6H-SiC single crystals were grown by the physical vapor transport (PVT) technique. Misoriented domains (MDs) were observed in as-grown crystals. Raman spectra and X-ray diffraction indicated that the MDs are 4H polytype with either (1 0 (1) over bar 2) or (1 0 (1) over bar 6) growth plane. Formation probability of MDs increased continuously as the thermal insulator had been repeatedly used. Simulations based on heat transfer demonstrated that the changes of the temperature and the temperature axial gradient at the center of the growth front were responsible for the phenomenon. The formation mechanism was put forward in terms of atomic structure of various crystal planes. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.