Pb-free piezoelectric materials have grown in importance through increased environmental concern related to the presence of Pb and the subsequent legislation that has arisen including directives such as Waste Electrical and Electronic Equipment (WEEE) and the Restriction of Hazardous Substances Directive (RoHS). While much progress has been made on producing Pb-free bulk materials, the need to integrate these next generation Pb-free piezoelectric materials with substrates to form functional micro devices has received less attention and raises a number of challenges. With respect to the high temperature mixed oxide synthesis method, a simple, cost effective and robust low temperature molten hydroxide synthesis (MHS) method derived from the molten salt synthesis (MSS) method, has been developed to produce K0.5Na0.5NbO3 (KNN) small grain powders and is a method that lends itself easily to industrial scale up. A powder/sol gel composite ink film forming technique has been used to produce KNN thick films on silicon substrates. Characterisation of the produced films has shown the films to exhibit piezoelectric coefficients for un-doped material in the region of 30pC/N. The work will report on the Na ion favouring mechanism of the MSS and the related mechanism of the MHS. The work will also report on the dielectric and piezoelectric characteristics of initial KNN thick films produced and an investigation into use of dopants and process modification to improve the KNN thick film’s characteristics.

Neste trabalho pós de CaCu3Ti4O12 foram preparados por reação em estado sólido e por técnicas de solução: complexação de cátions e coprecipitação dos oxalatos. Foram realizados estudos de formação de fase, densificação e propriedades dielétricas das cerâmicas sinterizadas. Para efeito comparativo, ta is propriedades foram determinadas em amostras puras e contendo dissilicato de lítio (LSO) e fluoreto de lítio (LiF) como aditivos de sinterização. O principal objetivo foi verificar o efeito do uso dos diferentes aditivos de sinterização na microestrutura, densificação e propriedades dielétricas do CCTO. Os principais resultados revelaram que pós preparados por técnicas de solução apresentam fase única após calcinação em condições selecionadas. Foi verificado que os aditivos influenciam na densificação, possibilitando obter cerâmicas com 95% da densidade teórica do CCTO a 1025°C. As amostras preparadas por diferentes técnicas apresentam propriedades similares, com exceção das características microestruturais. A permissividade elétrica determinada à temperatura ambiente é da ordem de 104 independentemente do método de síntese. As menores perdas dielétricas foram obtidas para amostras contendo LiF como aditivo de sinterização. / In this work the effects of the method of synthesis and sintering additives on the microstructure and dielectric properties of CCTO were investigated. Powder mixtures were prepared by the cation complexation and coprecipitation methods, and by mixing of the starting oxides, for comparison purposes. Lithium dissilicate (LSO) and lithium fluoride (LiF) were used as sintering aids. The main results revealed that powders prepared by solution techniques have single phase after calcination at selected conditions. The additives were found to influence the densification allowing for obtaining high relative density (≥ 95%) at 1025ºC. Specimens prepared by different methods show similar properties except on microstructure features. The electric permittivity is of the order of 104 for all investigated specimens independent on the method of synthesis. The dielectric loss is found to be lower for specimens prepared with LiF as sintering aid.

abstract: The chemical, structural, and electrical properties of niobium-silicon, niobium-germanium, and YBCO-dielectric interfaces are characterized. Reduction in the concentration of interfacial defects in these structures can improve the performance of (i) many devices including low-loss coplanar, microstrip, and stripline microwave resonators used in next-generation cryogenic communication, sensor, and quantum information technologies and (ii) layers used in device isolation, inter-wiring dielectrics, and passivation in microwave and Josephson junction circuit fabrication. Methods were developed to synthesize amorphous-Ge (a-Ge) and homoepitaxial-Si dielectric thin-films with loss tangents of 1–2×10 -6 and 0.6–2×10 -5 at near single-photon powers and sub-Kelvin temperatures (≈40 mK), making them potentially a better choice over undoped silicon and sapphire substrates used in quantum devices. The Nb/Ge interface has 20 nm of chemical intermixing, which is reduced by a factor of four using 10 nm Ta diffusion layers. Niobium coplanar resonators using this structure exhibit reduced microwave losses. The nature and concentration of defects near Nb-Si interfaces prepared with commonly-used Si surface treatments were characterized. All samples have H, C, O, F, and Cl in the Si within 50 nm of the interface, and electrically active defects with activation energies of 0.147, 0.194, 0.247, 0.339, and 0.556 eV above the valence band maximum (E vbm ), with concentrations dominated by a hole trap at E vbm +0.556 eV (presumably Nb Si ). The optimum surface treatment is an HF etch followed by an in-situ 100 eV Ar ion mill. RCA etches, and higher energy ion milling processes increase the concentration of electrically active defects. A thin SrTiO 3 buffer layer used in YBa 2 Cu 3 O 7-δ superconductor/high-performance Ba(Zn 1/3 Ta 2/3 )O 3 and Ba(Cd 1/3 Ta 2/3 )O 3 microwave dielectric trilayers improves the structural quality of the layers and results in 90 K superconductor critical temperatures. This advance enables the production of more compact high-temperature superconductor capacitors, inductors, and microwave microstrip and stripline devices. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2020

