Distinguishing the 4H and 6H Polytypes of SiC Single Crystals

Silicon carbide single crystals, also called Moissanite, are an inexpensive gemstone substitute for diamonds.  They are a step up from cubic zirconia gemstone diamond substitutes in hardness and chemical inertness.  They are also more brilliant than either diamonds or cubic zirconia.  The gemstones are made artificially.  We were asked by a Moissanite merchant to find a way to distinguish the two crystal structures or polytypes that artificial SiC crystals are made in.  SiC crystals grow with bilayers of atoms of three arrangements, A, B, and C.  The two artificially produced polytypes of SiC are 4H and 6H, which differ in the sequence in which the bilayers A, B, and C are stacked.

Our report on how we learned to distinguish and identify these crystal structures is presented here with the permission of our customer: FTIR.4H 6H SiC.11July2016