A slab-coupled optical fiber sensor (SCOS) falls into a narrow class of all-dielectric optical fiber electric field sensors, which makes it a perfect candidate for measurements of high electric fields in environments where presence of conductors is highly perturbing to the system under test. Its nonlinear response to high fields requires a new nonlinear calibration technique. A nonlinear calibration method is explained and demonstrated to successfully measure high electric fields, as well as high voltages with dynamic range up to 50 dB. Furthermore, a SCOS can be fitted into narrow spaces and make highly localized measurements due to its small size. This allows a SCOS to be integrated inside a standard high voltage coaxial cable, such as RG-218. Effects of partial discharge and arcing is minimized by development of a fabrication method to avoid introduction of impurities, especially air-bubbles, into the cable during SCOS insertion. Low perturbation of the measured voltage is shown by simulating the introduced voltage reflections to be on the order of −50 dB. It is also shown that a SCOS can be inserted into other cables without significant perturbation to the voltage.A complete high voltage and high electric field measurement system is built based on the high-voltage modifications of the SCOS technology. The coaxial SCOS is enhanced for robustness. Enhancements include packaging a SCOS into stronger ceramic trough, strengthening the fiber with kevlar reinforced furcation tubing and protecting the sensor with metal braces and protective shells. The interrogator is protected from electromagnetic interference with an RF-shielded box. Reduction in power losses introduced by the new PANDA-SCOS technology allows interrogator bandwidths to be increased up to 1.2 GHz. The whole measurement process is streamlined with dedicated software, developed specifically for high voltage and electric field measurements with support for the nonlinear calibration.

Propriétés photorefringentes et photovoltaïques de linbo::(3) dope au fer. On décrit des expériences de traitement d'image en lumière partiellement cohérente dans lesquelles le cristal de linbo::(3) est utilise comme récepteur d'image. On peut obtenir ainsi la somme ou la différence de 2 distributions d'intensité. On développe une technique qui permet de réaliser soit une inversion de contraste soit une pseudo-coloration d'un objet noir et blanc. Sélectivité angulaire des réseaux de phase épais.

Transparent glasses embedded with TTB structured ferroelectric nano/micro crystals (K3Li2Nb5O15, Ba5Li2Ti2Nb8O30) were fabricated in various tellurite and borate based glass matrices and characterized for their physical properties. Nanocrystals of K3Li2Nb5O15 were successfully grown inside tellurite glass matrix via conventional heat-treatment route. Eventhough, tellurite glasses preferentially crystallize only on the surface, bulk uniform crystallization was achieved in the (100-x) TeO2 - x(1.5K2O-Li2O-2.5Nb2O5) system. Heat capacity studies revealed them to be thermodynamically less fragile than any other tellurite glasses ever reported in the literature. Pyroelectric and ferroelectric effects as well as second harmonic generation were demonstrated for the heat treated (glass nanocrystal composites) samples in this system. The conventional method of melt-quenching of constituent oxides could not yield Ba5Li2Ti2Nb8O30 crystallites. So, Ba5Li2Ti2Nb8O30 microcrystals were successfully formed in tellurite glass matrix by mixing pre-reacted Ba5Li2Ti2Nb8O30 ceramic powders with TeO2. The glass transition temperature was found to be the highest ever reported and this system was kinetically strong based on the fragility parameter. Dielectric studies revealed a frequency and temperature independent nature of the dielectric constant and very low dielectric loss. The SHG measurement which was carried out as a function of temperature demonstrated the incidence of blue second harmonic generation in the microcrystals present in the glass matrix. Ba5Li2Ti2Nb8O30 nanocrystals were successfully crystallized in the transparent glass system (100-x)Li2B4O7 – x(Ba5Li2Ti2Nb8O30). Dielectric constant increased while the dielectric loss decreased with the increase in Ba5Li2Ti2Nb8O30 content. Nuclear magnetic resonance spectroscopic studies were carried out to have an insight into the structure of this system. Transmission studies and refractive index measurements were performed and various optical parameters were calculated. Dielectric and transport properties were studied for the glasses and glass nano/microcrystal composites of all the systems reported in this thesis. Li+ ion was found to be responsible for conduction in all these systems. Evolution of self-organized nanopatterns of K3Li2Nb5O15 crystals has been demonstrated in the glass system (100-x) TeO2 - x(1.5K2O-Li2O-2.5Nb2O5) by excimer laser irradiation. The second harmonic signal observed by the Maker fringe technique has been attributed to the presence of well-aligned nano-sized grating structures in the glass system. Glasses belonging to the systems TeO2-K3Li2Nb5O15, TeO2-Ba5Li2Ti2Nb8O30 and V2Te2O9 undergo spinodal decomposition on exposing to KrF pulsed excimer laser. The spinodally phase separated structures were observed on all the surfaces of the samples. Ring shaped patterns were observed on several locations of the samples at higher frequency of laser pulses probably owing to the shock waves produced by the high intense laser beam. Line shaped patterns were found to originate on the sample surfaces when irradiated for longer periods.

