LOCAL ELECTRONEUTRALITY IN THE BETA-ALUMINA STRUCTURES

The structure of 'ideal, stoichiometric', β-alumina, NaAl11O17, showslarge departures from local electroneutrality and is unlikely to be stable. Local electroneturality may be better approached by adding extra positive charge to the conduction plane, either as Na+ or Al3+, and by removing positive charge from the spinel blocks, either by having Al3+ vacancies or substitution by M2+. In the commonly accepted structures of β and β″ alumina which contain excess soda, departures from local electroneutrality still occur but to a lesser degree. These departures may be real or an additional but unrecognised means of achieving local electroneutrality may be present. © 1979.