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Littérature scientifique sur le sujet « High permittivity ceramics »

Auteur : Grafiati

Publié le 9 mars 2023

Mis à jour le 10 mars 2023

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Articles de revues sur le sujet "High permittivity ceramics"

Hennings, D. F. K., B. Schreinemacher et H. Schreinemacher. « High-permittivity dielectric ceramics with high endurance ». Journal of the European Ceramic Society 13, n^o 1 (janvier 1994) : 81–88. http://dx.doi.org/10.1016/0955-2219(94)90062-0.

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Xiong, Zhao Xian, M. Y. Zhou, Hao Xue, Hong Qiu et F. Xiao. « Characterization of Microwave Ceramics with Low Permittivity and High Quality Factors ». Key Engineering Materials 434-435 (mars 2010) : 244–46. http://dx.doi.org/10.4028/www.scientific.net/kem.434-435.244.

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A new type of porous ceramics, Mg2SiO4, for microwave application with low permittivity and high quality factors were prepared via gel-casting processing in this paper. Microstructure of the ceramics was observed and crystal structure of the samples was also identified. Moreover, emphasis was paid on the characterization of the microwave ceramics. Dielectric properties of the ceramics were measured by an automatic system of microwave measurement, resulting in dielectric constant of 3.51 and quality factor of 11,774 for the ceramic sample at frequency about 10GHz. Mechanical performance of the samples were also evaluated with maximal bending strength of 140MPa.

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KOLAR, D., et D. SUVOROV. « ChemInform Abstract : High Permittivity Microwave Ceramics ». ChemInform 27, n^o 10 (12 août 2010) : no. http://dx.doi.org/10.1002/chin.199610337.

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Szwagierczak, Dorota, Beata Synkiewicz-Musialska, Jan Kulawik et Norbert Pałka. « Sintering, Microstructure, and Dielectric Properties of Copper Borates for High Frequency LTCC Applications ». Materials 14, n^o 14 (18 juillet 2021) : 4017. http://dx.doi.org/10.3390/ma14144017.

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New ceramic materials based on two copper borates, CuB2O4 and Cu3B2O6, were prepared via solid state synthesis and sintering, and characterized as promising candidates for low dielectric permittivity substrates for very high frequency circuits. The sintering behavior, composition, microstructure, and dielectric properties of the ceramics were investigated using a heating microscope, X-ray diffractometry, scanning electron microscopy, energy dispersive spectroscopy, and terahertz time domain spectroscopy. The studies revealed a low dielectric permittivity of 5.1–6.7 and low dielectric loss in the frequency range 0.14–0.7 THz. The copper borate-based materials, owing to a low sintering temperature of 900–960 °C, are suitable for LTCC (low temperature cofired ceramics) applications.

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Xiong, Zhao Xian, X. Xue, Hong Qiu, C. Zhang, C. Fang, J. Luo, D. Y. Bao et al. « Microwave Dielectric Ceramics and Devices for Wireless Technologies ». Key Engineering Materials 368-372 (février 2008) : 154–58. http://dx.doi.org/10.4028/www.scientific.net/kem.368-372.154.

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In this paper, several kinds of synthesis techniques were adopted; not only conventional solidstate reaction method but also solution synthesis techniques, including co-precipitation and hydrothermal synthesis, in addition to the gel-casting for complex shape of ceramic components and tape-casting of large scale thin plate for microwave IC. Different kinds of microwave ceramics were prepared, such as materials with low permittivity and high quality factor, moderate permittivity and good quality factor, and, high permittivity and reasonable quality factor, in addition to near zero of temperature coefficient of resonance frequency. Series of microwave devices were developed, for examples, dielectric resonators, dielectric filters, GPS antennas, communication connectors, and thin substrates for microwave IC.

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Lu, Huafei, Yuanhua Lin, Jiancong Yuan, Cewen Nan et Kexin Chen. « Dielectric and varistor properties of rare-earth-doped ZnO and CaCu3Ti4O12 composite ceramics ». Journal of Advanced Dielectrics 03, n^o 01 (janvier 2013) : 1350001. http://dx.doi.org/10.1142/s2010135x1350001x.

