The effect of B diffusion upon the polytype structure of 3C, 6H and 15R polytypes was studied at temperatures ranging from 1600 to 1900C. In the surface region, the partial polytype transitions, 15R  3C and 6H  3C were detected by means of reflection high-energy electron diffraction. Such diffraction spots could not be detected in the bulk. A maximum in the diffraction intensities of 3C in the -phase was observed at 1800C. No phase transitions in the 3C crystal were detected at temperatures ranging from 1600 to 1800C. During long diffusion times at 1800C, a phase transition of the 3C  15R type occurred. This reverse transition was suggested to be the cause of a decrease in the diffraction spot intensities of 3C in 15R and 6H crystals, when compared with crystals that had been treated by B diffusion at lower temperatures. It was proposed that one reason for the observed polytype transitions was the local generation of stacking faults. This led to the elimination of hexagonal sites in the stacking order of the -phase polytypes, and their stabilization by diffusion-induced stress fields.

J.Pezoldt: Materials Science and Engineering B, 1995, 29[1-3], 99-104