CHARACTERIZATION OF THE DEFECT STRUCTURE OF POLYCRYSTALLINE SR-BETA-ALUMINA CERAMICS USING HIGH-RESOLUTION TRANSMISSION ELECTRON-MICROSCOPY

Polycrystalline Sr-beta-alumina with the composition SrxLiyAl11-yO16.5 +x-y (0.9 < x < 1.18; 0.5<y<0.7) and a density of greater-than-or-equa l-to 95% was synthesized by solid-state reaction from the carbonates o f Sr and Li and a structurally cubic close-packed gamma-alumina precur sor. The structure was investigated by X-ray diffraction (XRD), transm ission electron microscopy (TEM) and high-resolution transmission elec tron microscopy (HRTEM). Investigations of the phase diagram at 1450-d egrees-C show the presence of only the beta-phase. The presence of Li (or Mg) dopants is necessary for the stabilization of Sr-doped beta-al umina. A defect model for the stabilization of the beta structure is g iven and includes neutrality of the mirror planes and the spinel block s. Analysis of the HRTEM results by image simulation techniques agreed with the assumption of Sr ions located only at BR positions. The cond uctivities of the ceramic samples obtained from impedance measurements are independent of the concentration of the dopant and the Sr ions in the conduction plane.