A dielectric filled cavity structure is currently being used to estimate the dielectric constant and loss factor over a wide range of frequencies of a dielectric material which fills the cavity structure [Saed, 1987]. A full field analysis is used to compute the effective complex permittivity of the sample material based on reflection coefficient measurements of the cavity structure and associated geometrical dimensions. The method has previously been used successfully to determine the dielectric constant of materials, but limitations in the Inethod have created difficulties in accurate determination of the dielectric loss factor. The effective loss in this method yields an estimate of the total cavity loss, including both the dielectric loss and that of the cavity conductor walls. In this dissertation a perturbation approach is used to separate the conductor loss from the total loss. The loss-free full-field analysis is used to determine the electric current at the conductor boundaries. This current is used to evaluate the perturbed power dissipated in the cavity walls based on known conductor properties. By subtracting the loss due to the conductor walls from the total loss measured in the structure, the dielectric loss and the resultant dielectric loss factor may be estimated. Measurements are presented for sample dielectric materials. The dielectric loss tangents computed by this new technique improve the unperturbed estimates in the microwave frequency range. / Ph. D.

Given the promise of the Inductive Power Transfer (IPT) technology for eRoad applications, the potential challenges for a successful integration of dynamic IPT technology into the physical road structure are explored extensively in this research work. The Finite Element Method (FEM) is selected for studying the structural performance of an eRoad under operational conditions. In this, an energy-based finite strain constitutive model for asphalt materials is developed and calibrated, to enable the detailed investigation of the structural response and optimization of the considered eRoad. In the context of enabling both dynamic charging and autonomous driving for future electric vehicles, the influences to the pavement (rutting) performance by the changed vehicle behaviour are investigated as well. Moreover, to study the effect on the IPT system by the integration, the potential power loss caused within eRoad pavement materials is further examined by a combined analytic and experimental analysis. The direct research goal of this Thesis is therefore to enhance the possibility of a sustainable implementation of the eRoad solutions into the real society. At the same time, it aims to demonstrate that the road structure itself is an important part of smart infrastructure systems that can either become a bottleneck or a vessel of opportunities, supporting the successful integration of these complex systems. / Givet de förutsättningar som induktiv energiöverföring (IPT Inductive Power Transfer) har för eRoad applikationerna, utforskas möjligheterna för en framgångsrik integration av dynamisk IPT i den fysiska vägkonstruktionen på en djupgående nivå i detta forskningsarbete. Speciellt har finita elementmetoden använts för att studera det strukturella beteendet hos en e-väg under driftsmässiga förhållanden. Inom detta har en energibaserad konstitutiv model för stora töjningar utvecklats och kalibrerats för att möjliggöra detaljerade undersökningar av strukturell respons och optimering av de föreslagna e-vägarna. I samband med att möjliggöra både dynamisk laddning och autonom körning för framtida elektriska fordon, har beläggningars (spårbildnings)egenskaper studerats utifrån de laddande fordonen beteende. Dessutom för att studera effekten av IPT-systemet har den potentiella energiförlusten inom e-vägars beläggningsmaterial undersökts genom en kombinerad analytisk och experimentell undersökning. Som sådant är det direkta forskningsmålet med denna avhandling att utöka möjligheterna för en hållbar implementering av eRoad systemet inom det verkliga samhället. Samtidigt är målet att visa att vägkonstruktionen i sig själv är en viktig del av det smarta infrastruktursystemet som antingen kan bli en flaskhals eller en bärare av möjligheter, stödjande en framgångsrik implementering av dessa komplexa system. / <p>QC 20161108</p>

