E loops, and no d33 was observed after poling.
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Herath, Mudiyanselage Dimuthu Prasad Wijethunge. "Theoretical investigation of ferroelectric properties in 2D materials and their applications." Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/235394/1/Dimuthu%2BWijethunge%2BThesis%283%29.pdf.
Full textAbstract:
This thesis examined two-dimensional ferroelectric materials and their applications using density functional theory calculations. The research has revealed several novel applications for 2D ferroelectric materials. It illustrated that ferroelectric materials can be used to modify electronic, photocatalytic and magnetic properties of two-dimensional materials. In addition to exploring applications, new two-dimensional ferroelectric material which exhibits metallic properties was discovered through high through output search. Two-dimensional ferroelectric metals are extremely rare and only handful of materials were ever discovered.
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Savia, S. B. "Computer-aided study of FSS and some applications of ferroic materials." Thesis, University of Kent, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322722.
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Kim, Yeongkwan. "Equilibrium and dynamical properties of epitaxial ferroelectric heterostructures." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/30507.
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Peng, Peng. "PREPARATION AND CHARACTERIZATION OF POLYMER/FERROELECTRIC CERAMIC PARTICLE COMPOSITES FOR ELECTROACTIVE ACTUATION." Case Western Reserve University School of Graduate Studies / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=case1443539252.
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Kim, Kwanlae. "Domain evolution processes in ferroelectric ceramics." Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:abd786e3-8461-4e75-ae99-2620d08099b1.
Full textAbstract:
The aim of this doctoral research is to understand domain evolution processes in ferroelectrics using piezoresponse force microscopy (PFM) and Monte Carlo simulation. The results provide improved knowledge of domain evolution processes, and systematic experimental methods for research on domain evolution. There has been extensive previous research on domain evolution in ferroelectrics, but the research was mainly constrained to simple domain patterns. However, ferroelectric domains tend to form complex patterns that generate low-energy domain configurations. In this research, several methods such as statistical analysis of PFM data, ex situ/in situ PFM observation under electrical/mechanical loading and combining PFM with electron backscatter diffraction are employed to study domain evolution processes in complex domain patterns. The results show that domain switching almost always takes place by the evolution of pre-existing domain patterns, rather than direct flipping of polarization. Also the net effect of domain evolution processes follows a primary principle that positive work is done by external loads. But this principle is not always followed for microscopic switching processes. Multiple types of domain switching occur simultaneously, and occasionally an overwriting process involves unfavourable as well as favourable domain switching. Domain switching is significantly constrained by the pre-existing domain patterns. Meanwhile, angle-resolved PFM is developed for the systematic interpretation of PFM signal. Using lateral PFM images taken from multiple sample orientations, angle-resolved PFM maps are generated based on the angle of phase reversal in the PFM signal. The resulting maps reliably show complex domain patterns which may not appear in vertical and lateral PFM images. A model of domain evolution is developed using Monte Carlo simulation. Polarization switching by electric field and mechanical stress in the model is shown to take place via the motion of domain walls between pre-existing domains. Typical domain broadening processes are reproduced through this simulation.