Characterization of Long Period Polytypoid Structures in The Al2O3-AlN System

Long period polytypoid structures observed along the pseudobinary Al2O3-AlN composition join at a composition of 95 mol% A1N have been investigated by convergent beam electron diffraction and lattice imaging. Two new long period structures, 32H (Ramsdell notation) and 16H with c-periodicities of 8.3 nm and 4.07 nm respectively, have been independently identified by these two techniques. However, the 32H polytypoid was sometimes found to be intergrown with faulted 27R long period structure of periodicity 7.2 nm. Further, it has been shown that the 32H polytypoid is stabilized by local compositional fluctuations during the sintering process.