Structural nano-defects in α-silicon nitride

Abstract

Two types of α-silicon nitride powder have been examined by transmission electron microscopy. Clustered, nano-dimension, coffee-bean shaped features can be seen: these are believed to be dislocation loops. The features are concentrated towards particle centres and appear to be formed by the condensation of lattice point defects during cooling from powder production temperatures probably in the region of 1300 to 1500 °C. Similar concentrations of features confirmed to be vacancy dislocation loops have been seen in the unconverted α-silicon nitride grains in hot-pressed silicon nitride. Calculations based on estimates of precursor defect concentrations suggest a very speculative value for the activation energy of formation of the Schottky type of lattice defect in α-Si 3N 4 of 670 kJ mol −1.