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To investigate the multi-functional ceramics with both high permittivity and large nonlinear coefficient, we have prepared rare-earth Tb -and- Co doped ZnO and TiO 2-rich CaCu3Ti4O12 (TCCTO) powders by chemical co-precipitation and sol–gel methods respectively, and then obtained the TCCTO/ ZnO composite ceramics, sintered at 1100°C for 3 h in air. Analyzing the composite ceramics of the microstructure and phase composition indicated that the composite ceramics were composed of the main phases of ZnO and CaCu3Ti4O12 (CCTO). Our results revealed that the TCCTO/ ZnO composite ceramics showed both high dielectric and good nonlinear electrical behaviors. The composite ceramic of TCCTO: ZnO = 0.3 exhibited a high dielectric constant of ~210(1 kHz) with a nonlinear coefficient of ~11. The dielectric behavior of TCCTO/ ZnO composite could be explained by the mixture rule. With the high dielectric permittivity and tunable varistor behaviors, the composite ceramics has a potential application for the higher voltage transportation devices.

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Chen, K., S. K. Yuan, P. L. Li, F. Gao, J. Liu, G. L. Li, A. G. Zhao, X. M. Lu, J. M. Liu et J. S. Zhu. « High permittivity in Zr doped NiO ceramics ». Journal of Applied Physics 102, n^o 3 (août 2007) : 034103. http://dx.doi.org/10.1063/1.2764217.

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Shi, Yongjie, Wentao Hao, Hui Wu, Li Sun, Ensi Cao, Yongjia Zhang et Hua Peng. « High dielectric-permittivity properties of NaCu3Ti3Sb0.5Nb0.5O12 ceramics ». Ceramics International 42, n^o 1 (janvier 2016) : 116–21. http://dx.doi.org/10.1016/j.ceramint.2015.08.009.

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Peng, Zhen, Hong Wang et Xi Yao. « Dielectric resonator antennas using high permittivity ceramics ». Ceramics International 30, n^o 7 (janvier 2004) : 1211–14. http://dx.doi.org/10.1016/j.ceramint.2003.12.079.

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Qin, Qun, Tian Guo Wang et Wen Jun Zhang. « Effect of Er₂O₃ on the Microstructure and Electrical Properties of WO₃ Capacitor-Varistor Ceramics ». Advanced Materials Research 233-235 (mai 2011) : 2503–6. http://dx.doi.org/10.4028/www.scientific.net/amr.233-235.2503.

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WO3-based capacitor-varistor ceramics doped with Er2O3 were prepared and the microstructures and nonlinear electrical properties were investigated. The results show that there exist second phase Er10W2O21 on the surface of WO3 grains. Doping Er2O3 in WO3 ceramic can inhibit the grain growth. A small quantity of Er2O3 can significantly improve nonlinear properties of the samples. The permittivity of doped samples was higher than that of the undoped, and the high permittivity makes Er2O3-doped WO3 ceramics be applicable as a kind of capacitor-varistor materials.

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Thèses sur le sujet "High permittivity ceramics"

Nicholls, Simon J. « High permittivity ceramics for dielectrically loaded applications ». Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/16354/.

