Dissertations / Theses on the topic 'Ferroelectric perovskite'
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Zednik, Ricardo Johann. "Stress effects in ferroelectric perovskite thin-films /." May be available electronically:, 2008. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
Full textChu, Fan. "The ferroelectric phase transition in complex perovskite relaxors /." [S.l.] : [s.n.], 1994. http://library.epfl.ch/theses/?nr=1248.
Full textWhittle, 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.
Full textZhang, Qingteng. "Properties of Ferroelectric Perovskite Structures under Non-equilibrium Conditions." Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/4422.
Full textSakamoto, Wataru, Asaki Iwata, and Toshinobu Yogo. "Ferroelectric properties of chemically synthesized perovskite BiFeO_3–PbTiO_3 thin films." American Institite of Physics, 2008. http://hdl.handle.net/2237/11988.
Full textRandall, C. A. "A transmission electron microscopy study of normal and relaxor perovskite ferroelectric materials." Thesis, University of Essex, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376749.
Full textChen, Chen. "Synthesis, structural and ferroelectric properties of perovskite-like layered structured materials." Thesis, Queen Mary, University of London, 2015. http://qmro.qmul.ac.uk/xmlui/handle/123456789/9526.
Full textHettiarachchi, Chaminda Lakmal. "Organometal Halide Perovskite Solar Absorbers and Ferroelectric Nanocomposites for Harvesting Solar Energy." Scholar Commons, 2017. http://scholarcommons.usf.edu/etd/7034.
Full textBing, Yonghong. "Synthesis, structure and properties of high piezo-and ferroelectric complex perovskite systems /." Burnaby B.C. : Simon Fraser University, 2005. http://ir.lib.sfu.ca/handle/1892/2032.
Full textDhuvad, Pratikkumar. "FIRST-PRINCIPLES STUDIES OF FERROELECTRIC PROPERTIES IN ORGANIC CRYSTAL AND PEROVSKITE SUPERLATTICES." Diss., Temple University Libraries, 2018. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/524696.
Full textPh.D.
This thesis discusses structural and ferroelectric properties of two well-known classes of materials, perovskite oxides and Hydrogen bonded ferroelectrics, using first-principles calculations. Certain aspects of first principles calculations are central to the problems presented in this thesis. Such as the ability to calculate polarization based on the modern theory of polarization and calculation of ferroelectric property under finite electric displacement field. Therefore, these fundamental theoretical approaches are discussed following an opening section on the basic methodology of density-functional theory. In addition to the discussion on theoretical methods, a brief review of different phenomena and techniques crucial to alter/enhance ferroelectric properties at the interfaces of perovskite materials has been presented along with examples. The first problem presented in this thesis proposes and validates an alternative quantitative measure of ferroelectric(FE) and antiferrodistortive(AFD) instabilities by means of calculating inverse capacitance and layer inverse capacitance of layered perovskites. The presented methodological approach is applied to BaTiO$_{3}$/CaTiO$_{3}$ and PbTiO$_{3}$/SrTiO$_{3}$ superlattices and it precisely estimates FE and AFD instabilities. Here we also present an approach to accurately predict the ferroelectric instabilities in large period superlattices from the statistical coefficients obtained from short period superlattices. In the second problem, we study ferroelectricity in an organic crystal(croconic acid) for which ferroelectric polarization is close to that of bulk BaTiO$_{3}$. We employ new meta-GGA functional named SCAN and revisit all structural and ferroelectric properties. Calculated X-ray absorption spectra(XAS) qualitatively and quantitatively agrees well with experimental O K-edge spectra. By discussing the origin of each XAS peak and their characteristic we demonstrate with a systematic approach the connection between ferroelectricity and XAS in croconic acid. Best to our knowledge such relation has not been realized in past. This study could prove XAS as a new way to measure ferroelectric instability in hydrogen-bonded organic ferroelectrics.
Temple University--Theses
Glazkova, Elena. "The Role of Partial Surface Charge Compensation in the Properties of Ferroelectric and Antiferroelectric Thin Films." Scholar Commons, 2016. http://scholarcommons.usf.edu/etd/6501.
Full textChapman, 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.
Full textRavel, 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.
Full textPeng, Jiangguli. "Effect of the microstructure and orientation of grains on the performance of perovskite ferroelectric ceramics." Thesis, Le Mans, 2020. http://www.theses.fr/2020LEMA1013.
Full textFerroelectric materials have been widely applied in transducers, high-pressure generators, actuators, sensors... In this context, the ferroelectric materials are generally regarded as being related to an important class of smart materials. Among the most popular ferroelectric materials, those based on Pb(Zr,Ti)O3 (PZT) structures show the best performances in operating devices. Despite such achievements, the fundamental understanding of the physical characteristics continues to arouse the interest of a wide scientific community. On the other hand, in view of the environmental-friendly requirement, more attention have been paid by the researchers to lead-free ferroelectric materials. Thus, BiFeO3-BaTiO3 (BF-BT) systems have attracted a great deal of interest as promising candidate for lead-free ferroelectric materials. In this dissertation, PZT-based and BF-BT-based ceramics were investigated systematically. Three contributions have been developed with the first dealing with the analysis of microstructures, crystalline phases and electric properties in doped PZT systems. It was revealed the involvement of softening-hardening features and the relation between defect dipoles and electric properties in acceptor doped materials. In a second part, the interplay of microstructures and electric properties was studied in BF-BT systems, providing the relevant analysis of the optimized performance such as the enhanced piezoelectric properties of lead-free systems. In the third contribution, experimental methods of synthesis and texturing BF-BT systems by BT templates ad the characterization of ferroelectric and electromechanical properties have been correlated with the structural and morphological organization of textured ceramics
Mccash, Kevin. "The Soft Mode Driven Dynamics of Ferroelectric Perovskites at the Nanoscale: an Atomistic Study." Scholar Commons, 2014. https://scholarcommons.usf.edu/etd/5269.
Full textKolodiazhnyi, Taras Petric Anthony. "Semiconducting and dielectric properties of barium titanates, tantalates and niobates with perovskite structure /." *McMaster only, 2002.
Find full textLappalainen, J. (Jyrki). "Laser-ablation deposition and characterization of polycrystalline Nd-modified Pb(Zr,Ti)O3 thin films." Doctoral thesis, University of Oulu, 1999. http://urn.fi/urn:isbn:9514254317.
Full textShoron, Omor Faruk. "Extreme Electron Density Perovskite Oxide Heterostructures for Field Effect Transistors." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1429714269.
Full textNascimento, Cássia Costa. "Síntese de cerâmicas tipo perovskita com potencial uso em células solares." Universidade Federal de São Carlos, 2017. https://repositorio.ufscar.br/handle/ufscar/8819.
