Rozprawy doktorskie na temat „Relaxeur ferroélectrique”
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Laulhé, Claire. "Structure locale dans un ferroélectrique relaxeur : BaTi(1-x)Zr(x)O3". Phd thesis, Grenoble INPG, 2007. http://tel.archives-ouvertes.fr/tel-00196922.
Pełny tekst źródłaTellier, Jenny. "Sur les phases d'Aurivillius : études structurales et transitions de phases". Limoges, 2006. https://aurore.unilim.fr/theses/nxfile/default/dd157e3d-cbb2-4ec9-95b3-2e5100ed9b30/blobholder:0/2006LIMO0019.pdf.
Pełny tekst źródłaAurivillius phases, with general formula (Bi2O2)2+(Am-1BmO3m+l)2- can be ferroelectric or relaxor materials. They display orthorhombic symmetry at room temperature and tetragonal at high temperature. Structural study of ferroelectric and relaxor compounds at room temperature show that relaxors' structure is legs distorted than that of ferroelectrics. Their fluorite slabs are independent and contain non-bismuth cations. Disorder in relax ors is showed using TEM analysis. It leads to local variations of structure which can be responsible for relaxor behaviour. Phase transition study cannot be carried out systematically for such compounds. The case of SrBi2Ta2O9, SrBi2Nb2O9 and Bi4Ti2,8Cr0,2O12 is considered, and additional information is given about other Aurivillius phases
Hentati, Mouhamed Amin. "Effets des inhomogénéités locales et des contraintes extérieures sur les propriétés diélectriques et structurales des monocristaux PZN-x%PT". Phd thesis, Châtenay-Malabry, Ecole centrale de Paris, 2013. http://tel.archives-ouvertes.fr/tel-01003354.
Pełny tekst źródłaAYDI, 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.
Pełny tekst źródłaGuerville, François de. "Films minces et superréseaux à base du ferroélectrique BaTiO3 et du relaxeur BaTi0,68Zr0,32O3 : élaboration, études par diffraction de rayons X et par spectroscopie Raman : modélisation des domaines ferroélectriques dans les films minces et les superréseaux". Amiens, 2008. http://www.theses.fr/2008AMIE0113.
Pełny tekst źródłaThis work deals with lead-free ferroelectric oxide thin films and superlattices, studied both experimentally (elaboration/characterization) and by modelling. In the experimental part, we have elaborated thin films and superlattices based on ferroelectric BaTiO3 and relaxor BaTi0. 68Zr0. 32O3 by pulsed laser deposition on MgO substrate buffered by La0. 5Sr0. 5CoO3. These samples were then studied by X ray diffraction and Raman spectroscopy in order to determine their structure, to estimate the stress therein and to evidence structural phase transitions. In superlattice, BaTiO3 layers show a quadratic ferroelectric structure with a1/a2 domains whereas BaTi0. 68Zr0. 32O3 layers are perpendicularly deformed to substrate plane. Dislocations appearance beyond a 260 Å critical period seems to relax these stresses. Against all expectations, superlattices Raman spectra have thinner lines than in films. We have attributed this phenomenon to a Ti4+ ion disorder decrease on the BaTiO3 perovskite structure B site. Temperature studies seem to show phase transition absence for BaTiO3 layers in superlattice. In addition, we have simulated thermodynamic and electric behaviour of ferroelectric domains in thin film and in ferroelectric/paraelectric superlattice. For this, we have modelled polarization profile taking into account finite size and interface effects, from 0 Kelvin to beyond phase transition temperature. We have shown nanometric thickness films properties are substantially modified by gradual polarization profile in these domains ; dielectric constant temperature evolution suits experimental behaviour observed around phase transition
Bouyanfif, Houssny. "Hétérostructures et super-réseaux à base du relaxeur PbMg1/3Nb2/3O3 et du ferroélectrique PbTiO3@ : croissance et étude des effets de contraintes par diffraction de rayons X et spectroscopie Raman". Amiens, 2005. http://www.theses.fr/2005AMIE0502.
