111 research outputs found
Electrocaloric coolers and pyroelectric energy harvesters based on multilayer capacitors of Pb(Sc0.5Ta0.5)O3
No full textThe following work investigates the development of heat pumps that exploit electrocaloric effects in Pb(Sc,Ta)03 (PST) multilayer capacitors (MLCs). The electrocaloric effect refers to reversible thermal changes in a material upon application (and removal) of an electric field. Electrocaloric cooling is interesting because 1) it has the potential to be more efficient than competing technologies, such as vapour-compression systems, and 2) it does not compel the use of greenhouse gases, which is crucial in order to slow down global warming and mitigate the effects of climate change.
The continuous progress in the field of electrocalorics has promoted the creation of several electrocaloric based heat pump prototypes. Despite the different designs and working principles utilized, these prototypes have struggled to maintain temperature variations as large as 10 K, discouraging their industrial development. In this work, bespoke PST-MLCs exhibiting large electrocaloric effects near room temperature were embodied in a novel heat pump with the motivation to surpass the 10 K-barrier. The experimental design of the heat pump was based on the outcome of a numerical model. After implementing some of the modifications suggested by the latter, consistent temperature spans of 13 K at 30 °C were reported, with cooling powers of 12 W / kg. Additional simulations predicted temperature spans as large as 50 K and cooling powers in the order of 1000 W / kg, if a new set of plausible modifications were to be put in place.
Similarly, these very same PST-MLCs samples were implemented into pyroelectric harvesters revisiting Olsen's pioneering work from 1980. The harvested energies were found to be as large as 11.2 J, with energy densities reaching up to 4.4 J / cm3 of active material, when undergoing temperature oscillations of 100 K under electric fields applied of 140-200 kV / cm. These findings are two and four times, respectively, larger than the best reported values in the literature.
The results obtained in this dissertation are beyond the state-of-the-art and show that 1) electrocaloric heat pumps can indeed achieve temperature spans larger than 10 K, and 2) pyroelectric harvesters can generate electrical energy in the Joule-range. Moreover, numerical models indicated that there is still room for improvement, especially when it comes to the power of these devices. This should encourage the development of these kinds of electrocaloric- and pyroelectric-based applications in the near future
NONLINEAR PYROELECTRIC MATERIALS FOR ELECTRO-THERMAL ENERGY HARVESTING
No full textNearly two-thirds of the global energy derived from primary resources is dissipated as low-grade waste heat, which remains a largely untapped source of recoverable energy. As global energy demand continues to increase, it is imperative to adopt alternative and sustainable energy conversion technologies that focus on reducing energy losses. One such technology is pyroelectric energy harvesting, which converts the heat directly into electrical energy by utilizing the intrinsic pyroelectric effect in certain polar dielectric materials. Moreover, this technology serves niche application areas where thermoelectric energy harvesting becomes ineffective, especially in harnessing low-grade heat. Unlike thermoelectric materials, which require a steady-state temperature difference, pyroelectric devices operate under temperature fluctuations, making them especially suitable for applications involving temperature variations over time. Although the concept of pyroelectric energy harvesting has been known for several decades, there is limited understanding of how nonlinear behaviour of pyroelectric materials, as a function of temperature and electric field, influences energy conversion performance. This work investigates the nonlinear pyroelectric conversion potential of a prototypical pyroelectric material, lead scandium tantalate (PST) in different device geometries, from thin films to bulk samples. Despite its excellent electrocaloric and pyroelectric properties, PST thin films were not widely studied due to the challenges associated with high processing temperatures. In this work, the processing conditions were carefully optimized to yield high quality PST thin films. Indeed, thin films can withstand high electric fields which directly enhance the pyroelectric energy output and are also suitable for integration in microelectronic devices. High-quality PST thin films developed in this work achieved a pyroelectric energy density of up to 9 J∙cm−3 under optimized thermal and electrical conditions. Furthermore, to expand the operating temperature range, the transition temperature of PST thin films was shifted to higher temperatures by systematically doping with Ti4+ ions. While thin films offer numerous advantages, their limited active volume restricts their applicability in macroscopic energy harvesting systems. To overcome this challenge, the study expanded to include both PST bulk ceramics and PST multilayer capacitors (MLCs). These geometries benefit from high B-site cation ordering, resulting in a first-order phase transition and high pyroelectric coefficient. In addition to the detailed electrical characterizations, direct pyroelectric energy conversion cycles were implemented on PST MLCs using a dedicated experimental setup. The results indicate that PST MLCs can achieve a maximum of 50% Carnot efficiency for a 5 K temperature span near their phase transition temperature, compared to 22% achieved by PST bulk ceramics for a ΔT of 10 K at their transition. These results were obtained under the Olsen pyroelectric conversion cycle without any