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Visible light accounts for the biggest fraction of the solar irradiance. One of the strategies for achieving higher photovoltaic power conversion efficiency is the application of low band-gap materials (Eg ideal≈1.4 eV) capable of absorbing this fraction of the solar spectrum. Ferroelectric semiconductors have been studied in this field due to the above-bandgap generated photovoltages and their ferroelectric polarization-driven carrier separation. Ferroelectric oxides usually present wide bandgaps which allow the absorption of only 8-20% of the solar spectrum. However, the development of new ferroelectric materials, particularly KBNNO [KNbO3]0,9[BaNi0,5Nb0,5O3-δ ]0,1 (Eg = 1.39 eV) and KBiFe2O5 (Eg=1,60 eV), has encouraged the use of such materials in solar cells. Simple synthesis routes, with short steps, time and temperatures are essential for the future progress of the application of such ferroelectric oxides in solar cells. KBNNO and KBiFe2O5 require high crystallization temperatures, which reduce the number of potential substrates and electrode materials that could be used in devices, as polymer-based flexible ones. Obtaining this oxides in a high surface-area powder form might be a strategy to further incorporation in solar cells composed of low-temperature processing materials. This work reports for the first time synthesis of KBNNO and KBiFe2O5 by solution combustion (SCS). Characterization by WAXD, SEM, EDS, TG/DSC and Diffuse Reflectance UV-Vis Spectroscopy and dielectric constants indicates the success of the synthesis. The optical properties show the visible-light absorption contribution and band-gaps closer to the ideal magnitude for solar applications compared to the non doped materials. The SCS was shown as an effective route to obtaining the phase. Furthermore, it is possible to improve it in order to produce powders with smaller particle size and absent of secondary phases.
A luz visível representa a fração mais relevante da radiação solar. Desta maneira, busca-se empregar nas camadas ativas das células solares materiais com baixos band-gaps (Eg ideal ≈1,4 eV), capazes de absorver fótons nessa região do espectro. Semicondutores ferroelétricos com estrutura da perovskita ou estruturas relacionadas têm sido estudados nesse campo devido ao potencial de obtenção de voltagens superiores à magnitude de seus band-gaps e à contribuição na separação de portadores de cargas decorrente da polarização intrínseca presente nesses materiais. Óxidos ferroelétricos geralmente possuem Eg elevados (2,7-4 eV), permitindo o aproveitamento de somente 8-20% do espectro solar. No entanto, o desenvolvimento de novos semicondutores ferroelétricos, particularmente a KBNNO [KNbO3]0,9[BaNi0,5Nb0,5O3-δ ]0,1 (Eg=1,39 eV) e KBiFe2O5 (Eg=1,60 eV), tem encorajado a aplicação desses materiais em células solares. Rotas de síntese simples, com etapas, tempos e temperaturas reduzidas são essenciais para o progresso futuro da aplicação de tais óxidos ferroelétricos em células solares. A KBNNO e KBiFe2O5 cristalizam em temperaturas mais elevadas do que perovskitas orgânico-inorgânicas, o que reduz a possibilidade de fabricação de dispositivos na presença de substratos e eletrodos sensíveis à temperatura, como substratos poliméricos flexíveis. Assim, a obtenção desses óxidos na forma de pós de elevada área superficial pode ser uma estratégia para posterior incorporação em dispositivos contendo materiais processados a baixas temperaturas. Neste trabalho, reporta-se pela primeira vez a síntese da KBNNO e KBiFe2O5 por combustão em solução. Caracterizações por DRX, MEV, EDS, TG/DSC, Espectroscopia UV-Vis e constantes dielétricas indicam a obtenção das fases com sucesso. As propriedades ópticas confirmam contribuição na absorção da luz visível com respeito aos materiais não dopados, KNbO3 e BiFeO3. A síntese por combustão em solução se mostra efetiva para obtenção das fases, mas passível de melhorias para produção de pós com menor tamanho de partícula e sem a presença de fases secundárias.
CNPq: 155305/2014-0
CONFALONIERI, GIORGIA. "LOCAL DISORDER IN THE STRUCTURE OF BA(TI,CE)O3 PEROVSKITE BY MEANS OF POWDER DIFFRACTION AND TOTAL SCATTERING. EFFECT OF TEMPERATURE, DOPING CONCENTRATION AND GRAIN SIZE." Doctoral thesis, Università degli Studi di Milano, 2017. http://hdl.handle.net/2434/478906.
Full textPreziosi, Daniele [Verfasser], Dietrich [Akademischer Betreuer] Hesse, Kathrin [Akademischer Betreuer] Dörr, and Ho Hyung [Akademischer Betreuer] Lee. "Studies on the ferroelectric field effect in perovskite oxide heterostructures / Daniele Preziosi. Betreuer: Dietrich Hesse ; Kathrin Dörr ; Ho Hyung Lee." Halle, Saale : Universitäts- und Landesbibliothek Sachsen-Anhalt, 2015. http://d-nb.info/1069875287/34.
Full textKöbernik, Gert. "Präparation und Charakterisierung ferroelektrischer perowskitischer Multilagen.: Preparation and electrical characterisation of multilayers of ferroelectric Perovskites." Doctoral thesis, Technische Universität Dresden, 2003. https://tud.qucosa.de/id/qucosa%3A24345.
