Dissertations / Theses on the topic 'Polarisation ferroélectrique'
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Rault, Julien. "Structure chimique et électronique des interfaces métal/ferroélectrique en fonction de la polarisation ferroélectrique." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2013. http://tel.archives-ouvertes.fr/tel-00840865.
Full textDuclere, Jean-René. "Croissance épitaxiale par ablation laser et caractérisations de couches minces du matériau ferroélectrique SrBi2Nb2O2." Rennes 1, 2002. http://www.theses.fr/2002REN10072.
Full textChmielowski, Radoslaw. "Bicouche oxyde ferroélectrique / oxyde conducteur Bi3. 25La0. 75Ti3O12 / Sr4Ru2O9 : élaboration par ablation laser, caractérisations structurales et propriétés électrique." Toulon, 2007. http://www.theses.fr/2007TOUL0007.
Full textBilayers ferroelectric oxide / conductive oxide, Bi3. 25La0. 75Ti3O12 (BLT) / Sr4Ru2O9 / Si[100] were elaborated by pulsed laser deposition. Structural characterizations were done by electron microscopy and X-ray diffraction; electrical properties were measured by impedance spectroscopy and Van der Pauw’s method. It is the first time that Sr4Ru2O9 is elaborated as thin films. We have shown that Sr4Ru2O9 is a conductive oxide at high temperature and has a semiconductor behavior at low temperature. The BLT thin films have polarization out of the substrate plane. Thick films of the BLT have polarization in the plane, which corresponds to a preferential orientation (00l). An intermediate layer, based on SrTiO3, between the substrate oxide Sr4Ru2O9 and the layer of BLT, was highlighted by electron microscopy. This phase grows at the cost of the ferroelectric material
Dubois, Frédéric. "Elaboration et caractérisations électro-optique et diélectrique de composites à cristaux liquides ferroélectriques dispersés dans une matrice polymère." Phd thesis, Université du Littoral Côte d'Opale, 2004. http://tel.archives-ouvertes.fr/tel-00009656.
Full textCe travail concerne l'élaboration et l'étude des propriétés structurales, diélectriques et électro-optiques de composites PDFLC. L'objectif principal est d'étudier l'influence de la nature dispersée et confinée du cristal liquide sur les propriétés des composites. Pour cela, deux cristaux liquides ferroélectriques présentant respectivement un pas d'hélice faible et élevé par rapport à la taille des gouttelettes ont été utilisés pour élaborer ces composites.
Une étude comparative des propriétés des cristaux liquides et des films PDFLC a été réalisée. Les composites étudiés présentent des propriétés électro-optiques intéressantes, tels que l'existence d'un ancrage bistable, des temps de réponse et des tensions de commutation relativement faibles. La caractérisation des mécanismes de relaxation observés pour les composites montrent qu'ils sont liés à la ferroélectricité des cristaux liquides utilisés. Les caractéristiques de ces mécanismes, à savoir leur amplitude et leur fréquence critique, diffèrent fortement de celles observées pour les cristaux liquides purs. Ces différences ont été attribuées à l'hétérogénéité diélectrique des composites PDFLC.
Xu, Qian. "Perovskite ferroelectric nanostructures for photo(electro)catalysis." Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPASF025.
Full textPhoto(electro)catalysis, which can directly harvest energy from solar illumination and convert it into chemical energy, has brought light to the depletion of fossil fuels and concerns about environmental issues. Significant attention has been dedicated to promoting charge separation and transport dynamics to enhance solar energy conversion to reach the requirements for practical applications. Ferroelectric and piezoelectric polarization that can trigger spatial charge redistribution and promote bulk or surface charge-carrier separation has been demonstrated as a promising strategy for designing highly efficient photocatalytic systems. In this PhD project, BaTiO₃ (BTO) has been selected as a typical ferroelectric semiconductor, with its ferroelectric and piezoelectric properties being employed to enhance directional charge carrier transfer and lifetime, explored through PEC water oxidation and Rhodamine B (RhB) degradation, respectively. More specifically, the principles and applications of piezo/ferroelectric-assisted photo(electro)catalysis were thoroughly discussed. We then developed core-shell BTO/TiO₂ nanostructures, deposited with Ni(OH)₂ oxygen evolution cocatalysts (OEC), as photoanodes for photoelectrochemical water oxidation. The relationship between ferroelectric polarization and charge separation and transport of TiO₂ was investigated by BTO crystalline phases and external electric fields. In addition, the role of piezoelectric polarization delivered by BTO in charge transport dynamics during the photocatalytic process was explored through the degradation of Rhodamine B (RhB), and was further discussed in detail based on the insights drawn from experimental characterizations and theoretical calculations
AYDI, Abdelhedi. "Elaboration et caractérisations diélectriques de céramiques ferroélectriques et/ou relaxeur de formule MSnO3-NaNbO3(M=Ba,Ca)." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2005. http://tel.archives-ouvertes.fr/tel-00009068.