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A temperature-stable, ultra-high permittivity dielectric ceramic, based on CTLNT, has been successfully fabricated at significantly reduced sintering temperatures with no deterioration of microwave properties, through the addition of a Bi_4B_2O_9 (BBO) sintering aid. This work has been an extension of previous findings where it was shown that 0.2CaTiO_3-0.8(Li_0.5Nd_0.5)TiO_3 (CTLNT) with 4wt% BBO as a liquid-phase sintering aid gives rise to exceptional microwave (MW) dielectric properties, (relative permittivity, ε_r = 127, quality factor, Qf_0 = 2700 GHz, and temperature coefficient of the resonant frequency, τ_f = +4 ppm/°C) at reduced sintering temperatures (1200°C). Prior to this, it has been exceptionally difficult to produce a large ε_r dielectric material, with both a low sintering temperature and near-zero temperature stability, without dramatic deterioration of the dielectric properties of the material. This contribution set out to investigate and understand the sintering mechanism between the CTLNT + xwt% BBO system, to aid in the development of designer sintering aids in the development of other microwave dielectric ceramic materials and devices. CTLNT + 1, 3, 4 and 5wt% BBO compositions were fabricated and a variety of analysis techniques were used, such as density, XRD, SEM, TEM, EDS and MW characterisation. Density increased with increasing BBO concentration and sintering temperature, and the MW results reflected the changes in density. The 1wt% BBO composition showed the greatest variation between the sintering temperatures, and 4wt% composition demonstrated optimum MW results of: ε_r=125, Qf_0=2518 GHz and τ_f=4 ppm/°C, at a sintering temperature of 1200°C. The variation of τ_f with changes in BBO concentration was non-linear, which suggested a chemical reaction was taking place. XRD results revealed no secondary phases, regardless of BBO concentration. SEM results showed increased crystal grain size as BBO concentration and sintering temperatures increased, as well as increased contrast variation on the polished surface and darker-contrast amorphous phase in the fracture surface. The contrast variation in the polished surfaces were also indicative of a chemical reaction. Using a combination of XRD, TEM and SEM it was demonstrated that highly polarisable Bi3+ ions entered the CTLNT perovskite lattice and locally increasing ε_r. The accompanying ex-solution of TiO2 precipitates, observed and analysed under SEM and TEM, as the BBO concentration increased implied the formation of Ti vacancies (V_Ti^'''') in the perovskite matrix to compensate for the extra positive charge of the Bi3+. The ex-solution of Ti indicates Bi3+ ions substitute onto the A-site of the perovskite crystal system for lower valence ionic elements, after the following generic defect equation: 4(A)_A^x+(Ti)_Ti^x⇒4(Bi)_A^∙+V_Ti^'''' The residual phase was found to be a boron-rich liquid-phase, which acted as the sintering aid, with a large negative τ_f which compensates for the positive τ_f of the CTLNT. The CTLST + xwt% BBO system (S = Sm) was then investigated to determine if a similar mechanism would occur. CTLST + 1, 2, 3 and 4wt% BBO compositions were fabricated and underwent the same analysis techniques. Density increased with increasing BBO concentration up to 1250°C, after which density fell for all samples; the 4wt% BBO composition exhibited the largest density, at 1250°C. The MW results reflected this trend, which saw a general increase in ε_r as BBO concentration and sintering temperature increased, which fell universally at 1300°C. 〖Qf〗_0 would generally increase with increased BBO concentration, across all sintering temperatures, while a dip was observed at 1250°C, and the 4wt% BBO composition demonstrated optimum properties of: ε_r = 105.7, Qf_0 = 3295 GHz and τ_f = -4 ppm/°C, sintered at 1200°C. Contrary to the CTLNT system, the variation of τ_f with BBO content and sintering temperature was linear. SEM reflected density changes, where crystal grain increased with increasing BBO concentration, up to 1250°C. At 1300°C, samples suffered from dissolution into the liquid-phase, increasing pore sizes, decreasing density and, thus, impacting on the MW properties of the samples. Similar to the CTLNT system, contrast variation was observed, in addition to darker B-rich liquid phase in the fracture surface. EDS from both SEM and TEM revealed that Bi was present within the CTLST matrix, however no TiO2 precipitates were observed. Large Zr contamination within CTLST is the likely cause of the difference in defect chemistry, as excess of Zr substitution onto the perovskite B-site compensates for Bi substitution onto the A-site, negating the need for TiO_2 precipitates to ex-solve. Multi-layer ceramic capacitors (MLCCs) of the CTLNT + 4wt% BBO composition were fabricated to determine whether the temperature stabilities of the material in conjunction with a large ε_r would allow the material to be a suitable candidate as a Class 1 C0G/NP0 MLCC device. Fabrication of the devices followed the conventional method, but required modification due to delamination. These modifications included: longer firing times to allow for binders and plasticisers to burn-out fully; calcined alumina powder base to fire and sinter samples upon, to avoid sticking issues; and solvent wetting of individual layers to adequately fuse layers together pre-firing and sintering. Successful MLCC devices had case sizes of EIA ‘2928’ and IEC ‘7472’. SEM and EDS revealed no mixing or exchange of materials between the dielectric and the platinum internal electrode, and generally good adhesion between both materials. Electrical tests revealed that, despite the temperature stability observed at 1-3 GHz in the MW study, that the MLCC devices would be classed as EIA “M8J” and IEC “P1000”, however maximum available test frequency of 1 MHZ is much lower than the average operating frequencies of class 1 devices, which lie between 100 MHz – 30 GHz.

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Baeraky, Thoria A. « High temperature measurements of the microwave dielectric properties of ceramics ». Thesis, University of Nottingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323185.

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PIZZICHEMI, MARCO. « Interaction of pulsed electric fields with cell membrane ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2009. http://hdl.handle.net/10281/7790.

