Origin of dislocation loops in α-silicon nitride

Abstract

Dislocation loops and stacking fault formation mechanism in α–Si3N4have been studied by annealing α–Si3N4powders at 1500 °C and 1750 °C. Thermally activated vacancies and the structural vacancies generated with replacement of nitrogen by oxygen have been tentatively suggested to be two sources of vacancies in α–Si3N4. From the point of view of mechanism, incorporation of these vacancies is believed to lie at the building-up stage of α–Si3N4lattice. As a result of the vacancies agglomeration, dislocation loops and stacking faults seem to be a distinctively structural feature of α–Si3N4fabricated by different routes [chemical vapor deposition (CVD), silicon nitridation, silica carbothermal reduction, and imide decomposition]. A general discussion has been extended to the historical controversy over the oxygen and vacancy stabilization of α–Si3N4lattice arisen from the fact that the observed unit cell dimension of α–Si3N4has a wide variation, and also to some related phenomena in processing of Si3N4.