Pełny tekst źródłaHornebecq, Virginie. "Nouveaux tantalates ferroélectriques de type bronze quadratique de tungstène : de la structure aux propriétés physiques". Phd thesis, Université Sciences et Technologies - Bordeaux I, 2000. http://tel.archives-ouvertes.fr/tel-00003498.
Pełny tekst źródłaBenyoussef, Manal. "Experimental and theoretical investigation of rare-earth doped lead-free relaxor ferroelectric Na0.5Bi0.5TiO3 system for high-temperature energy storage capacitors". Electronic Thesis or Diss., Amiens, 2020. http://www.theses.fr/2020AMIE0053.
Pełny tekst źródłaIn the present research work, we performed a comprehensive experimental and theoretical investigation on the lead-free relaxor ferroelectric Na0.5(Bi1-xREx)0.5TiO3 (xRENBT) systems (RE = rare earth) for high-temperature energy storage capacitors. The conventional solid-state method was used to synthesize the xRENBT (RE = Dy, and Nd) ceramics with different concentration levels. A Pure perovskite phase and dense microstructure were revealed through XRD and SEM investigations. Besides, a great structural diversity was found in the xRENBT systems and was observed to depend on the nature and level of the doped rare earth element. Temperature-dependent dielectric investigations revealed very low dielectric losses in the doped compounds, especially at high temperatures. High stability of the temperature coefficient of the capacitance (TCC) was obtained for the doped samples. Through the ferroelectric investigations, we observed that rare earth doping was found to break the long-range ferroelectric domains and instead induce polar nano regions within the studied systems. Accordingly, high energy storage properties were obtained with values reaching Wrec = 1.2 J/cm3 (η = 60%) at 95 kV/cm, with great temperature stability (120 – 200°C). Besides, the RE induced local structural heterogeneities within the NBT system, was found effective in improving the electrocaloric effect of the doped compositions in a broad temperature range, with an electrocaloric coefficient reaching high values of ΔT/ΔE ~ 0.30×10-6 K m/V. The effect of rare-earth doping on the structural, ferroelectric, electronic, and magnetic properties of the Na0.5(Bi3/4RE1/4)0.5TiO3 (RE = Nd, Gd, Dy, and Ho) system was thoroughly investigated using the FPLAPW based on the spin-polarized density functional theory implemented in the WIEN2k code. The mechanism driving ferroelectricity and the effect of doping on the relaxor properties of the system were thoroughly investigated. A modified Heisenberg model was used to simulate the phase transition and temperature-dependent hysteresis loops of the rare-earth-doped NBT system. The obtained results evidenced that tuning the polar domains in lead-free relaxor ferroelectrics is a powerful way to design materials with enhanced dielectric stability, energy storage, and electrocaloric properties over a broad temperature range
Albino, Marjorie. "Synthèse et caractérisation structurale et diélectrique de céramiques et de monocristaux relaxeurs de structure TTB". Phd thesis, Université Sciences et Technologies - Bordeaux I, 2013. http://tel.archives-ouvertes.fr/tel-00920357.
Pełny tekst źródłaLebon, 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.
Pełny tekst źródłaPb(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
Al-Zein, Ali. "Order and Disorder of Relaxor and Ferroelectric Materials : structural and Vibrational Studies". Thesis, Montpellier 2, 2010. http://www.theses.fr/2010MON20078/document.