heat regeneration. Based on these results, PST MLCs were selected to demonstrate two proofs of concept to highlight the practical feasibility of non-linear pyroelectric energy harvesting devices. First, a standalone autonomous pyroelectric energy harvester was developed using only two PST MLCs. The device automatically initiates the Stirling pyroelectric conversion cycle based on the temperature profile of the material obtained from a thermocouple and the energy harvested by the materials is reused to initiate successive cycles without drawing energy from external power sources. Following the same device concept, a macroscopic self-powered pyroelectric energy harvester consisting of 60 PST MLCs was developed. To successfully implement this system, a closed-loop fluidic control system was introduced for the first time, enabling nonlinear pyroelectric energy harvesting in a macroscopic device without relying on heat regeneration or large volumes of heat transfer fluid. The energy extracted from the device was used not only to sustain the autonomous operation of the device but also to continuously power an external Bluetooth communication module for more than 30 minutes, thereby demonstrating a fully self-sustaining pyroelectric energy harvesting device. The results presented in this dissertation highlight the practical feasibility of nonlinear pyroelectric energy conversion, showing that high electrical output and efficiency can be achieved by carefully tuning both the material properties and the device architecture. Furthermore, the macroscopic self-powered pyroelectric energy harvester indicate that this technology can be used to develop autonomous devices or serve as a supplementary energy source to extend device lifetime by harnessing energy from ambient sources such as the ubiquitous waste heat. These outcomes not only open new avenues for real-world applications but also suggest that future efforts in nonlinear pyroelectric energy harvesting should shift from purely material-focused improvements toward system-level design and integration.THERMODIMAT7. Affordable and clean energ
Scale law on energy efficiency of electrocaloric materials
No full textCaloric materials are suggested as energy-efficient refrigerants for future cooling devices.
They could replace the greenhouse gases used for decades in our air conditioners, fridges,
and heat pumps. Among the four types of caloric materials (electro, baro, elasto, magneto caloric), electrocaloric materials are more promising as applying large electric fields is
much simpler and cheaper than the other fields. The research in the last years has been
focused on looking for electrocaloric materials with high thermal responses. However, the
energy efficiency crucial for future replacement of the vapor compression technology has
been overlooked. The intrinsic efficiency of electrocaloric has been barely studied. In the
present dissertation, we will study the efficiency of EC materials defined as materials efficiency. It is the ratio of the reversible electrocaloric heat to the reversible electrical work
required to drive this heat. In this work, we will study the materials efficiency of the benchmark lead scandium tantalate in different shapes (bulk ceramic and multilayer capacitors).
A comparison to other caloric materials is presented in this dissertation. Our work gives
more insights on the figure merit of materials efficiency to further improve the efficiency of
our devices.CAMELHEAT C17/MS/11703691/Defa
High cooling performance in a double-loop electrocaloric heat pump
No full textCooling through solid-state electrocaloric materials is an attractive replacement for vapor compression. Despite recent efforts, devices that are potentially commercially competitive have not been developed. We present an electrocaloric cooler with a maximum temperature span of 20.9 kelvin and a maximum cooling power of 4.2 watts under the moderate applied electric field of 10 volts per micrometer without any observed breakdown. Moreover, the maximum coefficient of performance, even taking into account energy expended on fluid pumping, reaches 64% of Carnot’s efficiency as long as energy is properly recovered. We believe that this demonstration shows electrocaloric cooling to be a very promising alternative to vapor compression cooling.J.L., A.T., T. G., U.P., V.K., and E.D. acknowledge the Fonds National de la Recherche (FNR) of Luxembourg for supporting this work through the projects BRIDGES2021/MS/16282302/CEC0HA/Defay, THERMODIMAT C20/MS/14718071/Defay and RIDGES2020/MS/15410586/CALPOL/DefayPeer ReviewedPostprint (author's final draft
Elaboration et caractérisation de couches minces piézoélectriques de Pb(Zr, Ti)O3 sur silicium pour applications aux microsystèmes.
No full textCe travail repose sur la réalisation de couches minces de PZT (Pb(Zr, Ti)O3), matériau aux propriétés piézoélectriques remarquables, sur substrat silicium pour des applications microsystèmes. Le PZT est déposé par pulvérisation cathodique sur le substrat Si/SiO2/Ti/Pt puis est cristallisé dans la phase pérovskite piézoélectrique par recuit rapide. Les paramètres de dépôt ont été optimisés par plan d\u27expérience. Les couches présentent une forte constante diélectrique et les propriétés ferroélectriques ont été mises en évidence en fonction des conditions d\u27élaboration. Ces résultats ont permis de proposer une technique de réalisation des films de PZT conformes aux exigences des microtechnologie comme une épaisseur de l\u27ordre du micromètre et des tailles d\u27électrodes importantes. Les points principaux de ce procédé sont la pulvérisation à pression élevée (8 Pa) qui permet d\u27augmenter la tenue mécanique des films, un prérecuit de l\u27électrode inférieure qui favorise l\u27orientation cristallographique du PZT...
