Дисертації з теми "Ferroelectric Phase Transitions"
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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.
Повний текст джерелаRowley, Stephen Edward. "Quantum phase transitions in ferroelectrics." Thesis, University of Cambridge, 2011. https://www.repository.cam.ac.uk/handle/1810/252224.
Повний текст джерелаRavel, 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.
Повний текст джерелаWhittle, 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.
Повний текст джерелаChapman, 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.
Повний текст джерелаFranzbach, Daniel Jason [Verfasser], Jürgen [Akademischer Betreuer] Rödel, and 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.
Повний текст джерелаvon, 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.
Повний текст джерелаThe 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.
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.
Повний текст джерелаFerroelectric 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.
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.
Повний текст джерелаHentati, 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.
Повний текст джерелаSchmidbauer, Martin [Gutachter], Christoph [Gutachter] Koch, and Brice [Gutachter] Gautier. "Ferroelectric domains in potassium sodium niobate thin films: impact of epitaxial strain on thermally induced phase transitions / Gutachter: Martin Schmidbauer, Christoph Koch, Brice Gautier." Berlin : Humboldt-Universität zu Berlin, 2019. http://d-nb.info/120492404X/34.
Повний текст джерелаLin, Yaochen. "Dispersion de nanoparticules ferroélectriques dans un cristal liquide : élaboration, transitions de phases et propriétés diélectriques." Thesis, Littoral, 2017. http://www.theses.fr/2017DUNK0443/document.
Повний текст джерелаLiquid crystals are organic materials used to make electronic devices ; before using this material in applications, it is necessary to study their physical-chemical and dielectric properties in order to optimize their performance. This study is devoted to the nanocolloids obtained by dispersing ferroelectric nanoparticles in a nematic liquid crystal ; it means an inclusion influences the phase transitions temperatures and the dielectric properties of the host. The phase transitions measured by using Differential scanning calorimetry (DSC) evidenced the ferroelectric nanoparticles influence ; which is attributed two effects : the nanoparticles spontaneous polarization and the anchoring effect between nanoparticles and liquid crystal. The dielectric characterisation revealed the coupling between the macroscopic polarization of the inclusions and the electric field ; this coupling is manafested by an increase of phase transition temperatures compared to those determined by DSC. The competition between the polarization effect under an electric field and the anchoring effect induces a modification of the permittivities (parallel and perpendicular) and the dielectric anisotropy. Using harvested nanoparticles, the study confirmed the importance of the nanoparticles polarization to increase the properties of the studied nanocolloids. In fact, very small quantity of the harvested nanoparticles presents more significant improvements than those obtained with the non-harvested nanoparticles
Cherifi, Ryan. "Experimental design of a strong Magneto-Electric coupling system between a ferroelectric and a magnetic phase transition alloy : BaTiO3/FeRh, and theoretical study of the metamagnetic transition of FeRh." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066309.
Повний текст джерелаOne of the most practical concept used in physics and engineering is the concept of triggeror switch, consisting of a means to start a controlled chain of energy transformation.A switch can lead to reversible or irreversible consequences. Technological developmentusually seeks to make use of the former because it allows for repetitive logical tasks. Suchtriggers exist via the coupling between two or more types of energetic transformations.It is formally described by the interaction between two or more distinct fields and theirexpression on a system. Amongst the most studied coupling in material physics, we findelectro-mechanical couplings such as piezoelectricity or ferroelectricity, electro-caloric ormagneto-caloric couplings such as pyroelectricity and pyro-magnetism, magneto-electric,etc. The fundamental and experimental domestication and understanding of these couplingsis usually followed (and very often motivated) by the design of practical applicationin electronics engineering technology
PIMENTA, MARCOS ASSUNCAO. "Transitions de phase a haute temperature et conduction ionique dans likso:(4) et composes apparentes." Orléans, 1987. http://www.theses.fr/1987ORLE2045.
Повний текст джерелаSharma, Henu. "Theoretical studies of PbTiO3 and SrTiO3 under uniaxial mechanical constraints combining firstprinciples calculations and phenomenological Landau theory." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENI078.
Повний текст джерелаIn the present thesis we present theoretical studies of perovskite compounds under uniax-ial mechanical constraints combining first-principles DFT calculations approach and phe-nomenological Landau theory. ABO3 perovskites form a very important class of functionalmaterials that can exhibit a broad range of properties (e.g., superconductivity, magnetism,ferroelectricity, multiferroism, metal-insulator transitions. . . ) within small distortions ofthe same simple prototype cubic structure. Though these compounds have been exten-sively studied both experimentally and computationally, there are still unresolved issuesregarding the effect of pressure. In recent years, strain engineering has reported to bean original approach to tune the ferroelectric properties of perovskite ABO3 compounds.While the effect of epitaxial biaxial strain and hydrostatic strain is rather well understoodin this class of materials, very little is yet known regarding the effect of uniaxial mechanicalconstraints. Our study is motivated by the little existing understanding of the effect ofuniaxial strain and stress, that has been up to now almost totally neglected. Two proto-type compounds are studied in detail: PbTiO3 and SrTiO3. After a general introductionon ABO3 compounds and calculations techniques (ab initio and phenomenological Landaumodel), we studied the effect of mechanical constraints in these compounds in our thesis.PbTiO3 is a prototypical ferroelectric compound and also one of the parent components ofthe Pb(Zr,Ti)O3 solid solution (PZT), which is the most widely used piezoelectrics. ForPbTiO3, we have shown that irrespectively of the uniaxial mechanical constraint applied,the system keeps a purely ferroelectric ground-state, with the polarization aligned eitheralong the constraint direction (FEz phase) or along one of the pseudocubic axis perpen-dicular to it (FEx phase). This contrasts with the case of isotropic or biaxial mechanicalconstraints for which novel phases combining ferroelectric and antiferrodistortive motionshave been previously reported. Under uniaxial strain, PbTiO3 switches from a FEx groundstate under compressive strain to FEz ground-state under tensile strain, beyond a critical strain !czz! +1%. Under uniaxial stress, PbTiO3 exhibits either a FEx ground state undercompression ("zz < 0) or a FEz ground state under tension ("zz > 0). Here, however, anabrupt jump of the structural parameters is also predicted under both compressive andtensile stresses at critical values "zz! +2 GPa and −8 GPa. This behavior appears similarto that predicted under negative isotropic pressure and might reveal practically useful toenhance the piezoelectric response in nanodevices.The second compound of interest is SrTiO3. It has been widely studied in the past decadesdue to its unusual properties at low temperature. In this work, we have extended ourprevious investigations on PbTiO3 by exploring theoretically the pressure effects on per-ovskite SrTiO3 combining the first-principles calculations and a phenomenological Landaumodel. We have discussed the evolution of phonon frequencies of SrTiO3 with the threeisotropic, uniaxial and biaxial strains using first-principles calculations. We also reproducethe previous work done in SrTiO3 with epitaxial strain and hydrostatic strain. Finally,we have calculated the phase diagram of SrTiO3 under uniaxial strain, as obtained fromLandau theory and discussed how it compares with the first-principles calculations
Dos, Santos Adenilson Oliveira. "Difração de raios-X de n-feixes na caracterização estrutural de monocristais sob a ação de temperatura e campo elétrico externo." [s.n.], 2006. http://repositorio.unicamp.br/jspui/handle/REPOSIP/278132.
