The A_a Body-Centered Tetragonal Lattice

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 a body-centered tetragonal (bct) structure, a distortion of the bcc lattice and the monatomic analog of the L1₀ structure. In addition, this structure has exactly the same symmetry as the A6 structure. In the A6 structure, c/a is near the fcc ratio of 2^1/2, while in the A_a structure, c/a is near the bcc ratio of 1.

Also note that when

c/a = (2/3)^½ = 0.816

this system has a coordination of 10. In Pa the c/a ratio is 0.827.

• Prototype: alpha-Pa
• Pearson Symbol: tI2
• Strukturbericht Designation: A_a
• Space Group: I4/mmm (Cartesian and lattice coordinate listings available)
• Number: 139
• Other Elements with this Structure: In (See above) and beta Hg, where the c/a ratio is near
  2^-1/2.
• Primitive Vectors:
  • A₁ = aX
  • A₂ = aY
  • A₃ = ½ a X + ½ a Y + ½ c Z
• Basis Vector:
  • B₁= 0

See these vectors in a better notation.

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