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Pulsed Electric Fields (PEF) allow non-thermal pasteurization and sterilization of liquids, involving the application of high intensity electric field pulses (20-80 kV/cm) of short duration (1-10 microseconds). The electric field interacts with microorganisms at the level of plasma membrane, through the mechanism of electroporation, but, although many theories have been proposed to describe this phenomenon, a satisfactory explanation has not been found yet. An extensive description of the state of the art of the knowledge on this field is given, along with the current research needs and the main obstacles to a wide diffusion of PEF applications. The time course of cell transmembrane voltage is studied, developing an analytical expression for planar, spherical, cylindrical and prolate spheroidal membranes, with the aim to evaluate the charging time constants and the steady state intensity upon variation of treatment conditions. The results of this approach are used to investigate the impact of the electric field in rod-like bacteria. The electric field distribution in test chamber is studied by means of computer simulations for various electrode geometries, optimizing the shape for intensity and uniformity of electric field. The impact on PEF treatment of a normal distribution of cell dimensions in a microbial population and the rotational movement of bacteria inside treatment chambers are also investigated. Computer simulations are used to obtain a possible explanation to the deviations from first order inactivation kinetics, and to the intrinsic variability of microbial laboratory results. PEF inactivation experiments of Escherichia Coli are carried out in a test system under different conditions of treatment duration and microbial concentration. Inactivation kinetics is compared to theories of electroporation and computer simulations previously carried out. Experimental evidence of a variation in the effectiveness of PEF as a function of bacterial concentration is discovered and a possible explanation proposed. The application of high permittivity ceramics materials to PEF is also studied, with the aim of increasing the volumes of treatment chambers, improving the duration of electrodes, and allowing the use of the most energy efficient square wave pulses to large volumes of liquid. These materials can also be used to test the possibility of a relation between energy deposited in treatment chambers and microbial inactivation, in order to acquire more insight on the interaction between Pulsed Electric Fields and cell membranes. A novel chamber is prepared with the use of a high permittivity non-toxic material (Sodium Potassium Niobate) and it is ready to be tested in PEF applications.

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Garreau, Jonathan. « Étude de filtres hyperfréquence SIW et hybride-planaire SIW en technologie LTCC ». Phd thesis, Université de Bretagne occidentale - Brest, 2012. http://tel.archives-ouvertes.fr/tel-00858068.

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La maîtrise de la communication et de l'information est un atout primordial dans les stratégies de pouvoir, qu'elles soient militaires, politiques ou commerciales. Celui qui est capable de transmettre l'information plus vite prend l'avantage sur les autres. Tel est le moteur de la croissance et du progrès dans le domaine des télécommunications. L'omniprésence grandissante des dispositifs communicants témoigne de l'expansion exponentielle qu'a connu ce domaine depuis les premières communications sans fil. À l'époque du all-in-one, la multiplication des applications au sein d'un même appareil nécessite l'utilisation de composants toujours plus performants et petits . Au cœur de ces systèmes, les filtres ont une importance grandissante. Dans un environnement spatial, les contraintes de fiabilité et d'encombrement sont particulièrement drastiques. Le choix des matériaux est par ailleurs limité, ce qui réduit les possibilités d'innovation. Cependant, l'amélioration de la précision et de la fiabilité dans les technologies de fabrication ouvre de nouvelles perspectives d'innovation et d'amélioration des composants. Ces travaux ont ainsi été motivés par ce souci d'apporter toujours plus de performance et de fiabilité, pour un encombrement moindre en tirant profit du potentiel offert par l'association du concept SIW et de la technologie LTCC. Les résultats mettent à jour de sérieuses dispersions technologiques. Cependant, le potentiel de l'association SIW/LTCC est démontré, et les difficultés rencontrées sont surmontables. Les filtres SIW en technologie LTCC présentent donc des atouts pour s'imposer comme une alternative sérieuse aux solutions existantes.

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Di, Geronimo Camacho Elizabeth Carolina. « Synthesis, high-pressure study and dielectric characterization of two lead-free perovskite materials : SrTi1-xZrxO3 and KNb1-xTaxO3 ». Thesis, Montpellier, 2016. http://www.theses.fr/2016MONTT208/document.

