Abstract
The formation of 15 R-type SiC in the Lely's procedure has been studied experimentally with the method of steplike nitrogen doping, and the thermal stability of the 6 Hand the 15 R-types are discussed through heating experiments of the colourless single crystals of both types in a small graphite capsule. The results obtained are summarized as follows:
1) The 6 H-type has the higher thermal stability than the 15 R-type in the range from 2100°C to 2600°C.
2) Structural change is not recognized in the single crystals of 4 H, 15 R and 6 H after heating at 2100°C for 500 hours.
3) The 15 R-type has marked tendency to grow from the twinning (the angle between basal plane; ca. 70°30′) of 6 H-type.
4) This type twinning of 6 H is explained as the developed feature of spinel type twinning of β-SiC which formed in the initial stage of recrystallization.
5) The effect of nitrogen to the relationship of the thermal stability among polytypes is discussed. It is negligible small at 2500°C, if the partial pressure of nitrogen is in the order of 60mmHg or below.
