Synthesis and thermal stability of dense polycrystalline barium β″-alumina

Techniques for preparation of dense polycrystalline Ba β″-alumina ceramic shapes by ion exchange of sintered Li2 O-stabilized Na β″-alumina containing ∼19% of a β-phase have been examined. Full exchange of both phases has been achieved in all cases. Ba β″-alumina was found to be thermally unstable, transforming above 700°C to a β-phase. X-ray powder diffraction patterns for Ba β″-alumina and for Ba β-alumina resulting from heating the Ba β″-alumina to 1550°C are reported. Direct synthesis by solid state high temperature reactions leads only to the formation of the β-phase, regardless of the precursor materials (oxides and carbonates or nitrates).