PRODUCTION AND CHARACTERIZATION OF POLYCRYSTALLINE (NA,BA) BETA''-ALUMINAS

Polycrystalline (Na,Ba) beta" aluminas with different barium content were produced from commercial Na beta" alumina by ion exchange in suitable molten mixtures of NaNO3, Ba(NO3)2 and BaCl2. The extent of crack and pore formation could be reduced by increasing the barium content gradually from one equilibrium concentration in the solid electrolyte to the next higher one. The equilibrium distribution curve was determined for the polycrystalline materials and verified by measurements on single crystals. The curve of the specific conductivity versus the extent of exchange suggest that the Na+ ion is the conducting species in a wide range of soda content. The transition to conduction by Ba2+ occurs in a relatively narrow region at high extents of exchange. The said transition is mainly caused by the change of the properties of the grain boundaries.