NLO materials have been researched for nearly five decades from the point of view of understanding the basic mechanisms and also in the pursuit of new materials possessing improved properties. Materials satisfying a set of physico-chemical properties such as wide transmission range, good mechanical hardness, high po-larizablity, noncentric crystal structure, good chemical stability, etc are the ones which are sought after. Several organic and inorganic molecules have been synthe-sized with the hope of finding materials that possess the desired NLO properties. Most of the organic materials are known to possess high figure of merit. However, their poor mechanical strength and needle like growth habit are hindrances to practical applications. Inorganic NLO materials have better mechanical properties but many of them possess small deff and laser induced damage threshold. Semi-organic NLO materials are intended to have the merits of both organic and inorganic counterparts. In this investigation, three important NLO crystals, viz cesium hydrogen L-malate monohydrate (CsLM, CsH[C4H4O5]H2O), cesium lithium borate(CLBO,CsLiB6O10)and near stoichiometric lithium niobate codoped with Nd and Zn (Nd:Zn:LiNbO3)are chosen for detailed study. The thesis is organized into 6 chapters. First chapter contains the theoretical background of the physical and chemical phenomena including a review of nonlin-ear optics, second harmonic generation, multiphoton absorption & refraction con-cepts, single crystal growth, principles of ferroelectricity and the scope of the work involved. For better connectivity, a brief review of the earlier work carried out on the chosen materials is given in the beginning of each chapter. The second chapter discusses the methodology of work and experimental details used in the present study. The third chapter deals with studies on CsLM, the new organometallic NLO crystal. Its structure, electro-optical properties and dielectric properties in FIR region are reported very recently. This material is also reported to show a phase transition at 50 0C though not much is understood about its nature. Further details of crystal growth conditions, nonlinear optical properties and laser damage thresholds are little known on this newly discovered NLO material. In this chapter detailed crystal growth studies and investigations of physical properties are presented. During growth, CsLM crystals manifest in platy and prismatic morphologies depending on level of super saturation invoked. The maximum dimensions of the grown crystal are 20 x15 x35 mm3. It has very good transmission in the range, 250-1300 nm and dislocation density of ≈104/cm2 . The dc conductivity measurements place this crystal between an ionic conductor and a dielectric. Dielectric properties show considerable frequency dispersion and axial anisotropy with є′ being the highest along the polar b axis. Maker fringes experiment reveals that CsLM possesses good second harmonic generation efficiency, an order of magnitude higher than KDP. It also has high laser damage threshold for fundamental and second harmonic wavelengths of Nd:YAG pulsed laser. TGA/DTA experiments are performed on the crystals grown below and above the reported transition temperature(labelled as CsLM and Anhydrous-CsLM respectively). The present investigations on Anhydrous-CsLM show that it crystallizes in a structure different from that of CsLM and the nature of the reported ′phase transition ′is driven by sluggish hydration and dehydration processes. Recently UV transparent nonlinear optical materials were evaluated for the fab-rication of all solid state UVlasers and CLBO is one such NLO material. It crystal-lizes in non-centrosymmetric tetragonal space group, I42d. It is highly transparent in the wide range of wavelengths from 180 to 2500 nm and has good deff. It pos-sesses very good angular and spectral bandwidth tolerances compared to its contemporaries such as lithium triborate(LBO) and beta barium borate(β-BBO). There is, however, a problem associated with this material that it cracks when exposed to atmosphere due to its hygroscopic nature. This chapter details the fabrication of the required instrumentation to grow single crystals of this material and the study of possible solutions to avoid cracking problem besides its new nonlinear properties. Since the melts of borate materials are known