Full textEs wurden (001) und (111) orientierte symmetrische BTO/STO-Multilagen auf niobdotierten STO-Einkristallen abgeschieden. Hierbei wurde sowohl die Gesamtschichtdicke, als auch deren Periodizität variiert. Zum Vergleich wurden weiterhin Ba0.5Sr0.5TiO3-Mischschichten unterschiedlicher Dicke präpariert. Aus den HRTEM und XRD Untersuchungen kann geschlossen werden, dass alle erhaltenen Schichten sowohl phasenrein als auch perfekt biaxial texturiert sind. Im Falle der (001) orientierten Multilagen konnten atomar scharfe Grenzflächen zwischen Einzellagen erhalten werden, wobei sich die Einzellagendicke bis auf eine Monolage (0.4 nm) reduzieren lässt. Aus der Schichtdickenabhängigkeit von d(001), dem mittleren out-of-plane Gitterparameter der Schicht, wird geschlossen, dass die Schichten auf den STO-Einkristallen Spannungsgradienten in den Schicht-normalen besitzen und an der Grenzfläche zum Substrat am stärksten verspannt sind. Die (111) orientierten Multilagen auf den STO-Einkristallen zeigen gegenüber den Schichten auf den (100) orientierten STO-Einkristallen eine deutlich erhöhte Interfacerauhigkeit. Vermutet wird, dass dies einerseits durch die andere kristallographische Orientierung der Wachstumsnormalen bedingt ist, weil damit jeweils keine geschlossenen SrO- bzw. BaO- und TiO3-Lagen ausgebildet werden. Andererseits zeigen die TEM-Aufnahmen eine deutliche Zunahme der Welligkeit der Einzellagen mit wachsendem Abstand vom Substrat, die rein mechanischen Effekten zugeschrieben wird. Die Verwölbung der Einzellagen könnte damit der Reduzierung der mechanischen Energie innerhalb des Systems dienen, wobei die Netzebenen dem Verlauf der Einzellagen folgen. Auf platinbeschichteten Siliziumsubstraten konnten erstmals phasenreine (111) fasertexturierte Mischschichten und BTO/STO-Multilagen abgeschieden werden. Grundlage hierfür war die Optimierung des Pt/Ti/SiO2/Si Schichtsystems hinsichtlich seiner thermischen Stabilität bis zu 800°C. Die Textur der Schichten wird von der Platingrundelektrode übernommen und deren Rauhigkeit teilweise verstärkt. Eine mechanische Verwölbung der Einzellagen konnte hier nicht beobachtet werden. Für die elektrischen Messungen wurden auf allen Schichten etwa 50 nm dicke Platinelektroden durch eine Hartmaske mittels Elektronenstrahlverdampfung im Hochvakuum bei etwa 300°C aufgebracht. Anschließend wurden die Schichten an Luft getempert, um das Sauerstoffdefizit, dass sich bei der Elektrodenabscheidung einstellt, auszugleichen. Die elektrischen Messungen zeichnen sich durch den sehr großen untersuchten Temperaturbereich aus. Temperaturabhängige Messungen im Bereich von 30-600 K finden sich für ferroelektrische Dünnschichten sehr selten in der Literatur und stellen für BTO/STO-Multilagen ein Novum dar. Auch die biasabhängige und teilweise auch temperaturabhängige Messung der Kapazität der Multilagen (C-V-Messungen) ist bisher einmalig. Durch die temperaturabhängigen Hysteresemessungen wurden Einblicke in den elektrischen Polungszustand der Schichten erhalten. Dadurch wird eine sinnvolle Interpretation der ε(T)-Kurven erst möglich. Der Vorteil der Integration des Polarisationsstromes unter Verwendung einer Dreieckspannung als Messsignal besteht in der direkten physikalischen Aussage der Strom-Spannungskurven über die Schaltspannung der Schichten.
Di, Geronimo Camacho Elizabeth Carolina. "Synthesis, high-pressure study and dielectric characterization of two lead-free perovskite materials : SrTi1-xZrxO3 and KNb1-xTaxO3." Thesis, Montpellier, 2016. http://www.theses.fr/2016MONTT208/document.
Full textPerovskite materials whose general chemical formula is ABO3 are one of the most study ferroelectrics due to the interesting properties that they have for technological applications. However, their properties are directly related to structural phase transitions that could depend of temperature, composition and pressure. In the studies presented here, we first examined the high-pressure behavior of two perovskite materials SrTi1-xZrxO3 (STZ) and KNb1-XTaXO3 (KNT), and we later continued to investigate different sintering techniques in order to improve the densification, dielectric and ferroelectric properties of K(Nb0.40Ta0.60)O3 and (KxNa1-x)Nb0.6Ta0.4O3 ceramics.High-pressure Raman scattering and X-ray diffraction investigations of SrTi1-xZrxO3 (x= 0.3, 0.4, 0.5, 0.6, 0.7) and KNb1-XTaXO3 (x=0.4, 0.5, 0.6, 0.9) powders were conducted in diamond anvil cells. Raman scattering experiments showed and increased of Raman modes with pressure for the STZ samples, which indicates that pressure induced phase transitions towards lower symmetry for these compounds.Moreover, high pressure Raman spectroscopy experiments showed a decrease of the Raman modes as the pressure was increased for the KNT samples, showing that pressure induced phase transitions towards higher symmetries. The evolution of the main Raman modes for the orthorhombic and tetragonal phases were followed until the cubic phase was reach, and allowed us to propose a pressure-composition phase diagram for the KNT compounds.Three different sintering techniques, sintered aids, two step sintering and spark plasma sintering, were used on K(Nb0.4Ta0.6)O3 and (KxNa1-x)Nb0.6Ta0.4O3 ceramics. The use of KF as sintered aid and the two step sintering method showed an improvement of the dielectric constant and dielectric losses of these samples. SPS samples presented a fine microstructure with the highest density and the best ferroelectric behavior. We did not detect any changes on the Curie temperature due the amount of Na but and increase of the dielectric constant and the ferroelectric properties was observed due to the amount of Na
Marlec, Florent. "Nouveaux matériaux perovskites ferroélectriques : céramiques et couches minces issues de la solution solide (Sr₂Ta₂O₇)₁₀₀₋ₓ(La₂Ti₂O₇)ₓ." Thesis, Rennes 1, 2018. http://www.theses.fr/2018REN1S024/document.
Full textThis research focuses on the study of a new material resulting from the combination of two ferroelectric perovskite oxides Sr2Ta2O7 and La2Ti2O7; the resulting solid solution is formulating according to (Sr2Ta2O7)100 x(La2Ti2O7)x (STLTO). Our study includes the synthesis of powders, the realization of ceramics, thin film deposition and their structural, morphological, elemental, optical, dielectric and ferroelectric characterizations. The medium-term objective for this material is its integration into miniature and reconfigurable microwave devices. For this, high permittivity, variable under electric field, is required in order to achieve a tunability of the material, then a reconfigurability of the antennas, for example. Structural analysis by X-ray diffraction confirmed, by the linear variation of the cell parameters, the formation of the solid solution for the compositions x ∊ [0-5]. The dielectric analyzes carried out at low frequencies (1 - 100 kHz) on STLTO ceramics showed maximum values of permittivity (375) and tunability (55% at 3 kV/cm), associated with weak loss tangents (0,01), for the composition x = 1.65. The measurements at high frequencies (200 MHz – 18 GHz) are in agreement with the results obtained at low frequencies. The deposition of thin film by reactive sputtering, made from a target of composition x = 1.65, produces films similar at Sr2.83Ta5O15 phase, which denotes a loss of strontium. However, at low frequencies, the films have relatively high permittivity (130) for low losses (0.01) with moderate tunability (A= 14.5% at 340 kV/cm at f = 100 kHz). Deposition of oxynitride thin film (Sr,La)(Ta,Ti)O2N, carried out in Ar + N2 reactive atmosphere, leads to coloured samples having high permittivity (up to about 3000), but with equally high losses (up to 2) and without tunability. Moreover, the study of SrTaO2N showed that these compounds are suitable for the decomposition of water under visible light
Liu, Hairui. "Cristallogenèse et caractérisations de monocristaux piézoélectriques sans plomb à base de KNN." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0197/document.
