α-FeSe Structure: AB_oC8_67_a_g-001
- We follow (Louca, 2010) in calling this $\alpha$–FeSe. While some authorities list this as a prototype of $\alpha$–PbO, we find that the difference in structures is enough to warrant giving FeSe its own prototype.
- (Louca, 2010) note that
the Se ion concentration is close to 1.
- The data is presented for the structure at 7 K.
- The ICSD entry is from the (Lehman, 2010) conference proceedings.
- (Louca, 2010) find $a ≈ b$. As with orthorhombic $\alpha$–PbO and tetragonal ($B10$) PbO, this causes AFLOW to place this in the tetragonal $P4/nmm$ #129 space group if the default settings are used. The experimentally reported structure is only obtained if we use the command
- aflow --proto=AB_oC8_67_a_g --tolerance=0.001 --params=a,c/a,z$_{2}$ .
- $\alpha$–FeSe and $\alpha$–PbO have the same AFLOW prototype label, AB_oC8_67_a_g. They are generated by the same symmetry operations with different sets of parameters (
--params) specified in their corresponding CIF files.
\[ \begin{array}{ccc}
\mathbf{a_{1}}&=&\frac{1}{2}a \,\mathbf{\hat{x}}- \frac{1}{2}b \,\mathbf{\hat{y}}\\\mathbf{a_{2}}&=&\frac{1}{2}a \,\mathbf{\hat{x}}+\frac{1}{2}b \,\mathbf{\hat{y}}\\\mathbf{a_{3}}&=&c \,\mathbf{\hat{z}}
\end{array}\]
Basis vectors
| Lattice coordinates | Cartesian coordinates | Wyckoff position | Atom type | |||
|---|---|---|---|---|---|---|
| $\mathbf{B_{1}}$ | = | $\frac{1}{4} \, \mathbf{a}_{1}+\frac{1}{4} \, \mathbf{a}_{2}$ | = | $\frac{1}{4}a \,\mathbf{\hat{x}}$ | (4a) | Fe I |
| $\mathbf{B_{2}}$ | = | $\frac{3}{4} \, \mathbf{a}_{1}+\frac{3}{4} \, \mathbf{a}_{2}$ | = | $\frac{3}{4}a \,\mathbf{\hat{x}}$ | (4a) | Fe I |
| $\mathbf{B_{3}}$ | = | $\frac{3}{4} \, \mathbf{a}_{1}+\frac{1}{4} \, \mathbf{a}_{2}+z_{2} \, \mathbf{a}_{3}$ | = | $\frac{1}{2}a \,\mathbf{\hat{x}}- \frac{1}{4}b \,\mathbf{\hat{y}}+c z_{2} \,\mathbf{\hat{z}}$ | (4g) | Se I |
| $\mathbf{B_{4}}$ | = | $\frac{1}{4} \, \mathbf{a}_{1}+\frac{3}{4} \, \mathbf{a}_{2}- z_{2} \, \mathbf{a}_{3}$ | = | $\frac{1}{2}a \,\mathbf{\hat{x}}+\frac{1}{4}b \,\mathbf{\hat{y}}- c z_{2} \,\mathbf{\hat{z}}$ | (4g) | Se I |
References
- D. Louca, K. Horigane, A. Llobet, R. Arita, S. Ji, N. Katayama, S. Konbu, K. Nakamura, T.-Y. Koo, P. Tong, and K. Yamada, Local atomic structure of superconducting FeSe$_{1-x}$Te$_{x}$, Phys. Rev. B 81, 134524 (2010), doi:10.1103/PhysRevB.81.134524.
- M. C. Lehman, A. Llobet, K. Horigane, and D. Louca, The crystal structure of superconducting FeSe$_{1-x}$Te$_{x}$ by pulsed neutron diffraction, J. Phys: Conf. Ser. 251, 012009 (2010), doi:10.1088/1742-6596/251/1/012009.
First cited in
- D. Hicks, M. J. Mehl, E. Gossett, C. Toher, O. Levy, R. M. Hanson, G. L. W. Hart, and S. Curtarolo, The AFLOW Library of Crystallographic Prototypes: Part 2, Comp. Mat. Sci. 161, S1-S1011 (2019). (doi=10.1016/j.commatsci.2018.10.043)
Geometry files
Prototype Generator
aflow --proto=AB_oC8_67_a_g --params=$a,b/a,c/a,z_{2}$