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / CerÃmica Aurivillius sÃo conhecidas por sua excelente resistÃncia à fadiga e a sua alta temperatura de Curie, a qual apresenta cÃlula unitÃria ortorrÃmbica. A cerÃmica a ser estudada, SrBi2Nb2O9 (SBN), à matÃria-prima potencial na fabricaÃÃo de memÃrias ferroelÃtricas, com polarizaÃÃo espontÃnea e bons coeficientes piezelÃtricos. Dentro deste grupo cerÃmico, o SrBi2Nb2O9 (SBN) à o material com menor estrutura octaÃdrica distorcida. Apesar disto, o SBN sofre de perda dielÃtrica elevada, devido à evaporaÃÃo de Ãxido de bismuto durante a preparaÃÃo, vindo a limitar sua utilizaÃÃo. A ativaÃÃo mecÃnica usada foi a de moinho planetÃrio, que nos permite calcinar o composto por temperaturas mais baixas que as geralmente apresentadas na literatura. ApÃs a calcinaÃÃo, moemos por mais duas horas, e obtemos um pà de boa densidade e reduzida temperatura de sinterizaÃÃo. Este fato previne a perda de elementos volÃteis (Pb ou Bi) e controla o crescimento do grÃo que à produzido quando a alta temperatura à necessÃria para a obtenÃÃo dessa cerÃmica. No presente trabalho, esta cerÃmica Aurivillius serà estudada em suas propriedades estruturais e dielÃtricas com dopagem de Ãxido de lantÃnio, de bismuto e de chumbo, em diversas porcentagens. Adicionalmente, houve a necessidade de um estudo comparativo com respeito a diferentes tipos de ligantes, e os testes obedeceram Ãs dopagens mencionadas acima. Os resultados foram obtidos pelo mÃtodo Hakki & Coleman, pela Espectroscopia de ImpedÃncia e medidas de RadiofreqÃÃncia, para a caracterizaÃÃo elÃtrica. DifraÃÃo de Raios-X, juntamente com o Refinamento Rietveld, Espectroscopia Raman e de Infravermelho, para anÃlise estrutural, dentre outras medidas e mÃtodos. / Aurivillius ceramic are know by is excellent resistence to high use and itÂs high Curie temperature, in wich it presents unicell ortorrÃmbic. The ceramic to be study SrBi2Nb2O9 (SBN), is a potential prime-mater in the production of ironelectric memories with sponteneous polarization and good piezelectric coeficient. Within this ceramic group, SrBi2Nb2O9 (SBN) is the material with less twisted octaÃdric structure. Even so, SBN, have high loss of dielectric, due to the evaporation of bismut oxide during preparation, inposing a limit to is use. The mechanical activation used was of a planetarium will, that allows us to calcinate the compost by very low temperatures that are presented in literature. After the calcination, we will it for two more hours and have dust that have good density and low sinterization temperature. That fact privine us the lost of volatile elements ( Pb or Bi ) and controls the grow of the seed wich is produced when high Temperature is needed to obtain this ceramic . In the present work, this Aurivillius ceramic wil be studyed in is dielectric and structure properties with dopage of lantÃnium oxide, lead oxide and bismut oxide, on different percentages. In addiction there was necessety of a comparative study, regarding the different types of leagues and tests obay the dopage already menttionated. The results were obtained by the Hakki & Coleman method by the Impendence Espectroscopic and radiofrequense mesures, to the electric caracterization . X-rays Defraction with Rictveld refiament , Raman and infrared espectroscopic, to structural analises , within other mesures and methods .

