Modderite (CoAs) Structure: AB_oP8_33_a_a

Picture of Structure; Click for Big Picture
Prototype : CoAs
AFLOW prototype label : AB_oP8_33_a_a
Strukturbericht designation : None
Pearson symbol : oP8
Space group number : 33
Space group symbol : $\mbox{Pna2}_{1}$
AFLOW prototype command : aflow --proto=AB_oP8_33_a_a
--params=
$a$,$b/a$,$c/a$,$x_{1}$,$y_{1}$,$z_{1}$,$x_{2}$,$y_{2}$,$z_{2}$


Other compounds with this structure

  • FeAs

  • (Lyman, 1984) arbitrarily set $z_{2}=1/4$, which is allowed for this space group. When $z_{1} = z_{2} = 1/4$, the space group becomes Pnma and the structure is equivalent to MnP (B31). (Lyman, 1984) lists both space groups for both CoAs and FeAs, and prefers the MnP structure for these compounds.

Simple Orthorhombic primitive vectors:

\[ \begin{array}{ccc} \mathbf{a}_1 & = & a \, \mathbf{\hat{x}} \\ \mathbf{a}_2 & = & b \, \mathbf{\hat{y}} \\ \mathbf{a}_3 & = & c \, \mathbf{\hat{z}} \end{array} \]

Basis vectors:

\[ \begin{array}{ccccccc} & & \mbox{Lattice Coordinates} & & \mbox{Cartesian Coordinates} &\mbox{Wyckoff Position} & \mbox{Atom Type} \\ \mathbf{B}_{1} & =& x_{1} \, \mathbf{a}_{1} + y_{1} \, \mathbf{a}_{2} + z_{1} \, \mathbf{a}_{3}& =& x_{1} \, a \, \mathbf{\hat{x}} + y_{1} \, b \, \mathbf{\hat{y}} + z_{1} \, c \, \mathbf{\hat{z}}& \left(4a\right) & \mbox{As} \\ \mathbf{B}_{2} & =& - x_{1} \, \mathbf{a}_{1} - y_{1} \, \mathbf{a}_{2} + \left(\frac12 + z_{1}\right) \, \mathbf{a}_{3}& =& - x_{1} \, a \, \mathbf{\hat{x}} - y_{1} \, b \, \mathbf{\hat{y}} + \left(\frac12 + z_{1}\right) \, c \, \mathbf{\hat{z}}& \left(4a\right) & \mbox{As} \\ \mathbf{B}_{3} & =& \left(\frac12 + x_{1}\right) \, \mathbf{a}_{1} + \left(\frac12 - y_{1}\right) \, \mathbf{a}_{2} + z_{1} \, \mathbf{a}_{3}& =& \left(\frac12 + x_{1}\right) \, a \, \mathbf{\hat{x}} + \left(\frac12 - y_{1}\right) \, b \, \mathbf{\hat{y}} + z_{1} \, c \, \mathbf{\hat{z}}& \left(4a\right) & \mbox{As} \\ \mathbf{B}_{4} & =& \left(\frac12 - x_{1}\right) \, \mathbf{a}_{1} + \left(\frac12 + y_{1}\right) \, \mathbf{a}_{2} + \left(\frac12 + z_{1}\right) \, \mathbf{a}_{3}& =& \left(\frac12 - x_{1}\right) \, a \, \mathbf{\hat{x}} + \left(\frac12 + y_{1}\right) \, b \, \mathbf{\hat{y}} + \left(\frac12 + z_{1}\right) \, c \, \mathbf{\hat{z}}& \left(4a\right) & \mbox{As} \\ \mathbf{B}_{5} & =& x_{2} \, \mathbf{a}_{1} + y_{2} \, \mathbf{a}_{2} + z_{2} \, \mathbf{a}_{3}& =& x_{2} \, a \, \mathbf{\hat{x}} + y_{2} \, b \, \mathbf{\hat{y}} + z_{2} \, c \, \mathbf{\hat{z}}& \left(4a\right) & \mbox{Co} \\ \mathbf{B}_{6} & =& - x_{2} \, \mathbf{a}_{1} - y_{2} \, \mathbf{a}_{2} + \left(\frac12 + z_{2}\right) \, \mathbf{a}_{3}& =& - x_{2} \, a \, \mathbf{\hat{x}} - y_{2} \, b \, \mathbf{\hat{y}} + \left(\frac12 + z_{2}\right) \, c \, \mathbf{\hat{z}}& \left(4a\right) & \mbox{Co} \\ \mathbf{B}_{7} & =& \left(\frac12 + x_{2}\right) \, \mathbf{a}_{1} + \left(\frac12 - y_{2}\right) \, \mathbf{a}_{2} + z_{2} \, \mathbf{a}_{3}& =& \left(\frac12 + x_{2}\right) \, a \, \mathbf{\hat{x}} + \left(\frac12 - y_{2}\right) \, b \, \mathbf{\hat{y}} + z_{2} \, c \, \mathbf{\hat{z}}& \left(4a\right) & \mbox{Co} \\ \mathbf{B}_{8} & =& \left(\frac12 - x_{2}\right) \, \mathbf{a}_{1} + \left(\frac12 + y_{2}\right) \, \mathbf{a}_{2} + \left(\frac12 + z_{2}\right) \, \mathbf{a}_{3}& =& \left(\frac12 - x_{2}\right) \, a \, \mathbf{\hat{x}} + \left(\frac12 + y_{2}\right) \, b \, \mathbf{\hat{y}} + \left(\frac12 + z_{2}\right) \, c \, \mathbf{\hat{z}}& \left(4a\right) & \mbox{Co} \\ \end{array} \]

References

  • P. S. Lyman and C. T. Prewitt, Room– and high–pressure crystal chemistry of CoAs and FeAs, Acta Crystallogr. Sect. B Struct. Sci. 40, 14–20 (1984), doi:10.1107/S0108768184001695.

Geometry files


Prototype Generator

aflow --proto=AB_oP8_33_a_a --params=

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