Full textThe thesis aims to find possible approaches for improved electromechanical properties in KNN-based piezoelectric single crystals. Both submerged-seed and top-seeded solution growth techniques were employed to produce single crystals. Conclusions from the crystal growth aspect are: (i) For individual elements, segregation coefficients highly rely on the initial concentration in the liquid solution. (ii) A competition between elements occupied on the same lattice site was found. (iii) The very low Li segregation coefficient in the KNN matrix is responsible for the occurrence of a secondary phase with the tetragonal tungsten bronze structure. (iv) Observed optically-cloudy regions in as-grown crystals decrease the electrical response and can be reduced by thermal treatment with slow cooling. In the second part, we used three approaches to enhance the piezoelectric and ferroelectric behavior of KNN-based single crystals. Ta or Sb substitutions indicates that enhanced electromechanical response is achieved when the orthorhombic-tetragonal phase transition is near room temperature. Thermal treatment in pure O2 atmosphere resulted in a twofold increase of the piezoelectric coefficient and ferroelectric parameters of a (K,Na,Li)(Ta,Nb,Sb)O3 single crystal. The highest room-temperature piezoelectric coefficient in annealed KNN-based single crystals of 732 pC/N was obtained. The third approach, doping with Mn ions in (K,Na,Li)(Ta,Nb)O3 single crystals, is also presented
Xin, Cong. "Cristallogenèse et caractérisation de monocristaux piézoélectriques sans plomb dans le système BaTiO3-CaTiO3- BaZrO3." Thesis, Bordeaux, 2018. http://www.theses.fr/2018BORD0211/document.
Full textSolid solutions belonging to BaZrO3–BaTiO3–CaTiO3 (BCTZ) pseudo-ternary system are promising candidates for lead-free piezoelectrics. This thesis aims at growing and characterizing various single crystals of the BCTZ system: the end members BaZrO3 and CaTiO3 as well as Ba1-xCaxTi1-yZryO3 solid solution compounds with zirconium (Zr) and calcium (Ca) contents close to Ba(Zr0.2Ti0.8)O3-50(Ba0.7Ca0.3)TiO3 composition (BZT-50BCT) where high piezoelectric performances are expected.CaTiO3 and BaZrO3 single crystals were both grown from high temperature solution by the flux method and from the melt by the optical floating zone technique. In the case of CaTiO3 grown with a mirror furnace at 1975°C, aluminum (Al), magnesium (Mg) and barium (Ba) as main impurities were detected. The Raman spectra of CaTiO3 are in good agreement with the spectra referenced in the literature. The growth of BaZrO3 was more challenging because of its very high melting point (2700°C). BaB2O4 flux was successfully used to produce 150-200 μm-sized BaZrO3 crystals at half its melting point (1350°C) and bulk centimeter-sized BaZrO3 boules were grown from the melt. Sr, Hf, Ca and Ti were detected by GDMS and SIMS as main impurities in the range of 0.3-0.5 at.%. The optical band gap is found to be ~4.8 eV and indicates the high quality of the BaZrO3 crystals grown with mirror furnace. Low temperature dielectric properties of BaZrO3 are displayed and confirmed the absence of structural phase transition. Raman investigations reveal that even though BaZrO3 does not have any phase transition at low temperatures, it exhibits a high-pressure phase transition from cubic to tetragonal at 11GPa at room temperature.In the second part, BCTZ centimeter-sized single crystals have been successfully grown by the top seeded solution growth technique. Ca and Zr content profiles throughout the as-grown boules indicate that their effective segregation coefficients are highly dependent on their initial concentration in the liquid solution. Concentrations evolve substantially during the crystal growth, making the BCTZ crystal growth a tricky issue when a narrow compositions range is targeted, as in the vicinity of the phase convergence region. Furthermore, spinodal decomposition was observed, indicating the coexistence of two solid solutions with close compositions in BCTZ crystals. Dielectric and piezoelectric properties were measured for some crystals, which were found to display a variety of behavior form relaxor to pure ferroelectric. In addition, an abnormal double-like PE hysteresis loop was observed, that was associated to an irreversible effect disappearing upon poling
Jeddy, Shehnaz. "Thermal stability of defects in strontium titante [i.e., titanate] susbtrates for multiferroic materials." Birmingham, Ala. : University of Alabama at Birmingham, 2008. https://www.mhsl.uab.edu/dt/2008m/jeddy.pdf.
Full textZubko, Pavlo. "Electrical properties of ferroelectric perovskites." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612136.
Full textQuignon, Sébastien. "Synthèse et caractérisations de couches minces de matériaux piézoélectriques sans plomb." Thesis, Valenciennes, 2013. http://www.theses.fr/2013VALE0038/document.
Full textIndustrial interest, political pressure: two major reasons for the synthesis of unleaded piezoelectric thin layers with high performances have become an important research topic. The objective of this work is the synthesis and characterization of a promising material: NBT. The development of NBT thin films by rf-magnetron sputtering was optimized. The study shows that annealing at 675°C under oxygen allows better crystallization of NBT. Electrical characterizations showed good dielectric, ferroelectric and piezoelectric properties. Polarization and displacement values obtained by applying an electric field are remarkable. However, values of remnant polarization are low. The temperature study was used to determine phase transitions and highlighted the relaxor character of NBT. The mixture of BT with the NBT in a solid solution should improve the electrical performances. Leakage currents caused the opposite effect, that is to say, a degradation of the properties of our thin films
Viola, Giuseppe. "Domain switching dynamics in ferroelastic and ferroelastic/ferroelectric perovskites." Thesis, Queen Mary, University of London, 2010. http://qmro.qmul.ac.uk/xmlui/handle/123456789/382.
Full textVillaurrutia, Arenas Rafael. "Microstructure, nanostructure, and local crystallography in perovskite ferroelectrics and antiferroelectrics." Thesis, University of Glasgow, 2010. http://theses.gla.ac.uk/2362/.
Full textGao, Zhipeng. "Perovskite-like layered structure A₂B₂O₇ ferroelectrics and solid solutions." Thesis, Queen Mary, University of London, 2013. http://qmro.qmul.ac.uk/xmlui/handle/123456789/15025.
Full textQu, Weiguo. "In-situ TEM investigation of the phase transitions in perovskite ferroelectrics." [Ames, Iowa : Iowa State University], 2008.
Find full textKöbernik, Gert. "Präparation und Charakterisierung ferroelektrischer perowskitischer Multilagen." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2004. http://nbn-resolving.de/urn:nbn:de:swb:14-1088508748390-02540.