Pełny tekst źródłaAmong piezoelectric materials, lead-based ferroelectric perovskites are known to have the largest piezoelectric coefficients and electromechanical coupling. They are widely used in dfferent industrial and technological applications. The so-called "relaxors" belong to this family. Their structure is characterized by the presence of randomly oriented polar nanoregions. In this thesis, we are interested in studying the structural and dynamical properties of prototypical ferroelectric materials and relaxors such as PbTiO3, PbZr0.52Ti0.48O3, PbMg1/3Nb2/3O3 (PMN), PbZn1/3Nb2/3O3, and PbMg1/3Ta2/3O3 (PMT). The long and short range structure has been investigated by neutron diffraction and X-ray absorption fine structure (XAFS), while hyper-Raman scattering (HRS) is used to probe the vibrations. The local structure analysis of complex perovskite materials AB'B''O3 shows that pressure reduces the static disorder of the large cation occupying the B-site, while an applied electric field has an opposite effect. This field-induced distortion might relate to the large piezoelectric coefficient in such materials. HRS in PMN and PMT allows the first observation of the "primary" soft mode responsible for the temperature dependence of the dielectric constant. The selection rule analysis reveals the nature of the HRS active vibrational bands and enables us to get insights about the involvement of each atom in the structural modifications upon temperature
Nahas, Yousra. "Gauge theory for relaxor ferroelectrics". Phd thesis, Ecole Centrale Paris, 2013. http://tel.archives-ouvertes.fr/tel-01003357.
Pełny tekst źródłaAydi, Abdelhedi. "Élaboration et caractérisations diélectriques de céramiques ferroélectriques et/ou relaxeur de formule MSnO3-NaNbO3(M = Ba,Ca)". Bordeaux 1, 2005. http://www.theses.fr/2005BOR12964.
Pełny tekst źródłaThe present work reports the elaboration process and physical investigation of ceramics belonging to the chemical systems NaNbO3-(Ba, Ca)SnO3. These materials are terefore free of lead and all poisonous elements in order to answer to the protective norms of the environment. The studied systems presnt some continuous solid solutions between the NaNbO3 antiferroelectric phase - that becomes easily ferroelectric by low rate substitutions and the paraelectric stannate phase. Two different dielectric behavior have been evidenced : ferroelectric and relaxor. According to the whole of studies done during this work one can confirm that caionic substitutions in the A site either in the B site of a perovskite ABO3 can modifiy the dielectric properties of the material. The introduction of Sn4+ cation in B sites favours a relaxor effect. The transition temperature should be modulatedd by varying the rate of cationic substitution. One can get so relaxor materials close to room temperature
Trujillo, Tovar Maria Sonia. "Synthèse et caractérisation de matériaux ferroélectriques relaxeurs à base de Na1/2Bi1/2TiO3 (NBT)". Grenoble INPG, 2006. http://www.theses.fr/2006INPG0066.
Pełny tekst źródłaThis work lies within the broader scope of research related to so-called relaxor ferroelectrics with currently attract considerable attention from both a fundemental and an application point of view. The first part of this work is related to the synthesis of thin films. Our results highlight the difficulty in synthesizing thin films of Na1/2Bi1/2TiO3 by chemical processes. This difficulty is directly related to a complex chemistry during the deposition of bysmuth and sodium. The second part of our work concerns the fundamental understanding of pure Na1/2Bi1/2TiO3 and NBT doped with Baryum (NBT-BT). Two techniques of characterization have been used in our work: Raman spectroscopy and X-tays scattering, in particular diffuse scattering. We have carried out the first high-pressure study of NBT-BT by Raman scattering. The spectral analysis shows that NBT-BT evolves under pressure in two regimes: a first, where the pressure forces NBT-BT towards the structure of NBT (pc=1,8 GPa) and a second where NBT-BT evolves like NBT with a new phase transition around 12 GPa. The study by X-ray scattering enable us to follow the structural evolution with the chemical composition. With regard to the local structure, we present evidence that the diffuse X-ray scattering evolves significantly with Barium substitution. It is particularly interesting to note that diffuse scattering does not only change in intensity but that its distribution in the reciprocal space does also change notably
Detalle, Mikaël. "Élaboration et caractérisations de films ferroélectriques relaxeurs de PMN-PT : intégration sur silicium et applications MEMS". Thesis, Lille 1, 2008. http://www.theses.fr/2008LIL10031/document.