Повний текст джерелаTese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
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Resumo: Como primeira contribuição deste trabalho, as varreduras Renninger (VR) da difração múltipla de raios-X foram empregadas no estudo da transição de fase estrutural do Sal de Rochelle (monoclínica-ortorrômbica) induzida por temperatura. Devido ao caráter tridimensional e sensibilidade dessa técnica acompanhamos as deformações na célula unitária com a temperatura, através do deslocamento dos picos secundários com maior sensibilidade. Foi possível determinar os parâmetros de rede e simular cada VR com o programa UMWEG. Os picos secundários de 4-feixes ( 0 0 0 ) ( 0 0 10 )( 1 0 9 )(1 0 1 ) e (0 0 0 )( 0 0 10 )( 2 3 0 )(2 3 10 ) da fase ortorrômbica foram medidos na VR para 24ºC (Tc). Os coeficientes de expansão térmica do sal de Rochelle também foram obtidos, e estão em bom acordo com a literatura. Como segunda contribuição, usamos a VR na determinação precisa dos parâmetros de rede dos materiais magnetocalóricos PrAl2, NdAl2e PrNi5. Implementamos uma rotina baseada na simulação da VR com o programa UMWEG, através da qual escolhe-se o comprimento de onda adequado para a medida de picos secundários muito sensíveis à distorção na célula unitária. Na aplicação no caso do PrAl2 usamos o caso de 4-feixes ( 0 0 0 )( 6 0 0 )( 1 3 7 )( 7 3 7 ) com 2.... =6.663(3)º e obtivemos com grande precisão a=8,03332(7)Å. O efeito de polimento mecânico na superfície dessa amostra foi analisado pelo mapeamento das reflexões de superfície (BSD) e o comportamento mosaico do cristal foi evidenciado. Nas outras medidas, como utilizamos a mesma geometria da estação XRD1, não foi possível obter a melhor condição para a rotina apresentada, mas foram obtidos para o NdAl2 (a=7,9972(5)Å) e PrNi5 (a=4,9590(8)Å e c=3,9794(5)Å) com boa precisão. Outra contribuição foi o estudo do efeito de campo elétrico no cristal orgânico MBANP através do monitoramento por curvas de rocking da reflexão ( 10 0 0 ). Observou-se uma histerese "asa de borboleta", ainda não observada em cristais orgânicos, e sem modelo para cristais monoclínicos. Cálculos usando mecânica quântica para moléculas isoladas de MBANP mostram que as principais características da forma de histerese podem ser explicadas em termos de mudanças induzidas pelo campo elétrico nos perfis de carga e na geometria de moléculas isoladas de MBANP
Abstract: As the first contribution of this work, the Renninger scan (RS) of the X-ray multiple diffraction were used in the study of the Rochelle salt structural phase transition (monoclinic-orthorhombic) induced by temperature. Due to its three-dimensional feature and sensitivity of the technique was possible to follow the unit cell deformations with temperature, through the angular shifts of the most sensitive secondary peaks. We were able to determine the lattice parameters as well as to simulate each RS by using the UMWEG program. The ( 0 0 0 )( 0 0 10 )( 1 0 9 )(1 0 1 ) and ( 0 0 0 )( 0 0 10 )( 2 3 0 )(2 3 10 ) 4-beam peaks for the orthorhombic phase were measured in the RS at 24ºC (Tc). Rochelle salt thermal expansion coefficients were also obtained in good agreement with literature values. As the second contribution, we have also used the RS in the precise lattice parameter determination of PrAl2 , NdAl2 and PrNi5 magnetocaloric materials. We have implemented a routine based on the RS simulation (UMWEG program), through which, one can choose the adequate wavelength to measure the most sensitive secondary peaks to the unit cell variations. The application of thid method in the case of PrAl 2, has allowed to measure the ( 0 0 0 )( 6 0 0 )( 1 3 7 )( 7 3 7 ) 4- beam case that presents 2.... =6.663(3)º and hence, to determine a=8.03332(7)Å, with high precision. PrAl2surface polishing effect was also analyzed by the secondary surface peak (BSD) mapping, through which, the crystal mosaic behavior was exhibited. For the other crystals, the same LNLS geometry was used and the best condition to applying the routine could not be obtained, however good precision lattice parameters were obtained for NdAl2 (a=7.9972(5)Å) and PrNi5 (a= 4.9590(8)Å and c= 3.9794(5)Å). Another contribution to the study of the electric field application in the MBANP organic crystal through the monitoring of ( 10 0 0 ) rocking curves was performed. It was observed a (butterfly wing) hysteresis, not yet observed for organic crystals and with no model suggested for monoclinic crystals. Quantum mechanical calculations on isolated MBANP molecules show that the main features of the hysteresis shape can be explained in terms of field-induced changes in the charge profiles and geometry of isolated MBANP molecules
Doutorado
Física da Matéria Condensada
Doutor em Ciências
Chu, Fan. "The ferroelectric phase transition in complex perovskite relaxors /." [S.l.] : [s.n.], 1994. http://library.epfl.ch/theses/?nr=1248.
Повний текст джерелаQu, Weiguo. "In-situ TEM investigation of the phase transitions in perovskite ferroelectrics." [Ames, Iowa : Iowa State University], 2008.
Знайти повний текст джерелаLiu, Tieqi. "Electromechanical Behavior of Relaxor Ferroelectric Crystals." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4881.
Повний текст джерелаAl-Zein, Ali. "Order and Disorder of Relaxor and Ferroelectric Materials : structural and Vibrational Studies." Thesis, Montpellier 2, 2010. http://www.theses.fr/2010MON20078/document.
Повний текст джерелаAmong piezoelectric materials, lead-based ferroelectric perovskites are known to have the largest piezoelectric coefficients and electromechanical coupling. They are widely used in dfferent industrial and technological applications. The so-called "relaxors" belong to this family. Their structure is characterized by the presence of randomly oriented polar nanoregions. In this thesis, we are interested in studying the structural and dynamical properties of prototypical ferroelectric materials and relaxors such as PbTiO3, PbZr0.52Ti0.48O3, PbMg1/3Nb2/3O3 (PMN), PbZn1/3Nb2/3O3, and PbMg1/3Ta2/3O3 (PMT). The long and short range structure has been investigated by neutron diffraction and X-ray absorption fine structure (XAFS), while hyper-Raman scattering (HRS) is used to probe the vibrations. The local structure analysis of complex perovskite materials AB'B''O3 shows that pressure reduces the static disorder of the large cation occupying the B-site, while an applied electric field has an opposite effect. This field-induced distortion might relate to the large piezoelectric coefficient in such materials. HRS in PMN and PMT allows the first observation of the "primary" soft mode responsible for the temperature dependence of the dielectric constant. The selection rule analysis reveals the nature of the HRS active vibrational bands and enables us to get insights about the involvement of each atom in the structural modifications upon temperature
Labeeb, Abd El-Hamied Ahmad Mohammad. "The rotational viscosity and field-induced transitions in the intermediate phases of ferroelectric liquid crystals." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/the-rotational-viscosity-and-fieldinduced-transitions-in-the-intermediate-phases-of-ferroelectric-liquid-crystals(ab186cd9-0c25-4b31-83db-15ec9cfdaeab).html.
