DISORDER IN BETA''-ALUMINAS - DIELECTRIC-RELAXATION AND X-RAY ABSORPTION

Beta"-aluminas substituted with rare-earth elements (Pr, Nd, Er, and T b) and Sn have been studied using near-edge and extended x-ray-absorpt ion fine structure (NEXAFS and EXAFS). In addition, dielectric-relaxat ion (DR) measurements have been made on Na-beta-, Na-beta"-, and Na-Er -beta"-alumina. Both the DR and EXAFS results confirm that disorder, p articularly in the conduction plane, in the vicinity of the rare-earth ions is a key feature of the beta"-aluminas. The NEXAFS studies show that the rare-earth ions are ionized to trivalency and are highly loca lized; in contrast, Sn is clearly divalent, as in SnO.