to be highly viscous, the crystal growth apparatus should have the options for tuning the parameters like seed and crucible rotation rates, temperature isotherms, slow pulling rate, etc. Keeping the above in mind, a high temperature top seeded solution growth unit was designed and fabricated inhouse. Highly transparent single crystals of CLBO were grown using the above unit which were characterized for the defects/dislocations using X-ray topography. The average dislocation density estimated is ≈103/cm2. The nonlinear optical absorption(NLA) and refraction(NLR) properties are studied. Z-scan experiments reveal that five photon absorption(5PA )is responsible for nonlinear absorption when the wavelength and pulse width are 800 nm and 110 fs respectively. For 532 nm and 6 ns pulses, dielectric breakdown occurs before NLA could occur due to high pulse influence. CLBO is found to show negative nonlinear refraction under high intensities. Hygroscopicity of CLBO is attributed to the entry of water through the channels that are present along a and b axes, which in turn, cause cracking. Doping, is expected to modify the size of the channels. Since certain dopants are found to improve the stability of CLBO, substitution of Cs site with Zn and Gd is carried out to reduce the size of channels. As there was no significant improvement with doping experiments, an alternate approach is attempted by coating with SiO2 thin films on the optical elements to prevent the water molecules from entering lattice through the channels. The results and discussion of the above studies are presented in the chapter 4. Lithium niobate is the most widely used single crystal for fabricating optical modulators, waveguides, SAW devices and optical parametric oscillators. Although single crystals of this ferroelectric material were grown way back in 1965 by Ball-man and Fedulov independently, most of the work till the beginning of 90’s was concentrated on crystals with congruent composition(CLN) because there were no suitable methods available for growing homogeneous single crystals of stoichiomet-ric lithium niobate(SLN). Recently, Double Crucible Czochralski method with au-tomatic powder feeding technique and top seeded solution growth technique with Li2O and K2O fluxes are shown to produce SLN crystals. In this work, top seeded solution growth technique with58.6 mol% Li2O composition(self flux) is adopted to grow SLN crystals and the details of the growth and investigations are presented in chapter 5. Initially, crystal growth of SLN, and Zn & Nd codoped SLN are de-scribed. The maximum dimesions of the SLN crystals are 20 mm diameter and 35 mm length. CLN crystals(30mm diameter and 70 mm length) are also grown for comparison. The growth rate for SLN crystals is approximately 25 times lower than that for CLN. The maximum amount of Zn added to the melt is 2.5 mol%. For Nd codoping, four concentrations (0.2, 0.5, 0.9, 1.5 mol%) have been chosen with Zn concentration in the melt fixed at 2.5 mol%. Addition of Zn is to enhance the pho-torefractive damage threshold and Nd to use SLN as laser host. Structural studies on the grown crystals using powder X-ray diffraction show no additional phases. The domain structure analysis by chemical etching studies reveal that it is sensitive to doping and temperature gradient above the melt surface. The grown crystals possess good transmission in the UV-Vis-NIR region. Apparent increase in the dielectric constant found in doped crystals is attributed to space charge effect. In Nd:Zn codoped SLN, the parameters corresponding to lasing (Judd-Ofelt parameters, radiative transition probabilities, branching ratios) have been evaluated and found to be better than those obtained for codoped CLN. Surface laser damage and photorefractive damage thresholds are enhanced by 2 and 4 orders of magnitude respectively for the crystals grown with 2.5 mol% Zn in the melt. Nonlinear absorption and refraction studies using femtosecond Z-scan experiments reveal a correlation between the nonstoichiometric defects and nonlinear absorption & refraction coefficients. Polarization switching studies carried out on pure and Zn doped samples indicate an enhancement in switching rate at elevated temperatures. In the sixth and final chapter, a comprehensive summary of the present work and the scope for further investigations related to this work are given.

