Irradiation-induced defects in β'ppp-alumina examined by high-resolution electron microscopy

Electron-induced defects in β′′′′-alumina, Na₂O.3MgO.7Al₂O₃, are examined by high resolution electron microscopy. The phenomena can be reasonably explained in the same manner as previously done for a similar case in β′′′′-alumina [Matsui & Horiuchi (1981). Acta Cryst. A37, 51–61]; two spinel-like blocks (each having six oxygen layers) on both sides of the lost conduction plane are directly combined to form cubic close packing of twelve oxygen layers through the minimum shift vectors. The arrangements of cations in a resultant defect block are slightly different from those in the spinel lamella of the same thickness.