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Les matériaux de structure pérovskite de formule générale ABO3 sont les ferroélectriques les plus étudiés pour leurs propriétés intéressantes dans de nombreuses applications technologiques. Cependant leurs propriétés sont directement reliées à la structure et sont fortement conditionnées par les transitions de phases qui dépendent de la température, de la composition chimique et de la pression. Dans le manuscrit de thèse, le comportement sous haute pression de deux matériaux pérovskite SrTi1-xZrxO3 (STZ) et KNb1-XTaXO3 (KNT) est étudié et différentes techniques de frittage pour améliorer la densité des céramiques et optimiser les propriétés ferroélectriques des céramiques K(Nb0.40Ta0.60)O3 et (KxNa1-x)Nb0.6Ta0.4O3 sont examinées.Des analyses sous hautes pressions par spectroscopie Raman et diffraction des rayons X des poudres de SrTi1-xZrxO3 (x= 0.3, 0.4, 0.5, 0.6, 0.7) et KNb1-XTaXO3 (x=0.4, 0.5, 0.6, 0.9) en enclume diamant ont été réalisées. Les spectres Raman montrent une augmentation des modes Raman avec la pression pour les poudres de STZ indiquant que la pression induit des transitions de phases vers des symétries plus basses de la maille dans ces composés.De plus, les expériences de spectroscopie Raman ont fait apparaître une décroissance des modes Raman lorsque la pression est augmentée, montrant bien que la pression induit des transitions de phases vers des structure plus symétriques. L'évolution du mode Raman principal pour les phases orthorhombique et quadratique a été suivi jusqu'à ce que la phase cubique apparaîsse, ce qui nous a permis de proposer un diagramme de phase pression-composition pour les composés KNT.Trois différentes techniques de frittage, utilisation d'additifs, frittage en deux paliers et SPS ont été étudiées pour les céramiques de K(Nb0.4Ta0.6)O3 et (KxNa1-x)Nb0.6Ta0.4O3 . La constante diélectrique et les pertes en fonction de la température des céramiques ont été améliorées par l'utilisation du KF comme additif de frittage et par le frittage en deux paliers. Les échantillons densifiés par SPS présentent une microstructure fine et possèdent les plus fortes densités. Ils ont les meilleurs propriétés ferroélectriques. Aucun changement significatif de la température de Curie ne semble être induit par le taux de Na, et on observe cependant une augmentation de la constante diélectrique et des propriétés ferroélectriques suivant le taux de Na
Perovskite materials whose general chemical formula is ABO3 are one of the most study ferroelectrics due to the interesting properties that they have for technological applications. However, their properties are directly related to structural phase transitions that could depend of temperature, composition and pressure. In the studies presented here, we first examined the high-pressure behavior of two perovskite materials SrTi1-xZrxO3 (STZ) and KNb1-XTaXO3 (KNT), and we later continued to investigate different sintering techniques in order to improve the densification, dielectric and ferroelectric properties of K(Nb0.40Ta0.60)O3 and (KxNa1-x)Nb0.6Ta0.4O3 ceramics.High-pressure Raman scattering and X-ray diffraction investigations of SrTi1-xZrxO3 (x= 0.3, 0.4, 0.5, 0.6, 0.7) and KNb1-XTaXO3 (x=0.4, 0.5, 0.6, 0.9) powders were conducted in diamond anvil cells. Raman scattering experiments showed and increased of Raman modes with pressure for the STZ samples, which indicates that pressure induced phase transitions towards lower symmetry for these compounds.Moreover, high pressure Raman spectroscopy experiments showed a decrease of the Raman modes as the pressure was increased for the KNT samples, showing that pressure induced phase transitions towards higher symmetries. The evolution of the main Raman modes for the orthorhombic and tetragonal phases were followed until the cubic phase was reach, and allowed us to propose a pressure-composition phase diagram for the KNT compounds.Three different sintering techniques, sintered aids, two step sintering and spark plasma sintering, were used on K(Nb0.4Ta0.6)O3 and (KxNa1-x)Nb0.6Ta0.4O3 ceramics. The use of KF as sintered aid and the two step sintering method showed an improvement of the dielectric constant and dielectric losses of these samples. SPS samples presented a fine microstructure with the highest density and the best ferroelectric behavior. We did not detect any changes on the Curie temperature due the amount of Na but and increase of the dielectric constant and the ferroelectric properties was observed due to the amount of Na

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Carneiro, Filho Ranilson. « Desenvolvimento de substrato cer?mico BiNbO4 para antenas de microfita de sistemas de comunica??es sem fio ». Universidade Federal do Rio Grande do Norte, 2010. http://repositorio.ufrn.br:8080/jspui/handle/123456789/15147.

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Made available in DSpace on 2014-12-17T14:54:55Z (GMT). No. of bitstreams: 1 RanilsonCF_TESE.pdf: 2036029 bytes, checksum: f7ba8fa789f5420decc75fb98f14f807 (MD5) Previous issue date: 2010-07-27
The main purpose of this work was the development of ceramic dielectric substrates of bismuth niobate (BiNbO4) doped with vanadium pentoxide (V2O5), with high permittivity, used in the construction of microstrip patch antennas with applications in wireless communications systems. The high electrical permittivity of the ceramic substrate provided a reduction of the antenna dimensions. The numerical results obtained in the simulations and the measurements performed with the microstrip patch antennas showed good agreement. These antennas can be used in wireless communication systems in various frequency bands. Results were satisfactory for antennas operating at frequencies in the S band, in the range between 2.5 GHz and 3.0 GHz.
O objetivo principal deste trabalho foi o desenvolvimento de substratos diel?tricos cer?micos de niobato de bismuto (BiNbO4) dopados com pent?xido de van?dio (V2O5), com alta permissividade el?trica, usados na constru??o de antenas patch de microfita com aplica??es em sistemas de comunica??es sem fio. A alta permissividade el?trica do substrato cer?mico proporcionou uma redu??o no tamanho das antenas. Os resultados num?ricos obtidos nas simula??es e medi??es realizadas com as antenas patch de microfita mostraram boa concord?ncia. Essas antenas podem ser usadas em sistemas de comunica??es sem fio em v?rias faixas de freq??ncias. Foram obtidos resultados satisfat?rios em antenas com freq??ncias de opera??o na banda S, na faixa compreendida entre 2,5 GHz e 3,0 GHz.