Повний текст джерелаWang, Ge. "Phase switching behaviour in lead-free Na0.5Bi0.5TiO3-based ceramics." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/phase-switching-behaviour-in-leadfree-na05bi05tio3based-ceramics(267b315d-3757-4865-9f88-5eeed76d61c4).html.
Повний текст джерелаDžiaugys, Andrius. "Influence of impurities on dielectric properties of ferroelectric and superionic crystals." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2011. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2011~D_20110628_134612-56944.
Повний текст джерелаŠiai dienai ypač populiarūs ferroelektrikai susidedantys iš kelių feroiškai aktyvių subgardelių, kurių persitvarkymas fazinio virsmo temperatūroje atskleidžia naujų, dar neaprašytų reiškinių. Prie šių medžiagų priskiriami antiferoelektrikai, ferielektrikai ir multiferoikai. Šiame darbe buvo tiriama nauja medžiagų šeimos MNP2X6 (M = Cu, Ag; N=In, Cr, Bi; X=S, Se ), kurios pasižymi ferielektrinėmis bei multiferoinėmis savybėmis, ir kurių dielektrines ir elektrines savybes galima efektyviai keisti įvedant priemaišas. Minėtų medžiagų dielektrinės ir elektrinės savybės buvo tiriamos dielektrinės spektroskopijos metodais, kurie leidžia tirti kristalų kolektyvinius reiškinius susijusius su tvarkos – netvarkos bei poslinkio tipo faziniais virsmais, jonų migracija bei dipolių užšalimu (stiklėjimu) plačiame dažnių (10-5 Hz iki 3 GHz) bei temperatūrų (25 K iki 500 K) intervaluose. Įvedus 10% Ag jonų vietoj Cu jonų ferielektriniame kristale CuInP2S6 fazinio virsmo temperatūra pasislenka į žemesnias temperatūras, o padidinus indžio koncentraciją fazinio virsmo temperatūra pasislenka į aukštesnes temperatūras. Minėtų kristalų fazinių virsmų temperatūrų skirtumas 50 K. Sumaišius skirtingomis proporcijomis feroelektriką (CuInP2S6) su antiferoelektriku (CuCrP2S6) stebima dipolinio stiklo fazė. Iš dielektrinių matavimų stiklo fazėje buvo paskaičiuota relaksacijos trukmių pasiskirstymo funkcija, kurios aprašymas dvigubos potencialinės duobės modeliu leido susieti mikroskopinius kristalo... [toliau žr. visą tekstą]
Plonka, Rafael. "Impact of the interface on the paraelectric-to-ferroelectric phase transition in epitaxial BaSrTiO_tn3 thin film capacitors." Jülich Forschungszentrum, Zentralbibliothek, 2007. http://d-nb.info/1000127257/34.
Повний текст джерелаReis, Idalci Cruvinel dos [UNESP]. "Estudo das propriedades físicas de sistemas ferroelétricos com estruturas tipo Aurivillius." Universidade Estadual Paulista (UNESP), 2015. http://hdl.handle.net/11449/133940.
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Neste trabalho, as características estruturais, microestruturais, ferroelétricas e dielétricas de materiais ferroelétricos com estruturas laminares de bismuto (BLSFs), conhecidos como Aurivillius, foram investigadas. Os sistemas objetos de estudo foram compostos bicamadas (SrBi2Nb2O9, SrBi2Ta2O9, BaBi2Nb2O9) e tricamadas (Bi4Ti3O12), onde foi considerada a dopagem do sítio A da estrutura com lantânio (La3+). As propriedades físicas, portanto, foram investigadas considerando a influência do La3+ para várias concentrações. As cerâmicas foram preparadas pelo método de reação de estado sólido com sinterização em temperaturas acima de 1000 °C, para todos os casos. Para o estudo das propriedades estruturais e microestruturais, foram utilizadas as técnicas de difração de raios-x, Espectroscopia Raman, Microscopia Eletrônica de Varredura (MEV) e Espectrometria de Dispersão de Energia (EDS). As propriedades ferroelétricas e dielétricas foram investigadas a partir da dependência da polarização com o campo elétrico e resposta dielétrica com temperatura, respectivamente. Fases puras foram verificadas para todos os sistemas e analisadas com refinamento pelo método de Reitveld. Os resultados apresentaram indícios de alterações nas estruturas das cerâmicas, o que pode ser associado à influência do lantânio na estrutura. Essas alterações foram confirmadas nas medidas de MEV, onde foi possível observar um aumento significativo dos tamanhos médios dos grãos com aumento do dopante para os sistemas bicamadas e uma redução para o sistema tri-camadas. As medidas de Raman identificaram os modos ativos característicos dos sistemas Aurivillius para todos os sistemas estudados, com influência do conteúdo de lantânio na estrutura. As propriedades ferroelétricas foram confirmadas para todos os casos com uma pequena contribuição da condutividade, que pode ser a causa da obtenção de ciclos de histerese aquém da saturação para alguns casos. Em particular, o sistema SrBi2Ta2O9 revelou ciclos bem característicos e definidos, enquanto o sistema BaBi2Nb2O9 mostrou o comportamento esperado para os ferroelétricos relaxores. Picos bem definidos foram observados na resposta dielétrica para todos os casos, observando uma forte influência do conteúdo de dopante nos parâmetros dielétricos. As características da transição de fases revelam comportamentos associados tanto a um ferroelétrico normal quanto ao comportamento típico de relaxores. Este efeito foi discutido detalhadamente para cada caso. É importante destacar que, para todos os casos, baixos valores de perdas dielétricas foram obtidos, muito abaixo dos reportados na literatura para sistemas Aurivillius. Diante destes resultados, os sistemas aqui estudados são fortes candidatos para aplicações tecnológicas.
In this work the structural, microstructural, ferroelectric and dielectric characteristics of ferroelectric materials with bismuth layer structures (BLSFs), known as Aurivillius, were investigated. The studied materials were based on bi-layers (SrBi2Nb2O9, SrBi2Ta2O9, BaBi2Nb2O9) and tri-layer (Bi4Ti3O12) systems, where the lanthanum (La3+) doping in the A-site of the structure has been considered. The physical properties where, therefore, investigated considering the influence of La3+ at various concentrations. The ceramics were prepared by the solid state reaction method for temperatures above 1000 °C for all the cases. For the investigation of the structural and microstructural properties the x-ray diffraction technique, as well as Raman spectroscopy, Scanning Electron Microscopy (SEM) and Energy Dispersive of Spectrometry (EDS) were used. The ferroelectric and dielectric properties were investigated from the electric field dependence of the polarization and dielectric response with temperature, respectively. Pure phases were found for all the systems and analyzed with structural refinement by the Reitveld’s method. The results showed changes in the structure of the ceramics, which can be associated with the influence of the lanthanum content in the structure. These changes were confirmed in the SEM measurements, where a significant increase in average grain size with the increase of the doping content for bi-layer systems, as well as a reduction in average grain size for the tri-layer system, has been observed. The Raman measurements showed the characteristic bands of the Aurivillius systems, with influence of the lanthanum content in the structure, for all the cases. The ferroelectric properties were confirmed in all cases, with a small contribution of the conductivity, which can be the cause for the observation of unsaturated loops in some cases. Particularly, the SrBi2Ta2O9 system showed very well defined hysteresis loops and the BaBi2Nb2O9 system showed the expected behavior for relaxor ferroelectrics. On the other hand, well defined peaks were observed in the dielectric response for all cases, showing a strong influence of the dopant content in the dielectric parameters. The phase transition characteristics revealed behaviors associated with both normal and relaxor ferroelectrics. This effect has been discussed in details for all the cases. Very low values of the dielectric losses were found, when compared to those reported in the literature for typical Aurivillius systems. This result makes the materials studied here promissory systems for practical applications.
