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Increasing global energy demands continually heighten the need for novel, alternative energy conversion technologies, especially those that recover waste heat generated by traditional energy conversion processes. The so-called pyroelectric effect is one intrinsic material phenomenon that can be leveraged for waste heat energy scavenging. The pyroelectric effect is characterized by the pyroelectric coefficient (p), which describes the magnitude of the change in a material’s spontaneous polarization in response to a change in its temperature. The future of pyroelectric energy harvesting is dependent upon reliable experimental measurement technique, and an understanding of how to design harvesting systems to maximize their performance. In this thesis, we both describe measurement techniques for quantifying thin film pyroelectric materials and provide guidance for maximizing the power output of pyroelectric harvesting systems.We adapt an electrothermal technique commonly used for measuring thermal conductivity, the 3ω method, to measure p of mechanically clamped PZT thin films. Using the 3ω method combined with a 1D heat transport model, we simultaneously collect the thermally-generated pyroelectric current and measure the average temperature of the metallic heater line atop the thin film, allowing us to calculate p. Frequency sweeps across several decades allow us to identify the secondary (piezoelectric) contributions to the pyroelectric coefficient, which arise due to mismatched thermal expansion coefficients between the thin film and the bulk substrate. We develop and extend these techniques using the same physical system to directly measure the electrocaloric effect in thin films as a supplement to these pyroelectric measurements. Next, we experimentally quantify the performance of pyroelectric thin films as energy converters. Using the same experimental architecture as with the PZT measurements, we synchronize the temperature of PMN-0.32PT thin films with an externally-applied electric field to complete Ericsson cycles in the thermodynamic electric field-electric displacement space. The large pyroelectric coefficient of the PMN-0.32PT and fast cycle frequencies result in large energy and power densities. This combination of large energy and power density is a first in pyroelectric energy conversion, demonstrating the benefits of the thin film architecture and showing promise for pyroelectrics as a viable waste heat scavenging technology.We lastly analyze the heat transport in idealized, 1D pyroelectric energy harvesters to identify the physical constants (e.g. thermal conductivity and volumetric heat capacity) and system properties (e.g. length and heating frequency) that determine power harvesting performance. Modeling the pyroelectric as a current source and capacitor in parallel, we relate the spatially-averaged temperature amplitude of the pyroelectric material to the power delivered to a purely resistive external load. We consider both a temperature and a heat flux source as the driving thermal energy source for the pyroelectric harvester, and through dimensional analysis we isolate the effects of different system parameters on the power delivered to the external load. Finally, we identify figures of merit (FOM’s) for various operating regimes and provide general guidance for optimizing the power output of pyroelectric energy harvesters given freedom over different system variables.

Nanogenerator energy harvesting technologies that transform thermal energies into electricity may help address the growing need for green power. Therefore, this research aims to increase power generation by combining waste heat with pyroelectric nanogenerators as a sustainable energy source. Under optimal conditions, an external multi-pulse electric field can be utilized to generate power using thermoelectric cycle power generation. The greatest power may be gathered by applying various pulses of the external electric field at temperature changes on the surface of the pyroelectric materials. To generate pyroelectric power, a C9 BZT sample was used, and the lowest temperature difference for accomplishing this was 20 °C, with all measurements made on a sample with a lower limit of 120 °C. The maximum generation density was 0.104 mJ/cm2°CkV for a pulse width of 10 ms and 20 pulses of a low voltage (250 V/mm) input electric field. A multi-pulse electric field with low input voltage increases the power generation performance ratio (η) with the pulse count. At the largest number of pulses, the greatest η value for 250 V/mm was 7.834. Finally, it was determined that the developed pyroelectric power generation system may be more effective if a low-voltage, multi-pulse electric field is used.

X-rays are a type of electromagnetic energy which widely used in different areas. Since their discovery, x-rays have been used, especially for medical imaging applications. On the other hand, new efficient x-ray generation methods have still been under investigation. Although new imaging modalities arose, xrays have never lost their popularity in many applications like computed tomography and dental imaging. Among these new methods, x-ray generation using pyroelectric crystal materials is one of the promising technologies. Pyroelectric crystals generate an electric field when a temperature change occurs and are affected by various parameters like how many times (count) the crystal’s temperature changed in a second. Hence, this new technology needs more research. In this study, we investigated the relationship between the count number and x-rays’ energy level of pyroelectric materials using linear regression analysis. We used a commercial software package, which is called the Statistical Package for the Social Sciences (SPSS), for this purpose. As a result, we achieved a good fit value of R2 = 0.91.

