On the structural integrity of the spinel block in the β"-alumina structure.
The β''-alumina structure is examined in detail and an analysis is presented of the three-dimensional integrity of the lattice. The layer structure that is responsible for the very high sodium conduction rate is the specific focus. Rigid layers that are derived from the cubic spinel structure are interleaved by more open honeycomb pathways where rapid ion diffusion takes place. The three-dimensional rigidity of the spinel block in this structure makes it possible to accurately quantify the conduction layer thickness based only on the hexagonal unit-cell dimensions, as suggested originally by Harbach [(1983), J. Mater. Sci. 18, 2437-2452]. His calculation is tested rigorously against the many single-crystal structure determinations that have been made on the β''-alumina family compounds and excellent correlation is found.
Sodium–Sulfur Batteries
Sodium–sulfur (Na–S) battery technology has high potential for energy storage and load leveling in power systems, and it is one of the most developed types of high temperature battery. Owing to outstanding energy density, high efficiency of charge/discharge, low materials cost, and cycle life of up to 15 years, Na–S batteries are attractive for their use in relatively large-scale energy storage system applications. However, there are several challenges to overcome for the safe operation of Na–S batteries, mostly related to the high operation temperatures. In this sense, the development of new solid electrolytes that possess high ionic conductivities at intermediate or room temperature is crucial. β-Alumina and NASICON structure electrolytes are revised, and new alternatives, such as ceramic/polymer composites, are also gathered. There also exists novel focus on Na–S technology in order to increase the obtained capacity and cyclability consisting of using nanostructured carbon to host sulfur or to bind it to a polymer. In addition, hybrid technologies combining Na–S with ZEBRA or oxygen rocking-chair batteries are currently arising as alternative storage devices. As Na–S technology was introduced in the mid-1970s, a number of different patents have been developed. Trends observed in the new patents are twofold: on the one hand, they aim to integrate these batteries into the electrical grid in order to compensate the fluctuations of renewable energies; on the other hand, they show battery component improvements in order to obtain lower operating temperatures. 
 
 
Keywords: 
 
batteries; 
Na–S; 
Li–S; 
β-alumina; 
β″-alumina
Fast divalent ion conduction in Ba++, Cd++ and Sr++ beta″ aluminas
Abstract Single crystals of Ba ++ , Cd ++ and Sr ++ beta″ alumina were prepared from sodium beta″ alumina by ion exchange. The conductivities of these divalent ion solid electrolytes exceed 10 −3 (ohm-cm) −1 at 300°C. These compounds appear to exhibit fast divalent ion motion at moderate temperatures.