FAPEG: 201310267000048
Behrendt, Karsten. "Der Einfluss von Defekten auf das Schaltverhalten ferroelektrisch modulierter Substanzen." Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2015. http://hdl.handle.net/11858/00-1735-0000-0028-873E-C.
Повний текст джерелаLeist, Jeannis-Nicos, Jakob Sidoruk, Holger Gibhardt, Klaudia Hradil, Martin Meven, and Götz Eckold. "Domain redistribution and ferroelectric phase transition in SrTiO 3 under the influence of an electric field and mechanical stress." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-187976.
Повний текст джерелаLeist, Jeannis-Nicos, Jakob Sidoruk, Holger Gibhardt, Klaudia Hradil, Martin Meven, and Götz Eckold. "Domain redistribution and ferroelectric phase transition in SrTiO 3 under the influence of an electric field and mechanical stress." Diffusion fundamentals 12 (2010) 69, 2010. https://ul.qucosa.de/id/qucosa%3A13899.
Повний текст джерелаPeräntie, J. (Jani). "Electric-field-induced dielectric and caloric effects in relaxor ferroelectrics." Doctoral thesis, Oulun yliopisto, 2014. http://urn.fi/urn:isbn:9789526204406.
Повний текст джерелаTiivistelmä Tässä työssä tutkittiin dielektristen ominaisuuksien ja lämpötilan käyttäytymistä teknologisesti merkittävissä (1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) ja (1−x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 (PZN-PT) ferrosähköisissä relaksorimateriaaleissa sähkökentän vaikutuksen alaisena. Tutkimuksen erityishuomion kohteena olivat sähköisesti indusoidut faasimuutokset sekä sähkökalorinen ilmiö, jotka liittyvät läheisesti nykyisiin sekä tulevaisuuden sovellutuksiin. Monikiteisiä PMN-PT keraamikoostumuksia (x=0−0,3) valmistettiin sekä reaktiivisella sintrauksella että kolumbiittimenetelmällä. Lisäksi tutkimuksessa käytettiin kaupallisia PMN-PT erilliskiteitä, joiden koostumus on lähellä morfotrooppista faasirajaa. Työssä käytetty PZN-PT erilliskide kasvatettiin jäähdyttämällä korkean lämpötilan liuoksesta. Materiaaleja tutkittiin pääosin lämpötilan ja dielektristen ominaisuuksien mittauksilla. Kun PMN-PT keraamisysteemiin kohdistettiin alhainen sähkökenttä, sähkökalorisen ilmiön selkeä maksimiarvo havaittiin lähellä materiaalin termistä depolarisaatiolämpötilaa. Suuremmilla sähkökentän arvoilla sähkökalorinen ilmiö voimistui ja sen lämpötila-alue laajeni korkeampiin lämpötiloihin polaaristen nanoalueiden kytkeytymisen vuoksi. Sähkökalorisen lämpötilamuutoksen maksimi vaihteli välillä 0,77−1,55 °C sähkökentän arvolla 50 kV/cm. Lisäksi lämpötilamittaukset depoolatulle PMN-0,13PT koostumukselle osoittivat, että sähkökalorisen ilmiön ohella materiaalissa esiintyy makroskooppisen polarisaation muodostumiseen liittyvä palautumaton lämpöenergia depolarisaatiolämpötilaa pienemmissä lämpötiloissa hystereesihäviön ja mahdollisen faasimuutoksen vaikutuksesta. PMN-PT erilliskiteiden dielektrisyys- ja lämpötilavasteessa havaittiin selkeitä muutoksia sähkökentän vaikuttaessa <001> ja <011> kidesuuntiin. Nämä muutokset ovat selitettävissä PMN-PT:n polarisaation kompleksisten rotaatiosuuntien ja erityyppisten sähkökenttä-lämpötila -faasidiagrammien stabiilisuusalueiden avulla. PMN-PT kiteiden mittauksissa havaittiin myös ensimmäinen suora osoitus väliaikaisesti käänteisestä sähkökalorisesta ilmiöstä sähkökentän kasvaessa. Lisäksi mitatut PZN-PT erilliskiteen sähkökaloriset ominaisuudet transitiolämpötilan läheisyydessä pystyttiin pääpiirteittäin mallintamaan käyttämällä yksinkertaista hilamallia ja keskimääräisen kentän approksimaatiota. Mallinnuksen mukaan sähkökalorinen ilmiö aiheutuu pääasiassa sähköisesti indusoidusta dipolientropian alenemisesta
Cheng, Juan. "Light scattering study on phase transition and micro-heterogeneity in relaxor ferroelectrics (1-x)Pb(Mg₁/₃Nb₂/₃)O₃-xPbTiO₃ and (1-x)Pb(Zn₁/₃Nb2₂/₃)O₃-xPbTiO₃ /." access full-text access abstract and table of contents, 2009. http://libweb.cityu.edu.hk/cgi-bin/ezdb/thesis.pl?phd-ap-b23749179f.pdf.
Повний текст джерела"Submitted to Department of Physics and Material Sciences in partial fulfillment of the requirements for the degree of Doctor of Philosophy." Includes bibliographical references (leaves 140-167)
Džiaugys, Andrius. "Priemaišų įtaka feroelektrinių ir superjoninių kristalų dielektrinėms savybėms." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2011. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2011~D_20110628_134724-71267.
Повний текст джерелаNowadays the ferroelectrics containing of several feroically active sublattices are very attractive, because interactions between these sublattices can caused novel phenomena. Antiferroelectrics, ferrielectrics and multiferoics belong to these materials. In this work new crystalline materials MNP2X6 (M = Cu, Ag; N=In, Cr, Bi; X=S, Se) were investigated, which have ferrielectric and multiferoic properties. The dielectric and electric properties of above mentioned materials have been investigated by broadband dielectric spectroscopy methods, which allows to analyze the collective processes related to order – disorder and displacive phase transitions, ions migration and freezing of dipoles (glassy state) in wide temperature (25 K - 500 K) and frequency (10-5 HZ - 3 GHz) ranges. By substitution or doping it becomes possible to tailor the ferroelectric materials to different properties. In this work is determined that the substitution of 10% Cu ions by Ag ions shifts the phase transition temperature of CuInP2S6 crystal toward lower temperatures while the addition of In ions shifts the phase transitions temperature toward the higher ones. The phase transition temperature difference is about 50 K for mentioned crystals. If the ferroelectric crystal CuInP2S6 is mixed with the antiferroelectric CuCrP2S6 the dipole glass phase occupies the middle of the phase diagram. The distribution of relaxation times has been calculated from the broadband dielectric spectra of dipolar glasses. The... [to full text]
Schader, Florian Herbert [Verfasser], Kyle G. [Akademischer Betreuer] Webber, and Bai-Xiang [Akademischer Betreuer] Xu. "Mechanical Stability of the Electromechanical Properties and Phase Transitions in Lead-Containing and Lead-Free Ferroelectrics / Florian Herbert Schader. Betreuer: Kyle G. Webber ; Bai-Xiang Xu." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2016. http://d-nb.info/1112332995/34.
