Icing on materials surface causes operational failures as well as technical and safety issues. Furthermore, it reduces the energy efficiency of the power supply and passenger/freight transportation systems. Conventional active deicing methods are widely used to remove ice, but are often associated with uneconomically high energy consumption and high maintenance costs, often not being aware of their environmental impact. Instead, passive anti-icing methods are being sought to prevent or delay ice formation by means of physico-chemical surface treatment. Pyroelectric materials can be used as possible anti-icing surfaces after their ability to inhibit ice nucleation has been experimentally demonstrated. This makes use of the effect of the pyroelectrically induced surface charge, which changes with the ambient temperature and thus, hypothetically, exerts an influence on the dipole orientation of the water molecules at the surface. This is expected to affect the hydrogen bonding network of the interfacial water in the supercooled liquid phase, depending on the sign of surface charge. However, the Classical Nucleation Theory predicts an increased nucleation rate with increasing electric field strength of the pyroelectric surface charge irrespective of its polarity, as confirmed by many experiments. This raises the question of what exactly influences the ice nucleation. The main purpose of this thesis is to find a relationship between the pyroelectricity and the ice nucleation rate. Various theoretical and experimental investigation methods have been used to examine which of the possible influencing factors related to the pyroelectric material surface plays a major role in promoting or inhibiting ice nucleation.:Contents Abstract i List of figures xi List of tables xv 1 Introduction 1 1.1 Motivation 1 1.2 Objective and Tasks 4 1.3 Structure of the thesis 6 2 Basics 7 2.1 Pyroelectric materials 7 2.1.1 Fundamental properties 7 2.1.2 Lithium niobate, LiNbO3 14 2.2 Ice nucleation and water freezing 21 2.2.1 Thermodynamics of ice nucleation 21 2.2.2 Factors influencing ice nucleation 26 3 Materials and Methods 29 3.1 Sample materials used for the investigation 29 3.2 Theoretical methods 31 3.2.1 Theoretical background of computational quantum mechanical modeling 31 3.2.2 LiNbO3 model system 38 3.2.3 DFT implementation in CP2K 41 3.3 Experimental methods 42 3.3.1 Optical and vibrational spectroscopy 43 3.3.2 X-ray spectroscopy 47 3.3.3 Atomic force microscopy 48 3.3.4 Environmental scanning electron spectroscopy 51 3.3.5 Pyroelectric measurement 52 3.3.6 Contact angle measurement 53 3.3.7 Icing temperature measurement 54 3.4 Tabular overview of the different methods 57 ix4 Results and Discussion 59 4.1 Results 59 4.1.1 Several results of DFT calculations 59 4.1.2 MD simulations of interfacial water 75 4.1.3 Results of optical and vibrational spectroscopy 80 4.1.4 X-ray spectroscopy on LiNbO3 surfaces 96 4.1.5 Extended treatment of the Classical Nucleation Theory 100 4.1.6 Results of atomic force microscopy 108 4.1.7 ESEM images of ice crystals grown on LiNbO3 116 4.1.8 Results of pyroelectric measurements 122 4.1.9 Results of contact angle measurements 124 4.1.10 Results of icing temperature measurements 126 4.2 Discussion 135 4.2.1 Surface charge 135 4.2.2 Surface structure 144 4.2.3 Surface reactivity 149 4.3 Conclusion of the findings and remarks 151 5 Summary and Outlook 157 5.1 Conclusion of the thesis 157 5.2 Recommendations for further investigations 161 5.3 Outlook 164 Appendix 167 A.1 Additional information to the DFT calculations 167 A.2 Background spectrum for ATR spectroscopy 175 A.3 Additional information to SFG/SHG spectroscopy 176 A.4 Additional information to the XPS results 181 A.5 Additional information to the AFM measurement 182 A.6 ESEM images of ice accretion in the sample system 187 A.7 FEM simulation of local temperature and flow velocity distribution 190 A.8 Additional information to the icing temperature measurement 203 A.9 Temperature-dependent pH variation of water at LiNbO3 surface 207 List of abbreviations and symbols 213 References 217 Publications 276 Acknowledgements 277 Erklärung 281 / Vereisung auf Werkstoffoberflächen führt einerseits zu Betriebsausfällen und