Full textDionot, Jelle. "Topology of ferroelectric polarization at the BaTiO3(001) surface from ab initio calculations and electron microscopy-spectroscopy." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112182/document.
Full textAt a surface or interface of a ferroelectric material, the polarization can be destabilized and even suppressed by the depolarizing field which arises from uncompensated polarization charge. In the absence of external (adsorbates, electrodes) or internal (defects, dopants) screening mechanisms, domain ordering is the most natural way for a system to remain ferroelectric and minimize its electrostatic energy. This thesis focuses on the study of the stability of various possible domain configurations, and on how it depends and interplays on size, chemical and elastic factors, at the (001) surface of BaTiO3.First-principles calculations, based on density functional theory, have been performed to enlighten the influence of surface terminations, in-plane strain, system thickness and domain size in ultrathin films on the polarization in different ferroelectric phases. The effect of surface oxygen vacancies on the polarization and electronic structure has also been investigated. Low Energy electron microscopy (LEEM) and photoemission electron microscopy (PEEM) have been used to study the surface properties of ferroelectric polarization in reduced BaTiO3 single crystals, allowing to address the influence of oxygen vacancies on the ferroelectric polarization from experimental approaches, supporting the calculations results
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
Chanthbouala, André. "Jonctions tunnel magnétiques et ferroélectriques : nouveaux concepts de memristors." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2013. http://tel.archives-ouvertes.fr/tel-00932584.
Full textLebon, Alexandre. "Influence de la direction de polarisation sur la coexistence de phases et la structure en domaines du ferroélectrique - relaxeur Pb(Zn1/3Nb2/3)O3 : une étude sur monocristal par diffraction des rayons X et diffusion Raman." Châtenay-Malabry, Ecole centrale de Paris, 2001. http://www.theses.fr/2001ECAP0707.
Full textPb(Zn1l3Nb2/3)03 (PZN) is a complex lead based perovskite. This ferroelectric relaxor exhibits remarkable electromechanical properties that make necessary a study as a function of the direction of polarisation. In fact, even though the spontaneous polarisation is parallel to a <111> direction, its piezoelectric properties are optimised when the crystal is polarised along [001]. Spontaneously, the cubic → rhombohedral phase transition that occurs at Tc = 385 ± 5 K is diffuse in temperature. Rhombohedral microdomains appear within the cubic phase, as their number increases, they occupy all the crystal around 330 K. Below Tc, the application of an electric field along [111] induces a complex structure of rhombohedral macrodomains. These macrodomains of a few tens of microns are separated by regions that diffuse light and that belongs to {11O} plans. As the [001] direction of the applied electric field is concerned, a Monoclinic tetragonal phase coexistence is induced. In a field cooling process, a structure of 4 monoclinic microdomains is ordered symmetrically with respect to the direction of the electric field. All , our data enabled to build an electric field - temperature diagram (E-T) along [001]. At last, on the basis of structural data, a tetragonal symmetry is proposed for the nanopolar regions that give way to dielectric relaxation
MʾKadmi, Allal. "Caractérisation diélectrique des cristaux liquides ferroélectriques." Lille 1, 1988. http://www.theses.fr/1988LIL10059.
Full textJaulin, Albéric. "Imagerie de polarisation haute cadence à l'aide d'un modulateur de lumière à cristaux liquides ferroélectriques." Mulhouse, 2007. https://www.learning-center.uha.fr/opac/resource/imagerie-de-polarisation-haute-cadence-a-laide-dun-modulateur-de-lumiere-a-cristaux-liquides-ferroel/BUS4043663.
