Toward Commercialization of the Beta-Alumina Family of Ionic Conductors
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Commercialization of the Beta-Alumina Family of Ionic Conductors
J.L. Sudworth, P. Barrow, W. Dong, B. Dunn, G.C. Farrington, and J.O. Thomas Introduction The beta-alumina family of materials has played a central role in the field of solid-state ionics. - and -alumina have been a principal theme in the field ever since Yao and Kummer reported the extraordinarily high conductivity for sodium -alumina.1 The material “came of age” at a time when there was great interest in the science and technology of highconductivity solid electrolytes. A previous MRS Bulletin review2 introduced this broad family of materials, examining the range of compositions and the two major structures. The beta-alumina family emerged as almost an ideal system in which to explore structure-property relations, as its unusual structure is responsible for its remarkable ion-transport properties. Although the initial interest in this material, and the one which endures to this day, is its rapid sodium-ion transport, the rich ion-exchange chemistry added a dimension to this material that few inorganic systems can match, let alone exceed. -alumina, in particular, is an almost universal solid electrolyte for cations. It constitutes a broad family of solid electrolytes whose properties are dependent upon the nature of the ion inserted into the conduction plane. As a result, the -aluminas have served as model systems for a wide range of studies: proton transport and mixed-ion diffusion, order-disorder reactions, and superlattice phenomena. Moreover, these -alumina compositions demonstrated that fast-ion transport was not limited to a few mono22
valent ions, but could be extended to divalent and even trivalent cations. With the latter materials, the interest was not necessarily ion transport, but optical properties instead. The presence of trivalent cations in this unusual structure, coupled with the ability to control the chemistry of the local environment, enabled the -aluminas to exhibit a number of novel optical properties. The 1990s were a time of maturity for the beta-alumina family of materials. The one development that stands out during this time is the commercial production of beta-alumina ceramics for high-temperature batteries. Interestingly, this was not to support the sodium sulfur battery, which fueled the initial interest in the -aluminas, but the sodium nickel chloride system, which is now entering the commercialization phase. This article describes these developments, as a great many lessons are to be learned about how commercialization proceeds for advanced ceramics. A second area that emerged during this time was the synthesis of betaalumina thin films. This is an enabling technology, and it is simply a matter of time until thin films of beta-aluminas find their way into a variety of electrochemical and even optical applications.
Structure and Transport Properties This section is intended to provide a brief overview of the structure and iontransport properties of the - and
-aluminas. The topic has been st
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