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Gotowa bibliografia na temat „Ferroelectric Phase Transitions”

Autor: Grafiati

Data publikacji: 6 września 2023

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Artykuły w czasopismach na temat "Ferroelectric Phase Transitions"

Wang, Jin Song. "Irreversible Thermodynamic Discussions about Ferroelectric Phase Transitions". Advanced Materials Research 756-759 (wrzesień 2013): 4419–22. http://dx.doi.org/10.4028/www.scientific.net/amr.756-759.4419.

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The irreversibility of ferroelectric phase transitions has been studied by using the irreversible thermodynamics. The thermal hysteresis of first-order ferroelectric phase transitions and the polydomain structure of ferroelectrics can be explained on the basis of the principle of minimum entropy production. A conclusion has been derived that the thermal hysteresis is not an intrinsic property of a system in which a first-order ferroelectric phase transition occurs. The finiteness of the systems surface is connected with the thermal hysteresis.

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Randall, C. A., R. Guo, A. S. Bhalla i L. E. Cross. "Microstructure-property relations in tungsten bronze lead barium niobate, Pb1−xBaxNb2O6". Journal of Materials Research 6, nr 8 (sierpień 1991): 1720–28. http://dx.doi.org/10.1557/jmr.1991.1720.

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Transmission electron microscopy (TEM) has been used to explore details of the structural phase transitions and corresponding microstructural features in the solid solution of Pb1−xBaxNb2O6 (PBN) tungsten bronze ferroelectrics at compositions embracing the morphotropic phase boundary between orthorhombic and tetragonal ferroelectric phases. In addition to the ferroelectric domain structures that were consistent with the expected symmetries, incommensurate ferroelastic phases were observed. The “onset” and “lock-in” transition temperatures are a function of the Pb/Ba ratio, and for lead-rich compositions it appears that the incommensurate distortion may occur above the ferroelectric Curie temperature in the paraelectric phase.

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Zhang, J. P., i J. S. Speck. "Identification of the polarized microregions in PLZT". Proceedings, annual meeting, Electron Microscopy Society of America 52 (1994): 556–57. http://dx.doi.org/10.1017/s0424820100170517.

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Relaxor ferroe lee tries are classified by broad or diffuse transitions from their high temperature paraelectric (non-polar phase) to their low temperature ferroelectric phase. This is in contrast to conventional ferroelectrics such as PbTiO3 that show discrete ferroelectric transitions characterized by Curie-Weiss behavior in the dielectric susceptibility near the Curie transition temperature Tc. For relaxor ferroelectrics, the transition has a breadth on the order of 100°C The polarized domains normally show complex nanoscale mottled contrast in either bright field or dark field, two-beam or systematic row scattering contrast images; as an example, this contrast is shown in Fig. 1. The nanoscale contrast appears to be intimately associated with the relaxor phase; however, the physical origins of the contrast remain unclear. It is known that in classical treatments of ferroelectrics, the polarization and strain are the primary order parameters for the paralelectric-ferroelectric phase transition. For classical first order ferroelectric transitions, such as in PbTiO3 or BaTiO3, there is a concurrently spontaneous polarization and strain. However, these order parameters need not be directly coupled, and it may be possible that through the relaxor transition, strain and polarization are uncoupled. In this experimental effort we will demonstrate techniques that separate strain contrast from structure factor contrast, the latter being associated with polarization or compositional fluctuations.

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Whittle, Thomas, i Siegbert Schmid. "Diffraction Studies of Tungsten Bronze Type Relaxor Ferroelectrics". Acta Crystallographica Section A Foundations and Advances 70, a1 (5.08.2014): C78. http://dx.doi.org/10.1107/s2053273314099215.

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Ferroelectric materials are essential for modern electronic applications, from consumer electronics to sophisticated technical instruments. Relaxor ferroelectric materials provide the advantage of high dielectric constants over broad temperature ranges not seen in traditional ferroelectrics. Tungsten bronze type compounds have been shown to display a variety of industrially relevant optical and electronic properties amongst others. There is a fundamental relationship between the physical properties displayed by ferroelectrics and the crystal structures in which they form. Of particular interest are compositions and temperatures near phase transition. These are import because near phase transitions, particularly morphotropic phase transitions, electromechanical properties are often dramatically enhanced. [1,2] This work focuses on the structural investigation of the tungsten bronze type relaxor ferroelectric materials in the BaxSr3-xTi1-yZryNb4O15 (0 ≤ x ≤ 3; 0 ≤ y ≤ 1) system. A combination of X-ray, neutron (ToF and constant wavelength) and electron diffraction were employed to map the entire room temperature phase space. In addition, morphotropic phase boundary compositions were determined accurately. Variable temperature synchrotron X-ray diffraction studies were utilised to further explore the phase diagram for non-ambient conditions. Temperature dependent phase transitions were determined and the relationship between composition and transition temperature analysed. Structural models used in this work resulted from Rietveld refinements against powder diffraction data. [3] This work will shed light on new lead free relaxor ferroelectric materials.

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Shao, Yu-Tsun, i Jian-Min Zuo. "Nanoscale symmetry fluctuations in ferroelectric barium titanate, BaTiO3". Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 73, nr 4 (19.07.2017): 708–14. http://dx.doi.org/10.1107/s2052520617008496.

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Crystal charge density is a ground-state electronic property. In ferroelectrics, charge is strongly influenced by lattice andvice versa, leading to a range of interesting temperature-dependent physical properties. However, experimental determination of charge in ferroelectrics is challenging because of the formation of ferroelectric domains. Demonstrated here is the scanning convergent-beam electron diffraction (SCBED) technique that can be simultaneously used for imaging ferroelectric domains and identifying crystal symmetry and its fluctuations. Results from SCBED confirm the acentric tetragonal, orthorhombic and rhombohedral symmetry for the ferroelectric phases of BaTiO3. However, the symmetry is not homogeneous; regions of a few tens of nanometres retaining almost perfect symmetry are interspersed in regions of lower symmetry. While the observed highest symmetry is consistent with the displacive model of ferroelectric phase transitions in BaTiO3, the observed nanoscale symmetry fluctuations are consistent with the predictions of the order–disorder phase-transition mechanism.

