Observations of silicon carbide by high resolution transmission electron microscopy

High resolution transmission electron microscopy techniques, principally involving direct lattice imaging, have been used as part of a study of the crystallography and phase transformation mechanics of silicon carbide polytypes. In particular, the 3C (cubic) and 6H (hexagonal) polytypes have been examined together with partially transformed structural mixtures. Although direct observation of two‐dimensional atomic structures was not possible at an operating voltage of 100 kV, considerable microstructural information has been obtained by careful choice of the experimental conditions. In particular, tilted beam observations of the 0·25 nm lattice fringes have been made in the 3C polytype for two different {111} plane arrays in order to study the dimensions and coherency of finely‐twinned regions together with {0006} and lattice images in the 6H polytype which allow the detailed stacking operations to be resolved. Lower resolution lattice images formed with axial illumination have also been used to study the nature of the 3C → 6H transformation and results are presented showing that the transformation interface may originate with fine twinning of the 3C structure followed by growth of the resultant 6H regions. Observations have been made of the detailed stepped structure of this interface together with the stacking fault distribution in the resultant 6H material. The images obtained suggest that tilted beam techniques will be useful for studying the one‐dimensional disorder in other SiC polytypes and related ceramic materials. Some of the possible advantages of future observations with high voltage, high resolution instruments are considered. 1978 Blackwell Science Ltd