Im Rahmen der vorliegenden Arbeit wurden zwei verschiedene Klassen oxidischer Nanomaterialien nasschemisch synthetisiert und strukturell-morphologisch charakterisiert. Zum einen betrifft dies TiO2-, TiO2/SiO2-, Ag/TiO2- und Pd/TiO2-Sole, welche die photokatalytisch aktive Modifikation Anatas in nanokristalliner Form enthalten und über einen solvothermalen Sol-Gel-Prozess hergestellt werden konnten. Im Hinblick auf eine potentielle Anwendung in der Desinfektionstechnologie und für den Abbau organischer Umweltschadstoffe wurde die photokatalytische Aktivität von Pulvern und Beschichtungen auf Textil durch E. coli-Abtötung bzw. Modellfarbstoffabbau untersucht. Im Weiteren wurde die antimikrobielle Aktivität pyroelektrischer LiNbO3- und LiTaO3-Pulvermaterialien unter zyklischer thermischer Anregung nachgewiesen. Diese als Pyroelektrokatalyse bezeichnete Nutzung des pyroelektrischen Effektes in einem katalytischen bzw. elektrochemischen Prozess ist dabei von grundlegender Neuheit. Aufsetzend auf den physiko-chemischen Grundlagen dieses Phänomens wurde eine Hypothese des Mechanismus entwickelt und in Analogie zur Photokatalyse diskutiert. / This thesis deals with two classes of oxidic nanomaterials that were synthesized by chemical solution routes and characterized with respect to structure and morphology. Sols of TiO2, TiO2/SiO2, Ag/TiO2 and Pd/TiO2 containing the photocatalytically active modification anatase in nanocrystalline form were prepared via a solvothermal sol-gel process. With regard to potential application in disinfection and environmental remediation technology the photocatalytic activity of powders and coatings on textile was investigated by means of E. coli decomposition and organic dye degradation. Further the antimicrobial activity of pyroelectric LiNbO3 and LiTaO3 powder materials under cyclical thermal excitation was demonstrated. In this context the application of the pyroelectric effect in a catalytic or electrochemical process – termed as pyroelectrocatalysis – is of fundamental novelty. Based on the physico-chemical principles of the phenomenon a hypothesis of the mechanism was developed and discussed in analogy with photocatalysis.

Nonlinear optics and ferroelectrics have been recognized for several decades as promising fields with important applications in the area of opto-electronics, photonics, memory devices, etc. High performance electro-optical switching elements for telecommunications and optical information processing are based on the material properties. Hence, there is always a continuous search for new and better materials. In this thesis we have investigated the growth and physical properties of four crystals viz. two NLO and two ferroelectric crystals. This thesis consists of eight chapters. The first chapter gives an overview of historical perspectives of nonlinear optical phenomenon, ferroelectricity and materials developed therein. The second chapter gives a brief description of the underlying theories of crystal growth, nonlinear optics and ferroelectricity. A major portion of this chapter consists of gist of the earlier work carried out on compounds of our interest viz. urea L-malic acid, sodium p-nitrophenolate dihydrate, glycine phosphite and lithium niobate. Synthesis, growth, crystal structure details and some physical properties of these materials are briefed. The third chapter describes the experimental techniques needed to grow as well as characterize these crystals. The experiments are performed on single crystals grown in the laboratory using the solution growth setup and Czochralski crystal puller. These growth units are described in detail. Preliminary characterization techniques like powder Xray diffraction, optical transmission, scanning electron microscopy, Vickers and Knoop hardness are described briefly. Various experimental methods viz. dielectric, polarization reversal, photoacoustic spectroscopy and laser induced damage for characterizing the grown crystals are explained. Urea L-malic acid (ULMA) is a new NLO organic material which is reported to exhibit second harmonic efficiency three times that of the widely used inorganic crystal, KDP. Hence, this material is selected for detailed investigation and the results obtained are discussed in chapter 4. This chapter contains details of