The C19 Structure (alpha Sm)

Last modified 5 April 2001

You can now

• see the structure from several perspectives;
• examine the structure with an external viewer; or
• download the coordinates of the atoms in these pictures in XYZ format.

This is also the ground state structure for Lithium proposed by A. W. Overhauser in Phys. Rev. Lett. 53 64-65 (1984). This is a close-packed structure with stacking ABCBCACAB..., as opposed to ABCABC... in the fcc (A1) structure and ABABAB... in the hcp (A3) structure. In the ``ideal'' case, c = 9 (2/3)^½ a, z = 2/9, and each atom has twelve neighbors a distance `a' away. The atoms on the (1a) site see an fcc-like arrangement of nearest neighbors, while the atoms on the (2c) sites see an hcp-like arrangement.

• Prototype: alpha Sm
• Pearson Symbol: hR3
• Strukturbericht Designation: C19
• Space Group: R(-3)m (Cartesian and lattice coordinate listings available)
• Number: 166
• Other Elements and Compounds with this Structure: Li, Nd₂Tm, NbS₂
• Primitive Vectors:
  • A₁ = ½ a X - ½ 3^-1/2 a Y + 1/3 c Z
  • A₂ = 3^-1/2 a Y + 1/3 c Z
  • A₃ = - ½ a X - ½ 3^-1/2 a Y + 1/3 c Z
• Basis Vector:
  • B₁ = 0   (1a)
  • B₂ = + z (A₁ + A₂ + A₃) = + z c Z   (2c)
  • B₃ = - z (A₁ + A₂ + A₃) = - z c Z   (2c)

See these vectors in a better notation.

Go back to the hexagonal-close packed structures page.

Go back to Crystal Lattice Structure page.

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