Повний текст джерелаRoukos, Roy. "Transitions de phases dans des oxydes complexes de structure pérovskite : cas du système (1-x)Na0,5Bi0,5TiO3 - xCaTiO3." Thesis, Dijon, 2015. http://www.theses.fr/2015DIJOS020/document.
Повний текст джерелаThe solid solutions (1-x)Na0,5Bi0,5TiO3 (NBT) – xCaTiO3 (CT) were studied by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, impedance spectroscopy and DSC. These materials have a perovskite crystalline structure. This study reveals not only the complexity but also the richness of physical phenomena in these compounds: phases transitions sequences, the Ca2+ effect on the physical-chemistry properties and the relation between dielectric properties and crystalline structure. Thereby, (1-x)NBT – xCT solid solutions (0 ≤ x ≤ 1.00) were synthesized by chemical solid route, then they were sintered by a particular procedure in order to avoid sodium and bismuth volatilization. The solid crystalline characteristics obtained prove clearly the necessity to distinguish three fields as a function of x values. First of all, for increasing x at room temperature, there is a first region so called region I (x ≤ 0.07), wherein the crystalline structure of solid solutions obtained has a space group R3c identical to that of pure NBT. For the highest values of x, (Region II, x ≥ 0.15), the solid obtained has a space group Pnma, identical to that of pure CT. Finally, between these two regions, (0.09 ≤ x ≤ 0.13), the solid solutions obtained are biphasic, R3c + Pnma, limited to appellations of the space groups formed phases. In region I, upon heating, phase transition sequence R3c → R3c + Pnma → Pnma was determined; the corresponding transition temperatures move to low values with increasing Ca2+ concentration. These solids are ferroelectric at room temperature and then develop a relaxor character, by coexistence of two phases, with increasing temperature. In region II, these solids reveal a relaxor behavior at room temperature. However, a diffuse phase transition within the orthorhombic phase Pnma has been identified; the solid changes from relaxor to paraelectric while maintaining the same crystal structure. This phenomenon was explained by the formation of micro or nano-polar regions. Region III, demonstrated for the first time, is characterized by thermal hysteresis, and explained by the relation between crystalline microstructure and dielectric properties. Finally, all our results were assembled in an original phase diagram as a function of concentration of Ca2+ dopant and temperature
Nóbrega, Jaldair Araújo e. "Síntese e Caraterização de MgxPb(1-x)TiO3." Universidade Federal de São Carlos, 2015. https://repositorio.ufscar.br/handle/ufscar/9373.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
We report the investigation of structural, optical and electrical properties of the MgxPb(1- x)TiO3 ceramic system produced by mechanosynthesis. The solid state reaction manufacturing method has been proved to be an efficient alternative to manufacture this type of material. By using Raman spectroscopy techniques it was possible observe the effects induced by pressure, from 0 up to 14 GPa, and by temperature from 10 up to 723 K for the samples with x ranging from 0.2 to 1.0. Complementary characterization techniques were also used, including X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Optical Absorption Spectroscopy and Electrical Impedance. XRD enabled the study of structural changes related to the increase in Mg concentrations. Raman analysis allowed the study of vibrational modes, in particular the transversely optical mode E(1TO) of lower frequency in order to characterize the phase transition from tetragonal-ferroelectric to cubic-paraelectric phases. From these results it was possible to construct a phase diagram that relates Mg concentration, temperature and hydrostatic pressure, yielding determine critical temperature (Tc) and critical pressure (Pc) in which phase transition occurs for each sample. Permittivity dielectric measurements were performed for each material, through which it was possible to compare the effects of Mg ratios in the modification of the values of these properties. Finally, a study of optical absorption as a function of Mg concentration was conducted, evidencing changes in gap energies related to the increase of Mg incorporation. The lowest values, 2.86 and 2.9 eV correspond to samples with concentrations of 0.4 and 0.2, respectively. Thus, from a technological point of view, these characteristics are interesting for applications in devices operating in the microwave region.
Neste trabalho foram investigados os efeitos estruturais, ópticos e elétricos do sistema cerâmico MgxPb(1-x)TiO3 produzido por mecano-síntese. O método de fabricação de reação de estado sólido mostrou-se uma alternativa eficiente de fabricação do material. Utilizandose de técnicas de espectroscopia Raman, foram observados os efeitos da pressão, de 0 a 14 GPa, e temperatura, de 10 a 723 K, para as amostras com x variando de 0,2 a 1,0. Também foram usadas técnicas complementares de caracterização entre elas a Difração de Raio-X (DRX), Microscopia Eletrônica de Varredura (MEV), Absorção Óptica e de Espectroscopia de Impedância Elétrica. A técnica de DRX possibilitou o estudo da alteração estrutural relacionada ao aumento das concentrações de Mg. As análises Raman permitiram o estudo dos modos vibracionais, em especial o modo transversal óptico E(1TO) de mais baixa frequência, a fim de caracterizar a transição de fase, da fase tetragonal ferroelétrica para a cúbica paraelétrica. A partir desses resultados foi possível construir um diagrama de fase relativo à concentração de Mg, com a temperatura e pressão hidrostática, obtendo-se temperatura crítica (Tc) e pressão crítica (Pc) nas quais ocorrem transição de fase para cada amostra. Foram realizadas medidas de permissividades dielétricas para cada material, por meio das quais foi possível a comparação dos efeitos das proporções Mg na alteração dos valores dessas propriedades. Por fim, foi realizado um estudo de absorção óptica em função da concentração de Mg, onde mostrou-se que há alteração do gap relacionada ao aumento da concentração de Mg. Os valores mais baixos, 2,86 e 2,9 eV correspondem a amostras com concentração de 0,4 e 0,2, respectivamente. Assim, do ponto de vista tecnológico, as características encontradas mostram-se úteis para dispositivos que operam na região das micro-ondas.
Kvitek, Zdenek. "Etude de la transition ferroélectrique-ferroélastique du KD2PO4 : forme du front de phase en fonction du gradient thermique." Université Joseph Fourier (Grenoble), 1995. http://www.theses.fr/1995GRE10046.
Повний текст джерелаPlonka, Rafael [Verfasser]. "Impact of the interface on the paraelectric-to-ferroelectric phase transition in epitaxial BaSrTiO_tn3 thin film capacitors / Rafael Plonka. [Forschungszentrum Jülich in der Helmholtz-Gemeinschaft, Institut für Festkörperforschung (IFF), Elektronische Materialien (IFF-6)]." Jülich : Forschungszentrum, Zentralbibliothek, 2007. http://d-nb.info/1000127257/34.