Full textWe propose the implementation of an imaging polarimeter prototype using a ferroelectric liquid crystal light modulator. This study lies on the characterization and the optimized control of this modulator to obtain a high speed polarimetric Stokes image at a frame rate higher than 200 Hz. The ferroelectric liquid crystal modulator is first used as a rotating polarization waveplate to obtain images of partial linear degree of polarization. Then, images of total linear degree of polarization can be obtained at the modulator reference wavelength and can be used to observe moving depolarizing objects. Using another wavelength, we can obtain the complete degree of polarization and the Stokes vector of the considered light wave. We implemented a high-speed device for polarization imaging. Prospects of this implementation are observations of other polarization parameters (eg Mueller Matrix) of moving objects
Kondovych, Svitlana. "Électrostatique des charges dans les couches minces diélectriques et ferroélectriques." Thesis, Amiens, 2017. http://www.theses.fr/2017AMIE0031/document.
Full textWe explore the various types of electrostatic interaction between charges in thin films with high dielectric permittivity, including the special case of the two-dimensional logarithmic Coulomb interaction, and propose a method of tuning the interaction regime using the external gate electrode. Changing the gate-to-film distance, one may alter the electrostatic screening length of the dielectric sample and control the ranges of different interaction types. We investigate next the electrostatics of extended charges in dielectric media, modeling the electrostatic potential distribution for charged wires, stripes and domain walls, with either homogeneous or periodic linear charge density. Basing on the calculated dependencies of the potential on the system geometry and material parameters, we discuss several possible applications: i ) we suggest the non-destructive method for measuring the dielectric constant of substrate deposited thin films by a two-wire capacitor; ii ) we study the domain structure formation in ferroelectric films with in-plane polarization. We show that for the in-plane striped 180˚ domain structure, induced by the discontinuity of the order parameter at the film edge, the equilibrium domain width violates the Kittel's square root law, being instead inversely proportional to the film thickness. The calculations for the in-plane domains, generated by the microscope tip or charged domain wall in the ferroelectric slab, demonstrate the conformity of the optimal domain length to the characteristic electrostatic length of the sample, and accord with the experimental data
Kondovych, Svitlana. "Électrostatique des charges dans les couches minces diélectriques et ferroélectriques." Electronic Thesis or Diss., Amiens, 2017. http://www.theses.fr/2017AMIE0031.
Full textWe explore the various types of electrostatic interaction between charges in thin films with high dielectric permittivity, including the special case of the two-dimensional logarithmic Coulomb interaction, and propose a method of tuning the interaction regime using the external gate electrode. Changing the gate-to-film distance, one may alter the electrostatic screening length of the dielectric sample and control the ranges of different interaction types. We investigate next the electrostatics of extended charges in dielectric media, modeling the electrostatic potential distribution for charged wires, stripes and domain walls, with either homogeneous or periodic linear charge density. Basing on the calculated dependencies of the potential on the system geometry and material parameters, we discuss several possible applications: i ) we suggest the non-destructive method for measuring the dielectric constant of substrate deposited thin films by a two-wire capacitor; ii ) we study the domain structure formation in ferroelectric films with in-plane polarization. We show that for the in-plane striped 180˚ domain structure, induced by the discontinuity of the order parameter at the film edge, the equilibrium domain width violates the Kittel's square root law, being instead inversely proportional to the film thickness. The calculations for the in-plane domains, generated by the microscope tip or charged domain wall in the ferroelectric slab, demonstrate the conformity of the optimal domain length to the characteristic electrostatic length of the sample, and accord with the experimental data
Ragheb, Mostafa. "Modélisation des propriétés des matériaux ferroélectriques displacifs monocristallins." Nantes, 2013. http://www.theses.fr/2013NANT2017.
Full textThe ferroelectric displacive materials present an increasing interest in the industrial field, in particular for telecommunications, because of the tunability of the permittivity or of the piezoelectric coefficient. The objective of this PhD thesis is a better understanding of the properties of these materials by carrying out a theoretical study. At the nanometric scale, the effects of temperature, of a mechanical stress or of an applied electric field are examined in particular in terms of the deformation of the unit cell and the change of the dipole moment. It is then possible to obtain the permittivity or the piezoelectric coefficient according to these variables, in the both polar and non-polar phases. To describe the properties of a ferroelectric displacive material at microscopic scale, we must add to the previous description the notion of domain of polarization. When the material is submitted to an external solicitation, the walls separating the different domains move. The study of this motion provides the variation of the polarization, of the deformation, of the permittivity or of the piezoelectric coefficient as a function of applied electric field or mechanical stress (hysteresis and butterfly loops). The role of defects in the material is taken into account by considering pinning and depinning of the walls by these defects. A distinction is carried out between minor loops, for which the density of domain walls is constant, and the major loops where one must take into account the variation of the density of walls
Boulos, Madona. "Elaboration de poudres de titanates par chimie douce, caractérisation, mise en forme de céramiques et de couches, et propriétés électriques : application aux matériaux à très fortes valeurs de permitivité." Toulouse 3, 2005. http://www.theses.fr/2005TOU30261.