Pyroelectricity is mainly affected by the structure of materials. To explore the influence of the structure on pyroelectricity, a new type of pyroelectric materials with structure of tourmaline consisting of Li9Mg3[PO4]4F3, Ba3Sr4(BO3)3F5 and tourmaline have been systematically studied in this work. Based on the comparison results of the pyroelectric coefficient of Li9Mg3[PO4]4F3 and Ba3Sr4(BO3)3F5 after heating and the variations of electric dipole moment, it suggests the tetrahedron is less stable than trigon, and is easily to cause the distortion and deformation of structure, which leads to the great enhancement of pyroelectricity. Additionally, it can find that the tetrahedron has the most contribution to the pyroelectricity by comparing the pyroelectric coefficient and total electric dipole moment of Li9Mg3[PO4]4F3, Ba3Sr4(BO3)3F5 and tourmaline which have different polyhedrons.

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

Termal görüntüleme cihazlarının, askeri, endüstri ve uzay araştırmaları gibi geniş uygulama alanlarından dolayı, sıcaklığa bağlı polarize olan pyroelektrik maddeleri üzerindeki çalışmalar, araştırmacıların ilgisini çekmektedir. Bu maklede, pyroelektrik olayın, pyroelektrik maddelerin ve bu maddelere ait bazı uygulamaların genel bir değerlendirilmesi verilecektir, The wide range of applications of thermal imaging devices existing in military, industrial and space fields attract researchers to study pyroelectric materials which exhibit a temperature-dependent spontaneous polarisation. A brief review of pyroelectricity, pyroelectric materials and some commercial applications of these materials we will be given in this paper

This review covers energy harvesting technologies associated with pyroelectric materials and systems. Such materials have the potential to generate electrical power from thermal fluctuations and is a less well explored form of thermal energy harvesting than thermoelectric systems. The pyroelectric effect and potential thermal and electric field cycles for energy harvesting are explored. Materials of interest are discussed and pyroelectric architectures and systems that can be employed to improve device performance, such as frequency and power level, are described. In addition to the solid materials employed, the appropriate pyroelectric harvesting circuits to condition and store the electrical power are discussed.

An attempt has been made to provide the ranking of piezoelectric and pyroelectric materials using technique for order preference by similarity to ideal solution (TOPSIS) method. To calculate weight (priority) for all the attributes (properties) understudy, entropy method is used. Interestingly my results suggest that dielectric constant is a key parameter (after d33 coefficient) which governs selection of piezoelectric materials. PLZT (8/65/35) and LiTaO3 ceramics place on first rank among studied piezoelectric and pyroelectric materials, respectively. These materials are classified using hierarchical clustering which shows similarities between the materials irrespective to their ranking obtained using TOPSIS method.

This paper is concerned with directly converting waste heat into electricity using pyroelectric materials. A prototypical pyroelectric converter is simulated by solving the two-dimensional mass, momentum, and energy equations using finite element methods. The pumping power and the electrical power generated are estimated from the computed pressure, temperature, and velocity. The results show that the energy efficiency increases as the density and specific heat of the working fluid and of the pyroelectric material decrease. Moreover, the power density increases as the density and specific heat of the working fluid increase and those of the pyroelectric material decrease. One can reasonably achieve an energy efficiency of 40% of the Carnot efficiency and a power density of 24 W/L of pyroelectric materials.

A method of continuously harvesting energy from pyroelectric materials is demonstrated using an innovative cyclic heating scheme. In traditional pyroelectric energy harvesting methods, static heating sources are used, and most of the available energy has to be harvested at once. A cyclic heating system is developed such that the temperature varies between hot and cold regions. Although the energy harvested during each period of the heating cycle is small, the accumulated total energy over time may exceed traditional methods. Three materials are studied: a commonly available soft lead zirconate titanate (PZT), a pre-stressed PZT composite, and single-crystal PMN-30PT. Radiation heating and natural cooling are used such that, at smaller cyclic frequencies, the temporal rate of change in temperature is large enough to produce high power densities. The maximum power density of 8.64 μW/cm3 is generated with a PMN-30PT single crystal at an angular velocity of 0.64 rad/s with a rate of 8.5°C/s. The pre-stressed PZT composite generated a power density of 6.31 μW/cm(3), which is 40% larger than the density of 4.48 μW/cm3 obtained from standard PZT.