Les nanocomposites polymères diélectriques ayant une constante diélectrique élevée et une faible perte diélectrique ont reçu un grand intérêt pour une utilisation dans le domaine du condensateur électrostatique. De manière générale, les performances diélectriques améliorées des nanocomposites sont déterminées par le type et la nature des polymères et des nanocharges sélectionnés, ainsi que par l'effet de couplage interfacial entre les matrices et les nanocharges. Parmi ces facteurs, les propriétés physiques, les géométries et les structures des composants des nanocharges jouent un rôle essentiel dans la détermination des performances diélectriques des nanocomposites. Selon les conductivités des nanocharges, les nanocomposites polymères diélectriques peuvent être classés en deux types: les nanocomposites polymères diélectriques conducteurs (CDPN) et les nanocomposites polymères diélectriques-diélectriques (DDPN). Cependant, la perte diélectrique élevée accompagnée au voisinage du seuil de percolation pour les CDPN et la charge élevée de nanocharges en céramique entravent le développement de nanocomposites polymères diélectriques à haute performance.Tout d'abord, des nanocomposites ternaires BNNS/CNT/PVDF ont été fabriqués. L'incorporation de BNNS dans les nanocomposites binaires CNT/PVDF a amélioré la dispersion des NTC et optimisé le réseau conducteur. La connexion directe entre les CNT pourrait être entravée en augmentant le contenu de BNNS.Deuxièmement, des hybrides CNT@AC à structure cœur-coquille ont été préparés par méthode CVD. La couche de carbone amorphe entrave non seulement le contact direct des NTC, mais améliore également la dispersibilité des NTC dans la matrice de PVDF. Le seuil de percolation augmente avec la prolongation du temps de dépôt du carbone. Plus important encore, la perte diélectrique a subi une forte diminution après le processus de revêtement. Troisièmement, les hybrides BNNSs@C avec des teneurs en carbone différentes ont été synthétisés par la méthode CVD. La fraction de carbone dans les hybrides BNNSs@C pourrait être ajustée avec précision en contrôlant le temps de dépôt de carbone. Les propriétés diélectriques des nanocomposites BNNSs@C/PVDF pourraient être ajustées avec précision en ajustant la teneur en carbone. Les polarisations interfaciales améliorées des interfaces BNNS/C et C/PVDF ont doté les nanocomposites de performances diélectriques améliorées.Quatrièmement, les hybrides TiO2@C NW structurés en noyau et en coquille ont été synthétisés par une combinaison d'une réaction hydrothermale et du procédé CVD. L'épaisseur de la couche de carbone dans les hybrides TiO2@C NW obtenus pourrait être précisément ajustée en contrôlant le temps de dépôt du carbone. De plus, les propriétés diélectriques des nanocomposites TiO2@C NWs/PVDF pourraient être ajustées avec précision en ajustant l'épaisseur de la coque en carbone. Les polarisations interfaciales améliorées des interfaces TiO2/C et C/PVDF ont doté les nanocomposites d'excellentes performances diélectriques.Enfin, des nanofils structurés de TiO2@C@SiO2 structurés à double coques ont été synthétisés par une combinaison de réactions hydrothermales modifiées, de CVD et de réactions sol-gel. L'introduction de carbone comme enveloppe interne entre le noyau de TiO2 et l'enveloppe externe de SiO2 a induit deux types supplémentaires de polarisation interfaciale. Les nanocomposites de PVDF obtenus avec TiO2@C@SiO2 NWs présentaient simultanément une constante diélectrique améliorée et des caractéristiques de perte diélectrique supprimées. La constante diélectrique et la perte de nanocomposites ont augmenté avec l'augmentation de l'épaisseur de la couche interne de carbone et ont diminué avec l'augmentation de l'épaisseur de la couche externe de SiO2. La relation entre la perte diélectrique et l'épaisseur de l'enveloppe extérieure en SiO2 a été démontrée par les résultats de la simulation finie. / Dielectric polymer nanocomposites with a high dielectric constant and low dielectric loss have received broad interest for use in the field of the electrostatic capacitor and they are usually composed of dielectric polymers as matrix and inorganic or organic nanofillers as the reinforcement. Generally, the improved dielectric performance of nanocomposites is decided by the type and nature of selected polymers and nanofillers as well as interfacial coupling effect between matrices and nanofillers. Among these factors, the physical properties, geometries, component structures of nanofillers play a critical role in deciding the dielectric performance of nanocomposites. According to the conductivities of nanofillers, the dielectric polymer nanocomposites can be classified into two types: conductive-dielectric polymer nanocomposites (CDPNs) and dielectric-dielectric polymer nanocomposites (DDPNs). However, the accompanied high dielectric loss in the vicinity of the percolation threshold for CDPNs and high loading of ceramic nanofillers hinders the development of high performance dielectric polymer nanocomposites.Firstly, ternary BNNSs/CNTs/PVDF nanocomposites were fabricated. The incorporation of BNNSs into the binary CNTs/PVDF nanocomposites improved the dispersion of CNTs and optimized the conductive network, which contributed to the enhanced dielectric constant. The direct connection between CNTs could be hindered by increasing the content of BNNS.Secondly, core-shell structured CNTs@AC hybrids were prepared by CVD method. The amorphous carbon layer not only hindered the direct contact of CNTs but also improved the dispersibility of CNTs in the PVDF matrix. The percolation threshold increased with the prolongation of carbon deposition time. More importantly, the dielectric loss underwent a sharp decrease after the coating process, which was attributed to the decrease in leakage current. The results suggested that the influence of AC interlayer on the final dielectric performance after percolation was much more obvious than that before percolation.Thirdly, BNNSs@C hybrids with different carbon contents were synthesized by the CVD method. The carbon fraction in the BNNSs@C hybrids could be accurately adjusted through controlling the carbon deposition time. The dielectric properties of BNNSs@C/PVDF nanocomposites could be accurately tuned by adjusting the carbon content. The improved interfacial polarizations of BNNSs/C and C/PVDF interfaces endowed the nanocomposites with enhanced dielectric performance.Fourthly, core-shell structured TiO2@C NW hybrids were synthesized by a combination of a hydrothermal reaction and the CVD method. The carbon shell thickness in the obtained TiO2@C NW hybrids could be precisely tuned by controlling the carbon deposition time. The TiO2@C NWs/PVDF nanocomposites exhibited a percolative dielectric behavior. Moreover, the dielectric properties of the TiO2@C NWs/PVDF nanocomposites could be accurately adjusted by tuning the carbon shell thickness. The enhanced interfacial polarizations of the TiO2/C and C/PVDF interfaces endowed the nanocomposites with excellent dielectric performance.Lastly, core@double-shells structured TiO2@C@SiO2 nanowires were synthesized by a combination of modified hydrothermal reaction, CVD, and sol-gel reaction. The introducing of carbon as an inner shell between the TiO2 core and SiO2 outer shell induced two additional types of interfacial polarization. The obtained PVDF nanocomposites with TiO2@C@SiO2 NWs exhibited simultaneously enhanced dielectric constant and suppressed dielectric loss characteristics. The dielectric constant and loss of nanocomposites increased with the increase of carbon inner shell thickness and decreased with the increasing of SiO2 outer shell thickness. The relationship between the dielectric loss and SiO2 outer shell thickness was further demonstrated by the finite simulation results.