single crystal growth and characterization of ULMA. The crystals are grown by slow cooling technique. The complete morphology of the crystal is evaluated using optical goniometry. The grown crystals are characterized for their optical and thermal properties. The defect content in the grown crystal is evaluated by chemical etching. As the surface damage of the crystal by high power lasers limits its performance in NLO applications, a detailed laser induced damage studies are performed on ULMA. Both single shot and multiple shot damage threshold values for 1064 nm and 532 nm laser radiation are determined and correlated with the mechanical hardness. In addition, the thermal diffusivity and thermal conductivity of ULMA along various crystallographic orientations are evaluated using laser induced photoacoustic spectroscopy and the results are interpreted in terms of crystal bonding environment. Another NLO crystal taken up for study is sodium p-nitrophenolate dihydrate (NPNa 2H2O), a semiorganic material. This crystal is a very efficient NLO material and has the advantages of both organics and inorganics. Earlier investigations on growth of NPNa.2H2O in various solvents have shown methanol as the most suitable solvent for growth. Growth from aqueous solution was discarded as it did not yield crystals which are stable. In the present investigation, stable, NLO active NPNa.2H2O crystals are obtained using aqueous solution itself by varying the crystallization conditions and exploring the suitable temperature range. The details of growth and characterization form the subject of fifth chapter. The grown crystals are characterized using optical transmission, XRD and thermo gravimetric analysis. Later, laser induced damage threshold is evaluated for both 1064 nm and 532 nm laser radiation and compared wit the methanol grown ones. A possible mechanism of damage is given. The sixth and seventh chapters deal with growth and characterization of ferroelectric materials namely glycine phosphite and lithium niobate respectively. Glycine phosphite is a low temperature ferroelectric crystal which is well studied in terms of its dielectric and ferroelectric properties. But very few radiation damage studies are reported. The effect of ionizing radiation on ferroelectrics is of considerable interest as it significantly modifies the physical properties of these materials. In the present investigation, effects of X-ray irradiation (_ = 1.5418 °A) on the lattice parameters, dielectric constant, loss tangent, polarization switching characteristics and domain dynamics of glycine phosphite are investigated. X-ray irradiation is performed in the non-polar phase of the sample. The effect as a function of duration of exposure is studied. X-ray irradiation in GPI has resulted in drastic reduction in _ values and shift in transition temperature towards lower temperatures. X-ray irradiation on polarization switching properties of the crystal are also investigated. The activation energy and threshold field of switching increase with the irradiation time. The behaviour of domain wall mobility is quite different from that exhibited by other well known ferroelectrics. These results are discussed in chapter 6 and a possible explanation for the unusual behaviour of domain wall mobility is given. The defect generated is identified as PO32− radical by electron paramagnetic measurement. Lithium niobate (LiNbO3) is an extensively studied material in terms of its NLO and ferroelectric properties. This material has high piezoelectric coupling coefficients along certain directions which makes it suitable for wide band surface acoustic wave applications. Hence there is a demand for good quality, single domain YZ-LiNbO3 substrates. Chapter 7 describes the growth of Z-pulled congruent LiNbO3 using Czochralski technique. Large single crystals of diameter 30 mm and length 80 mm are grown from congruent composition employing Czochralski technique. The grown crystals are multidomain and hence electric field poling is performed to get single domain crystals. Their subsequent characterization for SAW devices upto 200 MHz was performed and compared with the imported substrate. The general conclusions are given in chapter 8 along with possible future work that could be performed on these crystals.

