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Zur Messung pyrelektrischer Koeffzienten wurde ein Messplatz nach einem erweiterten SHARP-GARN-Verfahren entwickelt und zur Untersuchung von Phasenumwandlungen in Pyroelektrika eingesetzt. Einerseits konnten pyroelektrische Messungen im elektrischen Feld die Pyroelektrizität einer neuen durch elektrisch angetriebene Defektmigration erzeugten Phase in Strontiumtitanat nachweisen. Andererseits gelang es, Ferroelektrizität in der Hochtemperaturphase von Poly(Vinylidenfluorid-Trifluorethylen), mittels phasenreiner Präparation der Hochtemperaturphase unterhalb der CURIEtemperatur und anschließender Polarisierung, nachzuweisen. Ferner ließen sich mittels thermisch angeregter Pyroelektrika Redoxprozesse antreiben, was durch Desinfektion von Escherichia coli Bakterien in wässriger Lösung mittels Lithiumniobat und -tantalat gezeigt wurde. Die Hypothese der Desinfektion durch reaktive Sauerstoffspezies konnte durch spektroskopisch nachgewiesene OH-Radikale - erzeugt mittels thermisch angeregter Bariumtitanatnanopartikel - belegt werden.

Nous avons démontré que la correction de fronts d'onde de faisceaux lasers impulsionnels (nanoseconde) pouvait être réalisée par mélange d'ondes dans un cristal photoréfractif. Nous avons commence par déterminer le matériau photoréfractif le mieux adapte pour cette application. Pour des raisons d'efficacité photoréfractive et de tenue en puissance, notre choix s'est porte sur le titanate de baryum. Cela a conditionne le choix de la longueur d'onde utilisée (532 nm) pour cette démonstration. Nous avons étudié un premier dispositif de correction base sur le transfert d'énergie d'un faisceau fort vers un faisceau faible qui, par mélange d'ondes photoréfractif, peut être obtenu sans qu'il y ait de transfert de phase. Dans cette étude nous avons mesure les variations de l'amplification en fonction de différents paramètres (cohérence temporelle, rapport des énergies des faisceaux) et observe les variations de l'effet photorefractif en fonction de la densité de puissance dans le titanate de baryum. Nous avons aussi démontré la correction des déformations introduites par un objet de phase et cela pour différentes densités d'énergie incidente. Une deuxième méthode de correction est basée sur la compensation d'un aberrateur de phase par double passage. On a commence par préciser la notion de conjugaison de phase. Puis, nous avons étudié en particulier un miroir a conjugaison de phase auto pompe, l'oscillateur a boucle de réaction, qui fonctionne sur le principe du mélange a quatre ondes dans un cristal photoréfractif. Nous avons montre expérimentalement que des transformations des faisceaux dans la boucle de réaction améliorent la qualite de la conjugaison de phase et nous avons réalisé la compensation d'objets de phase par double passage en régime impulsionnel. La dernière partie est consacrée a l'étude comparative des deux dispositifs tels qu'ils pourront être mis en oeuvre pour la correction dynamique des lentilles thermiques dans les amplificateurs lasers solides.

