Silver-ammonium beta alumina

Abstract

The exchange of ammonium by silver ions in beta alumina is described and the thermal evolution of silver-ammonium beta alumina is outlined. Treatment of silver beta alumina in molten ammonium nitrate yields two separate beta-alumina phases within the same crystal rather than a mixed single-phase materials as is generally assumed to occur in beta alumina ion exchanges. The extent of exchange at 210°C is indicated by an opaque exchange front and the c-axis lattice constants on either side are close but not identical to those of the ammonium and silver compounds. On heating, the two compositions interdiffuse and, ultimately, stoichiometric silver beta alumina is formed within the crystal. As well as providing a single-stage preparation of a stoichiometric metal beta alumina, such a mixed crystal should provide a fascinating vehicle for the study of the interaction of related but insoluble phases produced by controlled solid state reaction. The conclusions drawn from the silver-to-ammonium exchange are confirmed by study of the exchange of partially-decomposed ammonium beta alumina in molten silver nitrate.