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Florêncio, Odila, Paulo Sergio Silva, José Antônio Eiras, Ducinei Garcia i Eriton Rodrigo Botero. "Study of the Anelastic Behavior of PZT and PLZT Ferroelectric Ceramics". Defect and Diffusion Forum 326-328 (kwiecień 2012): 719–24. http://dx.doi.org/10.4028/www.scientific.net/ddf.326-328.719.

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The anelastic behavior of the ferroelectric ceramics (Pb)(Zr/Ti)O3(PZT) and (Pb/La)(Zr/Ti)O3(PLZT), with Zr/Ti = 65/35, La = 5 at.% and 8 at.%, was investigated in the region of the ferroelectric phase transitions. Anelastic spectroscopy experiments were performed in an acoustic elastometer system, operating in a kilohertz bandwidth, at temperatures rising from 300 K to 770 K, at a heating rate of 1 K/min, under pressure of 10-5mbar. Anelastic measurements on PZT showed only one anomaly, associated with the occurrence of a ferroelectric-paraelectric phase transition, while the PLZT data showed two anomalies, which were associated with the following transitions: the ferroelectric-paraelectric phase transition and a ferro-ferroelectric phase transition between distinct rhombohedral ferroelectric phases. The behavior of the relative variation of the elastic moduli with temperature, near the phase transitions, which describes the change in the type of coupling between strain and the order parameter in ferroelectric-paraelectric phase transition, with the increase of lanthanum amount and, linear coupling in the strain and order parameter type to PZT ceramic and linear coupling in the strain but quadratic in order parameter type for PLZT ceramics.

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Ivliev M. P., Raevskaya S. I., Titov V. V. i Raevski I. P. "Formation of phase states in PbFe-=SUB=-0.5-=/SUB=-Nb-=SUB=-0.5-=/SUB=-O-=SUB=-3-=/SUB=-: Description based on multiminima models". Physics of the Solid State 64, nr 12 (2022): 2034. http://dx.doi.org/10.21883/pss.2022.12.54403.437.

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Two ferroelectric phase transitions are observed in the PbFe0.5Nb0.5O3 crystal. The first is between the cubic and tetragonal phase, the second is between the tetragonal and monoclinic phases. To describe phase transitions and emerging phases, a statistical model is proposed, based on the composition of two multi-minimum models --- a six-minima model for the Pb cation and an eight-minima model for the Nb cation. Adjusting the model parameters, makes it possible to reproduce all the characteristic features of the thermodynamic behavior of the crystal. The most interesting is the formation of a ferroelectric, complexly ordered monoclinic phase with Cm symmetry. It is shown that the mentioned monoclinic phase arises due to the fact that the first-order phase transition to the rhombohedral ferroelectric phase occurs in the presence of an "external field" of tetragonal symmetry. The contribution of the subsystems of Pb and Nb cations to the features of the dielectric and structural properties of the crystal is estimated. Keywords: ferroelectric relaxors, phase transitions, multiminima models, ferroelectric monoclinic phase.

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Streiffer, S. K., i D. D. Fong. "Phase Transitions in Nanoscale Ferroelectric Structures". MRS Bulletin 34, nr 11 (listopad 2009): 832–37. http://dx.doi.org/10.1557/mrs2009.233.

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AbstractOver decades of effort, investigations of the intrinsic phase transition behavior of nanoscale ferroelectric structures have been greatly complicated by materials processing variations and by the common and uncontrolled occurrence of spacecharge, which interacts directly with the polarization and can obscure fundamental behavior. These challenges have largely been overcome, and great progress in understanding the details of this class of phase transitions has been made, largely based on advances in the growth of high-quality, epitaxial ferroelectric films and in the theory and simulation of ferroelectricity. Here we will discuss recent progress in understanding the ferroelectric phase transition in a particular class of model systems: nanoscale perovskite thin-film heterostructures. The outlook for ferroelectric technology based on these results is promising, and extensions to laterally confined nanostructures will be described.

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Bin Anooz, S., Y. Wang, P. Petrik, M. de Oliveira Guimaraes, M. Schmidbauer i J. Schwarzkopf. "High temperature phase transitions in NaNbO₃ epitaxial films grown under tensile lattice strain". Applied Physics Letters 120, nr 20 (16.05.2022): 202901. http://dx.doi.org/10.1063/5.0087959.

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We have investigated high temperature phase transitions in NaNbO3 thin films epitaxially grown under tensile lattice strain on (110) DyScO3 substrates using metal-organic vapor phase epitaxy. At room temperature, a very regular stripe domain pattern consisting of the monoclinic a1a2 ferroelectric phase was observed. Temperature-dependent studies of the refractive index and the optical bandgap as well as in situ high-resolution x-ray diffraction measurements prove a ferroelectric–ferroelectric phase transition in the range between 250 and 300 °C. The experimental results strongly suggest that the high-temperature phase exhibits a distorted orthorhombic a1/a2 crystal symmetry, with the electric polarization vector lying exclusively in the plane. A second phase transition was observed at about 500 °C, which presumably signifies the transition to the paraelectric phase. Both phase transitions show a pronounced temperature-dependent hysteresis, indicating first-order phase transitions.

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Shirokov, Vladimir B., i Mikhail V. Talanov. "Phase transitions in Bi4Ti3O12". Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 75, nr 6 (7.11.2019): 978–86. http://dx.doi.org/10.1107/s2052520619011843.