Le remplacement de la fibre monomode a maintien de polarisation par de la fibre monomode standard dans les gyroscopes a fibre est un véritable enjeu économique. En effet, il permettrait a ces systèmes d'être compétitifs au niveau du coût sur le marche des centrales de navigations inertielles actuellement domine par les gyroscopes laser. Cependant, les problèmes de non réciprocités et d'effondrement du signal provoqués par l'utilisation de ce type de fibre n'ont pas été résolus de façon satisfaisante à ce jour. C'est a ce niveau que l'utilisation de la double conjugaison de phase apparaît comme une solution intéressante. L'objectif de ce travail consistait à valider cette solution d'une part en mettant au point un cristal photoréfractif adapte à cette application et d'autre part en insérant un miroir a double conjugaison de phase dans un gyroscope commercial fonctionnant a 850 mn. Dans un premier temps, nous avons donc etudie un nouveau cristal photorefractif : le titanate de barium calcium (bct) dont l'interet repose sur le fait qu'il ne subit pas de transition de phase de 120\ a 98\ c, contrairement au cristal de titanate de baryum dont il est dérivé. Ce cristal, généralement utilise pour la conjugaison de phase en raison de sa bonne efficacité est en effet détruit si sa température devient inférieure a 10\ c. Notre étude a permis de démontrer les bonnes propriétés photorefractives de ce matériau (coefficients electro-optiques élevés, sensibilité proche infrarouge) et de comprendre les différences de comportement par rapport au titanate de baryum. Dans un second temps, nous avons étudié et optimise un miroir a double conjugaison de phase réalisé avec un cristal de titanate de baryum que nous avons ensuite insere dans un gyromètre a fibre. Ainsi, nous avons pu montrer que le gyrometre a double conjugaison de phase permet de mesurer des rotations et n'introduit pas de non-reciprocités supérieures a la précision du montage que nous avons utilise (200 \/h).

System on Chip (SoC) and System in Package (SiP) are two electronic technologies that involve integrating multiple functionalities onto a single platform. When the platform is a single wafer, as in SOC, it requires the ability to deposit various materials that enable the different functions on to an underlying substrate that can host the electronic circuitry. Transition metal oxides which have a wide range of properties are ideal candidates for the functional material. Si wafer on which micro-electronics technology is widely commercialized is the ideal host platform. Integrating oxides with Si, generally in the form of thin films as required by microelectronics technology, is however a challenge. It starts with the fact that the properties of crystalline oxides to be exploited in performing various functions are direction dependent. Thus, thin films of these oxides need to be deposited on Si in certain crystallographic orientations. Even if a suitably oriented Si wafer surface were available, it does not always provide for epitaxial growth a critical requirement for controlling the crystalline orientation of thin films. This is because Si surface is covered by an amorphous oxide of Si (SiOx). Thus, during growth of the functional oxide, an ambience in which the Si itself will not oxidize needs to be provided. In addition, during thin film growth on either Si or SiOx surface stresses are generated from various sources. Stress and its relaxation are also associated with the formation and evolution of defects. Both, stress and defects need to be managed in order to harness their beneficial effects and prevent detrimental ones. Given the requirement of SoC technology and the problem associated, the research work reported in this thesis was hence concerned with the precise controlling the stress and microstructure in oxide thin films deposited on Si substrates. In order to do so a versatile, ultra high vacuum (UHV) thin film with a base pressure of 10-9 Torr was designed and built as part of this study. The chamber is capable of depositing films by both sputtering (RF & DC) and pulsed laser ablation (PLD). The system has been designed to include an optical curvature measurement tool that enabled real-time stress measurement during growth. Doped zirconia, ZrO2, was chosen as the first oxide to be deposited, as it is among the few oxides that is more stable than SiOx. It is hence used as a buffer layer. It is shown in this thesis that a change in the growth rate at nucleation can lead to (100) or (111) textured films. These two are among the most commonly preferred orientation. Following nucleation a change in growth rate does not affect orientation but affects stress. Thus, independent selection of texture and stress is demonstrated in YSZ thin films on Si. A quantitative model based on the adatom motion on the growth surface and the anisotropic growth rates of the two orientations is used to explain these observations. This study was then subsequent extended to the growth on platinized Si another commonly used Si platform.. A knowledge of the stress and microstructure tailoring in cubic zirconia on Si was then extended to look at the effect of stress on electrical properties of zirconia on germanium for high-k dielectric applications. Ge channels are expected to play a key role in next generation n-MOS technology. Development of high-k dielectrics for channel control is hence essential. Interesting stress and property relations were analyzed in ZrO2/Ge. Stress and texture in pulsed laser deposited (PLD) oxides on silicon and SrTiO3 were studied. It is shown in this thesis that stress tuning is critical to achieve the highest possible dielectric constant. The effect of stress on dielectric constant is due to two reasons. The first one is an indirect effect involving the effect of stress on phase stability. The second one is the direct effect involving interatomic distance. By stress control an equivalent oxide thickness (EOT) of 0.8 nm was achieved in sputter deposited ZrO2/Ge films at 5 nm thickness. This is among the best reported till date. Finally, the effect of growth parameters and deposition geometry on the microstructural and stress evolution during deposition of SrTiO3 on Si and BaTiO3 on SrTiO3 by pulsed laser deposition is the same chamber is described.