andererseits zur Reduzierung der Energieeffizienz von Energieversorgungs- sowie Personen- und Gütertransportsystemen. Sie stellt nicht selten ein sicherheitstechnisches und gesundheitliches Risiko dar. Da die konventionellen aktiven Enteisungsmethoden mit hohem Energieaufwand und hohen Wartungskosten verbunden sind, wird nach passiven Anti-icing-Methoden als vorbeugende Maßnahmen zur Vermeidung/Verzögerung von Eisbildung auf physikalisch-chemisch behandelten Oberflächen gesucht. Der Einsatz dieser Werkstoffoberflächen senkt nicht nur den Energieverbrauch, sondern soll auch die Umwelt schonen. Pyroelektrische Materialien kommen als passive Anti-icing-Oberflächen in Frage, nachdem ihre eiskeimbildungshemmende Fähigkeit experimentell nachgewiesen wurde. Dabei wird der Effekt der pyroelektrisch induzierten Oberflächenladung ausgenutzt, die sich mit der Umgebungstemperatur ändert und somit, hypothetisch gesehen, einen Einfluss auf die Dipolorientierung der Wassermoleküle an der Oberfläche ausübt. Das hat je nach Vorzeichen der Oberflächenladung Auswirkungen auf das Wassermolekülbindungsnetzwerk des Grenzflächenwassers in der unterkühlten flüssigen Phase. Da die klassische Keimbildungstheorie jedoch eine erhöhte Keimbildungswahrscheinlichkeit mit zunehmender Stärke des elektrischen Feldes der pyroelektrischen Oberflächenladung unabhängig von ihrem Vorzeichen voraussagt, wie es ebenfalls in vielen Experimenten nachgewiesen wurde, stellt sich die Frage, was genau die Eiskeimbildung beeinflusst. Das Hauptanliegen dieser Arbeit ist, einen Zusammenhang zwischen der Pyroelektrizität der Oberfläche und der Eiskeimbildungsrate zu finden. Mithilfe einer Vielzahl von verschiedenen theoretischen und experimentellen Methoden wird untersucht, welcher der möglichen Einflussfaktoren im Zusammenhang mit der pyroelektrischen Materialoberfläche eine große Rolle bei der Eiskeimbildung spielt.:Contents Abstract i List of figures xi List of tables xv 1 Introduction 1 1.1 Motivation 1 1.2 Objective and Tasks 4 1.3 Structure of the thesis 6 2 Basics 7 2.1 Pyroelectric materials 7 2.1.1 Fundamental properties 7 2.1.2 Lithium niobate, LiNbO3 14 2.2 Ice nucleation and water freezing 21 2.2.1 Thermodynamics of ice nucleation 21 2.2.2 Factors influencing ice nucleation 26 3 Materials and Methods 29 3.1 Sample materials used for the investigation 29 3.2 Theoretical methods 31 3.2.1 Theoretical background of computational quantum mechanical modeling 31 3.2.2 LiNbO3 model system 38 3.2.3 DFT implementation in CP2K 41 3.3 Experimental methods 42 3.3.1 Optical and vibrational spectroscopy 43 3.3.2 X-ray spectroscopy 47 3.3.3 Atomic force microscopy 48 3.3.4 Environmental scanning electron spectroscopy 51 3.3.5 Pyroelectric measurement 52 3.3.6 Contact angle measurement 53 3.3.7 Icing temperature measurement 54 3.4 Tabular overview of the different methods 57 ix4 Results and Discussion 59 4.1 Results 59 4.1.1 Several results of DFT calculations 59 4.1.2 MD simulations of interfacial water 75 4.1.3 Results of optical and vibrational spectroscopy 80 4.1.4 X-ray spectroscopy on LiNbO3 surfaces 96 4.1.5 Extended treatment of the Classical Nucleation Theory 100 4.1.6 Results of atomic force microscopy 108 4.1.7 ESEM images of ice crystals grown on LiNbO3 116 4.1.8 Results of pyroelectric measurements 122 4.1.9 Results of contact angle measurements 124 4.1.10 Results of icing temperature measurements 126 4.2 Discussion 135 4.2.1 Surface charge 135 4.2.2 Surface structure 144 4.2.3 Surface reactivity 149 4.3 Conclusion of the findings and remarks 151 5 Summary and Outlook 157 5.1 Conclusion of the thesis 157 5.2 Recommendations for further investigations 161 5.3 Outlook 164 Appendix 167 A.1 Additional information to the DFT calculations 167 A.2 Background spectrum for ATR spectroscopy 175 A.3 Additional information to SFG/SHG spectroscopy 176 A.4 Additional information to the XPS results 181 A.5 Additional information to the AFM measurement 182 A.6 ESEM images of ice accretion in the sample system 187 A.7 FEM simulation of local temperature and flow velocity distribution 190 A.8 Additional information to the icing temperature measurement 203 A.9 Temperature-dependent pH variation of water at LiNbO3 surface 207 List of abbreviations and symbols 213 References 217 Publications 276 Acknowledgements 277 Erklärung 281