Full textEs wurden (001) und (111) orientierte symmetrische BTO/STO-Multilagen auf niobdotierten STO-Einkristallen abgeschieden. Hierbei wurde sowohl die Gesamtschichtdicke, als auch deren Periodizität variiert. Zum Vergleich wurden weiterhin Ba0.5Sr0.5TiO3-Mischschichten unterschiedlicher Dicke präpariert. Aus den HRTEM und XRD Untersuchungen kann geschlossen werden, dass alle erhaltenen Schichten sowohl phasenrein als auch perfekt biaxial texturiert sind. Im Falle der (001) orientierten Multilagen konnten atomar scharfe Grenzflächen zwischen Einzellagen erhalten werden, wobei sich die Einzellagendicke bis auf eine Monolage (0.4 nm) reduzieren lässt. Aus der Schichtdickenabhängigkeit von d(001), dem mittleren out-of-plane Gitterparameter der Schicht, wird geschlossen, dass die Schichten auf den STO-Einkristallen Spannungsgradienten in den Schicht-normalen besitzen und an der Grenzfläche zum Substrat am stärksten verspannt sind. Die (111) orientierten Multilagen auf den STO-Einkristallen zeigen gegenüber den Schichten auf den (100) orientierten STO-Einkristallen eine deutlich erhöhte Interfacerauhigkeit. Vermutet wird, dass dies einerseits durch die andere kristallographische Orientierung der Wachstumsnormalen bedingt ist, weil damit jeweils keine geschlossenen SrO- bzw. BaO- und TiO3-Lagen ausgebildet werden. Andererseits zeigen die TEM-Aufnahmen eine deutliche Zunahme der Welligkeit der Einzellagen mit wachsendem Abstand vom Substrat, die rein mechanischen Effekten zugeschrieben wird. Die Verwölbung der Einzellagen könnte damit der Reduzierung der mechanischen Energie innerhalb des Systems dienen, wobei die Netzebenen dem Verlauf der Einzellagen folgen. Auf platinbeschichteten Siliziumsubstraten konnten erstmals phasenreine (111) fasertexturierte Mischschichten und BTO/STO-Multilagen abgeschieden werden. Grundlage hierfür war die Optimierung des Pt/Ti/SiO2/Si Schichtsystems hinsichtlich seiner thermischen Stabilität bis zu 800°C. Die Textur der Schichten wird von der Platingrundelektrode übernommen und deren Rauhigkeit teilweise verstärkt. Eine mechanische Verwölbung der Einzellagen konnte hier nicht beobachtet werden. Für die elektrischen Messungen wurden auf allen Schichten etwa 50 nm dicke Platinelektroden durch eine Hartmaske mittels Elektronenstrahlverdampfung im Hochvakuum bei etwa 300°C aufgebracht. Anschließend wurden die Schichten an Luft getempert, um das Sauerstoffdefizit, dass sich bei der Elektrodenabscheidung einstellt, auszugleichen. Die elektrischen Messungen zeichnen sich durch den sehr großen untersuchten Temperaturbereich aus. Temperaturabhängige Messungen im Bereich von 30-600 K finden sich für ferroelektrische Dünnschichten sehr selten in der Literatur und stellen für BTO/STO-Multilagen ein Novum dar. Auch die biasabhängige und teilweise auch temperaturabhängige Messung der Kapazität der Multilagen (C-V-Messungen) ist bisher einmalig. Durch die temperaturabhängigen Hysteresemessungen wurden Einblicke in den elektrischen Polungszustand der Schichten erhalten. Dadurch wird eine sinnvolle Interpretation der ε(T)-Kurven erst möglich. Der Vorteil der Integration des Polarisationsstromes unter Verwendung einer Dreieckspannung als Messsignal besteht in der direkten physikalischen Aussage der Strom-Spannungskurven über die Schaltspannung der Schichten
Liu, Samuel. "Layered Perovskites as Tailored Functional Materials." Thesis, The University of Sydney, 2015. http://hdl.handle.net/2123/15448.
Full textRodriguez, Brian Joseph. "NANOSCALE INVESTIGATION OF THE PIEZOELECTRIC PROPERTIES OF PEROVSKITE FERROELECTRICS AND III-NITRIDES." NCSU, 2003. http://www.lib.ncsu.edu/theses/available/etd-10072003-122453/.
Full textNing, Huanpo. "Perovskite-like layered structure A2B20 & ferroelectrics with super-high Curie points." Thesis, Queen Mary, University of London, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.538668.
Full textTirumala, Sridhar. "Integration of Ferroelectric Materials into High Density Non-Volatile Random Access Memories." Diss., Virginia Tech, 2000. http://hdl.handle.net/10919/28800.
Full textPh. D.
Amorín, González Harvey. "Preparation and properties of ferroelectric single crystals and ceramics of bismuth layered perovskites." Doctoral thesis, Universidade de Aveiro, 2005. http://hdl.handle.net/10773/4924.