Pełny tekst źródłaFor miniaturization considerations, emergence ofMEMS has been observed. The objective ofthis study is to examine a very promising active material for such applications, with exceptional e1ectromechanica1 properties: PMN-PT. The deve10pment of thin 1ayers of PMN-PT has been optimized. The study shows that it is possible to crystallize PMN-PT at 400 ° C independently of the considered PT percentage or bottom e1ectrode nature (TiOx / Pt and LNO). Volumic nucleation, which could be at the origin of a quite atypical crystallization mechanism, has been highlighted in thin films. The dielectric, ferroe1ectric and electromechanica1 performances comparison of PMN-PT deposited on TiOx / Pt (sputtering) and LNO (solgel), shows a strong dependence of these properties with respect to the orientation and interfaces films / electrode, with an advantage for films deposited on LNO. Relaxor behavior is more and more pronounced as annealing temperature becomes optimal. LNO Sputtering deposition have permit to improve PMN-PT performances, in particular through top electrodes achievement. This underline the importance of the role played by the interfaces in the overall response of the structure e1ectrode / PMN-PT / e1ectrode
Al, Majzoub Al Sabbagh Maryam. "Vibrations polaires de basse fréquence de composés ferroélectriques et relation avec leurs propriétés diélectriques géantes : relaxeurs et nanocéramiques". Thesis, Montpellier, 2016. http://www.theses.fr/2016MONTT253.
Pełny tekst źródłaMaterials that exhibit giant dielectric properties have received a huge amount of attention from the scientific and industrial communities due to their potentialities and applications in technological devices, in particular for microelectronic applications. In this work, we are interested in studying the vibrational properties of a prototypical relaxor single crystal, PbMg1/3Nb2/3O3 (PMN), as well as nanoceramics of SrTiO3 (STO) with controlled grain sizes. The experiments have been mostly performed by hyper-Raman scattering (HRS), an original non-linear inelastic light scattering spectroscopy. Special attention was devoted to low frequency vibrations, and structural models were developed to relate the vibrational signatures to the giant dielectric responses of these systems.HRS spectroscopy was pushed towards its limit and provided a comprehensive picture of the polarization dynamics of PMN in the THz-range within the whole temperature sequence of its characteristic relaxor states. The widespread hypothesis of two paraelectric soft modes is convincingly excluded. The observation of the split ferroelectric mode reveals the local anisotropy below about 400 K. In contrast, the spectral anomalies observed at higher temperatures are explained as due to avoided crossing of the primary polar soft mode with a temperature-independent, non-polar spectral feature. The temperature changes of the vibrational modes involved in the measured fluctuation spectra of PMN were captured in a simple model that accounts for the temperature dependence of the dielectric permittivity as well.On the other hand, HRS experiments were carried-out on STO single crystal and nano-ceramics of different grain sizes, 80nm and 150nm. Contrary to IR-absorption which gives an effective spectral response of the core and the shell(s) constituting the grains, we show that hyper-Raman provides information of the individual core and shell responses. The spectral analysis reveals that except from their volume, the grains in the two ceramics exhibit very similar structures and properties: same value and temperature dependence of the shell thickness surrounding the core, and same dielectric response of the core as well as of the shell in the two samples. Structural models relating the vibrational properties to the effective dielectric permittivity were developed, and confirm that in STO the grains are composed by one core and two surrounding shells. We demonstrate that between 150 nm and 80 nm the decrease of the effective dielectric permittivity with grain size relates mostly to a change in core and shell volume fraction
Carreaud, Julie Léonie. "Effets de taille dans les poudres et céramiques de composés ferroélectriques relaxeurs à base de plomb PbMg1/3Nb2/3O3-PbTiO3". Châtenay-Malabry, Ecole centrale de Paris, 2007. http://www.theses.fr/2007ECAP1045.