The development of low-cost, uncooled (room temperature operation) thermal detector arrays has been accelerating in recent years and now commercial products are becoming widely available. As costs come down and volumes rise, these devices are entering the consumer marketplace, providing everything from sophisticated security and people-monitoring devices to hand-held thermal imagers for preventative maintenance and building inspection. Two technologies have established significant market shares in uncooled thermal detector array products. These are resistive microbolometers and pyroelectric ceramics. To address the true mass market, the pyroelectric arrays offer significant cost advantage. In this paper, recent developments in a variety of products based on pyroelectric ceramic arrays are described and their performance and applicability are compared and contrasted with competing technologies. This includes the use of low-element-count arrays for applications in people counting and queue measurement, and the drive for cost-effective imaging arrays for mass-market thermal imaging. The technical challenges in materials production, device development, and low-cost manufacture are reviewed and future opportunities and challenges are outlined.

Properties of a new type of pyroelectric ceramic structure containing a layer of known porosity laminated between two dense layers, to form a functionally gradient material (FGM), are reported. The combination of theoretical models for pyroelectric, dielectric, and thermal properties gave a model for the pyroelectric voltage figure of merit (F v ) in good agreement with experiment, which had shown a 20% improvement for an introduced central layer porosity of 27%. Preliminary pyroelectric responsivity measurements on FGM infrared detectors indicated an even better improvement. It is postulated that this is due to the porous layer acting as a thermal barrier in the structure.

Thin-film electrocaloric and pyroelectric sources for electrothermal energy interconversion have recently emerged as viable means for primary and auxiliary solid-state cooling and power generation. Two significant advances have facilitated this development: (1) the formation of high-quality polymeric and ceramic thin films with figures of merit that project system-level performance as a large percentage of Carnot efficiency and (2) the ability of these newer materials to support larger electric fields, thereby permitting operation at higher voltages. This makes the power electronic architectures more favorable for thermal to electric energy interconversion. Current research targets to adequately address commercial device needs including reduction of parasitic losses, increases in mechanical robustness, and the ability to form nearly freestanding elements with thicknesses in the range of 1–10 μm. This article describes the current state-of-the-art materials, thermodynamic cycles, and device losses and points toward potential lines of research that would lead to substantially better figures of merit for electrothermal energy interconversion.

Pyroelectrics form a very broad class of materials. Any material which has a crystal structure possessing a polar point symmetry—i.e. one which both lacks a centre of symmetry and has a unique axis of symmetry—will possess an intrinsic, or spontaneous, polarisation and show the pyroelectric effect. The pyroelectric effect is a change in that spontaneous polarisation caused by a change in temperature. It is manifested as the appearance of free charge at the surfaces of the material, or a flow of current in an external circuit connected to it. The effect is a simple one, but it has been used in a range of sensing devices, most notably uncooled pyroelectric infra-red (PIR) sensors, and has thus come to be of some engineering and economic significance, enabling a wide range of sensing systems, ranging from burglar alarms through FTIR spectroscopic instruments to thermal imagers.

Pyroelectric energy conversion offers a way to convert waste heat directly into electricity. It makes use of the pyroelectric effect to create a flow of charge to or from the surface of a material as a result of heating or cooling. However, an existing pyroelectric energy converter can only operate at low frequencies due to a relatively small convective heat transfer rate between the pyroelectric materials and the working fluid. On the other hand, energy transfer by thermal radiation between two semi-infinite solids is nearly instantaneous and can be enhanced by several orders of magnitude from the conventional Stefan–Boltzmann law as the gap separating them becomes smaller than Wien’s displacement wavelength. This paper explores a novel way to harvest waste heat by combining pyroelectric energy conversion and nanoscale thermal radiation. A new device was investigated numerically by accurately modeling nanoscale radiative heat transfer between a pyroelectric element and hot and cold plates. Silica absorbing layers on top of every surface were used to further increase the net radiative heat fluxes. Temperature oscillations with time and performances of the pyroelectric converter were predicted at various frequencies. The device using 60/40 porous poly(vinylidene fluoride–trifluoroethylene) achieved a 0.2% efficiency and a 0.84 mW/cm2 electrical power output for the cold and hot sources at 273 K and 388 K, respectively. Better performances could be achieved with 0.9Pb(Mg1/3Nb2/3)–0.1PbTiO3 (0.9PMN-PT), namely, an efficiency of 1.3% and a power output of 6.5 mW/cm2 between the cold and hot sources at 283 K and 383 K, respectively. These results are compared with alternative technologies, and suggestions are made to further improve the device.

An automated system for the pyroelectric imaging of polar substrates has been developed. The principle of operation, details of the optical and mechanical subsystems, and a description of the system hardware, interface, and software for data acquisition and display are given. The automation has made possible routine scans of high resolution and/or large areas of pyroelectric materials, such as LiNbO/sub 3/ and ZnO. Features of the system are highlighted by means of a pyroelectric imaging of proton-exchanged LiNbO/sub 3/, which is an important material for optical waveguides. >