Defauts dans la wurtzite lies a la presence de petites inclusions de cerium

Abstract A defect structure of wurtzite crystals activated by cerium is proposed, for the occurence of a domain structure. Possible models for this domain structure, resulting from the introduction of (CeO) n+ n sheets, are examined and discussed, taking into account the domain structure and the contrast effects observed in zinc sulfide and described previously by S. Amelinckx and al. It is concluded that this type of insertion has not been observed. Evidence is presented to show that the precipitation of point defects observed on (1100) habit planes in the electron microscope, and their subsequent collapse into dislocation loops results from Ce 3+ or Eu 2+ arrangement in octaedral holes of closed packed stacking.