Pełny tekst źródłaWe have studied size effects on dielectric and structural properties (X-Ray diffraction, Raman spectroscopy) of the lead-based relaxor system PMN(1-x)PTx with x = 0 (relaxor) ; 0. 20 ; 0. 35 (morphotropic) and 1 (classical). Sizes studied here are in the range of about 10 nm up to 4microns. Among the elaboration methods used, freeze-drying, citrate-gel and mechanochemical processes for the nanopowder synthesis, powders with the smallest grain size (10-20 nm) were obtained by mechanochemical synthesis. Ceramics with a relative density > 95% and grain size of about 110 nm were prepared by hot pressing and SPS. When diminishing the grain size, we observe: 1) The dielectric maximum decreases and becomes more and more diffuse2) For compounds having a structural phase transition PMN-PT20, PMN-PT35, and PT, the temperature associated with this transition and their structural distortion both decreases. At room temperature, the polarisation of PMN-PT20 rotates in the monoclinic plane Cm to finally reach the rhomboedral R3m direction below ≈ 200 nm with no diminishing in the amplitude of the polarisation. PMN-PT35, with monoclinic structure at micrometric sizes, transforms into a cubic phase at very small size (≈ 15 nm). In PT, by extrapolation of the tetragonal distortion for the lowest grain size, we found a critical grain size of 4 to 10 nm in agreement with the literature values. 3) The dielectric behaviour of PMN (relaxor) and PMN-PT35 (ferroelectric) changes:In PMN, the dielectric relaxation decreases and vanishes below a critical size of about 30 nm whereas in PMN-PT35 it appears below ≈ 200 nm
Idoumou, Ould Ahmedou. "Elaboration et caractérisation structurale et diélectrique de matériaux relaxeurs ferroélectriques dans le système Pb(Mg1/3Nb2/3))O3-Pb(Zn1/3Nb2/3)O3". Châtenay-Malabry, Ecole centrale de Paris, 1997. http://www.theses.fr/1997ECAP0526.
Pełny tekst źródłaDorcet, Vincent. "Etude de la relation entre structure et propriétés des pérovskites pseudo-cubiques du système Na0,5Bi0,5TiO3 – BiFeO3". Limoges, 2008. https://aurore.unilim.fr/theses/nxfile/default/add20181-deb8-407a-94b4-82709f0b469f/blobholder:0/2008LIMO4002.pdf.
Pełny tekst źródłaThe perovskite type compounds of the solid solution (1-x)Na0. 5Bi0. 5TiO3 (NBT) – xBiFeO3 (BF) were studied by transmission electron microscopy and impedance spectroscopy in order to decipher the origin of their dielectric and ferroelectric properties. The solid solution presents two distinct domains. Close to NBT (x < 0. 5), a first phase transition from the rhombohedral ferroelectric low temperature phase to an original orthorhombic one revealed for the first time, is achieved through a modulated phase that accounts for the antiferroelectric and the relaxor behaviours of NBT. The orthorhombic phase then evolves to a tetragonal one by a diffuse phase transition leading to a paraelectric state. Above x = 0. 5, the compounds behave as “normal” ferroelectrics. The relaxor behaviour is here due to the occurrence of oxygen vacancies arising as a consequence of the mix valence of iron atoms
Gomah-Pettry, Jean-Richard. "Propriétés diélectriques et transitions de phases de composés ferroélectriques exempts de plomb : Na(0,5)Bi(0,5)TiO(3) (M = Ba, Sr, Ca)". Limoges, 2002. http://www.theses.fr/2002LIMO0034.