Ferroelectricity in hafnium oxide thin films is known to be induced by various doping elements and in solid-solution with zirconia. While a wealth of studies is focused on their basic ferroelectric properties and memory applications, thorough studies of the related pyroelectric properties and their application potential are only rarely found. This work investigates the impact of Si doping on the phase composition and ferro- as well as pyroelectric properties of thin film capacitors. Dynamic hysteresis measurements and the field-free Sharp-Garn method were used to correlate the reported orthorhombic phase fractions with the remanent polarization and pyroelectric coefficient. Maximum values of 8.21 µC cm−2 and −46.2 µC K−1 m−2 for remanent polarization and pyroelectric coefficient were found for a Si content of 2.0 at%, respectively. Moreover, temperature-dependent measurements reveal nearly constant values for the pyroelectric coefficient and remanent polarization over the temperature range of 0 °C to 170 °C, which make the material a promising candidate for IR sensor and energy conversion applications beyond the commonly discussed use in memory applications.

Le développement et l’utilisation de nouveaux matériaux, tel que le carbure de silicium (SiC) et le nitrure de gallium (GaN), a permis un accroissement sensible des densités d’énergie traitées par les nouveaux composants de l’électronique de puissance, assortie d’une augmentation de leur compacité. Parallèlement à ces progrès technologiques, la généralisation de l’électricité en tant que vecteur d’énergie primaire au sein de systèmes de plus en plus répartis, incluant des moyens de traitement de l’information au plus près de la fonction réalisée, ouvre la voie à une nouvelle génération de systèmes mécatroniques hautement intégrés. Or, l’émergence de ces nouvelles fonctions soulève une question critique liée au mode de refroidissement de ces éléments. Cette question est intimement couplée aux aspects énergétiques et à leur impact environnemental, imposant une amélioration significative des rendements énergétiques mesurés à l’échelle de la fonction complète. C’est dans ce contexte que l’étude présentée traite tout d’abord de systèmes de récupération de la chaleur résiduelle dissipée au sein de systèmes électroniques de puissance en vue d’alimenter de manière autonome des capteurs, où autres systèmes fonctionnels, via l’énergie « ambiante » ainsi récupérée. Parmi les consommateurs plus particulièrement ciblés, des fonctions innovantes d’intensification par voie électromécanique des échanges de chaleurs au sein d’échangeurs thermique sont étudiées et mises en œuvre. A terme, l’idée serait ainsi d’alimenter les systèmes d’actionnement assurant l’optimisation des échanges de chaleur au sein du système de refroidissement d’une carte électronique au moyen même de la chaleur qu’elle dissipe, récupérée sous forme d’énergie électrique. A cette fin, les différents procédés de conversion de la chaleur en électricité sont examinés, modélisés et mis en œuvre dans la suite de ce travail. Deux types de conversion d’énergie complémentaires sont tour à tour considérés : La conversion par effet thermoélectrique, utilisant l’effet Seebeck qui a lieu en présence d’un gradient de température et l’effet pyroélectrique qui apparait en présence de variation temporelle de la température. Ces deux phénomènes sont analysés et décrits à l’aide de modélisations physiques et comportementales, incluant une approche expérimentale ayant nécessité la mise en place de bancs d’essai spécifiques. L’électricité récupérée par conversion pyroélectrique est par la suite mise en forme grâce à des systèmes de redressement à faible tension de seuil spécialement développés. La faisabilité de systèmes d’alimentation autonomes de capteurs déportés, où de systèmes d’émission (ponctuelle) de mesure, est alors concrètement démontrée en se basant sur les résultats obtenus. Ouvrant la voie à un concept de refroidissement actif des puces électroniques, tirant directement parti de la chaleur dissipée pour son alimentation grâce aux deux procédés préalablement étudiés, la problématique de l’intensification