Full textNanometric powders of BaTiO3 have been prepared by hydrothermal method at 150 and 250°C using BaCl2. 2H2O/TiCl3 or TiO2 as precursors. Ceramics showing 95% of densification are obtained after sintering at 1250°C for 10 and 20 h. These ceramics present a heterogeneous microstructure. The grain size and the grain distribution in the ceramic bulk govern the electrical properties. Thick layers present a relative permittivity higher then 4000 at the curie temperature. La-doped BaTiO3 has been prepared by the oxalate method. The obtained ceramics showed a uniform microstructure. The Curie temperature is displaced to lower temperatures and the relative permittivity increases up to 10000 with increasing La3+ concentration. Ceramics sintered by spark plasma sintering showed electrical properties that are significantly different from those of conventionnally sintered ones. The coprecipitation has been used to synthesize materials based on CaCu3Ti4O12. Three main types of ceramics were obtained. The presence of CuO phase beside the CCT plays an important role for enhancing the dielectric properties
Gallé, Nicolas. "Propriétés optiques et électro-optiques de cellules de cristaux liquides ferroélectriques en configuration torsadée." Lille 1, 2007. https://pepite-depot.univ-lille.fr/LIBRE/Th_Num/2007/50376-2007-333.pdf.
Full textMartin, Simon. "Caractérisation électrique multi-échelle d'oxydes minces ferroélectriques." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI145/document.
Full textFerroelectric materials show a spontaneous dielectric polarisation even in the absence of applied electric field, which confers them interesting possibilities of applications. The reduction of the thickness of ferroelectric layers towards ultra-thin values has been necessary in view of their integration in micro and nano-electronic devices. However, the reduction of thickness has been accompanied by unwanted phenomena in thin layers such as tunneling currents and more generally leakage currents. The electrical characterization of these materials remains a challenge which aims at better understanding the physical mechanisms at play, and requires now a nanometric spatial resolution. To do so, it is thus mandatory to enhance the techniques of electrical measurement. In this work, we measure the dielectric polarisation of ferroelectric films from mesoscopic scale down to the nanometric scale using purely electric characterisation techniques (Polarisation vs Voltage, Capacitance vs Voltage, Current vs Voltage), but also electro-mechanical techniques like Piezoresponse Force Microscopy which derives from Atomic Force Microscopy. We show the limits of several classical techniques as well as the artefacts which affect electrical or electro-mechanical measurement and may lead to an incorrect interpretation of the data. In order to push the investigation further, we have developed and we describe new measurement techniques which aim at avoiding some parasitic signals. We present the first direct measurement of the remnent polarisation at the nanoscale thanks to a technique which we call « nano-PUND ». These techniques and methods are applied to a large variety of materials like Pb(Zr,Ti)O3, GaFeO3 or BaTiO3 which (for some of them), ferroelectricity has not been measured experimentally
Haumont, Raphaël. "Rotation de la polarisation dans les systèmes morphotropiques : cas de Pb(Sc1/2Nb1/2)O3-PbTiO3." Châtenay-Malabry, Ecole centrale de Paris, 2004. http://www.theses.fr/2004ECAP0960.
