Structure and composition analysis of silicon aluminium oxynitride polytypes by combined use of structure imaging and microanalysis

The Nature of Oxygen-Related Polytypoids in the Aluminum Nitride-Aluminum Oxide System

Previous investigations into the nature of polytypoid structures in the A1N-A12O3 and A1NSiO2 systems have concluded that these structures are comprised of ordered stacking faults which accommodate oxygen (and silicon) in the basic wurtzite (2H) AIN structure. The polytypoids are distinct chemical phases intimately related to the pure 2H AIN. More recent work in low oxygen content (<6 at.%) A1N has elucidated the evolution of oxygen-related point defects, and transformation of these defects into extended structures. These studies have shown that all oxygenrelated extended defects in the A1N-A12O3 system are inversion domain boundaries (IDBs).

We present here extensions of the concepts developed from low oxygen content studies which lead to direct application in understanding the polytypoid structures. High resolution electron microscopy (HREM), specific electron diffraction experiments, and structural models are utilized to prove that the polytypoid structures are not based on stacking faults, but, in fact are based on IDBs.

High-resolution electron microscopy of ceramic interfaces

Three observations described here were chosen not only to represent our recent interface studies in ceramics, but also to demonstrate how different the present status of interface research is with respect to the level of high-resolution electron microscopy. Certain common features may be found among the problems of ceramic interface studies. Importance of basal plane grain boundary, for example, is one of the characteristics of this type of heterogeneous compound. The crystalline heterogeneity has been ignored largely in the grain boundary structure study since it has been developed primarily for cubic metals. The new area of basic grain boundary interface structure study is opened now that description of this type of interface has become engineeringly important.