Characterization of the defect structure of polycrystalline Sr-β-alumina ceramics using high-resolution transmission electron microscopy
Polycrystalline Sr-β-alumina with the composition SrxLiyAl11–yO16.5+x–y(0.9<x<1.18; 0.5<y<0.7) and a density of 95% was synthesized by solid-state reaction from the carbonates of Sr and Li and a structurally cubic close-packed γ-alumina precursor. The structure was investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). Investigations of the phase diagram at 1450 °C show the presence of only the β-phase. The presence of Li (or Mg) dopants is necessary for the stabilization of Sr-doped β-alumina. A defect model for the stabilization of the β structure is given and includes neutrality of the mirror planes and the spine) blocks. Analysis of the HRTEM results by image simulation techniques agreed with the assumption of Sr ions located only at BR positions. The conductivities of the ceramic samples obtained from impedance measurements are independent of the concentration of the dopant and the Sr ions in the conduction plane.