Ferroelectric materials, especially the polycrystalline ceramics, are very promising material for a variety of applications such as high permittivity dielectrics, ferroelectric memories, piezoelectric sensors, piezoelectric/electrostrictive transducers, electrooptic devices and PTC thermistors. Among the ferroelectric based piezoelectric ceramics the lead–zirconate-titanate Pb(Zr1-xTix)O3 (PZT) have dominated transducer and actuator market due to its excellent piezoelectric and dielectric properties, high electromechanical coupling, large piezoelectric anisotropy, ease of processing and low cost. However, the toxicity of lead based compounds has raised serious environmental concerns and therefore has compelled the researchers to look for new lead free alternatives with good piezoelectric and ferroelectric properties. (Na0.5Bi0.5)TiO3 (NBT) and its solid solution is one of the leading lead free piezoceramic ceramics due to their interesting ferroelectric, piezoelectric, electromechanical and dielectric property. The parent compound NBT is a ferroelectric with a moderately high Curie temperature (~250 oC), large ferroelectric polarization (~40µC/cm2) polarization, promising piezoelectric properties with 0.08% strain and longitudinal piezoelectric coefficient (d33) ~ 80 pC/N. X-ray and neutron diffraction studies in the past have shown that NBT exhibits rhombohedral (R3c) at room temperature. Neutron diffraction studies have suggested that NBT undergo a gradual rhombohedral to tetragonal (P4bm) transformation in a temperature region 200-320 ºC. Though the structure and phase transition behavior of NBT has been extensively investigated for over six decades now, this subject has again become debatable in recent few years, with some group reporting formation of orthorhombic phase above room temperature and another group suggesting monoclinic distortion at room temperature using high resolution x-ray diffraction technique. Interestingly the intermediate orthorhombic instability, reported by electron diffraction studies, has never been captured by neutron diffraction method though neutron diffraction is an equally powerful tool for studying (oxygen) octahedral tilts in perovskites. Needless to mention, the understanding of the subtle structural distortions have great significance with regard to the determination of the structure-piezoelectric property correlations in NBT based piezoceramics. The present thesis deals with such subtle structural issues in great detail. The systems investigated in the thesis are Ca and Ba modified NBT. While the Ca modified system was chosen to understand the subtle orthorhombic instability that has been reported above room temperature (only) by detailed electron diffraction work, Ba-modified NBT is the most investigated among the NBT-derived piezoelectric material systems and this thesis attempts to address some of the very complex nature of the structure-piezoelectric property correlation of this system. The first chapter of the thesis provides a brief introduction to the field of ferroelectrics, perovskite structure and their phase transition. A brief exposure to the conventional lead based relaxor ferroelectric and piezoelectric material is provided. A detailed overview of the existing knowledge related to room temperature structure of NBT and its phase transition studies with temperature has been discussed in the later part of this chapter. The second chapter includes various the experimental techniques that have been employed to synthesis and characterize the specimens under investigation. The third chapter deals with the phase transition behaviour of Ca modified NBT as a function of composition and temperature in the dilute concentration region. This work was carried out with the view to obtain a better understanding and compliment the intrinsic high temperature orthorhombic instability in NBT reported by electron diffraction technique. Interestingly, inspite of the fact that neutron diffraction method is a very sensitive tool for investigating subtle change in the nature of octahedral tilt in oxide perovskites, the intermediate orthorhombic distortion proposed by the electron diffraction studies has so far never been captured in any of the neutron diffraction studies. In this work we have verified the genuineness of the intrinsic instability with regard to the non-polar orthorhombic structure using neutron powder diffraction by adopting a special strategy which helped in