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Bi4Ti3O12 is a representative of the Aurivillius family of layered perovskites. These are high-temperature ferroelectric materials with prospects for applications in random-access memory and are characterized by an extremely confused interaction of their structural degrees of freedom. Using group-theoretical methods, structural distortions in the Bi4Ti3O12 high-symmetry phase, caused by rotations of rigid octahedra and their displacements as a single unit, have been investigated, taking into account the connections between them. Within the Landau theory, a stable thermodynamic model of phase transitions with three order parameters has been constructed. It is shown that, according to the phenomenological phase diagram, the transition between the high-temperature tetragonal phase and the low-temperature ferroelectric can occur both directly and through intermediate states, including those observed experimentally. The role of improper ordered parameters and possible domain configurations in the structure formation of the low-temperature ferroelectric phase are discussed.

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Rozprawy doktorskie na temat "Ferroelectric Phase Transitions"

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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Rowley, Stephen Edward. "Quantum phase transitions in ferroelectrics". Thesis, University of Cambridge, 2011. https://www.repository.cam.ac.uk/handle/1810/252224.

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Ravel, Bruce D. "Ferroelectric phase transitions in oxide perovskites studied by XAFS /". Thesis, Connect to this title online; UW restricted, 1997. http://hdl.handle.net/1773/9784.

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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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Chapman, Brandon D. "The role of disorder in structural phase transitions in perovskite ferroelectrics /". Thesis, Connect to this title online; UW restricted, 2003. http://hdl.handle.net/1773/9692.

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Franzbach, Daniel Jason [Verfasser], Jürgen [Akademischer Betreuer] Rödel i Ralf [Akademischer Betreuer] Müller. "Field Induced Phase Transitions in Ferroelectric Materials / Daniel Jason Franzbach. Betreuer: Jürgen Rödel ; Ralf Müller". Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2014. http://d-nb.info/1112332642/34.

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von, Helden Leonard. "Ferroelectric domains in potassium sodium niobate thin films: impact of epitaxial strain on thermally induced phase transitions". Doctoral thesis, Humboldt-Universität zu Berlin, 2019. http://dx.doi.org/10.18452/20185.

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Gegenstand dieser Arbeit ist die experimentelle Untersuchung der Verspannungs-Temperatur-Phasenbeziehungen in epitaktischen KxNa1-xNbO3 Dünnschichten, sowie deren Zusammenhang mit ferro- und piezoelektrischen Eigenschaften. Die präsentierten Ergebnisse ermöglichen es KxNa1-xNbO3 Dünnschichten für neuartige technologische Anwendung zu optimieren. Zunächst wird eine detaillierte strukturelle Untersuchung der ferroelektrischen Domänenstruktur in epitaktischen K0.7Na0.3NbO3 Schichten auf (110) TbScO3 vorgestellt. Eine Analyse der ferroelektrischen Domänenstruktur mittels lateral aufgelöster Piezoresponse-Kraftmikroskopie (PFM) zeigt vier Arten von Superdomänen. Durch die ergänzende Untersuchung der zweidimensionalen und dreidimensionalen Abbildung des reziproken Raumes mittels hochauflösender Röntgenbeugung (HR-XRD) wird nachgewiesen, dass dieses Domänenmuster mittels monokliner Einheitszellen in einem MC Domänenmodell beschrieben werden kann. Im Anschluss an die strukturelle Untersuchung wurden die elektromechanischen Eigenschaften der KxNa1-xNbO3 Schichten auf (110) TbScO3untersucht. Mittels Doppelstrahl-Laserinterferometrie (DBLI) wurde ein makroskopischer effektiver piezoelektrischer Koeffizient von bis zu d33,f = 23 pm/V nachgewiesen. Zudem wurden Oberflächenwellen-Experimente (SAW) durchgeführt. Diese zeigten außergewöhnlich hohe Signalstärken. Um die Temperatur der ferroelektrischen Phasenübergänge gezielt einstellen zu können, wurde der Zusammenhang zwischen epitaktischer Verspannung und der Phasenübergangstemperatur untersucht. Dazu wurden KxNa1-xNbO3 Schichten mit unterschiedlicher Verspannung gewachsen. Die Änderung der Domänenstruktur und der piezoelektrischen Eigenschaften aufgrund von Temperaturänderung wurde in-situ durch temperaturabhängige PFM, HR-XRD und DBLI Messungen untersucht. Die Untersuchung zeigte, dass die Übergangstemperatur des Übergangs von der MC- in die c-Phase mit zunehmender kompressiver Verspannung kontinuierlich um mehr als 400 °C abnahm.
The subject of this thesis is the experimental investigation of the strain-temperature-phase relations in epitaxial KxNa1-xNbO3 thin films and their connection to ferro- and piezoelectric properties. This will enable the optimization of KxNa1-xNbO3 layers for novel technological devices. First, a detailed structural investigation of the ferroelectric domain structure in epitaxial K0.7Na0.3NbO3 films on (110) TbScO3 is presented. An analysis of the ferroelectric domain structure with laterally resolved piezoresponse force microscopy (PFM) reveals four types of superdomains. By complementary two-dimensional and three-dimensional high resolution X-ray reciprocal space mapping this domain pattern is proven to be describable by an MC domain structure with monoclinic unit cells. Subsequently to the structural investigation, the electromechanical properties of KxNa1-xNbO3 layers on (110) TbScO3 were investigated. Double beam laser interferometry (DBLI) revealed a macroscopic effective piezoelectric coefficient of up to d33,f = 23 pm/V. Furthermore, surface acoustic wave (SAW) experiments were performed. They exhibited extraordinary signal intensities. In order to be able to selectively tune such phase transition temperatures, the correlation between epitaxial strain and the phase transition temperature was investigated. For this purpose, KxNa1-xNbO3 films with different compressive strain conditions were grown. The change of domain structure and piezoelectric properties upon temperature variation was investigated in-situ by temperature-dependent PFM, HR-XRD and DBLI measurements. The transition temperature between the MC- and c-phase was shown to continuously decrease by more than 400 °C with increasing compressive strain.

