Oxygen incorporation in aluminum nitride via extended defects: Part III. Reevaluation of the polytypoid structure in the
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Robert A. Youngman Carborundum Microelectronics Company, 10409 S. 50th Place, Phoenix, Arizona 85044
Martha R. McCartney Center for Solid State Science, Arizona State University, Tempe, Arizona 85287
Alastair N. Cormack New York State College of Ceramics, Alfred University, Alfred, New York 14802
Michael R. Notis Department of Materials Science and Engineering, Lehigh University, Bethlehem, Pennsylvania 18015 (Received 23 January 1995; accepted 22 June 1995)
This paper extends the concepts that were developed to explain the structural rearrangement of the wurtzite AIN lattice due to incorporation of small amounts of oxygen, and to directly use them to assist in understanding the polytypoid structures. Conventional and high-resolution transmission electron microscopy, specific electron diffraction experiments, and atomistic computer simulations have been used to investigate the structural nature of the polytypoids. The experimental observations provide compelling evidence that polytypoid structures are not arrays of stacking faults, but are rather arrays of inversion domain boundaries (IDB's). A new model for the polytypoid structure is proposed with the basic repeat structural unit consisting of a planar IDB-P and a corrugated IDB. This model shares common structural elements with the model proposed by Thompson, even though in his model the polytypoids were described as consisting of stacking faults. Small additions (—1000 ppm) of silicon were observed to have a dramatic effect on the polytypoid structure. First, it appears that the addition of Si causes the creation of a new variant of the planar IDB (termed IDB-P'), different from the IDB-P defect observed in the A1N-A12O3 polytypoids; second, the addition of Si influences the structure of the corrugated IDB, such that it appears to become planar.
I. INTRODUCTION Jack and Wilson1 and Oyama and Kamigaito2 are recognized as having independently discovered the group of technologically important engineering ceramics known as "SiAlON's". The ever increasing list of "SiAlON" ceramics take their name from the prototype pseudoquaternary system for this group, S i 3 N 4 - S i 0 2 - A l 2 0 3 - A l N . In the AIN-rich corner of this system, the polytypoid "phases", 8H, 15R, 12H, 21R, and 27R, are found to exist, as shown in Fig. 1.4~10 (Polytypoids are crystallographically distinct structures that belong to a subset of the more general classification of polytypism,3 with which the reader is probably more familiar. Polytypism is the phenomenon of the existence of an element or compound in two or more a)
Present address: Union Carbide Technical Center, Bound Brook, New Jersey 08805. J. Mater. Res., Vol. 10, No. 10, Oct 1995 http://journals.cambridge.org
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layer-like crystal structures that differ in layer stacking sequence. The layers need not be crystallographically identical, but their chemical composition may not vary by more than 0.25 atoms per formula unit of a constituent element. Polytypoids are layer structures whose chemistry may differ
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