Повний текст джерелаBarbosa, Quiroga David Antonio. "Processamento e propriedades do sistema ferroelétrico livre de chumbo (Bi, Na)TiO3 (Bi, K)TiO3 BaTiO3." Universidade Federal de São Carlos, 2015. https://repositorio.ufscar.br/handle/ufscar/5075.
Повний текст джерелаFinanciadora de Estudos e Projetos
In this work, the lead-free ceramic powders of xBi0,5Na0,5TiO3 - (0,7186 - 0,7143x) Bi0,5K0,5TiO3 - (2814 - 2857x) BaTiO with x = 0,8200; 0,8625; 0,8792, 0,9126 and 0,9300 (BNBK1000x) were prepared by the solid state reaction method, followed by conventional densification. The ceramic bodies showed high density, which was higher than 95% in obtained samples. For the all ceramics were performed structural, micro structural, electric and anelastic characterizations. The X-ray diffraction (XRD) analysis indicated the formation of the complex perovskite type crystaline structure for all compositions analyzed without the presence of spurious phases. By the structural refinement by the Rietveld method of XRD data and by Raman spectroscopy were observed that for BNBK912 and BNBK930 compositions, at room temperature, the predominant symmetry is rhombohedral (R3c), while the BNBK820 composition exhibits a tetragonal crystalline symmetry (P4mm). For the BNBK879 and BNBK826 compositions presented a mixture of phases, possibly with rhombohedral and tetragonal symmetry, reaveling the morphotropic phase boundary (MPB) of this system. The microstructure of BNBK1000x ceramics was investigated by scanning electron microscopy (SEM), where the morphology grains with irregular sizes and shapes, where the increased levels of K+ and Ba2+ ions suppressed the growth of the grains. The characterizations by Raman spectroscopy at room temperature showed broad Raman modes, due to the chemical and/or structural disorder related to the substitution of elements Bi and Na for Ba and K. The ferroelectric characterizations at room temperature of the BNBK1000x ceramics showed that all compositions studied are ferroelectric. Through the comparison among the measurements of electrical impedance and mechanical spectroscopy, was possible to identify the different structural and electric phase transitions that were employed in the construction of a pseudodiagram of phases for the BNBK1000x compositions.
Neste trabalho, os pós-cerâmicos livres de chumbo xBi0,5Na0,5TiO3 - (0,7186 - 0,7143x) Bi0,5K0,5TiO3 - (2814 - 2857x) BaTiO com x = 0,8200; 0,8625; 0,8792, 0,9126 e 0,9300 (BNBK1000x) foram obtidos através do método de reação de estado sólido, seguido por densificação convencional. Os corpos cerâmicos obtidos apresentaram elevada densificação, sendo maior que 95% nas amostras produzidas. Para todas as cerâmicas foram realizadas caracterizações estruturais, microestruturais, elétricas e anelásticas. As análises por difração de raios-X (DRX) indicaram a formação da estrutura cristalina tipo perovkista complexa para todas as composições analisadas, sem a presença de fases espúrias. O refinamento estrutural, pelo método de Rietveld, dos resultados de DRX e os resultados de espectroscopia Raman apontam que para as composições BNBK930 e BNBK912 a simetria predominante em temperatura ambiente é romboédrica (R3c), enquanto que a composição BNBK820 apresenta a simetria cristalina tetragonal (P4mm). Já as composições BNBK879 e BNBK862 apresentaram uma mistura de fases, possivelmente com simetrias romboédrica e tetragonal, evidenciando o contorno de fase morfotrópico (CFM) deste sistema. A microestrutura das cerâmicas de BNBK1000x foi investigada por microscopia eletrônica de varredura (MEV), onde a morfologia apresentada pelas diferentes composições estudadas possuíam grãos com tamanhos e formatos irregulares, sendo que o aumento dos teores dos íons de K+ e Ba2+ inibiram o crescimento dos grãos. A caracterização por espectroscopia Raman, em temperatura ambiente, apresentou modos Raman amplos, mostrando um elevado grau de desordem química e/ou estrutural devido à substituição dos elementos Bi e Na por Ba e K. As caracterizações ferroelétricas, também em temperatura ambiente das cerâmicas de BNBK1000x mostraram que todas as composições estudadas possuem propriedades ferroelétricas. Através da comparação entre as medidas de impedância elétrica e anelástica, levando em consideração as caracterizações estruturais e ferroelétricas com temperatura, foi possível identificar diferentes transições de fase estruturais e elétricas, que foram empregadas na construção de um pseudo-diagrama de fases para as composições de BNBKx.
Si, Ahmed Fariza. "Elaboration et caractérisation de matériaux de type pérovskite, à faible teneur en plomb ou dépourvus de plomb." Thesis, Bourgogne Franche-Comté, 2017. http://www.theses.fr/2017UBFCK005.
Повний текст джерелаMost of ferroelectric materials currently used in the industrial applications are lead-based ceramics. Such compounds are harmful to the environment due to the toxicity and volatility of lead oxide during the preparation process of these materials. Therefore, environmental friendly lead-free ceramics or low-lead content materials with equivalent properties has become one of the main topics as an alternative to lead-based ceramics. In this view, the present work focuses on investigating materials with formulas :Ba1-xPbx(Ti1-yZry)O3 (2.5% ≤ x ≤ 10%) and Ba1-xEr2x/3(Ti1-yZry)O3.Solid state route was used for materials elaboration. The experimental techniques used are thermogravimetric analysis, dilatometry, X-ray diffraction, scanning electron microscopy coupled to an EDX microanalysis system and impedance spectrometry. The use of these various processes allowed us to optimize the synthesis conditions and to obtain dense ceramics with density superior to 90%. In addition, the structural parameters were refined by the Rietveld method and then discussed. Furthermore, these ceramics exhibited normal and/or relaxor ferroelectric properties then some of them have very interesting dielectric characteristics in the vicinity of room temperature. Such lead-free ceramics or low-lead content materials reduce significantly the environmental pollution. Due to their good dielectric performances, they could be potential candidates for replacing lead-based materials currently used in various electronic equipments
Crossley, Samuel. "Electrocaloric materials and devices." Thesis, University of Cambridge, 2013. https://www.repository.cam.ac.uk/handle/1810/245063.
Повний текст джерелаHerklotz, Andreas. "Einfluss reversibler epitaktischer Dehnung auf die ferroische Ordnung dünner Schichten." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-87097.