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Chapitres de livres sur le sujet "High permittivity ceramics"

Xiao, F., R. Chen, Z. Y. Huang et Zhao Xian Xiong. « Two Methods for the Measurement of Complex Permittivity of Microwave Dielectric Ceramics ». Dans High-Performance Ceramics III, 61–64. Stafa : Trans Tech Publications Ltd., 2007. http://dx.doi.org/10.4028/0-87849-959-8.61.

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Zhao, Dong Lin, Hong Feng Yin, Yong Dong Xu, Fa Luo et Wan Cheng Zhou. « Complex Permittivity of 3D Textile SiC/C/SiC Composites Fabricated by Chemical Vapor Infiltration at X-Band Frequency ». Dans High-Performance Ceramics V, 1028–30. Stafa : Trans Tech Publications Ltd., 2008. http://dx.doi.org/10.4028/0-87849-473-1.1028.

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Tkach, Alexander, et Paula M. Vilarinho. « Nonstoichiometry Role on the Properties of Quantum-Paraelectric Ceramics ». Dans Structure Processing Properties Relationships in Stoichiometric and Nonstoichiometric Oxides. IntechOpen, 2020. http://dx.doi.org/10.5772/intechopen.89499.

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Among the lead-free perovskite-structure materials, strontium titanate (SrTiO3—ST) and potassium tantalate (KTaO3—KT), pure or modified, are of particular importance. They are both quantum paraelectrics with high dielectric permittivity and low losses that can find application in tunable microwave devices due to a dependence of the permittivity on the electric field. Factors as Sr/Ti and K/Ta ratio in ST and KT ceramics, respectively, can alter the defect chemistry of these materials and affect the microstructure. Therefore, if properly understood, cation stoichiometry variation may be intentionally used to tailor the electrical response of electroceramics. The scientific and technological importance of the stoichiometry variation in ST and KT ceramics is reviewed and compared in this chapter. The differences in crystallographic phase assemblage, grain size, and dielectric properties are described in detail. Although sharing crystal chemical similarities, the effect of the stoichiometry is markedly different. Even if the variation of Sr/Ti and K/Ta ratios did not change the quantum-paraelectric nature of ST and KT, Sr excess impedes the grain growth and decreases the dielectric permittivity in ST ceramics, while K excess promotes the grain growth and increases the dielectric permittivity in KT ceramics.

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Bai, Yang. « The Ferroelectric-Ferromagnetic Composite Ceramics with High Permittivity and High Permeability in Hyper-Frequency ». Dans Ferroelectrics. InTech, 2010. http://dx.doi.org/10.5772/13393.

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Newnham, Robert E. « Dielectric constant ». Dans Properties of Materials. Oxford University Press, 2004. http://dx.doi.org/10.1093/oso/9780198520757.003.0011.

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The dielectric constant K is a measure of a material’s ability to store electric charge. In scalar form the defining relations are as follows: . . . D = εE, . . . where D is the electric displacement measured in C/m2, ε is the electric permittivity in F/m, and E is electric field in V/m. The dielectric constant K is the relative permittivity: . . . K = ε/ε0, . . . where ε0 = 8.85 × 10−12 F/m is the permittivity of free space. The electric displacement D is equal to the sum of the charges stored on the electrode plus those originating from the polarization, P [C/m2] . . . D = ε0 E + P. . . . In this chapter we discuss the tensor nature of the dielectric constant, how it is represented geometrically, and some typical structure–property relationships. Dielectric constants range over about four orders of magnitude in insulator materials. Because of their low density, gases have dielectric constants only slightly larger than one. At one atmosphere, the dielectric constant of air is 1.0006. Most common ceramics and polymers have dielectric constants in the range between 2 and 10. Polyethylene is 2.3 and silica glass is 3.8. These are low-density dielectrics with substantially covalent bonding. More ionic materials like NaCl and Al2O3 have slightly higher K values in the 6–10 range. High K materials like water (K ∽ 80) and BaTiO3 (K∽1000) have special polarization mechanisms involving rotating dipoles or ferroelectric phase transformations. A schematic view of the principal types of polarization mechanisms is illustrated in Fig. 9.1. The electronic component of polarization arising from field-induced changes in the electron cloud around each atom is found in all matter. The ionic contribution is also common and is associated with the relative motions of cations and anions in an electric field. Orientational polarizability arises from the rotation of molecular dipoles in the field. These motions are common in organic substances. Many materials also contain mobile charge carriers in the form of ions or electrons that can migrate under applied fields.