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PACIARONI, MORENO. "A mechanical model for ferroelectric materials: from atomic scale to finite elements". Doctoral thesis, Università Politecnica delle Marche, 2011. http://hdl.handle.net/11566/242132.

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I materiali ferroelettrici sono largamente utilizzati in molte applicazioni quali sensori, attuatori e memorie non volatili. Negli ultimi anni la ricerca ha prodotto una miriade di modelli analitici e numerici, sia per la forma cristallina sia per quella amorfa. Gli approcci adottati sono differenti a seconda della scala di lunghezza da cui si osserva il problema: i modelli atomistici descrivono il comportamento intrinseco ed hanno portato ad un grande sviluppo nella chimica dei ferroelettrici, i modelli macroscopici ingegneristici catturano il comportamento statico indipendente dal tempo. Il presente lavoro giace nel mezzo dei due approcci e cerca di fornire un ponte concettuale tra la scala atomica e quella ingegneristica attraverso un modello termodinamico microstrutturale. Un materiale ferroelettrico esibisce una polarizzazione spontanea al di sotto di un valore critico della temperatura detto temperatura di Curie, a cui è associata anche una deformazione spontanea. La maggior parte dei materiali ferroelettrici presenta una simmetria cristallografica cubica nella fase ad alta temperatura, detta fase paraelettrica, e una simmetria più bassa nella fase ferroelettrica: ciò riflette a scala macroscopica la distorsione del reticolo di lattice legato all'insorgere della polarizzazione. Non essendo forniti apporti esterni, il materiale si ritroverebbe con uno scompenso di energia sia elettrostatica sia meccanica, per cui tende a minimizzare questi contributi attraverso la formazione di domini a polarizzazione uniforme e di geminati meccanici. Tale processo non prosegue in modo indefinito perché una parte dell'energia si accumula nelle pareti di dominio: queste ultime sono interfacce dello spessore di poche costanti di lattice attraverso cui la polarizzazione cambia rapidamente da un valore a quello opposto. All'equilibrio si ha una polarizzazione netta nulla. La polarizzazione spontanea può essere riorientata ad alte temperature (comunque inferiori a quella di Curie) per mezzo di forti campi elettrici e il risultato è un materiale piezoelettrico che esibisce un forte accoppiamento elettromeccanico. L'intensità dei campi elettrici dipende da una serie di fattori quali la dimensione dei grani e dei domini e la simmetria del cristallo. Un tipico esempio di materiale ferroelettrico è il titanato-zirconato di piombo Pb(Zr1-xTix)O3, in seguito identificato con l'acronimo PZT. Questa ceramica presenta una fase paraelettrica con simmetria cubica al di sopra dei 650K, mentre al di sotto la fase ferroelettrica può essere associata a diverse simmetrie cristallografiche in ragione della composizione chimica: alti contenuti in titanio favoriscono una simmetria tetragonale, viceversa alti contenuti in zirconio producono una simmetria romboedrale. Intorno al bordo di fase morfotropico, ovvero la linea di separazione tra le diverse simmetrie, è stata scoperta l'esistenza di una fase monoclina, la quale sarebbe all'origine delle eccezionali proprietà del PZT. In effetti per composizioni 0.47 < x < 0.51 al di sotto dei 500K si hanno alti valori della costante dielettrica, la massima rigidezza meccanica e una certa facilità di polarizzazione con molte possibili orientazioni. Nel presente lavoro la modellazione del comportamento elettromeccanico dei materiali ferroelettrici partirà da un'analogia formale con la Density Functional Theory, la quale viene ad esempio impiegata dai fisici dello stato solido per valutare la struttura di atomi e molecole: in questo modo si stabilisce un collegamento tra modelli atomistici e meccanica dei continui. Sulla base di alcuni risultati di letteratura si formula il problema dell'equilibrio in termini di potenza spesa e il problema di minimo in termini di energia. La descrizione della transizione di fase è affidata alla teoria di Landau, di cui si riportano gli aspetti fondamentali. Inoltre viene proposto un approccio originale in cui l'energia libera è sviluppata in serie di potenze a partire da un'opportuna configurazione iniziale: questo permette di descrivere le varie simmetrie di arrivo limitando lo sviluppo al quarto ordine nella variabile che descrive il fenomeno. Per dare una lettura immediata dei risultati, si rappresentano graficamente degli opportuni diagrammi di fase. Essendo la polarizzazione accompagnata da un deformazione spontanea, si analizzerà la compatibilità delle varianti ferroelettriche (le deformazioni omogenee a tratti associate al fenomeno ferroelettrico) all'interfaccia dei domini attraverso la teoria delle deformazioni con discontinuità a salti. Oltre ai classici geminati (o twins) di tipo I, II e composti, verranno presi in considerazione anche twins non generici che possono avere origine per particolari composizioni del materiale calcolando nel caso gli angoli di inclinazione delle pareti dei domini. Infine si provvederà a fornire una traccia sommaria per la minimizzazione del funzionale ferroelettrico sia con approccio analitico ottenendo le equazioni di Eulero-Lagrange sia con il metodo degli elementi finiti. In quest'ultimo caso verranno riportati i risultati ottenuti su un semplice modello monodimensionale.
Ferroelectric materials are widely used in many applications such as sensors, actuators and non-volatile memories. In recent years, an ever-increasing theoretical investigation generates many analytical and numerical implementations. Single-crystal specimens may be modeled in an easier way than polycrystalline ones, but the technological process is very hard and expensive, so that both are considered. Different approaches are followed depending on what one focuses on, from the atomic level to the macroscopic engineering one. Atomistic models describe the intrinsic behavior and have led to a great improvements in the chemistry of ferroelectric materials; macroscopic phenomenological models capture the empirical static and time-independent behavior. The present work lies at the interface of two apparently disjointed approaches: it is a thermodynamic and microstructural model that provides a conceptual link between the atomic and the engineering scales. The most important feature of a ferroelectric material is the transition that it undergoes from the paraelectric phase to the ferroelectric one when it is cooled under the Curie temperature: as a result, a spontaneous polarization onsets and it is accompanied by an electric self-field and a spontaneous strain. Most of the ferroelectric materials exhibits a cubic crystallographic point group in the paraelectric phase and a lower symmetry in the ferroelectric phase: within the Cauchy-Born rule this reflects the distortion of the crystal lattice at the macroscopic scale. The associated electrostatic and elastic energies are reduced by means of the formation of domains, i.e. uniformly polarized regions in which electric dipoles are aligned in the same direction. This process does not go on indefinitely, since a certain amount of energy is stored at the so-called domain walls: the latter are thin interfaces (only a few lattice constants) and within them the spontaneous polarization will decrease in magnitude, passing through zero, and increase on the other side with opposite sign. Domain thickness does not approach zero, in fact it has a finite dimension which arises from the competition between the energetic terms. At the equilibrium, ferroelectric materials have a null net polarization. In order to exhibit piezoelectric properties, the spontaneous polarization must be reoriented in the same direction by applying strong electric fields at high temperature below the Curie point: this process is called domain switching or polarization reversal. The magnitude of the electric fields depends on the size of the grains and of the domains and on the symmetry point group. One of the most widely used ferroelectric material is the lead zirconate titanate Pb(Zr1-xTix)O3 (PZT) which shows a cubic point group in the paraelectric phase above 650K, whereas the symmetry in the ferroelectric phase is defined by the composition of the ceramic: titanium-rich compositions favor cubic-to-tetragonal transition and zirconium-rich compositions which favor cubic-to-rhombohedral transition. Close to the morphotropic phase boundary a stable monoclinic phase was recently discovered and it is at the origin of the exceptional properties of the PZT: indeed such compositions are characterized by a very large piezoelectric coupling between electric and mechanical variables related to the presence of a maximum in the dielectric constant, an ease of poling with a large number of reorientable polarization directions and a maximum mechanical compliance. In the present work we would like to establish a conceptual link between the atomistic and the macroscopic continuum models: to this effect, we begin from the Density Functional Theory which is used in the solid state physics to describe the structure of complex atoms, molecules and crystals and their interactions. By a formal analogy we get the equilibrium problem in terms of power expended and the minimum problem in terms of energy. Then we describe the transition from the paraelectric to the ferroelectric phase within the Landau theory: we propose an original approach in which below the transition temperature (and accordingly in a ferroelectric phase) the parameters of the crystallographic potential depends on the composition of the ceramic: then, starting from a suitable reference configuration we attempt to describe all the possible symmetries with a fourth-order expansion of the spontaneous polarization. Because of the formation of domains, different deformations associated with different polarizations may occur within the same grain: using the Hadamard lemma and the Ericksen-Silhavy condition we find all the possible twins arising in PZT and in BaTiO3 and some other non generic non conventional twins which are predicted by our developments from the Landau theory. Finally we propose a three dimensional model for ferroelectric materials with the associated Euler-Lagrange equation, which are integro-differential ones because of the electric field. We also deal with a one dimensional model on which we perform both a stability and a finite element analyses.