Pełny tekst źródłaThis work is concerned with the study of lead-free ferroelectric ceramics. The investigated materials are Na0,5Bi0,5TiO3 - BaTiO3 (NBT-BT), Na0,5Bi0,5TiO3 - SrTiO3 (NBT-ST) and Na0,5Bi0,5TiO3 - CaTiO3 (NBT-CT) solid solutions prepared by the conventional ceramic method. The room temperature solubility ranges were determined by XRD. From the results of dielectric measurements as a function temperature and frequency, several behaviours were obtained dependent on the composition. The main feature is the occurrence of a relaxor-type behaviour the origin of which being due to the cationic disorder provoked by the substitutions. A diagram of electrical states was proposed for the NBT-BTand NBT-ST systems. The values of the piezoelectric coefficients are likely to predict that some compositions would be used in electromechanical devices as lead-free components
Aoujgal, Ahmed. "Etude des propriétés physico-chimiques et électroniques de matériaux ferroélectriques sous forme de céramiques et de films minces en vue d'applications radiofréquences et microondes". Littoral, 2010. http://www.theses.fr/2010DUNK0285.
Pełny tekst źródłaThe main objective of this work is to design, implement and optimize tunable materials for electronic applications at high frequencies. The easiest component to build on this study is the tunable capacitor with a voltage which can then be integrated into microwave devices such as tunable or reconfigurable resonators, filters, antennas. . . Etc. The capacitor can be either thin film or ceramic-based. To produce such components we must use materials which must have low dielectric loss, high dielectric permittivity, high tunability and stability of the resonant frequency of the capacitor with the temperature. For this, we conducted a detailed study of classical and relaxor ferroelectric materials in order, firstly to optimize the synthesis conditions, and secondly to improve their electrical properties for radiofrequencies and microwave applications. We have studied ferroelectric materials with perovskite phase, namely barium titanate strontium (BST) which is a classical ferroelectric and barium zirconium (BZT) which according to its composition can be a classical ferroelectric or relaxor ferroelectric and the derivatives of BaZr0. 1Ti0. 9O3 obtained by substituting bismuth and zinc-niobium respectively at A and B sites of the perovskite phase. We also synthesized and characterized the pyrochlore phase materials of bismuth zinc niobate, with composition of Bi1. 5ZnNb1. 5O7. The studies we have done range from the development of these materials in the form of ceramics and thin films, followed by characterizations to determine their physico-chemical properties, structural dielectric and ferroelectric in a range wide of frequencies and temperature
Castagnos, Anne-Marie. "Les relaxeurs ferroélectriques BaTi0,65 Zr0,35 O3 et Pb(1-x)BixMg(1+x)3Nb(2-x)/3O3(0< ou égalx". Toulouse 3, 2002. http://www.theses.fr/2002TOU30197.
Pełny tekst źródłaDielectric relaxation (frequency dispersion of the dielectric permittivity) is explained by the impossibility for the polar order to establish at long range. In PbMg1/3Nb2/3O3, this is attributed to a complex nanostructure where a local chemical order (ordering of the cations on the B site) coexists with a local polar order due to correlations of atomic displacements. These correlations expand up to a temperature known as freezing point, where they block. The Pb lone pair also plays a role in relaxation. In order to specify the role of each component, we have synthesised and studied the following relaxors. .
Neradovskaia, Elizaveta. "Formation de structures de domaines dans des ferroélectriques uniaxiaux : Applications à l'amplification paramétrique optique de grande ouverture". Thesis, Université Côte d'Azur, 2020. http://theses.univ-cotedazur.fr/2020COAZ4012.
