SILICON-NITRIDE CRYSTAL-STRUCTURE AND OBSERVATIONS OF LATTICE-DEFECTS

In view of the considerable progress that has been made over the last 40 years on the microstructural design of silicon nitride and related materials of tailored properties for specific applications, a clear re view of the current understanding of the crystal structure and crystal chemistry of silicon nitride is timely. The crystal structures, cryst al chemistry, and lattice defect nature of silicon nitride are critica lly reviewed and discussed, with emphasis placed firstly on the struct ural nature of alpha-silicon nitride (whether it is a pure silicon nit ride, or should better be regarded as an oxynitride); and secondly on the space group of beta-silicon nitride (whether it is P6(3)/m or P6(3 )). In conjunction with recent observations of vacancy clusters in alp ha-silicon nitride, a comprehensive view compatible with all the exper imental facts with respect to the structural nature of alpha-silicon n itride is tentatively presented.