Повний текст джерелаIn this work, the effect of epitaxial strain on the properties of ferromagnetic and ferroelectric perovskite thin films is studied. Single-crystalline piezoelectric Pb(Mg1/3Nb2/3)0.72Ti0.28O3 (001) substrates (PMN-PT) are utilized to reversibly change the biaxial strain state of the films. The measurements performed by this “dynamic” approach are complemented by studying statically strained films grown on LaAlxSc1-xO3 buffer layers with deliberately tuned lattice misfit. Three different material systems are investigated: the ferromagnetic oxides La0.8Sr0.2CoO3 and SrRuO3 and the ferroelectric compound Pb(Zr,Ti)O3. In case of La0.8Sr0.2CoO3 a strain-induced transition from the known ferromagnetic phase to a magnetically less ordered spinglas-like phase is observed. No indications for an effect on the Co spin state are found. In epitaxial SrRuO3 films tensile strain is causing a structural phase transition from the bulk-like orthorhombic structure to an out-of-plane oriented tetragonal phase. The magnetic easy axis is in the film plane. Reversible strain experiments show a significant effect on the ferromagnetic ordering temperature and point to a small change of the magnetic moment. The strain effect on the electric transport properties is also determined. Pb(Zr,Ti)O3 as a standard ferroelectric material is used to study the influence of biaxial strain on the ferroelectric switching behaviour of thin films for the first time. At small electric fields the measurements reveal the typical signs of creep-like domain wall motion caused by wall pinning. In this regime the switching process is accelerated strongly under piezo-compression. For higher electric fields a transition of the domain wall motion to the depinning regime is observed. Here, the switching kinetics is slowed down moderately by compressive strain
Lu, Teng. "Structure and Property Evolution Induced by the Phase Transitions in Several Antiferroelectric Materials." Phd thesis, 2017. http://hdl.handle.net/1885/144426.
Повний текст джерелаLee, Jiun-Ting. "Phase transitions and diffusion of colloid-polymer systems and thin ferroelectric films for device applications." Thesis, 2000. http://hdl.handle.net/1911/19527.
Повний текст джерелаSchiemer, Jason Alexander. "Average and local structure, phase transitions and physical properties of key lead-free ferroelectric materials." Phd thesis, 2012. http://hdl.handle.net/1885/149880.
Повний текст джерелаLi, Chen-Liang, and 李振良. "Behavior of Field-Induced Strain and Ferroelectric/ Antiferroelectric Phase Transitions in Lead Zirconate Titanate Stannate System." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/21339131023772881095.
Повний текст джерела國立台灣工業技術學院
機械工程技術研究所
85
ABSTRACT In this thesis, the ferroelectric to antiferroelectric phase transformation of Pb0.99Nb0.02[(Zr1- xSnx)1-yTiy]0.98O3 (PNZST) as a function of temperature and field as well as the annealing effect on material properties were investigated by measuring P-E curves, dielectric constants, field-induced strains and remanent polarizations as function of frequency.The PNZST powders were prepared by solution coating method.Samples were sintered at 1200 ℃for 2 hours and heat treatedat 1250℃for 2~60 hours using double-crucible method. Polarization curves were measured with various frequenciesby modified Sawyer-Tower circuit, and dielectric constants were studied using a gain-phase analyzer. Field-induced strains as a function of temperature were measured by means of a triangular laser measuring system with an oil bath. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed in microstructural analysis. Experimental results show that samples can get larger remanent polarization(Pr) by appropriate heat treatments, but Pr decreased with increasing frequency and decreasing Ti content. Dielectric constant maximum that occurs before multiple cell shows significant increase by suitable heat treatment and increasing Ti content. Dielectric relaxation disappeared at ferroelectric to antiferroelectric transformation. Field-induced strains are temperature dependent and the strains that use the same field strength of 30kV/cm for 43/7/2 specimens treated at 1250 ℃for 20 hours can produce a maximum value of 0.22﹪around the ferroelectric to antiferroelectric transition temperature (TF/A) (at 77℃). When the temperature increased over TF/A, the field- induced strain still showed a pronounced value of 0.16﹪, and can achieve higher by increasing the field. The P-E curves of 43/7/2 show complete ferroelectric behavior, but the specimens contain incommensurate phase from the results of microstructural investigations, and the P-E curves can change to antiferroelectric by increasing frequency, indicating that the transition between the ferroelectric commensurate and the antiferroelectric incommensurate phase is relatively easy, and the incommensuration is the origin of the second-order transition in this material. Ferroelectric to antiferroelectric phase transition which shows similar behavior of the soft-mode produces a maximum strain during transition. When the specimen is over transformation temperature and in the antiferroelectric imcommensurate phase range, high strain is produced by field- induced AFE/FE transformation with a decoupling of the polarization of the modulated polar structure.
Maier, Bernd Jens [Verfasser]. "Phase transitions in advanced relaxor-ferroelectric materials with a perovskite-type structure / vorgelegt von Bernd Jens Maier." 2010. http://d-nb.info/1003355994/34.
Повний текст джерелаYeh, Chien-Hung, and 葉建宏. "Successive Phase Transitions in Relaxor Ferroelectric PMN-PT and PZN-PT Single Crystals by Brillouin Light Scattering." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/49729987007008618697.
Повний текст джерела輔仁大學
物理學系
88
Abstract The longitudinal Brillouin back-scattering spectra and dielectric permittivities have been measured as a function of temperature in relaxor ferroelectric crystal (Pb(Mg1/3Nb2/3)O3) 1-x(PbTiO3)x (PMN-xPT:x=0.24, 0.32, 0.31 and 0.33), and (Pb(Zn1/3Nb2/3)O3)1-x(PbTiO3)x (PZN-xPT:x=0.085 and 0.095). These crystals have successive phase transitions (beside PMN- 24%PT). A sharp ferroelectric phase transition which is associated with a minimum in phonon frequency and an abrupt change in polarization, was observed in the high tempre- ature region (above 400 K). As temperature decreases, a diffuse phase transition which is associated with a broad frequency dependent dielectric spectrum and a gradual evolution in polarization. In addition, the nature of the thermal hysteresis for the dielectric permittivity confirms that these transition are first-order (high-temperature phase transition) and diffuse first-order (low-temperature diffuse phase transition), respectively.
Chih-Hung, Chen, and 陳志洪. "Phase Transitions and Electric-Field Effects in Relaxor—Based Ferroelectric Single Crystals (PbZn1/3Nb2/3O3)1-x(PbTiO3)x." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/00722933631130246761.
Повний текст джерелаChen, Horng-Ying, and 陳虹穎. "Phase transition in ferroelectric liquid crystal." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/01028338628113076240.
Повний текст джерела國立中央大學
物理研究所
91
Abstract High-resolution heat-capacity measurements have been conducted near the Sm-A to Sm-C transition in free-standing films of liquid-crystal compound C7. We find that the profiles of associated heat-capacity anomalies are strongly thickness-dependent and exhibit a novel crossover behavior in reduced dimensions. This result is similar to the observed in MDW1397 liquid-crystal films. Furthermore, heat-capacity measurements have provided the direct confirmation of surface transitions from Sm-C immediately to the Sm-G phase in C7. The molecular interactions are found to be Thermal-Casimir force.
Liou, Sheng-Cheng, and 劉信成. "Electrical properties and Ferroelectric Phase Transition of Donor-Doped Barium Titanate." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/40249470827692241316.