Relaxor ferroelectrics have been a subject of intense research owing to their interesting physical properties such as high dielectric constant and giant electro-striction. Unlike the conventional lead based relaxors, the relaxors belonging to Aurivillius family of oxides have received much less attention because of the poor understanding of the origin of the relaxor behavior and high processing temperatures involved. In the present investigations, an attempt has been made to understand the origin of relaxor behavior of the materials belonging to Aurivillius family of oxides. The structure and relaxor behavior of BaBi2Nb2O9 (BBN) has been established via the XRD, electron diffraction and dielectric spectroscopy. The results are compared with that of a normal ferroelectric like SrBi2Nb2O9 belonging to the same family as well with that of a conventional relaxor like PMN. The results indicate that the dielectric behavior of BBN is significantly different from that of the conventional relaxors like BBN with very slow broadening of relaxation times and was attributed to the absence of significant polar ordering. To substantiate the existing understanding, studies have been carried out by adopting different strategies such as B-site and A-site cationic substitutions and texturing of the ceramics. Vanadium doping on B-site was found to decrease the sintering temperatures significantly. Aliovalent La3+ doping was found to affect the dielectric behavior strongly with substantial decrease of the freezing temperature and dielectric constants which shows that the relaxor behavior of BBN is highly sensitive to A-site order-disorder. The (00l) textured ceramic of pure and vanadium doped BBN was fabricated via a simple melt-quenching technique and was found to exhibit a significant dielectric and pyroelectric anisotropy. A new class of relaxor compositions (K0.5La0.5Bi2Nb2O9 & K0.5La0.5Bi2Ta2O9) have been synthesized and characterized. These new compounds exhibited interesting physical properties which are akin to that of the conventional lead based relaxors. The presence of superlattice reflections in the electron diffractin patterns recorded on these compounds establish the presence of polar nano regions of significant size. These relaxor crystallites at nano/micro level embedded in a glass matrix have been found to be very promising from their physical properties view point.

Im Mittelpunkt der vorliegenden Arbeit stehen Bauelemente, die auf der Basis von sog. akustischen Oberflächenwellen, in der Fachsprache üblicherweise mit dem Begriff SAW (surface acoustic wave) bezeichnet, arbeiten. In den vergangenen ca. 40 Jahren haben SAW-Bauelemente einen außerordentlich starken Aufschwung erlebt. Den Beginn markierte ein neuartiger Zwischenfrequenz-Filter für Fernsehgeräte am Ende der 1960er Jahre. Heute finden sich unterschiedliche Arten dieser Bauelemente in nahezu jedem Bereich unseres täglichen Lebens wieder. Als Beispiele können hier allgemein die draht-, funk- und fasergestützte Daten- und Signalübertragung und im Speziellen Mobil- und Schnurlostelefone oder Fernbedienungen genannt werden. Inzwischen sind auch neue Anwendungen in der Sensorik sowie der Identifikationstechnik hinzugekommen. Es gibt für SAW-Bauelemente eine Entwicklung hin zu höheren Arbeitsfrequenzen, steigenden Leistungen, erhöhter Zuverlässigkeit, weiterer Miniaturisierung und zunehmender Modulintegration, wobei alle Anforderungen bei gleichzeitig sinkenden Herstellungskosten realisiert werden müssen. Dabei zeichnet sich ab, dass mit den herkömmlichen Herstellungstechnologien nicht alle Bedürnisse erfüllt werden können. So ist z.B. die Lift-off-Technik, mit der ein Großteil der Bauelemente hergestellt wird, nicht auf beliebig kleine Strukturen anwendbar. Eine Alternative bildet die sog. Damaszentechnologie, die auch zur Herstellung modernster Mikroprozessoren eingesetzt wird. Dabei werden die Metallelektroden anstatt auf dem Substrat aufzuliegen, in das Substrat eingelassen, woraus sich für zukünftige SAWBauelemente Vorteile ergeben können, wie z.B. eine erhöhte Leistungsbeständigkeit, kostengünstige Abscheideverfahren, eine Reduktion der Strukturgrößen und eine planare Oberfläche. Das Ziel der vorliegenden Arbeit liegt darin, die Damaszentechnologie erstmalig auf SAW-Strukturen anzuwenden und mit den Vorteilen der Cu-Technologie zu kombinieren. Als inhaltliche Schwerpunkte wurden die Herstellung von Demonstratorbauelementen und die Bewertung der Prozessschritte, die Eigenschaftsbestimmung der Strukturen sowie deren Schädigungsverhalten bei Leistungsbelastung definiert.