Ferroelectric dielectrics integrated on silicon
No full textThis book describes up-to-date technology applied to high-K materials for More Than Moore applications, i.e. microsystems applied to microelectronics core technologies.After detailing the basic thermodynamic theory applied to high-K dielectrics thin films including extrinsic effects, this book emphasizes the specificity of thin films. Deposition and patterning technologies are then presented. A whole chapter is dedicated to the major role played in the field by X-Ray Diffraction characterization, and other characterization techniques are also described such as Radio frequency characteriza
OZONE GAS SENSORS BASED ON OFF-STOICHIOMETRIC COPPER-CHROMIUM-OXIDE THIN FILMS
No full textOzone is a major concern for indoor office pollution. Recurring exposure to low levels of ozone (in ppb range) can be associated with several cardiopulmonary diseases. As such, there is a need for cheap, easy-to-integrate ozone gas sensors that can achieve good performance and work as an alarm for dangerous ozone concentrations. In this work, we propose the use of off-stoichiometric copper-chromium-oxide, that has shown great reversible measurements at low temperature for ozone detection, as low as 50 ppb. The selectivity compared with molecular oxygen is shown. Near-Atmospheric Pressure X-Ray Photoelectron Spectroscopy led to the understanding of the ozone - delafossite surface reaction. This work discloses pioneering results in the fabrication of low cost, high sensitivity ozone sensors based on a p-type material.MASSENA ANTUNES AFONS
Inkjet-printed piezoelectric films for transducers
No full textLead zirconate titanate (PZT) thin films are a popular choice for piezoelectric devices such as microelectromechanical systems, micro-pumps, micro-mirrors or energy harvesters. Various fabrication techniques exist for the deposition of PZT in the form of thin films. Physical vapor deposition (PVD) methods are particularly cost-intensive, as they require vacuum conditions and expensive infrastructure. Fabrication costs can be decreased by the use of chemical solution deposition (CSD), where the metal precursors are dispersed in a solvent medium and coated onto a substrate. Thermal treatments convert the liquid precursor into a functional solid film.
Spin coating is a conventional coating technique allowing for the deposition of homogeneous layers over large-area substrates. However, it is inherently wasteful, as most of the precursor material is spun off the substrate in the coating process. In addition, as spin coating results in complete coverage of the substrate, layer patterning requires lithography, which adds up extra steps and costs to the overall process. Inkjet printing is an additive manufacturing technique that has the potential to address both of these issues, thus further decreasing manufacturing costs and the associated ecological footprint.
The working principle of inkjet printing can be described as the deposition of individual ink droplets at digitally determined locations on the substrate surface, which then merge into a continuous film. Inkjet printing is compatible with CSD processing of PZT thin films, as demonstrated by the previous works in the field. However, the adaptation of standard CSD processing for inkjet printing comes with several challenges, which have to be considered to obtain state-of-the-art functional PZT layers.
In the present work, we explore several issues related to the processing of PZT thin films by inkjet printing and we provide possible solutions to address them, in a way that had not been described yet by the state of the art. In particular, we describe a novel strategy that uses inkjet-printed alkanethiolate-based self-assembled monolayers for direct patterning of PZT thin films on platinized silicon. Then, we present a systematic study of the pyrolysis step of the process, which enabled us to print dense and textured layers with state-of-the-art electrical properties. We also developed a proof-of-concept piezoelectric energy harvesting device based on inkjet-printed PZT films. Finally, we unveil a comparative study where we identified an alternative solvent for CSD processing of PZT thin films.CO-FERMAT (FNR/P12/4853155/Kreisel
PROCESSING OF PIEZOELECTRIC OXIDE FILMS FOR SURFACE HAPTICS
No full textHuman-machine interaction (HMI) relies mainly on vision and hearing, but touch is
essential for perceiving the environment, especially for those who are visually impaired. To incorporate touch into HMI systems, haptic technologies have been developed, with piezoelectric actuators being a promising solution. However, challenges exist in integrating these actuators into touch screens due to their thickness and lack of transparency. Researchers have turned to piezoelectric PZT thin films that provide acceptable haptic performance and optical transparency. Depositing these films onto glass substrates presents challenges, requiring a low-temperature process to enable cost-effective and large-scale production. Transparent electrodes, particularly indium tin oxide, are necessary for creating
transparent actuators, but their production process is complex and costly. Chemical
solution deposition (CSD) based on inkjet printing technology is a low-cost and largescale deposition method, enabling direct film patterning without expensive lithography. In this thesis these challenges were addressed by developing a low-temperature flash-lamp process for PZT film growth, low-temperature combustion processed and inkjet printed ITO electrodes, and an all inkjet printed haptic device. Additionally, we proposed the use of thick piezoelectric films for low-power consumption and large deflection in haptic applications that do not require transparency.R-AGR-3444 - PRIDE17/12246511 PACE_Common (01/03/2019 - 31/08/2025) - DALE Phillip9. Industry, innovation and infrastructur
Locally-confined electrodeposition of Cu(In,Ga)Se2micro islands for micro-concentrator solar cells.
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