Pełny tekst źródłaThe study of the evolution of the domain structure in ferroelectric crystals is extremely important from a fundamental and applied point of view. Scanning probe microscopy provides a unique opportunity for local investigation of the processes of polarization reversal, the results of which can be used to optimize the classical methods of domain engineering. Using of ferroelectric crystals with slanted polar axis opens new opportunities for in situ investigation of domain kinetics.In addition, interest in the practical application of ferroelectric single crystals has greatly increased in connection with the development of strong field physics, which requires the creation of new nonlinear optical elements with a large aperture. This problem is solved with the help of domain engineering.This work presents both the fundamental study of domain kinetics in classical and relaxor ferroelectrics and the applied investigation of modeling, creation, and characterization of large aperture optical mixers for high-power lasers on the base of periodical poled congruent lithium niobate crystals with the slanted polar axis (slanted CLN).Chapter 1 contains the theoretical basis for the physics of ferroelectrics and nonlinear optics. Also, the state of the art is presented.Chapter 2 is dedicated to experimental methods and setups used for investigation of domain structure in ferroelectrics.The investigation of the evolution of domain structure in relaxor ferroelectrics on the example of model relaxor strontium barium niobate (SBN) is presented in chapter 3. The influence of an initial domain state on domain kinetics during polarization reversal by both integral and local methods of poling is shown.Chapter 4 is devoted to the investigation of domain kinetics in congruent lithium niobate crystals with slanted polar axis. Forward domain growth during electric field poling and e-beam poling is studied.Modeling of large-aperture frequency mixer on base of periodical poled slanted CLN with different crystal axis orientations is offered in chapter 5. Model is based on the principals of angular quasi-phase matching.Study of chirped pulse optical parametric amplification (OPA) in periodical poled 64˚ Y-cut CLN is presented in chapter 6. Angular dependences of gain and spectral bandwidth are described
Castel, Elias. "Synthèse de nouveaux matériaux multiferroïques au sein de la famille des bronzes quadratiques de formule Ba2LnFeNb4O15". Phd thesis, Université Sciences et Technologies - Bordeaux I, 2009. http://tel.archives-ouvertes.fr/tel-00464154.
Pełny tekst źródłaRoukos, 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.
Pełny tekst źródłaThe 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
Heijboer, Pierre. "Etude des propriétés diélectriques et structurales de monocristaux et céramiques de structure TTB". Thesis, Bordeaux, 2014. http://www.theses.fr/2014BORD0096/document.
Pełny tekst źródłaThe present work deals with Ba2LnNb4O15 (Ln = La ou Nd) niobates crystallizing with the "Tetragonal Tungsten Bronze" (TTB) structure. These researches, at the interface of chemistry and physics of dieletrics, aim at establishing structure / dielectric properties relationships. They were performed on TTB materials elaborated in ceramic and single crystal forms. Following optimization of growth parameters with an image furnace, single crystals were obtained and characterized. The results obtained suggest that composition, aperiodically modulated structure and dielectric behavior are closely tied in TTBs. Meanwhile, two new ceramic solid solutions with different substitutions schemes were investigated, deepening the insight on crystal-chemistry and ferroelectricity of TTBs. These solid solutions exhibit a relaxor-ferroelectric crossover, an original behaviour previously observed in solid solutions derived from the same family of TTB niobates. Advanced physical characterization (ferro-, pyro- and piezoelectric measurements, polarization loops), and composition/temperature resolved structural studies, allowed for the determination of a dielectric phase diagrams showing the presence of a metastable ferroelectric state. Finally, the existence of a two-dimensional structural modulation in single crystals and ceramics has been confirmed, and the whole set of experimental results points towards its implication in the original dielectric behavior observed in these TTBs
Castel, Elias. "Synthèse de nouveaux matériaux multiferroïques au sein de la famille des bronzes quadratiques de formule Ba2LnFeNb4O15". Thesis, Bordeaux 1, 2009. http://www.theses.fr/2009BOR13865/document.
Pełny tekst źródłaMultiferroics are materials which possess several ferroic properties, e.g. ferroelectricity, ferromagnetism. The search for multiferroics arises a growing activity, due to their potential applications in memories, spintronic… Yet the materials displaying the adequate properties for future application are very few. Niobates with the formula Ba2LnFeNb4O15, potentially ferroelectric and ferromagnetic, have been synthesized. The magnetic properties of the ceramics are related to a secondary phase, thus making them composite multiferroics. Their crystal-chemical flexibility allows for the composites properties tuning by cationic substitutions into the TTB framework. To complete the crystal-chemical study, the growth of TTB single-crystals was successfully engaged