capturing the characteristic signatures (the superlattice reflections) of the orthorhombic phase in the neutron powder diffraction patterns. It was found that small fraction of Ca-substitution (8-10 mol %) was good enough to amplify the magnitude of the orthorhombic (Pbnm) distortion, without altering the sequence of the structural evolution with temperature of the parent compound (NBT) itself, and stabilizing it at the global length scale at lower temperatures than pure NBT. This chapter presents the innovative approach that was used to extract reliable information about the very complex phase transition behaviour, involving coexistence of the various similar looking but crystallographically different phases in different temperature regimes by Rietveld analysis of temperature dependent neutron powder diffraction pattern in conjunction with temperature dependent dielectric and ferroelectric characterization of the specimens. The detailed study revealed the following sequence of structural evolution with temperature: Cc+Pbnm →Pbnm + P4/mbm → P4/mbm →Pm3 m. The fourth chapter gives a detail account of the structure-property correlations and the phase transition behaviour of (1-x)(Na0.5Bi0.5)TiO3 – (x)BaTiO3 (0≤x≤0.10), the most important solid solution series with NBT as reported in the literature. The phase transformation behaviour of this system has been investigated as a function of composition (0<x≤0.10), temperature, electric field and mechanical-impact by Raman scattering, ferroelectric, piezoelectric measurements, x-ray and neutron powder diffraction methods. The structure of the morphotropic phase boundary (MPB) compositions of this system, which is interesting from the piezoelectric property point of view, has been under controversy for long. While some groups report the structure to be pseudocubic, other groups suggest it to be combination of rhombohedral and tetragonal. A perusal of the literature suggests that the reported nature and composition range of MPB is dependent on the method of synthesis and characterization technique used. In the present study, crystal structure of the NBT-BT solid solution has been investigated at the close interval near the MPB (0.05≤x≤0.10). Though x-ray diffraction study revealed three distinct composition ranges characterizing different structural features in the equilibrium state at room temperature: (i) monoclinic (Cc) + rhombohedral (R3c) for 0≤x≤0.05, (ii) “cubic-like” for 0.06≤x≤0.0675 and (iii) MPB like for 0.07≤x<0.10, Raman and neutron powder diffraction studies revealed identical symmetry for the cubic like and the MPB compositions. Both the cubic like compositions and the MPB compositions exhibit comparatively large d33. In the later part of this chapter this apparent contradiction is resolved by the fact that the cubic like structure transforms irreversibly to MPB after electric poling, a procedure which involves applying high dc electric field (well above the coercive field) to the pellet before carrying out the piezoelectric measurements. The effect of electrical field and mechanical impact has been studied for all the three different composition range, and it was found that electric field and mechanical impact both led to irreversible phase transformation in the same direction, though the transformation with mechanical impact remains incomplete in comparison to electric field. The most pronounced effect was observed for the cubic like compositions 0.06≤x≤0.0675 – they undergo phase separation to rhombohedral and tetragonal phases by electrical and mechanical perturbations. In the non-perturbed state the cubic-like critical compositions mimics features of relaxor ferroelectrics and extremely short coherence length (~ 40-50 Å) of the out-of-phase octahedral tilts. In the poled state this coherence length grows considerably and the system behaves like a normal ferroelectric. This confirmed a strong coupling between the lattice, octahedral tilts and polarization degrees of freedom. Neutron diffraction study of compositions exhibiting cubic-like and the MPB like revealed that the traditional P4bm tetragonal structure model fails to account for the intensity of the superlattice reflections. Thus the tetragonal structure stabilized above room temperature in pure NBT is different from the tetragonal phase observed at room temperature in the NBT-BT system. The results of the effect of mechanical impact and electric field has also been reported in this chapter