Abstract
The incorporation of large Ce ions into the interstitial sites in an alpha -(Si-Al-O-N) crystal structure is found to have produced a high density of structural defects. The defects are of planar nature and connect to form domain boundaries. Analysis via transmission electron microscopy has revealed that only a single lattice translation of 1/3(1010) type is involved in the formation of domains which are enveloped by some specific faces in this strongly bonded covalent compound, that is (0001), {1011} and the common surface with the matrix crystal on {1010}. Development of the domain-boundary structures is discussed via the application of image simulation based on different structural models of defects.