Crystal Lattice Structures:	Creation Date: 16 May 1997
	Last Modified: 21 Oct 2004

The αUranium (A20) Structure

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.
• visualize the structure (Uses the JMOL Applet)

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• Vohra and Spencer recently showed that at pressures above 116 GPa titanium transforms from the hexagonal omega (C32) phase to this phase.
• This structure was studied by Wentzcovitch and Cohen as a possible pathway for the pressure-induced transformation of Magnesium from the hcp (A3) to the bcc (A2) phase.
• Much like the trigonal omega phase (C6), we can generate several high-symmetry structures from this phase by the appropriate choice of parameters. These include:
  
  

  Lattice Parameter	hcp	bcc	fcc	simple cubic
  a	ahcp	abcc	afcc	asc
  b	3½ ahcp	2½ abcc	afcc	asc
  c	chcp	2½ abcc	afcc	2 asc
  y	1/6	1/4	1/4	0
  Phase Description	hcp	bcc	fcc	simple cubic
  Strukturbericht	A3	A2	A1	Ah
  Pearson Symbol	hP2	cI2	cF4	cP1
  Space Group	P63/mmc	Im3m	Fm3m	Pm3m

  
  
  
• Thanks to Thomas Adler of DOE for suggesting the addition of this structure.
• 15 March 2003:: Corrected the Cartesian coordinates.

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• Prototype: αU
• Pearson Symbol: oC4
• Strukturbericht Designation: A20
• Space Group: Cmcm (Cartesian and lattice coordinate listings available)
• Number: 63
• Reference: Pearson, Alloys, p. 764.
• Other systems with this structure: Tb, Dy, Ge (metastable), AgCd (random alloy), γTi

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• Primitive Vectors:

  A1	=	½ a X - ½ b Y
  A2	=	½ a X + ½ b Y
  A3	=	c Z

• Basis Vectors:

  B1	=	- y A1 + y A2 + ¼ A3	=	+ y b Y + ¼ c Z	(4c)
  B2	=	+ y A1 - y A2 - ¼ A3	=	- y b Y - ¼ c Z	(4c)

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Structures indexed by: Strukturbericht Symbol Pearson Symbol Space Group Prototype

This is a mirror of an old page created at the Naval Research Laboratory Center for Computational Materials Science The maintained successor is hosted at http://www.aflowlib.org/CrystalDatabase/ and published as M. Mehl et al., Comput. Mater. Sci. 136 (Supp.), S1-S828 (2017).