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Contacting Methods for C12A7 Electride Ceramic
K. Waetzig1, A. Rost1, J. Schilm1, M. Tajmar2, A. Michaelis1
1 Fraunhofer IKTS, Institute for Ceramic Technology and Systems, Winterbergstrasse 28, D-01277 Dresden, Germany
2 Institute of Aerospace Engineering, Technische Universität Dresden, D-01307 Dresden, Germany
received June 13, 2019, received in revised form September 5, 2019, accepted October 18, 2019
Vol. 11, No. 1, Pages 11-16 DOI: 10.4416/JCST2019-00032
Abstract
C12A7:e- ([Ca24Al28O64]4+4e-) ceramic is a material with high electrical conductivity and low work function, so that this ceramic is suitable as an electron-emitting material. Although the bulk material indicates these extraordinary properties, the surface of the ceramic is insulating. Therefore, a metallization film is needed to realize an electrical contact with low ohmic losses for the application of the material. In this study, we investigated three different metal pastes (Pt, Au and Cusil-ABA®) for contacting the surface and measured the reduction of the resistance during the firing process of the pastes. The resistance of the contacted C12A7:e- was determined as a function of the temperature under nitrogen atmosphere. Additionally, the oxidation behaviour of the electride was observed based on increasing resistance when the material was heated in air.
The lowest resistance was measured with Ag-based braze (Cusil-ABA®), however, cracking of the contacted ceramic was observed. Alternatively, contacting with Au reached a specific resistance of 5.4 Ω cm (T = 800 °C).
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Keywords
Electron emitter, conductive ceramic, C12A7, calcium aluminate, metallization, contacting
References
1 Boysen, H., Lerch, M., Stys, A., Senyshyn, A.: Structure and oxygen mobility in mayenite (Ca12Al14O33): a high-temperature neutron powder diffraction study, Acta Cryst., B63, 675 – 682, (2007).
2 Bartl, H., Scheller, T.: The structure of 7CaO.12Al2O3, in german, Neues Jahrb. Mineral. Monatsh., 35, 547 – 552, (1970).
3 Hosono, H.: Functioning of traditional ceramics 12CaO·7Al2O3 utilizing built-in nano-porous structure, Sci. Tech. Adv. Mater., 5, 409 – 416, (2004).
4 Jeevaratnam, J., Glasser, F.P., Dent Glasser, L.S.: Anion substitution and structure of 12CaO.7Al2O3, J. Am. Ceram. Soc., 47, 105 – 106, (1964).
5 Hayashi, K.: Heavy doping of H- ion in 12CaO.7Al2O3, J. Solid State Chem., 184, 1428 – 1432, (2011).
6 Ebbinghaus, S.G., Krause, H., Syrowatka, F.: Floating zone growth of large and defect-free Ca12Al14O33 single crystals, Cryst. Growth Des., 13, 2990 – 2994, (2013).
7 Toda, Y., Kubota, Y., Hirano, M., Hirayama, H., Hosono, H.: Surface of room-temperature-stable electride [Ca24Al28O64]4+(e-)4: preparation and its characterization by atomic-resolution scanning tunneling microscopy, ACS Nano, 5, 1907 – 1914, (2011).
8 Hosono, H., Abe, Y.: Occurrence of superoxide radical ion in crystalline 12CaO.7Al2O3 prepared via Solid-state reactions, Inorg. Chem., 26, 1192 – 1195, (1987).
9 Kim, S.-W., Hayashi, K., Hirano, M., Hosono, H.: Electron carrier generation in a refractory oxide 12CaO.7Al2O3 by heating in reducing Atmosphere: conversion from an insulator to a persistent conductor, J. Am. Ceram. Soc., 89, 3294 – 3298, (2006).
10 Trofymluk, O., Toda, Y., Hosono, H., Navrotsky, A.: Energetics of formation and oxidation of microporous calcium Aluminates: A new class of electrides and ionic conductors, Chem. Mater., 17, 5574 – 5579, (2005).
11 Hayashi, K., Ueda, N., Hirano, M., Hosono, H.: Effect of stability and diffusivity of extra-framework oxygen species on the formation of oxygen radicals in 12CaO.7Al2O3, Solid State Ionics, 173, 89 – 94, (2004).
12 Williams, J.D., Sanmartin, J.R., Rand, L.P.: Low work-function coating for an entirely propellantless bare electrodynamic tether, IEEE Transactions on plasma science, 40, 1441 – 1445, (2012).
13 Drobny, C., Nürmberger, F., Tajmar, M.: Development of a compact hall thruster with a C12A7 low-power hollow cathode, Proc. of the Space Propulsion Conference, Paper 3124751, Rome, March 2 – 6, (2016).
14 Toda, Y., Kim, S.W., Hayashi, K., Hirano, M., Kamiya, T., Hosono, H., Haraguchi, T., Yasuda, H.: Intense thermal field electron emission from room-temperature stable electride, Appl. Phys. Lett., 87, 254103, (2005).
15 Somiya, S. (Ed.), Handbook of Advanced Ceramics, 2nd edition, Elsevier Inc., 466 – 467, (2013).
16 Matsuishi, S., Toda, Y., Miyakawa, M., Hayashi, K., Kamiya, T., Hirano, M., Tanaka, I., Hosono, H.: High-density electron anions in a nanoporous single Crystal: [Ca24Al28O64]4+(4e-), Science, 301, 626 – 629, (2003).
17 Lobo, R.P.S.M., Bontemps, N., Bertoni, M.I., Mason, T.O., Poeppelmeier, K.R., Freeman, A.J., Park, M.S., Medvedeva, J.E.: Optical conductivity of Mayenite: from insulator to metal, J. Phys. Chem. C, 119, 8849 – 8856, (2015).
18 Kim, S.-W., Matsuishi, S., Miyakawa, M., Hayashi, K., Hirano, M., Hosono, H.: Fabrication of room temperature-stable 12CaO.7Al2O3 electride: a review, J. Mater. Sci.: Mater. Electron., 18, S5 – S14, (2007).
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