The Moissanite-4H CSi Crystal Structure

Last modified 3 July 2001

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This is a hypothetical alternate stacking (ABAC) for tetrahedral structures. Compare this to Zincblende (ABCABC), Wurtzite (ABABAB), 6H (ABCACB), and 9R (ABCBCACAB). The 4H refers to the fact that there are 4 CSi dimers in a hexagonal unit cell. Zincblende is denoted 3C, and Wurtzite is 2H.

This structure is related to the aLa (A3') structure in the same way that Zincblende (B3) is related to the fcc (A1) lattice.

The spacings in structure file assume that the local environment is similar to Zincblende CSi. Thus the internal parameters have the values given in the table below, and c/a = 2 (8/3)^1/2.

• Prototype: CSi
• Pearson Symbol: hP8
• Space Group: P6₃mc (Cartesian and lattice coordinate listings available)
• Number: 186
• Primitive Vectors:
  • A₁ = ½ a X - ½ 3^1/2 a Y
  • A₂ = ½ a X + ½ 3^1/2 a Y
  • A₃ = c Z
• Basis Vectors:

  The ``ideal'' positions of the atoms in the this structure are:

  z1 = 0 (Of course, we can always choose one of the zi = 0)

  z2 = 1/4

  z3 = 3/16

  z4 = 7/16

  B1	=	z1 A3	=	z1 c Z	(C-I)	(2a)
  B2	=	½ + z1 A3	=	(½ + z1) c Z	(C-I)	(2a)
  B3	=	2/3 A1 + 1/3 A2 + z2 A3	=	½ a X - a/(2 3½) Y + z2 c Z	(C-II)	(2b)
  B4	=	1/3 A1 + 2/3 A2 + (½ + z2) A3	=	½ a X + a/(2 3½) Y + (½ + z2) c Z	(C-II)	(2b)
  B5	=	z3 A3	=	z3 c Z	(Si-I)	(2a)
  B6	=	½ + z3 A3	=	(½ + z3) c Z	(Si-I)	(2a)
  B7	=	1/3 A1 + 2/3 A2 + z4 A3	=	½ a X + a/(2 3½) Y + z4 c Z	(Si-II)	(2b)
  B8	=	2/3 A1 + 1/3 A2 + (½ + z4) A3	=	½ a X - a/(2 3½) Y + (½ + z4) c Z	(Si-II)	(2b)

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