Full textThe work of this thesis aims to explore the crystallographic structure of the Morphotropic Phase Boundary (MPB) of the solid solutions with perovskite structure (relaxor-PbTiO3) with the remarkable piezoelectric properties like PMN-PT, PZN-PT and PSN-PT. The MPB delimits the rhomboedral symmetry R3m area (PSN) of the tetragonal P4mm (PbTiO3) area. We established that, with the increasing of titanium substitution, spontaneous polarization undergoes a complex rotation between the <111> and <001> directions via the symmetry planes of monoclinic phases (Cm and Pm space groups): R3m (PSN) - Cm - (Cm + Pm) - (Pm + P4mm) - P4mm (Pt). Thanks to complete treatments of the diffraction profiles versus temperature, it is possible to follow the thermal stability of these various ferroelectric phases and thus, a complete diagram of phase of PSN-PT was proposed. We also characterized PSN-PT thin films : with chemical substitution and the temperature, the bidirectional mechanical constraint induced by a substrate is a parameter which deeply modifies the ground state. Gathered and correlated with results extracted of the x-ray and neutrons diffractions, data obtained by Raman spectroscopy, dielectric measurements and calculation ab-initio allowed to propose a microscopic model accounting for the appearance and the disappearance of these monoclinic phases in system PSN-PT. This mechanism, -that we think can be generalizable of the others morphotropic systems, is based on the very strong intrinsic chemical heterogeneity of these systems and on the dominating role of the (polar) disorder of lead atoms
Nguyen, Dinh Quang. "Etude de matériaux ferroélectriques à base de titanate de baryum : application à l'intégration de composants passifs en électronique de puissance." Toulouse 3, 2006. http://www.theses.fr/2006TOU30015.
Full textThis work concerns the study of ferroelectric materials based barium titanate and their application to the integration of passive components in power electronics. The main electric characteristics of pure or doped barium titanate materials are determined (permittivity, dielectric losses) for two different types of samples (ceramics or thick films) and whatever the technique of sintering (classical or spark plasma sintering). The ceramics obtained from powders synthesised by hydrothermal or by co-precipitation method and classical sintering (1250°C during 10h or 20h) present a high permittivity (11000 at the Curie temperature and 3100 at room temperature). These values are respectively of 9400 and of 8500 for the La – doped BaTiO3 ceramics. The ceramics with identical composition and sintered by SPS (Spack Plasma Sintering) present a colossal (270000 at room temperature) and a behaviour stable permittivity with the temperature. Correlations between the electrical properties, the microstructure and the manufacture process of the ceramics are proposed. .
Kaczmarek, Jean. "Mise en évidence des phénomènes de photoconduction dans des cristaux liquides ferroélectriques photosensibles." Thesis, Lille, 2018. http://www.theses.fr/2018LIL1R028.
Full textFerroelectrical materials possess the remarkable property to orienting themselves and generating surfaces charges under electric field. Dipole movements can be observed by measuring internal electric field or spontaneous polarization under alternative electric field. These organic materials are widely used in fast display devices. The aim of this work was to propose a direct current measurement of photoconduction phenomenon in ferroelectric non-photosensitive and photosensitive liquid crystals by charge carrier transport in SSFLC devices using time of flight methodology. The proposed method is based on charge carrier transport determination which providing access to characteristics parameters like mobility. Differentprocedures have been presented for mobility estimation from adding increasing dopant concentrations, electrical field and temperature, as well as charge behaviour pattern for exploitation and description. This materials show real influence of several parameters on the photocurrent shape signal and different mobility values under large scales of temperature. The validation of the method on photosensitive ferroelectric materials and obtained results by data treatment show that this method can be used to characterize another liquid crystal whatever its phase including SmC*
Wicker, Arsène. "Films minces de polymères ferroélectriques : étude de la croissance orientée par épitaxie et de la polarisation par génération du second harmonique de la lumière." Grenoble 1, 1990. http://www.theses.fr/1990GRE10053.
Full textDubreuil, Matthieu. "Développement d'un polarimètre de Mueller instantané par codage en longueur d’onde : application à la caractérisation de cristaux liquides ferroélectriques." Brest, 2010. http://www.theses.fr/2010BRES2042.
Full textMueller matrix polarimeters allow the acquisition of the full linear polarimetric response of a medium, and lead to the knowledge of its dichroism, birefringence and depolarization properties. By now, those setups used to generate the multiple states of polarization necessary for the calculation of a Mueller matrix in a sequential way, which limits their acquisition time at the millisecond scale. In this work, we propose the development of the first experimental Mueller matrix polarimeter with a spectral encoding of the polarization, so as to parallelize the generation of polarization’s states. The acquisition time of a Mueller matrix is thus limited by the acquisition time of the detector, and could be very short (
Gendre, Luc. "Conception et réalisation d'un polarimètre de Stokes haute cadence à division temporelle utilisant un unique modulateur à cristaux liquides ferroélectriques pour moduler la polarisation." Phd thesis, Université de Haute Alsace - Mulhouse, 2011. http://tel.archives-ouvertes.fr/tel-00713656.