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Newnham, Robert E. « Nonlinear phenomena ». Dans Properties of Materials. Oxford University Press, 2004. http://dx.doi.org/10.1093/oso/9780198520757.003.0017.

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The physical properties discussed thus far are linear relationships between two measured quantities. This is only an approximation to the truth, and often not a very good approximation, especially for materials near a phase transformation. A more accurate description can be obtained by introducing higher order coefficients. To illustrate nonlinearity we discuss electrostriction, magnetostriction, and higher order elastic, and dielectric effects. These phenomena are described in terms of fourth and sixth rank tensors. Many of the recent innovations in the field of electroceramics have exploited the nonlinearities of material properties with factors such as electric field, mechanical stress, temperature, or frequency. The nonlinear dielectric behavior of ferroelectric ceramics (Fig. 15.1), for example, has opened up new markets in electronics and communications. In these materials the electric polarization saturates under high fields. Electric displacement Di varies with applied electric field Ej as . . . Di = εijEj + εijkEjEk + εijklEjEkEl +· · · , . . . where εij is the dielectric permittivity and εijk and εijkl are higher order terms. The data in Fig. 15.1 were collected for a relaxor ferroelectric in its paraelectric state above Tc where the symmetry is centrosymmetric. Therefore the third rank tensor εijk is zero, and the shape of the curve is largely controlled by the first and third terms. For cubic crystals, the fourth rank tensor εijkl is similar in form to the elastic constants discussed in Chapter 13. Tunable microwave devices utilize nonlinear dielectrics in which the polarization saturates as in Fig. 15.1. By applying a DC bias the dielectric constant can be adjusted over a wide range.

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Actes de conférences sur le sujet "High permittivity ceramics"

Wang, Y., Y. B. Liu, X. H. Hu, Y. T. He, J. H. Gao et L. S. Zhong. « High dielectric permittivity in BaTiO3−xBaSnO3 ceramics ». Dans 2017 1st International Conference on Electrical Materials and Power Equipment (ICEMPE). IEEE, 2017. http://dx.doi.org/10.1109/icempe.2017.7982140.

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Yu, Chuying, Yang Zeng, Robert Donnan et Bin Yang. « High Permittivity and Low-Loss Millimeter-wave Dielectric Ceramics ». Dans 2018 11th UK-Europe-China Workshop on Millimeter Waves and Terahertz Technologies (UCMMT). IEEE, 2018. http://dx.doi.org/10.1109/ucmmt45316.2018.9015710.

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Chen, Y. C., J. Y. Lin et S. M. Tsao. « Planar Patch Antenna Using Temperature Stable High-Permittivity Ceramics ». Dans 2007 IEEE Conference on Electron Devices and Solid-State Circuits. IEEE, 2007. http://dx.doi.org/10.1109/edssc.2007.4450237.

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Chen, Y. C., S. M. Tsao et C. S. Lin. « Dielectric Resonator Antenna Using 0.95MgTiO3 - 0.05CaTiO3 High Permittivity Ceramics ». Dans 2008 IEEE International Workshop on Antenna Technology. IEEE, 2008. http://dx.doi.org/10.1109/iwat.2008.4511342.

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Wang, Jun, Jiafu Wang, Liyang Li, Hua Ma, Shaobo Qu et Zhuo Xu. « Achieving fishnet all-dielectric left-handed metamaterial via high permittivity ceramics ». Dans 2016 Progress in Electromagnetic Research Symposium (PIERS). IEEE, 2016. http://dx.doi.org/10.1109/piers.2016.7735103.

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Li, Liyang, Jun Wang, Mingde Feng, Jiafu Wang, Hua Ma, Hongya Chen, Hongliang Du, Jieqiu Zhang et Shaobo Qu. « Frequency selective polarization conversion metasurface using E-shaped high permittivity ceramics ». Dans 2018 International Workshop on Antenna Technology (iWAT). IEEE, 2018. http://dx.doi.org/10.1109/iwat.2018.8379158.