No description available.

Um der Mikrowellenerwärmung als Single- oder Hybridanwendung im industriellen Ofenbau ein weiteres Anwendungsspektrum zu eröffnen, wird dem Anlagenkonstrukteur im Rahmen dieser Arbeit eine Aufstellung von Entwicklungsprioritäten und Konstruktionshinweisen übergeben. Für eine energieeffiziente Ausnutzung des technologischen Potenzials wird hierbei nicht - wie in der Vergangenheit - die Feldstärkenverteilung, sondern das Reflexionsverhalten in den Vordergrund gestellt. Durch die Entwicklung und den Aufbau eines Messplatzes zur Bestimmung temperaturspezifischer Dielektrizitätsparameter konnte die Realitätsnähe der Simulation für die anwendungsorientierte Applikatorentwicklung gesteigert werden. Die Anwendbarkeit der Auslegungskriterien wird im Rahmen der Projektierung und des Aufbaus einer Beispielanlage zur Entbinderung von keramischen Grünkörpern und bei der Entwicklung zahlreicher mikrowellenspezifischer Anlagenbauteile verifiziert.

This master´s thesis deals about insulation and dielectric properties of water. It describes the structure of water, covalent and hydrogen bonds. It outlines primary chemical and physical properties of water and then it describes parameters of water - dynamic viscosity, conductivity, surface tension, pH and also describes dielectric properties - dielectric loss, loss factor, permittivity, polarization. Part of the work is practical section, which includes measurements of deionized water, destilled water, tap water and shows primary dependence such as dependence loss factor on frequency or relative permittivity on frequency.