The Polytypes of Diamond

Rgure 11.6. Schematic of the structure of hexagonal diamond (lonsdaleite).  

Some meteorites contain diamond such as the one found in Canyon Diablo in Arizona. The diamond is in the form of polycrystalline compacts made up of submicron crystals. These crystals are mostly cubic although the hexagonal form is also found. 

6H Diamond. Recent investigations have revealed the existence of another intermediate diamond polytype known as 6H diamond.f l This material is believed to belong to a hypothetical series of diamond types with structures intermediate between hexagonal and cubic. The membersof this series are tentatively identified as 4H, 6H, 8H, 10H. The series would include hexagonal (2H) diamond on one end and cubic (3C) diamond on the other (the digit indicatesthe number of layers). The existence of 4H, 8H and 10H diamonds has yet to be confirmed. 

The 6H structure has a mixed six-l er hexagonal/cubic stacking sequence AA C B BC, shown schematically in Fig.11.7. 1 It may exist in CVD diamond. 

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