des transferts de chaleur au sein de boucles de refroidissement mécaniquement activées est abordée dans la dernière partie du mémoire. Cette activation est réalisée à l’aide d’un système d’actionnement multicellulaire réparti à base d’actionneurs piézoélectriques. Développée en étroite collaboration avec des équipes de thermodynamiciens, l’idée est de réaliser un pompage de fluide ainsi qu’une modification des échanges de chaleur au sein d’un système de transfert de chaleur en activant les parois de l’échangeur de chaleur par déformation. Le système d’actionnement préconisé est tout d’abord étudié et simulé par un calcul par éléments finis. Un prototype est construit et caractérisé sous conditions réelles dans un deuxième temps. [...] / The development and use of new materials, such as silicon carbide (SiC) and gallium nitride (GaN) has a significant increase in energy densities handled by the new components of power electronics, accompanied by an increase in compactness. Parallel to these technological advances, the widespread use of electricity as a primary energy carrier within systems increasingly distributed, including means for processing information closer to the function carried out, paving the way a new generation of highly integrated mechatronic systems. However, the emergence of these new features raises a critical question related to cooling mode thereof. This question is closely coupled to the energy aspects and their environmental impact, imposing a significant improvement in measured across the full energy function returns. It is in this context that the present study deals firstly recovery systems waste heat dissipated in power electronic systems for autonomous power sensors, where other functional systems via energy "room" and recovered. Particularly among targeted consumers, innovative features intensification electromechanically exchanges heat in heat exchangers are studied and implemented. Eventually, the idea would be to supply the operating systems for the optimization of heat exchange in the cooling system of an electronic card in the same way that heat dissipates, recovered in the form of electrical energy. To this end, various methods of conversion of heat into electricity are considered, modeled and implemented in the course of this work. Two complementary types of energy conversion are considered in turn : The thermoelectric conversion effect by using the Seebeck effect which takes place in the presence of a temperature gradient and the pyroelectric effect that appears in the presence of temporal variation of the temperature. These two phenomena are analyzed and described using physical and behavioral models, including an experimental approach requiring the establishment of specific test benches. The electricity recovered by pyroelectric conversion is then formatted with recovery systems, low voltage specially developed threshold. The feasibility of remote sensors autonomous supply, where emission (point) measuring systems, is then demonstrated concretely based on the results systems. Paving the way to a concept of active cooling computer chips, drawing directly from the heat dissipated for food through two methods previously studied the problem of intensification of heat transfer in cooling loops mechanically activated is discussed in the latter part of the memory. This activation is carried out using a distributed drive system multicellular based piezoelectric actuators. Developed in close collaboration with teams of thermodynamics, the idea is to provide a fluid pump and a change of heat transfer in a heat transfer system by activating the walls of the heat exchanger deformation. The operating system is called first studied and simulated by a finite element calculation. A prototype is built and characterized under actual conditions in a second time. The multicellular actuating system composed of a plurality of actuators and a supply system configurable multipath is then integrated into an exchange of heat testbed specifically developed. This experience is a fundamental first step in the development of electroactive systems, potentially autonomous, allowing the intensification of heat exchange in cooling loops for high-performance power electronics.