Charged domain walls (CDWs) in proper ferroelectrics are a novel route towards the creation of advancing functional electronics. At CDWs the spontaneous polarization obeying the ferroelectric order alters abruptly within inter-atomic distances. Upon screening, the resulting charge accumulation may result in the manifestation of novel fascinating electrical properties. Here, we will focus on electrical conduction. A major advantage of these ferroelectric DWs is the ability to control its motion upon electrical fields. Hence, electrical conduction can be manipulated, which can enrich the possibilities of current electronic devices e.g. in the field of reconfigurability, fast random access memories or any kind of adaptive electronic circuitry. In this dissertation thesis, I want to shed more light onto this new type of interfacial electronic conduction on inclined DWs mainly in lithium niobate/LiNbO3 (LNO). The expectation was: the stronger the DW inclination towards the polar axis of the ferroelectric order and, hence, the larger the bound polarization charge, the larger the conductivity to be displayed. The DW conductance and the correlation with polarization charge was investigated with a multitude of experimental methods as scanning probe microscopy, linear and nonlinear optical microscopy as well as electron microscopy. We were able to observe a clear correlation of the local DW inclination angle with the DW conductivity by comparing the three-dimensional DW data and the local DW conductance. We investigated the conduction mechanisms on CDWs by temperature-dependent two-terminal current-voltage sweeps and were able to deduce the transport to be given by small electron polaron hopping, which are formed after injection into the CDWs. The thermal activated transport is in very good agreement with time-resolved polaron luminescence spectroscopy. The applicability of this effect for non-volatile memories was investigated in metal-ferroelectric-metal stacks with CMOS compatible single-crystalline films. These films showed unprecedented endurance, retention, precise set voltage, and small leakage currents as expected for single crystalline material. The conductance was tuned and switched according to DW switching time and voltage. The formation of CDWs has proven to be extremely stable over at least two months. The conductivity was further investigated via microwave impedance microscopy, which revealed a DW conductivity of about 100 to 1000 S/m at microwave frequencies of about 1 GHz. / Geladene Domänenwände (DW) in reinen Ferroelektrika stellen eine neue Möglichkeit zur Erzeugung zukünftiger, funktionalisierter Elektroniken dar. An geladenen DW ändert sich die Polarisation sehr abrupt - innerhalb nur weniger Atomabstände. Sofern die dadurch hervorgerufene Ladungsträgeranreicherung elektrisch abgeschirmt werden kann, könnte dies zu faszinierenden elektrischen Eigenschaften führen. Wir möchten uns hierbei jedoch auf die elektrische Leitfähigkeit beschränken. Ein großer Vorteil für die Anwendung leitfähiger DW ist deren kontrollierte Bewegung unter Einwirkung elektrischer Felder. Dies ermöglicht die Manipulation das Ladungstransports, welches zum Beispiel im Bereich der Rekonfigurierbarkeit, schneller Speicherbauelemente und jeder Art von adaptiven elektronischen Schaltungen Anwendung finden kann. In dieser Dissertationsschrift möchte ich diesen neuen Typus grenzflächiger elektronischen Ladungstransports an geladenen DW hauptsächlich am Beispiel von Lithiumniobat/-LiNbO3 (LNO) untersuchen. Die Annahme lautete hierbei: umso stärker die DW zur ferroelektrischen Achse geneigt ist, also desto stärker die gebundene Polarisationsladung und folglich die elektrische DW-Leitfähigkeit. Die elektrische DW-Leitfähigkeit und die Korrelation mit der Polarisationsladung wurde mit verschiedenen experimentellen Methoden wie Rasterkraftmikroskopie, linearer und nichtlinearer optischer Mikroskopie als auch Elektronenmikroskopie untersucht. Es konnte eine klare Korrelation durch Vergleich der dreidimensionalen DW-Aufzeichnungsdaten mit der lokalen Leitfähigkeit gezeigt werden. Wir haben weiterhin den Leitfähigkeitsmechanismus an geladenen DW mittels temperaturabhängiger Strom-Spannungskennlinien untersucht und konnten hierbei einen Hopping-Transport kleiner Elektronenpolaronen nachweisen, welche nach