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Kilit, Emel. "Critical Behaviour Of The Thermodynamic Quantities For The Thermotropic And Ferroelectric Liquid Crystals Close To The Phase Transitions". Phd thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12612963/index.pdf.

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The specific heat Cp has been showed at various temperatures in the literature, which shows a sharp increase labeled as the lambda-transition at the critical temperature. This transition has been observed previously among the phases of solid-nematic-isotropic liquid in p-azoxyanisole (PAA) and anisaldazine (AAD), and among the phases of solid-smectic-cholesteric-isotropic liquid in cholesteryl myristate (CM). In this thesis work, we analyze the experimental data for the temperature dependence of Cp and the thermal expansion alpha_p and also pressure dependence of alpha_p by a power-law formula. From the analysis of pressure dependence of alpha_p, we calculate the temperature dependencies of specific heat Cp and of the isothermal compressibility kappa_T for the phase transitions considered in PAA, AAD and CM. Our calculations for the temperature dependence of the p and kappa_T can be compared with the experimental data when available in the literature. Polarization, tilt angle and the dielectric constant have been reported in the literature at various temperatures close to the solid-smectic C*-smectic A-isotropic liquid transition in the ferroelectric liquid crystals of A7 and C7. The mean field model with the free energy expanded in terms of the order parameters (polarization and tilt angle) has been reported in the literature previously. In this thesis work, we apply the mean field model first time by fitting the expressions derived for the temperature dependence of the polarization, tilt angle and the dielectric constant to the experimental data for A7 and C7 from the literature. Since the mean field model studied here describes adequately the observed behaviour of A7 and C7, the expressions for the temperature dependence of the polarization, tilt angle and the dielectric constant which we derive, can also be applied to some other ferroelectric liquid crystals to explain their observed behaviour.

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Hentati, Mouhamed Amin. "Effets des inhomogénéités locales et des contraintes extérieures sur les propriétés diélectriques et structurales des monocristaux PZN-x%PT". Phd thesis, Châtenay-Malabry, Ecole centrale de Paris, 2013. http://tel.archives-ouvertes.fr/tel-01003354.