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Li, Liyang, Jun Wang, Jiafu Wang, Hua Ma, Mingde Feng, Mingbao Yan, Jieqiu Zhang et Shaobo Qu. « All-dielectric metamaterial band stop frequency selective surface via high-permittivity ceramics ». Dans 2016 Progress in Electromagnetic Research Symposium (PIERS). IEEE, 2016. http://dx.doi.org/10.1109/piers.2016.7735298.

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Yadav, Vivek, Nitin Kumar, Udaybir Singh, Anil Kumar, S. C. Deorani et A. K. Sinha. « Estimation of permittivity and loss tangent of high frequency ceramics using free space method ». Dans 2013 14th International Vacuum Electronics Conference (IVEC). IEEE, 2013. http://dx.doi.org/10.1109/ivec.2013.6571063.

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Ghosh, Avishek. « 3D Printing of Designed Ultra-Low Loss Microwave Dielectrics for Beyond 5G Applications ». Dans ASME 2022 17th International Manufacturing Science and Engineering Conference. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/msec2022-85805.

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Abstract Low-temperature sintering ceramics with high dielectric permittivity and low loss are highly valuable to the communication industry. Additive Manufacturing (AM) exhibits excellent potential to process a wide range of engineering materials and deliver complex three-dimensional structures in various scales, with several benefits over traditional manufacturing methods used in electronics manufacturing. Therefore, the advent of AM has offered a radically new way of designing and manufacturing electronic and communication components with tailored performance. In this work, a stable ink has been formulated from ultra-low loss dielectric bismuth molybdate (Bi2Mo2O9) ceramics. The formulated ink exhibited suitable rheological properties responsive to the direct ink writing technique. The 3D printed components with good structural integrity and spatial resolution were sintered at 670°C for 4 hours using the conventional heating method, achieving > 94% density. A series of components with varying shapes and designed porosities were fabricated using the extrusion 3D printing method. The relative permittivity (εr) and loss tangent (tanδ) for the 3D printed and sintered Bi2Mo2O9 solid components were found to be 36.5 and 0.0005, respectively, at ∼8GHz, and the values can be tailored using designed porosity. The dielectric performance was found to be excellent and stable even at very high-frequency regimes (beyond 5G) between 70–90 GHz. Further, the addition of metallic infills in the designed pores of the ceramic scaffolds resulted in an increase in permittivity values. The preliminary investigation exhibited the potential to fabricate ceramic components for high-frequency applications via the design freedom offered by AM, that can enable further miniaturization of future communication devices.

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Raengthon, Natthaphon, Jason Nikkel, Troy Ansell et David P. Cann. « Dielectric and Piezoelectric Ceramics for High Temperature Applications ». Dans ASME 2011 International Manufacturing Science and Engineering Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/msec2011-50263.

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Perovskite materials have been widely embedded in many consumer and industrial electronics, both for capacitor applications in the case of dielectric materials, and for actuator, transducer and sensor applications in the case of piezoelectric materials. Functional devices used in high temperature environments, such as deep oil well instrumentation, geothermal exploration, and devices for aerospace applications require the persistence of materials’ properties at high temperatures. In this paper, high potential capacitor and piezoelectric ceramics for high temperature applications are presented. High dielectric constant (K) materials based on 0.8BaTiO3 – 0.2Bi(Zn1/2Ti1/2)O3 solid solutions have been shown to have superior properties for high temperature capacitor applications. Studies of the temperature dependence of the dielectric properties have shown that the composition with Ba vacancies exhibits a high relative permittivity (εr > 1150) and a low dielectric loss (tan δ < 0.05) that persist up to a temperature of 460 °C. This composition also shows a high resistivity in excess of 7.0 × 1010 Ω-cm which remains unchanged up to a temperature of 270 °C as well as a large RC time constant (RC > 20 s). In the case of high temperature piezoelectric ceramics, solid solutions of PbTiO3 – BiScO3 – Bi(M1/2Ti1/2)O3 ternary systems were studied, where M is Mg and Zn. The ratio of BiScO3 to Bi(M1/2Ti1/2)O3 was kept at 1:1, while the concentration of PbTiO3 was varied. X-ray diffraction patterns showed that tetragonal symmetry was observed in compositions which contain a high concentration of PbTiO3 (> 60 mol%). Evidence of a morphotropic phase boundary (MPB) was observed with compositions containing PbTiO3 in the range of 52–56 mol%. At 70 mol% PbTiO3 compositions, high Curie temperatures (TC) of 490 °C and 533 °C were observed for compositions containing Mg and Zn, respectively.

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