Повний текст джерела大同工學院
材料科學(工程)研究所
81
PTC鈦酸鋇之商品化應用已超過三十年,但是仍無法合理解釋為什麼室溫電 阻係數會隨著添加量而改變 以往研究各種摻雜施體的含量約在0.3%摩耳 比時室溫電阻值最低,遠離0.3%摩耳比時室溫電阻率均增加,相對使ρ/ ρ 值減少本研究為瞭解添加 Sm,Nd 和 Pr 三 室溫電阻率差異較大的元 素(Fig. 1) 之電導機構, 改變不同的含量測試電阻率,晶格常數, 介電 常數及飽和極化值等隨溫度變化的改變以了解晶界上電子能障減少或消失 的原因另外,為瞭解不同取代型式對鈦酸鋇半導體之電導機構的影響,實驗 中亦添加Nb對其做初步的探討由實驗結果中顯示添加Sm,Nd 和 Pr 其室溫 電阻率未見有甚大的差異此結果與以往報告有所不同(Fig.1) 並且由X- ray 繞射結果可知所添加之元素其室溫電阻率與在正方相的c/a值有密切 的關係而添加高含量的元素其居禮溫度有降低的趨勢,此結果有必要進一 步了解 Donor-doped semiconducting BaTiO has a remarkable property of positive temperature coefficient of resistivity(PTC). Although PTC BaTiO has been in use for more than 30 years,it is difficult even today to explain the resistivity at room temperature as a function of doping content. In past studies, the addition of 0.3 at% of donor dopes to BaTiO a dramatic decrease in the resistivity is observed at room temperature. Beyond this optimum doped, the room temperature resistivity will increase and the amount of increase depends on the kind of donors. The purpose of this study is to understand the conduction mechamism of Sm, Nd and Pr doped BaTiO which show large difference of room temperature resistivity.(Fig.1)We measured the variations of resistivity, lattice constant and saturation polarization of various amount donor - doped BaTiO. The measurementswill be under different temperature ranges.From the resultsofthose measurements willbe hopefully to understand the causes ofthediminished or decreased energy barrier at grain boundaries. In order to understand effect of different substitution type on conduction mechanism of semiconducting BaTiO, Nb is also used to as donor. From the results of ρ-T of Sm, Nd, and Pr doped BaTiO, We found that there is no much room temperature resistivity difference among those donors. This is results is different from that of O.Saburi. By examing X-ray diffraction results, the room temperature resistivity of donor-doped BaTiO is believed to be close-related to c/a ratio of tetragonal phase. Also, high room temperature resistivity for higher doping concentration samples is may be to shifting the Curie temperature to lower temperature. Although this result has to be examined in more detail.
Amorim, Carlos de Oliveira. "Experimental and modeling studies of magnetoelectric multiferroic heterostructured materials." Doctoral thesis, 2019. http://hdl.handle.net/10773/27751.
Повний текст джерелаMateriais Multiferróicos são um tipo de materiais bastante exótico que apresentam simultaneamente dois ou mais tipos de propriedades ferróicas. Multiferróicos magnetoelétricos, em particular, são uma classe de materiais muito proeminente, principalmente devido às suas espantosas aplicações tecnológicas, tais como sensores magnéticos, dispositivos de conversão/colheita de energia, e memórias the alta eficiência. Todavia, materiais magnetoelétricos intrínsecos são verdadeiramente raros e ainda não possuem propriedades adequadas ao uso do dia-a-dia. Uma das razões para que isto aconteça prende-se com o facto dos requisitos para existência de magnetismo e ferroeletricidade na matéria serem a priori contraditórios, uma vez que enquanto os primeiros necessitam de orbitais dn semipreenchidas, os últimos tendem a favorecer orbitais d0. Porém, Multiferróicos magnetoelétricos extrínsecos não sofrem desta limitação pois não partilham a mesma fase sendo portanto uma abordagem promissora para a construção de um bom Multiferróico magnetoelétrico. Esta tese focar-se-á no estudo de sistemas contendo Fe e BaTiO3 como meio de se alcançarem novos efeitos magnetoelétricos. Um auto-compósito de BaTiO3:Fe é apresentado, que apesar da sua diminuta concentração de Fe (apenas 113 ppm atómicas), ainda assim apresenta um comportamento magnético ordenado. A magnetização do Fe apresenta duas variações bruscas no seu valor espontâneo, uma com M/M ≈ 32% e outra com M/M ≈ 14%. Estas transições magnéticas estão correlacionadas com as transições de fase ferroelétricas do BaTiO3 (ortorrômbica↔tetragonal e tetragonal↔cúbica). Este auto-compósito magnetoelétrico foi a motivação par ao uso da Teoria de Densidade Funcional (DFT) como meio para descobrir os mecanismos microscópicos por trás deste acoplamento magnetoelétrico tão intenso. O estudo de uma mono-camada de Fe colocada sobre várias células unitárias de BaTiO3 levaram à descoberta de várias interfaces com mudanças abruptas na sua magnetização espontânea, ora através do aumento ou diminuição dos momentos magnéticos do Fe, ora através da mudança entre a natureza antiferromagnética ou ferromagnética da camada de Fe. Contudo, o destaque dos estudos de DFT reside na descoberta de um tipo particular de interfaces onde ocorre uma transição de estado High-Spin–Low-Spin que consegue colapsar completamente o momento magnético atómico dos átomos de Fe, dependendo do campo cristalino local sentido por esses mesmos átomos. Baseado neste efeito, um dispositivo Multiferróico magnetoelétrico foi proposto. Sabendo a importância do campo cristalino para as transições de estado High-Spin–Low-Spin state, um estudo minucioso foi feito relativo ao gradiente de campo elétrico (EFG) nos sítios possíveis do BaTiO3, usando um estudo combinado entre Correlações Angulares Perturbadas (PAC) e DFT. Neste estudo, concluiu-se que PAC não é uma técnica hiperfina adequada para o estudo quantitativo do tensor EFG de interfaces de BaTiO3/Fe, dados os efeitos não desprezáveis das sondas radioativas na matriz de BaTiO3. Finalmente, foi feita a deposição de Heteroestruturas de BTO/Fe em substratos de LaAlO3, MgO, Al2O3 e SrTiO3 usando RF-Sputtering, assim como deposição de camadas de Fe em substratos de BaTiO3 cortados nos planos (100), (110) e (111) planes, usando Molecular Beam Epitaxy (MBE), numa tentativa de recrear as interfaces com efeitos magnetoelétricos mais apelativos, previstos pela modelação DFT. Os filmes finos depositados por sputtering mostraram o crescimento de múltiplos óxidos de Fe, Ba-Ti-O e Fe-Ti-O dependendo fortemente do substrato onde foram crescidos, assim como das condições de deposição e tratamentos térmicos. Porém, nenhum efeito magnetoelétrico foi observado nestes filmes. Por outro lado, os filmes depositados nos substratos de BaTiO3 mostraram grandes acoplamentos magnetoelétricos entre as fases ferroelétricas do BTO e a magnetização das camadas de Fe (à semelhança do que aconteceu no auto-compósito de BaTiO3:Fe). A ordem de grandeza destes acoplamentos está fortemente correlacionada com a interface do BTO onde o Fe foi depositado, apresentando uma enorme variação na magnetização espontânea e na coercividade para o caso da transição romboédrica↔ortorrômbica, até M/M ≈ 148% e HC/HC ≈ 183% respetivamente para o caso da orientação (110).
Tese realizada com apoio financeiro da FCT através da bolsa SFRH/BD/93336/2013.
Programa Doutoral em Física