Full textImpulsionado pelo interesse em conhecer as propriedades intrínsecas dos compostos SrBi2Ta2O9 (SBT) e SrBi2Nb2O9 (SBN) que se apresentam como os materiais mais promissores para substituir o titanato de zircónio e de chumbo (PZT) nas memórias ferroeléctricas de acesso aleatório, surgiu a necessidade de monocristais destes compostos com dimensões e qualidade adequadas à medição de propriedades. No presente trabalho, fizeram-se crescer cristais simples de SBT e de SBN com qualidade e dimensões elevadas, usando um método de solução a alta temperatura, com um fluxo de Bi2O3 modificado com B2O3 e uma razão molar de 60/40 entre SBT (ou SBN) e fluxo (35 % em peso de Bi2O3 e 5 % em peso de B2O3). Primeiramente optimizaram-se as condições de processamento, testando-se diferentes perfis de temperatura para promover o crescimento e melhorar a qualidade dos cristais de SBT. As condições identificadas como óptimas foram usadas para fazer crescer cristais de SBN. Os cristais obtidos evidenciaram um hábito lamelar com morfologia de plaquetas com dimensões típicas de ∼ 7 × 5 × 0.2 e 5 × 5 × 0.4 mm3 para SBT e SBN, respectivamente. De acordo com as análises de topografia e de difracção de raios-X, ambos os cristais se apresentaram naturalmente orientados com a direcção [001] (eixo c) perpendicular à face de maior área do cristal e lados paralelos à direcção [110] da fase ortorrômbica (inclinação de 45º relativamente a ambos os eixos a e b). As primeiras medidas fiáveis sobre estrutura de domínios de cristais de SBT de boa qualidade foram realizadas no presente trabalho por microscopia de força piezoeléctrica. Ambos os domínios ferroeléctricos de 180º e ferroelásticos de 90º foram observados à temperatura ambiente após tratamento térmico dos cristais a 750 ºC, durante 10 horas. Os domínios apresentaram uma estrutura em “espinha” com paredes de domínios de 90º predominantemente planas. As paredes de domínios de 90º mostraram-se paralelas às arestas laterais do cristal [110], o que se coaduna com a orientação preferencial observada. A largura dos domínios de 90º situa-se entre 0,7 e 1,5 μm ao passo que a dos domínios de 180º varia entre 250 e 500 nm. A formação deste complexo padrão de domínios é atribuída a um processo de transição de fases em duas etapas, ou seja, a ocorrência não simultânea das transições de fase ferroelástica e ferroelétrica em SBT. A qualidade dos cristais de SBT e SBN foi também confirmada por medidas diélectricas, ferroelétricas e piezoeléctricas realizadas paralelamente ao eixo c (direcção [001]) e paralelamente ao plano ab (segundo a direcção [110]) demonstrando-se a elevada anisotropia das propriedades intrínsecas de ambos os cristais, i.e., a razão entre o valor médio de permitividade dieléctrica medida paralelamente ao plano ab e o valor medido paralelamente ao eixo c foi de cerca de 10 à temperatura de Curie, TC, diminuindo para 2 à temperatura ambiente. As baixas perdas dieléctricas acima e abaixo de TC (tanδ < 0.04) indicaram uma baixa concentração de defeitos nos cristais. Observaram-se ciclos de histerese saturados quando se aplicou um campo eléctrico alterno paralelamente ao plano ab do cristal SBT. A polarização espontânea segundo o eixo ferroeléctrico a foi estimada em cerca de ≈ 20 μC/cm2 para o SBT. Porém, no caso dos cristais de SBN, não foi possível obter ciclos de histerese saturados mesmo aplicando um campo eléctrico com o valor máximo de 100 kV/cm. O coeficiente piezoeléctrico d33 medido segundo a direcção [100] (eixo polar) é de ≈ 30 e de 62 pm/V para o SBT e o SBN, respectivamente. Os materiais ferroeléctricos com estrutura em camadas de bismuto (compostos BLSF) apresentam grande interesse para aplicações piezoeléctricas de elevada temperatura embora seja necessário prepará-los na forma texturizada devido à sua elevada anisotropia. O presente trabalho estuda a possibilidade de usar os cristais de SBT como sementes para induzir a texturização de cerâmicos de SBT pela via de template grain growth (TGG). Produziram-se cerâmicos de SBT texturizados com propriedades dieléctricas e ferroeléctricas melhoradas, usando sementes anisométricas e de morfologia lamelar, com tamanho médio de ~ 40 × 40 × 8 μm3. Dispersou-se uma pequena quantidade de sementes anisométricas de SBT numa matrix de partículas finas de SBT contendo um excesso de Bi2O3 para formar fase líquida e alinharam-se essas sementes por prensagem unidireccional. Avaliaram-se os efeitos de vários parâmetros de processamento tais como o excesso de Bi2O3, as sementes de SBT, as condições de prensagem e de sinterização, tentando obter-se cerâmicos densos, com elevada textura e propriedades melhoradas. Correlacionou-se a evolução da microestructura dos cerâmicos com as condições de processamento recorrendo a uma análise estereológica. Demonstrou-se a existência de anisotropia nas propriedades dieléctricas e no ciclo de histerese e a sua dependência do grau de textura. Mediram-se propriedades dieléctricas e ferroeléctricas melhoradas segunda uma direcção perpendicular à da prensagem unidirecional, observando-se valores de permitividade e de polarização acima dos apresentados pelos cerâmicos sem sementes. Mostrou-se que esta melhoria de propriedades resultou da orientação do grão, da anisotropia de propriedades dos monocristais e do grau de textura dos cerâmicos. Apresentou-se um modelo para descrever a polarização espontânea máxima de cerâmicos de SBT com orientação de grão aleatória ou com textura, em função do grau de textura, usando uma análise de textura baseada na distribuição da orientação dos grãos grandes e anisométricos. Seleccionou-se a equação de March-Dollase para descrever os dados experimentais referentes à distribuição de orientação e discutiu-se a distribuição espacial do vector polarização em grãos lamelares de materiais BLSF. A aplicação do referido modelo aos cerâmicos texturizados de SBT permitiu a comparação dos valores de polarização espontânea previstos pelo modelo com os valores experimentais obtidos a partir do ciclo de histerese ferroeléctrica dos mesmos cerâmicos.
The interest in the understanding of the intrinsic properties of SrBi2Ta2O9 (SBT) and SrBi2Nb2O9 (SBN), which are the most promising materials for substituting lead zirconate titanate in non-volatile ferroelectric random access memories, arouse the need of single crystals of these compounds with suitable size and quality for the properties measurement. In this work, high-quality SBT and SBN single crystals were successfully grown by a high-temperature selfflux solution method, using a B2O3 modified Bi2O3 flux and a molar ratio of 60/40 of SBT (or SBN) powder to flux (35 wt% Bi2O3 and 5 wt% B2O3). The processing conditions were optimized by testing different thermal profiles to increase the size and improve the quality of the grown SBT crystals. The optimized conditions were then applied for the growth of SBN crystals. The grown crystals showed a layered habit with a platelet morphology and typical sizes of ∼ 7 × 5 × 0.2 and 5 × 5 × 0.4 mm3 for SBT and SBN, respectively. According to x-ray diffraction and topography analyses, both crystals were naturally oriented with [001] direction (c-axis) perpendicular to the major face and edges parallel to [110] direction (45º to both a- and b-axes) of the orthorhombic phase. The first reliable measurements of the domain structure of high-quality SBT single crystals were performed in this work by piezoelectric force microscopy. Both ferroelectric 180º domains and ferroelastic 90º domains (twins) were revealed at room temperature after annealing the crystals at 750 ºC for 10 h. The coexisting domains form a well-defined “herringbone” structure with mostly flat 90º walls. The ferroelastic 90º walls were parallel to the single crystal edges [110], which agree with the observed preferential orientation. The width of 90º domains (twins) lies in the range of 0.7 - 1.5 μm, while that of 180º domains, which