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Dans ce travail, nous avons étudié l'effet des contraintes extérieures et des inhomogénéités locales sur les propriétés diélectriques et structurales des cristaux ferroélectriques- relaxeurs à base de plomb PZN-x%PT avec 0%≤x≤12%. Dans une première partie, nous avons déterminé les propriétés diélectriques et structurales du système PZN-6%PT. Pour l'état vierge, ce composé subit la séquence de transition de phase C  T  R, où C, T et R sont, respectivement, les phases cubique, quadratique et rhomboédrique. En appliquant un champ électrique statique, une phase orthorhombique est induite entre les phases T et R. Dans la deuxième partie, nous avons montré la présence d'une anomalie diélectrique à basse température observée sur le PZN-x%PT avec 0%≤x≤12%. Dans ce domaine de température, l'étude structurale ne montre aucune transition de phase. L'ensemble de ces résultats sont interprétés moyennant un modèle basé sur la présence des nano-régions polaires. En troisième partie nous avons déterminé les propriétés diélectriques et piézoélectrique du PZN-12%PT dopé au manganèse dans son état monodomaine. Le dopage affecte, principalement, la permittivité transverse et le coefficient piézoélectrique de cisaillement. Le dopage induit aussi la stabilité de la structure monodomaine et l'effet de mémoire de la microstructure. Ces résultats sont expliqués en utilisant le modèle de symétrie des défauts. Dans la dernière partie, nous nous sommes intéressés à la simulation de l'effet de la présence des dipôles-défaut (dopage) sur les propriétés physiques de BaTiO3. Nous avons mis en évidence l'induction d'un champ électrique interne responsable du décalage du cycle d'hystérésis vers les champs électriques négatifs.

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Książki na temat "Ferroelectric Phase Transitions"

1945-, Sigov A. S., red. Defects and structural phase transitions. New York: Gordon and Breach Science Publishers, 1988.

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Czapla, Zbigniew. Ferroelectricity and phase transitions in rubidium and ammonium hydrogen selenates. Wrocław: Wydawn. Uniwersytetu Wrocławskiego, 1985.

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Effective field approach to phase transitions and some applications to ferroelectrics. Singapore: World Scientific, 1991.

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Phase transitions in ferroelastic and co-elastic crystals: An introduction for mineralogists, material scientists, and physicists. Cambridge [England]: Cambridge University Press, 1990.

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Salje, Ekhard K. H. Phase transitions in ferroelastic and co-elastic crystals: An introduction for mineralogists, material scientists, and physicists. Cambridge [England]: Cambridge University Press, 1993.

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Nechaev, Vladimir, Andrey Shuba, Stanislav Gridnev i Vitaliy Topolov. Dimensional effects in phase transitions and physical properties of ferroics. ru: INFRA-M Academic Publishing LLC., 2022. http://dx.doi.org/10.12737/1898400.

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The monograph presents mathematical methods and a set of mathematical models describing, within the framework of phenomenological theory, phase transitions in 0D-. 1D-, 2D-, 3D-dimensional ferroelectrics, ferroelastics, ferromagnets and their static and dynamic physical properties near the phase transition point. The influence of the parameters characterizing the ferroic sample and its interaction with the environment on the features of the phase transition, phase transition temperature shift, heat capacity, generalized susceptibilities is analyzed. Mathematical models of multilayer thin-film structures and composite materials, where one of the components is a ferroic nanoparticle, are considered. In general, modern ideas about dimensional effects in ferroelectrics, ferroelastics, ferromagnets and mechanisms of purposeful influence on their properties are sufficiently fully covered. It is intended for researchers, students and postgraduates of physical specialties of universities interested in fundamental problems of formation of physical properties of low-dimensional materials. Research engineers, developers of new materials can use the presented material as a scientific and methodological basis to support the development of optimal solutions for their creation.

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Pavlov, Sergey. Methods of catastrophe theory in the phenomenology of phase transitions. ru: INFRA-M Academic Publishing LLC., 2020. http://dx.doi.org/10.12737/1004276.

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The monograph is devoted to describing the methods of catastrophe theory and building on the basis of these methods, phenomenological models of phase transitions in solids. Methods of constructing structurally stable normal forms of functions, including functions that are imposed on the symmetry conditions. The classification of phenomenological models of phase transitions for two interacting one-component order parameter, two-component and three-component order parameters the number of control parameters varied in the experiment. Theoretical dependence of the anomalies of the physical properties of the models are compared with experimental data in ferroelectrics, magnetic materials, solid solutions of rare earth metals, multiferroics and other solids that are experiencing phase transitions. For professionals in the field of solid state physics and phase transitions.

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Fu, Huaxiang. Unusual properties of nanoscale ferroelectrics. Redaktorzy A. V. Narlikar i Y. Y. Fu. Oxford University Press, 2017. http://dx.doi.org/10.1093/oxfordhb/9780199533053.013.19.

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This article describes the unusual properties of nanoscale ferroelectrics (FE), including widely tunable polarization and improved properties in strained ferroelectric thin films; polarization enhancement in superlattices; polarization saturation in ferroelectric thin films under very large inplane strains; occurrence of ferroelectric phase transitions in one-dimensional wires; existence of the toroidal structural phase in ferroelectric nanoparticles; and the symmetry-broken phase-transition path when one transforms a vortex phase into a polarization phase. The article first considers some of the critical questions on low-dimensional ferroelectricity before discussing the theoretical approaches used to determine the properties of ferroelectric nanostructures. It also looks at 2D ferroelectric structures such as surfaces, superlattices and thin films, along with 1D ferroelectric nanowires and ferroelectric nanoparticles.