Full textDubreuil, Matthieu. "Développement d'un polarimètre de Mueller instantané par codage en longueur d'onde. Application à la caractérisation de cristaux liquides ferroélectriques." Phd thesis, Université de Bretagne occidentale - Brest, 2010. http://tel.archives-ouvertes.fr/tel-00602923.
Full textBoudot, Cécile. "Transitions de phase sous champ électrique dans la thiourée." Nancy 1, 1988. http://www.theses.fr/1988NAN10087.
Full textRestoin, Christine. "Inversion périodique de domaines ferroélectriques par faisceau d'électrons sur Ti:LiNbO3 : Contribution à la réalisation d'un convertisseur en longueurs d'onde indépendant de la polarisation (lambda = 1,55 micro m)." Limoges, 2000. http://www.theses.fr/2000LIMO0010.
Full textBenabdallah, Feres. "Evolution des propriétés diélectriques, ferroélectriques et électromécaniques dans le système pseudo-binaire (1-x)BaTi0.8Zr0.2O3- xBa0.7Ca0.3TiO3 / Corrélations structures et propriétés." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2013. http://tel.archives-ouvertes.fr/tel-00879222.
Full textBruyer, Emilie. "Propriétés structurales, électroniques et ferroélectriques de systèmes Ln₂Ti₂O₇ (Ln=lanthanides) et d'hétérostructures SrTiO₃ / BiFeO₃." Thesis, Artois, 2012. http://www.theses.fr/2012ARTO0401/document.
Full textIn this work, first-principles calculations and experimental measurements have been done in order to investiguate the structural, electroniq and ferroelectric properties of Ln2Ti2O7 (Ln = La, Nd, Sm, Gd) and BiFeO3 oxydes. Calculations on La2Ti2O7 and Nd2Ti2O7 confirmed their ferroelectricity. Other oxydes belonging to the Ln2Ti2O7 family have also been investigated. The results showed an enhancement of the spontaneous polarization within these compounds compared to that of La2Ti2O7 and Nd2Ti2O7. The second part of this work is related to the structural and ferroelectric properties of bismuth ferrite BiFeO3. The evolution of its properties when undergoing an epitaxial strain have been investigated by ab initio calculations and piezoresponse force microscopy measurements on thin films deposited on a (001)-SrTiO3 substrate. Our results showed a modification of the inner structure of BiFeO3 under stain, leading to a continuous reorientation of the spontaneous polarization vector towards [001]. The third part of our study consists in the computational design and synthesis of (SrTiO3)n(BiFeO3)m superlattices. Our calculations showed that epitaxial strain imposed to the superlattice brings a further control of physical properties of BiFeO3 as compared with its behaviour when deposited alone in a thin film. PFM analysis showed a decrease of the coercive field for STO/LNO/(STO)n(BFO)m superlattices as compared with those measured on STO/BFO bi-layers and on BiFeO3 thin films
Rendón, Barraza Carolina. "Polarization-resolved nonlinear microscopy in metallic and ferroelectric nanostructures for imaging and control in complex media." Thesis, Aix-Marseille, 2016. http://www.theses.fr/2016AIXM4365.
Full textIn this work, we develop a novel polarized nonlinear microscopy method that exploits sub-diffraction resolution information. Fourier analysis of the polarization modulated nonlinear signal is performed on over-sampled, drift-corrected images (50nm pixel size). The information gained by polarization-induced modulation signals provides a higher level of spatial selectivity that is directly related to the local optical response of the investigated system, at a scale below the diffraction limit. The gain in spatial scale is due to the additional spatial sensitivity brought by polarization. This approach is applied to polarized second harmonic generation imaging in plasmonic nanostructures (150nm size) of multi-branched shapes, in which the vectorial nature of the local field confinement can be retrieved with a resolution of 40 nm. We also demonstrate the possibility to image spatial heterogeneities within crystalline ferroelectric BaTiO3 nanoparticles of 70nm to 500nm size, emphasizing in particular the existence of a centrosymmetric shell in small size structures. These nanostructures will be used as starting models for coherent optical probes in biological media (cells, tissue slices or in vivo) with two objectives. First, the nonlinear nature of their emission will make them stable and tunable nanosources, able to report their localization with high accuracy in 3D, potentially sensing local environment changes, and actively inducing perturbations such as controlled temperature increase at the nanoscale. Second, the coherent nature of their emission will make them useful as local nanoprobes for wavefront and polarization correction through scattering media