for the critical composition exhibiting MPB (x=0.07). A detailed structural analysis of the precritical compositions, x≤0.05, revealed coexistence of ferroelectric phases (Cc+R3c) in equilibrium state (annealed specimens). This transforms to single phase (R3c) state after poling. Thus though the precritical (x≤0.05) and critical compositions (0.06≤x<0.10) of NBT-BT exhibits coexistence of ferroelectric phases in the equilibrium state, the fact that the electric poling makes the specimen single phase, R3c, after poling for the precritical compositions and retains the two phase nature of the critical compositions makes the critical compositions exhibit considerably higher piezoelectric response than the precritical compositions. Chapter five is dedicated to phase transition behaviour of the post critical compositions of (1-x)(Na0.5Bi0.5)TiO3–(x)BaTiO3 (0.16≤x≤1) using temperature dependent XRD, dielectric and ferroelectric studies. Though structurally the entire composition range is tetragonal, several notable features were revealed during detailed examination of the structural and dielectric behaviour. This study is also important from the view point that pure BT is a major component of multilayer ceramic capacitors and that an increase in the Curie point would be a welcome step for better temperature stability of the device. NBT does this. The transition temperature increases from 120 ºC for pure BT to 275 ºC for x=0.30 along with simultaneous increase in c/a ratio from 1.009 (pure BT) to 1.02 (x=0.30). Detailed analysis of temperature and frequency dependent dielectric data revealed deviation from Curie-Weiss and suggests a gradual transformation to relaxor-ferroelectric state as the NBT concentration increases in BT. The measure of frequency dispersion ‘γ’ parameter was determined from modified Curie-Weiss law for various compositions in the system. The ferroelectric and piezoelectric properties have also been investigated in detail for this composition range and an attempt has been made to correlate the composition variation of these properties with their structural parameters. This chapter shows a systematic correlation between all physical quantities such as Curie point, piezoelectric coefficient, polarization and tetragonality as a function of composition.

Les matériaux ferroélectriques sont des matériaux qui possèdent une polarisation spontanée en l'absence de champ électrique, leur conférant plusieurs propriétés intéressantes du point de vue des applications possibles. La réduction de l'épaisseur des couches ferroélectriques vers des films minces et ultra-minces s'est avérée nécessaire notamment en vue de leur intégration dans les dispositifs de la micro et nano-électronique. Cependant, cette diminution a fait apparaître certains phénomènes indésirables au sein des couches minces tels que les courants de fuite. La caractérisation électrique de ces matériaux reste donc un défi afin de comprendre les mécanismes physiques en jeu dans ces films, d'autant qu'une information à l'échelle très locale est maintenant requise. Il est donc nécessaire de faire progresser les techniques de mesure électrique pour atteindre ces objectifs. Durant cette thèse, nous mesurons la polarisation diélectrique de l'échelle mésoscopique jusqu'à l'échelle nanométrique en utilisant des caractérisations purement électriques constituées de mesures Polarisation-Tension, Capacité-Tension et Courant-Tension mais aussi des mesures électromécaniques assurées par une technique dérivée de la microscopie à force atomique et nommée Piezoresponse Force Microscopy. Au cours de nos travaux, nous montrons la limite de certaines techniques de caractérisation classiques ainsi que les artéfacts affectant la mesure électrique ou électromécanique et pouvant mener à une mauvaise interprétation des résultats de mesure. Afin de pousser nos investigations plus loin, nous avons développé de nouvelles techniques de mesure pour s'affranchir de certains signaux parasites dont nous exposerons le principe de fonctionnement. Nous présentons les premières mesures directes de polarisation rémanente à l'échelle du nanomètre grâce à une technique que nous nommons nano-PUND. Ces techniques et méthodes sont appliquées à une variété importante de matériaux tels que Pb(Zr,Ti)O3, GaFeO3 ou BaTiO3 dont, pour certains, la ferroélectricité n'a jamais été démontrée expérimentalement sans ambiguïté. / Ferroelectric 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.