Elektroneninjektion in die geladene DW generiert werden. Der thermisch aktivierte Ladungsträgertransport ist in guter Übereinstimmung mit zeitaufgelöster Polaron-Lumineszenzspektroskopie. Die Anwendbarkeit dieses Effektes für nicht-volatile Speicherbauelemente wurde an Metall-Ferroelektrika-Metall Schichtstrukturen mit CMOS-kompatiblen einkristalliner Filmen untersucht. Die Filme zeigen bisher nichtgesehene Durchhalte- und Speichervermögen, genau definierte Schaltspannung sowie sehr geringe Leckageströme wie dies für einkristalline Materialsysteme erwartet wird. Die Leitfähigkeit konnte mittels entsprechender Wahl der elektrischen Schaltzeiten und -spannungen zielgerichtet manipuliert und geschalten werden. Es konnte darüber hinaus gezeigt werden, dass die hergestellten geladenen DW über eine Zeitspanne von mindestens zwei Monaten stabil sind und hierbei leitfähig bleiben. Die Leitfähigkeit der DW wurde weiterhin mittels Mikrowellenimpedanzmikroskopie untersucht. Dabei konnten DW-Leitfähigkeiten von 100 bis 1000 S/m für Mikrowellenfrequenzen von etwa 1GHz ermittelt werden.

Nous avons étudié l'influence de la fabrication de guides d'ondes optiques par échange protonique doux(SPE) sur les cristaux de niobate de lithium (LN) polarisé périodiquement et nous avons montré que,dans certains cas, ce processus conduit à la création de nanodomaines en surface. Ces nanodomaines enforme d'aiguille peuvent être responsables de la réduction de l'efficacité de conversion non linéaireobservée dans les guides qui sont affectés. Nous avons également étudié l'influence de différents typesd'échange protonique sur la formation, par application d'un champ électrique, de domaines dans le LNcongruent. Cette étude montre que le seuil de nucléation peut être fortement réduit par la présence duguide d'onde et que l'apparition et le développement des domaines en forme de traits est fortementmodifiée. Elle montre également que la fusion des nanodomaines existants au voisinage des parois dedomaine aboutit à la formation de parois élargies et de domaines en forme de dendrites. En irradiantavec un faisceau d'électrons la surface Z- d'un échantillon de LN préalablement soumis à un échangeprotonique doux et recouvert d'une couche de résine électronique, nous avons réussi à former desdomaines avec des formes arbitraires. Par cette technique, nous avons fabriqué des domainespériodiques d'excellente qualité dans des cristaux présentant des guides canaux SPE. Des expériences degénération de deuxième harmonique dans ces guides nous ont permis d'obtenir des efficacités deconversion de 48%/W.cm2 ce qui est conforme aux prédictions ainsi que la forme des spectres d'accordde phase que nous avons observés. Ceci démontre tout l'intérêt de ce processus / The investigation of influence of the soft proton exchange (SPE) optical waveguide (WG) creation onperiodically poled lithium niobate (PPLN) has been done. It has been shown that the WG fabricationprocess can induce the formation of needle like nanodomains, which can be responsible for thedegradation of the nonlinear response of the WG created in PPLN crystals. The domain structure (DS)evolution has been studied in congruent lithium niobate (LN) crystals with surface layers modified bythree different proton exchange techniques. The significant decrease of the nucleation threshold fieldand qualitative change of domain rays nucleation and growth have been revealed. The formation of abroad domain boundary and dendrite domain structure as a result of nanodomains merging in front ofthe moving rays has been demonstrated. The formation of DS in LN with SPE by irradiation of coveredby electron resist polar surface of LN has been investigated. Formation of domains with arbitrary shapesas a result of discrete switching has been revealed. Finally, it has been demonstrated that electron beamirradiation of lithium niobate crystals with surface resist layer can produce high quality periodical domainpatterns after channel waveguide fabrication. Nonlinear characterizations show that the conversionefficiencies and the phase matching spectra conform to theoretical predictions, indicating that thiscombination presents a great interest for device fabrication. Second harmonic generation withnormalized nonlinear conversion efficiency up to 48%/(W cm2) has been achieved in such waveguides