were oriented parallel to the [100] direction (polar axis), exhibited a periodicity of about 250 to 500 nm. Formation of the observed complex domain pattern was attributed to a two-stage process associated with the presence of separate ferroelastic and ferroelectric phase transitions in SBT. The high quality of the grown SBT and SBN single crystals was confirmed by dielectric, ferroelectric and piezoelectric measurements, which were performed in the ab-plane (along the [110] direction) and along the c-axis (the [001] direction), demonstrating the large anisotropy in the intrinsic properties of both crystals, i.e., the ratio between average permittivity along the [110] (ab-plane) and the [001] direction (c-axis) was about 10 at TC and decreased to ~ 2 at room temperature. The low dielectric losses above and below TC (tanδ < 0.04) indicate a low concentration of defects in the crystals. Saturated hysteresis loops were observed for switching in the ab-plane of the SBT single crystal and the spontaneous polarization along the ferroelectric a-axis was estimated to be PS ≈ 20 μC/cm2 for SBT. However, for SBN crystals, saturated hysteresis loops were not obtained for a maximum electric field of 100 kV/cm. The longitudinal piezoelectric coefficient d33 was measured along the [100] direction (polar-axis) in both crystals, and was estimated as ≈ 30 and 62 pm/V for SBT and SBN, respectively. Bi-layer structured ferroelectric (BLSF) materials like SBT present significant interest for high-temperature piezoelectric applications, though they are required to be prepared in a textured form due to their high anisotropy. This work studies the possibility of using the grown SBT crystals as seeds for the fabrication of textured SBT ceramics by templated grain growth (TGG). Seeded SBT ceramics with improved dielectric and ferroelectric properties were produced by using plate-like anisometric SBT templates with average sizes of ~ 40 × 40 × 8 μm3. A small amount of the anisometric SBT templates was distributed in a fine-grained matrix of SBT powder containing Bi2O3 excess as liquid phase, and then aligned by conventional uniaxial pressing. Several processing parameters, e.g., the Bi2O3 excess, the amount of templates, or the processing and sintering conditions including the uniaxial pressure, the sintering temperature and time, were examined in order to produce textured SBT ceramics with enhanced properties. The ceramics microstructure evolution was correlated with the processing parameters via a stereological analysis. Anisotropy in the dielectric and ferroelectric properties of the seeded SBT specimens and its dependence on the degree of texture were demonstrated. Enhanced properties were measured perpendicularly to the uniaxial pressing direction revealing permittivity and polarization values above those of unseeded SBT ceramics. Such improved properties were shown to result from the grain orientation, anisotropy of single crystal properties, and degree of texture of the sintered ceramics. A quantitative model was presented for predicting the maximum spontaneous polarization, PS, of randomly oriented and textured SBT ceramics as a function of the degree of texture, using a texture analysis accomplished via the orientation distribution of large anisometric grains. The March-Dollase equation was selected to fit the measured orientation distribution, and the spatial distribution of polarization vector in platelet grains of BLSF materials was discussed. The results were applied to the case of textured SBT ceramics, and the predicted PS values as a function of the degree of texture were compared with those measured from the hysteresis loops.
FCT - SFRH/BD/6619/2001
Höfling, Marion Anita [Verfasser], Jürgen [Akademischer Betreuer] Rödel, and Hans-Joachim [Akademischer Betreuer] Kleebe. "Dislocation-Based Functionality in Ferroelectric Perovskites / Marion Anita Höfling ; Jürgen Rödel, Hans-Joachim Kleebe." Darmstadt : Universitäts- und Landesbibliothek, 2021. http://d-nb.info/1236344901/34.
Full textPechkis, Daniel Lawrence. "First-principles Calculations of Nuclear Magnetic Resonance Chemical Shielding Tensors in Complex Ferroelectric Perovskites." W&M ScholarWorks, 2011. https://scholarworks.wm.edu/etd/1539623590.
Full textQuattropani, Alessandro. "Synthesis of ferroelectric oxides for photovoltaic applications." Thesis, Strasbourg, 2018. http://www.theses.fr/2018STRAD053/document.
Full textIn this work, we have produced Bi2FeCrO6 oxides (BFCO) by sol-gel technique and pulsed laser deposition (PLD). By sol-gel, precursors in solution were prepared, which are then deposited by centrifugation on silicon or quartz substrates. The numerous structural (XRD) and optical images (SEM, TEM) analyses carried out on these BFCO films show that the films are fairly homogeneous but exhibit many parasitic phases, which they can be partly eliminated by rapid thermal annealing. Finally, we present the first results obtained on BFCO-SG perovskite devices. On the other hand, BFCO films were deposited on STO and Nb:STO substrates. Their structural, optical and electrical properties are presented. High-quality epitaxial growth and pure-phase films are demonstrated by X-ray diffraction. We show that the band gap of the PLD-BFCO films can be tuned from 1, 9 to 2.6 eV thanks to the variation of growth conditions. Theoretical calculations has confirmed the observed behavior and highlight the importance of the ordering phase. The ferroelectric properties of the PLD films are studied by the piezoresponse force microscopy. Illumination is shown to have a strong effect on polarization. We show that the polarization memory affects the photovoltaic response. Finally, devices based on BFCO are manufactured and their photovoltaic properties are analyzed
Du, Hongchu. "Synthesis and Characterization of Ferroelectric Nanomaterials." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2008. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1216128809669-53267.
Full textRoukos, 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.
Full textThe 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
Felix, Anderson André. "Estudo da estabilização da fase perovskita PMN em filmes ultrafinos /." Ilha Solteira : [s.n.], 2009. http://hdl.handle.net/11449/92014.
Full textBanca: João Carlos Silos Moraes
Banca: Adolfo Franco Júnior
Resumo: O presente trabalho descreve os estudos realizados para a síntese de filmes ferroelétricos ultrafinos de Pb(Mg1/3Nb2/3)O3 (PMN) e o estudo sistemático da cinética de cristalização deste material visando a obtenção de filmes monofásicos. Os filmes foram produzidos a partir da modificação de um método químico baseado em precursores óxidos. A obtenção dos filmes de PMN se deu através de uma técnica de duplo estágio, que possibilita maior controle na supressão de fases pirocloro, e da técnica via Método dos Precursores Óxidos (MPO), através da reação direta dos óxidos. Filmes de PMN foram preparados sobre substratos Si(100) com diferentes números de deposições. Esses filmes foram submetidos a tratamentos térmicos entre 400oC e 800ºC, em forno convencional, sob diferentes condições de preparo. A estrutura dos filmes foi investigada pela técnica de difração de raios-X e refinamentos da estrutura pelo método de Rietveld. Os resultados apresentaram uma coexistência da fase pirocloro Pb1.86Mg0.24Nb1.76O6.5 e da fase perovskita Pb(Mg1/3Nb2/3)O3 (PMN) nos filmes preparados via rota da Columbita e a supressão da fase prirocloro nos filmes preparados pelo método MPO. Um estudo da morfologia por MEV indicou a preparação de filmes com boa homogeinidade e espessura média de 150nm Os resultados obtidos neste projeto indicam que a estabilização da fase perovkita do PMN e a supressão da fase pirocloro está relacionada a uma combinação particular de parâmetros tais como tempo e temperatura de cristalização e a adição de excessos de MgO e PbO a estequiometria.