The present research work mainly focuses on the fabrication of 0.85PMN-0.15PT thin film relaxor ferroelectrics for energy harvesting applications. Chapter 1 gives a brief review about why energy harvesting is required and the different ways it can be scavenged. An introduction to relaxor ferroelectrics and their characteristics structural features are discussed. A brief introduction is given about charge storage, electrocaloric effect , DC-EFM and integration over Si substrate is discussed. Finally, the specific objectives of the current research are outlined. Chapter 2 deals with the various experimental studies carried out in this research work. It gives the details of the experimental set up and the basic operation principles of various structural and physical characterizations of the materials prepared. A brief explanation of material fabrication, Microstructural and physical property measurements is discussed. Chapter3 involves the optimization process carried out to contain a phase pure PMN-PT structure without any pyrochlore phase. The optimization process is an important step in the fabrication of a thin film as the quality of any device is determined by their structural and Microstructural features. XRD, SEM, AFM were used to characterize the observed phase formation in these films. The optimizing domain images of polycrystalline 0.85PMN-0.15PT thin films on La0.5Sr0.5CoO3/ (111) Pt/TiO2/SiO2/Si substrates deposited at different oxygen partial pressures are presented. The oxygen pressure has a drastic influence on the film growth and grain morphology which are revealed through XRD and SEM characterization techniques. The presence of oxygen vacancies have found to influence the distribution of polar nanoregions and their dynamics which are visualized using domain images acquired by DC-EFM In Chapter 7 the piezoelectric response of 0.85PMN-0.15PT thin films are studied due to the electric field induced bias. From this the d33 value is calculated. d33 value is an important parameter which determines whether a material is suitable for device application (PZT). But, for a device fabrication it is important to integrate them with Si wafer which is not a straightforward work .Hence, buffer layers are used to obtain a pure perovskite PMN-PT film. We have deposited 0.85PMN-0.15PT thin films of 500 nm on a SOI wafer and tried to investigate their piezoelectric application. Chapter 8 summarizes the present study and discusses about the future work that could give more insight into the understanding of the0.85PMN-0.15 PT relaxor ferroelectric thin film.

In this thesis, the results pertaining to various investigations carried out on Triglycine sulphate (TGS) single crystals, polyvinylidene fluoride (PVDF) films, lithium tantalate (LT)/PVDF nanocomposites and LT thin films are presented with emphasis on the characteristics that are crucial for their use in pyroelectric sensors. TGS single crystals (size 68 x 45 x 42 mm3), which have high pyroelectric coefficients, were grown by slow cooling method using newly designed platform technique based crystal growth work stations. The problem of slow growth rate along c-direction was overcome by placing (010) oriented seeds on the platform. The grown TGS crystals were used for the fabrication of the laser energy meter and temperature sensor. One drawback of TGS is its low Curie temperature (490C). As a consequence when the operating temperature approaches the Curie temperature, the crystals start depolarizing owing to the movement of domains. As a result the linearity of the devices gets affected and restricts the use of TGS. Therefore pyroelectric materials possessing higher Curie temperatures and larger pyroelectric coefficients than that of TGS are desirable. LT in single crystalline form having Curie temperature of ≈6000C has already been in use for pyroelectric device applications. However, growing stoichiometric LT single crystal is very difficult. On the other hand PVDF polymer films (Tc≈1800C) have low pyrolectric coefficients and difficult to pole electrically. Therefore efforts were made to prepare LT/PVDF nanocrystal composites to increase the pyroelectric coefficient of PVDF and to reduce the poling field. Nanoparticles of LT were prepared using sol-gel route. Spherical nanoparticles of size 20-40nm were prepared from sol by adding oleic acid to it. These nanoparticles were characterized using XRD, TEM, DSC and Raman spectroscopy. PVDF films with large percentage of β-phase (ferroelectric phase) were fabricated from solutions prepared using dimethylsulphoxide (DMSO) solvent. PVDF films (30µm thick), embedded with 20-40nm sized nanocrystallites of LT were fabricated to utilize them for pyroelectric sensor applications. The ferroelectric and pyrolectric properties of nano composite films were studied for sensor applications point of view. As a replacement for the single crystals of LT in pyroelectric sensors, investigations were carried out on oriented LT thin films. The studies on LT thin films yielded promising results which could be exploited for pyroelectric sensor applications.