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Tiwari, Sandip. Phase transitions and their devices. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780198759874.003.0004.

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Phase transitions as a collective response of an ensemble, with appearance of unique stable properties spontaneously, is critical to a variety of devices: electronic, magnetic, optical, and their coupled forms. This chapter starts with a discussion of broken symmetry and its manifestation in the property changes in thermodynamic phase transition and the Landau mean-field articulation. It then follows it with an exploration of different phenomena and their use in devices. The first is ferroelectricity—spontaneous electric polarization—and its use in ferroelectric memories. Electron correlation effects are explored, and then conductivity transition from electron-electron and electron-phonon coupling and its use in novel memory and device forms. This is followed by development of an understanding of spin correlations and interactions and magnetism—spontaneous magnetic polarization. The use and manipulation of the magnetic phase transition in disk drives, magnetic and spin-torque memory as well as their stability is explored. Finally, as a fourth example, amorphous-crystalline structural transition in optical, electronic, and optoelectronic form are analyzed. This latter’s application include disk drives and resistive memories in the form of phase-change as well as those with electochemical transport.

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Fukada, E. Ferroelectric Polymers: A special issue of the journal Phase Transitions, Section B (Automedica,). Routledge, 1989.

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Części książek na temat "Ferroelectric Phase Transitions"

Tilley, D. R. "Phase Transitions in Thin Films". W Ferroelectric Ceramics, 163–83. Basel: Birkhäuser Basel, 1993. http://dx.doi.org/10.1007/978-3-0348-7551-6_6.

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Rigamonti, Attilio, i Pietro Carretta. "Dielectrics and Paraelectric-Ferroelectric Phase Transitions". W Structure of Matter, 477–503. Cham: Springer International Publishing, 2015. http://dx.doi.org/10.1007/978-3-319-17897-4_16.

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Strukov, Boris A., i Arkadi P. Levanyuk. "General Characteristics of Structural Phase Transitions in Crystals". W Ferroelectric Phenomena in Crystals, 1–29. Berlin, Heidelberg: Springer Berlin Heidelberg, 1998. http://dx.doi.org/10.1007/978-3-642-60293-1_1.

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Strukov, Boris A., i Arkadi P. Levanyuk. "Structural Phase Transitions in the Single-Ion Model". W Ferroelectric Phenomena in Crystals, 135–49. Berlin, Heidelberg: Springer Berlin Heidelberg, 1998. http://dx.doi.org/10.1007/978-3-642-60293-1_7.

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Strukov, Boris A., i Arkadi P. Levanyuk. "Dynamics of Displacive and Order-Disorder Phase Transitions". W Ferroelectric Phenomena in Crystals, 175–91. Berlin, Heidelberg: Springer Berlin Heidelberg, 1998. http://dx.doi.org/10.1007/978-3-642-60293-1_9.

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Tyunina, Marina. "Ferroelectric Phase Transitions in Epitaxial Perovskite Films". W Nanoscale Ferroelectrics and Multiferroics, 617–44. Chichester, UK: John Wiley & Sons, Ltd, 2016. http://dx.doi.org/10.1002/9781118935743.ch19.

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Strukov, Boris A., i Arkadi P. Levanyuk. "Proper Ferroelectrics: Anomalies of Physical Properties in Phase Transitions". W Ferroelectric Phenomena in Crystals, 49–71. Berlin, Heidelberg: Springer Berlin Heidelberg, 1998. http://dx.doi.org/10.1007/978-3-642-60293-1_3.

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Strukov, Boris A., i Arkadi P. Levanyuk. "Dielectric Anomalies in Structural Nonferroelectric and Improper Ferroelectric Phase Transitions". W Ferroelectric Phenomena in Crystals, 73–88. Berlin, Heidelberg: Springer Berlin Heidelberg, 1998. http://dx.doi.org/10.1007/978-3-642-60293-1_4.

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Abplanalp, M., M. Zgonik i P. Günter. "Scanning Probe Microscopy of Ferroelectric Domains near Phase Transitions". W Nanoscale Characterisation of Ferroelectric Materials, 193–220. Berlin, Heidelberg: Springer Berlin Heidelberg, 2004. http://dx.doi.org/10.1007/978-3-662-08901-9_7.

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Strukov, Boris A., i Arkadi P. Levanyuk. "Statistical Theory of Ferroelectric Phase Transitions of the Order-Disorder Type". W Ferroelectric Phenomena in Crystals, 151–73. Berlin, Heidelberg: Springer Berlin Heidelberg, 1998. http://dx.doi.org/10.1007/978-3-642-60293-1_8.

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Streszczenia konferencji na temat "Ferroelectric Phase Transitions"

Wang, Jinsong. "Irreversible Thermodynamic Discussions about Ferroelectric Phase Transitions". W 2nd International Conference on Computer and Information Applications (ICCIA 2012). Paris, France: Atlantis Press, 2012. http://dx.doi.org/10.2991/iccia.2012.193.

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Bratkovsky, A. M. "Ferroelectric phase transitions in films with depletion charge". W Fundamental physics of ferroelectrics 2000. AIP, 2000. http://dx.doi.org/10.1063/1.1324459.

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Davi´, Fabrizio. "Singularities in Landau-Devonshire Potentials for Ferroelectric Phase-Transitions". W ASME 2010 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. ASMEDC, 2010. http://dx.doi.org/10.1115/smasis2010-3667.

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Ferroelectrics phase transitions are studied in terms of fourth-order Landau potentials: a clever choice of the reference configuration allows for a complete description of all the possible transitions. The study of the stability conditions at the phase interface helps to explain the fairly complex nature of the observed twins.