Abstract: The present work describes the studies for the synthesis of ultrathin ferroelectric films of Pb(Mg1/3Nb2/3)O3 (PMN) and the systematic study of the crystallization kinetics of this material aimed at obtaining singlephase films. The films were produced from the modification of a chemical method based on oxide precursors. The obtention of the PMN films made by a technique of double stage, that allows greater control in the suppression of pyrochlore phases, and by technique via Oxide Precursors Method(OPM), through a direct reaction of the oxides. PMN films were prepared on Si(100) substrates with different numbers of depositions. These films were subjected to thermal treatments between 400ºC and 800°C, in conventional oven, under different preparation conditions. The structure of the films was investigated by the technique of X-ray diffraction and the structures refinements by the Rietveld method. The results showed a coexistence of pyrochlore phase Pb1.86Mg0.24Nb1.76O6.5 and perovskite phase Pb(Mg1/3Nb2/3)O3(PMN) in the films prepared via Columbita route and suppression of pyrochlore phase in films prepared by the OPM method. A study of morphology by SEM indicated the preparation of films with good homogeneity and medium thickness of 150 nm. The results obtained in this project suggest that the stabilization of PMN phase perovkite and the suppression of the pyrochlore phase is related to a particular combination of parameters such as time and temperature of crystallization and the addition of excess of MgO and PbO in the stoichiometry.
Mestre
Perks, Natasha J. "The role of charge and orbital ordering in quadruple perovskite materials with multiferroic potential." Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:c9287592-bcf4-40e0-ba2b-88f87e3b7450.
Full textFelix, Anderson André [UNESP]. "Estudo da estabilização da fase perovskita PMN em filmes ultrafinos." Universidade Estadual Paulista (UNESP), 2009. http://hdl.handle.net/11449/92014.
Full textFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
O presente trabalho descreve os estudos realizados para a síntese de filmes ferroelétricos ultrafinos de Pb(Mg1/3Nb2/3)O3 (PMN) e o estudo sistemático da cinética de cristalização deste material visando a obtenção de filmes monofásicos. Os filmes foram produzidos a partir da modificação de um método químico baseado em precursores óxidos. A obtenção dos filmes de PMN se deu através de uma técnica de duplo estágio, que possibilita maior controle na supressão de fases pirocloro, e da técnica via Método dos Precursores Óxidos (MPO), através da reação direta dos óxidos. Filmes de PMN foram preparados sobre substratos Si(100) com diferentes números de deposições. Esses filmes foram submetidos a tratamentos térmicos entre 400oC e 800ºC, em forno convencional, sob diferentes condições de preparo. A estrutura dos filmes foi investigada pela técnica de difração de raios-X e refinamentos da estrutura pelo método de Rietveld. Os resultados apresentaram uma coexistência da fase pirocloro Pb1.86Mg0.24Nb1.76O6.5 e da fase perovskita Pb(Mg1/3Nb2/3)O3 (PMN) nos filmes preparados via rota da Columbita e a supressão da fase prirocloro nos filmes preparados pelo método MPO. Um estudo da morfologia por MEV indicou a preparação de filmes com boa homogeinidade e espessura média de 150nm Os resultados obtidos neste projeto indicam que a estabilização da fase perovkita do PMN e a supressão da fase pirocloro está relacionada a uma combinação particular de parâmetros tais como tempo e temperatura de cristalização e a adição de excessos de MgO e PbO a estequiometria.
The present work describes the studies for the synthesis of ultrathin ferroelectric films of Pb(Mg1/3Nb2/3)O3 (PMN) and the systematic study of the crystallization kinetics of this material aimed at obtaining singlephase films. The films were produced from the modification of a chemical method based on oxide precursors. The obtention of the PMN films made by a technique of double stage, that allows greater control in the suppression of pyrochlore phases, and by technique via Oxide Precursors Method(OPM), through a direct reaction of the oxides. PMN films were prepared on Si(100) substrates with different numbers of depositions. These films were subjected to thermal treatments between 400ºC and 800°C, in conventional oven, under different preparation conditions. The structure of the films was investigated by the technique of X-ray diffraction and the structures refinements by the Rietveld method. The results showed a coexistence of pyrochlore phase Pb1.86Mg0.24Nb1.76O6.5 and perovskite phase Pb(Mg1/3Nb2/3)O3(PMN) in the films prepared via Columbita route and suppression of pyrochlore phase in films prepared by the OPM method. A study of morphology by SEM indicated the preparation of films with good homogeneity and medium thickness of 150 nm. The results obtained in this project suggest that the stabilization of PMN phase perovkite and the suppression of the pyrochlore phase is related to a particular combination of parameters such as time and temperature of crystallization and the addition of excess of MgO and PbO in the stoichiometry.
Verseils, Marine. "Interplay between magnetic ordering and ferroelectricity in multiferroics with quadruple perovskite structure." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066457/document.
Full textIn the present Thesis, we study the large ferroelectricity induced by magnetism in two quadruple perovskite compounds: (LaMn3)Mn4O12 and (YMn3)Mn4O12, which both display single-valent properties and a commensurate C-type antiferromagnetic structure of the B-sites. These simple features offer a playground to elucidate the contribution of the symmetric and antisymmetric exchange interactions to the polarization. Both compounds are metastable and stabilized under high-pressure. YMO is a new phase, where the small Y3+ ion exerts a large chemical pressure, which is expected to enhance the exchange interaction and, thus, the spontaneous polarization. We find an ordering temperature of the B-sites, 30 K higher than in LMO. On the other hand, we surprisingly find identical values of the spontaneous polarization, P = 0.54 μC cm-2, in both compounds. It is a record value for magnetic ferroelectrics. In spite of the similarities, the nature of magnetic ferroelectricity appears to be very different in the two compounds. In LMO, ferroelectricity is induced by the magnetic ordering of B-sites, although no indication of inversion symmetry breaking is detected. We argue that this puzzling observation is consistent with prediction of domain structure in improper ferroelectrics. On the other hand, in YMO, the occurrence of ferroelectricity at T*=70 K is consistent with a polar structural modulation below Ts=200 K, however T* does not correspond to any long-range magnetic transition. Indeed, T* marks a magnetic anomaly suggesting a latent magnetic phase. We put forward the hypothesis that the above polar distortion of the crystal structure may force the alignment of polar domains
Sharma, 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.
Full textIn 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
Waeselmann, Naëmi [Verfasser], and Boriana [Akademischer Betreuer] Mihaylova. "Structural transformations in complex perovskite-type relaxor and relaxor-based ferroelectrics at high pressures and temperatures / Naëmi Waeselmann. Betreuer: Boriana Mihaylova." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2012. http://d-nb.info/1024355527/34.
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