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Lashkarev, George V., i M. V. Radchenko. "Ferromagnetic and ferroelectric phase transitions in IV-VI semiconductors". W Fifth International Conference on Material Science and Material Properties for Infrared Optoelectronics, redaktor Fiodor F. Sizov. SPIE, 2001. http://dx.doi.org/10.1117/12.417771.

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Blazhevich, A. V., I. P. Raevski, S. P. Kubrin, E. I. Sitalo, S. I. Raevskaya, V. V. Titov, D. A. Sarychev, M. A. Malitskaya i I. N. Zakharchenko. "Ferroelectric and magnetic phase transitions in multiferroic PbFe0.5Ta0.5O3-PbTiO3 solid solutions". W 2012 Joint 21st IEEE ISAF / 11th IEEE ECAPD / IEEE PFM (ISAF/ECAPD/PFM). IEEE, 2012. http://dx.doi.org/10.1109/isaf.2012.6297783.

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Waghmare, U. V., K. M. Rabe, Henry Krakauer, Rici Yu i Cheng-Zhang Wang. "Effective Hamiltonian for the ferroelectric phase transitions in KNbO[sub 3]". W The 5th Williamsburg workshop on first-principles calculations for ferroelectrics. AIP, 1998. http://dx.doi.org/10.1063/1.56289.

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Matiyev, A. Ch, i R. T. Uspazhiev. "INFLUENCE OF POLYTYPY ON PHASE TRANSITIONS IN TlGaSe2 CRYSTALS". W «АКТУАЛЬНЫЕ ВОПРОСЫ СОВРЕМЕННОЙ НАУКИ: ТЕОРИЯ, ТЕХНОЛОГИЯ, МЕТОДОЛОГИЯ И ПРАКТИКА». Международная научно-практическая онлайн-конференция, приуроченная к 60-ти летию член-корреспондента Академии наук ЧР, доктора технических наук, профессора Сайд-Альви Юсуповича Муртазаева. Crossref, 2021. http://dx.doi.org/10.34708/gstou.conf..2021.76.13.002.

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It is shown that, in the C-polytype of TlGaSe2 crystals, the structural PT, which occurs at a temperature of T ~ 108 K, is accompanied by an abrupt change in the value of the parameter c (∆c ~ 0.004 Å). For the 2C-TlGaSe2 polytype, the c (T) dependence shows only one clearly pronounced maximum at the temperature Tc2. Moreover, at temperatures that are T1 ~ 30 K higher and T2~ 5 K below Tc2, the Curie-Weiss law is fulfilled. The absence of a fourfold increase in the parameter from the unit cell for 2C-TlGaSe2 samples in the temperature range T = 100-300 K indicates that spontaneous polarization is the order parameter of the ferroelectric PT

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Wiederrecht, Gary P., Thomas P. Dougherty i Keith A. Nelson. "Impulsive Stimulated Raman Scattering Study of Soft Mode Dynamics in Ferroelectric Crystals". W International Conference on Ultrafast Phenomena. Washington, D.C.: Optica Publishing Group, 1992. http://dx.doi.org/10.1364/up.1992.tha5.

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Soft Modes, ISRS, and Perovskite Ferroelectrics The dynamics of cooperative ordering in crystals near structural phase transitions have long been elusive. Most picosecond and femtosecond time-resolved measurements have involved rapid laser heating of a sample whose phase transition (e.g. melting) dynamics are then monitored1. In this case many lattice degrees of freedom are excited, and little information is provided about the roles or dynamics of particular lattice motions. In structural phase transitions, the order parameter is described by one or a very few specific ("soft") lattice modes whose motions bring crystalline constituents from their initial positions into their positions in a new crystalline phase. Experimental characterization of the dynamics is possible in some cases through Raman spectroscopy, but often the highly damped character of the soft mode leads to a central peak in the Raman spectrum which cannot be analyzed accurately. In many cases it is not even possible to tell whether the ordering motion is a heavily damped vibration, Debye relaxation, or some combination of the two. This information is essential for understanding the microscopic mechanism of a transition since vibrational or relaxational character is an indication of ionic motion within a single potential energy minimum (i.e. a displacive transition) or hopping between different sites (an order-disorder transition) respectively.

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Wang, Feiling, Gene H. Haertling i Kewen K. Li. "Photo-Activated Phase Transition In Antiferroelectric Thin Films For Optical Switching And Storage*". W Optical Data Storage. Washington, D.C.: Optica Publishing Group, 1994. http://dx.doi.org/10.1364/ods.1994.tud5.

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An electric field induced antiferroelectric (AFE)-to-ferroelectric (FE) phase transition in lead zirconate titanate (PZT) thin films was shown to produce a digital birefringent change in the materials. Such field-induced AFE-to-FE phase transitions may be influenced by the interface between the PZT thin films and certain electrode materials. It has been observed that soft-ultraviolet (UV) illumination to PZT thin films effectively lift the interfacial suppression to the phase transition. Therefore, soft-UV light may be used as a writing beam to change the polarization state of the PZT thin films via the photo-activated AFE-to-FE phase transition.

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Yin, Zhen, Ping Zhang i Ming-Sheng Zhang. "Raman spectroscopic study of phase transitions and configurations in ester ferroelectric liquid crystals". W International Symposium on Optical Science and Technology, redaktor David L. Andrews. SPIE, 2001. http://dx.doi.org/10.1117/12.447378.

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Raporty organizacyjne na temat "Ferroelectric Phase Transitions"

Hoover, B. D., B. A. Tuttle, W. R. Olson, D. M. Goy, R. A. Brooks i C. F. King. Evaluation of field enforced antiferroelectric to ferroelectric phase transition dielectrics and relaxor ferroelectrics for pulse discharge capacitors. Office of Scientific and Technical Information (OSTI), wrzesień 1997. http://dx.doi.org/10.2172/537385.

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