La Se$_{1.85}$ Structure: AB2_tP6_129_c_ac-003
Other compounds with this structure
CeSe$_{1.83}$, NdSe$_{1.83}$, SmSe$_{1.84}$
- (Graf, 2009) find the selenium (2a) site to be occupied only 85.1% of the time, giving the observed stoichiometry. They took the data for this structure at 130K.
- Cu$_{2}$Sb ($C38$), UP$_{2}$, and LaSe$_{1.85}$ have similar AFLOW prototype labels, A2B_tP6_129_ac_c for the first two and AB2_tP6_129_c_ac for the third. They are generated by the same symmetry operations with different sets of parameters (
--params) specified in their corresponding CIF files. - We consider all of these to be binary forms of Matlockite ($E0_{1}$)/PrOI.
- We somewhat arbitrarily assign
- Structures with c/a $<$ 2 to the Cu$_{2}$Sb prototype,
- Structures with 2 $<$ c/a $<$ 3 to the UP$_{2}$ prototype, and
- Structures with c/a ≈ 4 to the LaSe$_{1.85}$ prototype.
\[ \begin{array}{ccc}
\mathbf{a_{1}}&=&a \,\mathbf{\hat{x}}\\\mathbf{a_{2}}&=&a \,\mathbf{\hat{y}}\\\mathbf{a_{3}}&=&c \,\mathbf{\hat{z}}
\end{array}\]
Basis vectors
| Lattice coordinates | Cartesian coordinates | Wyckoff position | Atom type | |||
|---|---|---|---|---|---|---|
| $\mathbf{B_{1}}$ | = | $\frac{3}{4} \, \mathbf{a}_{1}+\frac{1}{4} \, \mathbf{a}_{2}$ | = | $\frac{3}{4}a \,\mathbf{\hat{x}}+\frac{1}{4}a \,\mathbf{\hat{y}}$ | (2a) | Se I |
| $\mathbf{B_{2}}$ | = | $\frac{1}{4} \, \mathbf{a}_{1}+\frac{3}{4} \, \mathbf{a}_{2}$ | = | $\frac{1}{4}a \,\mathbf{\hat{x}}+\frac{3}{4}a \,\mathbf{\hat{y}}$ | (2a) | Se I |
| $\mathbf{B_{3}}$ | = | $\frac{1}{4} \, \mathbf{a}_{1}+\frac{1}{4} \, \mathbf{a}_{2}+z_{2} \, \mathbf{a}_{3}$ | = | $\frac{1}{4}a \,\mathbf{\hat{x}}+\frac{1}{4}a \,\mathbf{\hat{y}}+c z_{2} \,\mathbf{\hat{z}}$ | (2c) | La I |
| $\mathbf{B_{4}}$ | = | $\frac{3}{4} \, \mathbf{a}_{1}+\frac{3}{4} \, \mathbf{a}_{2}- z_{2} \, \mathbf{a}_{3}$ | = | $\frac{3}{4}a \,\mathbf{\hat{x}}+\frac{3}{4}a \,\mathbf{\hat{y}}- c z_{2} \,\mathbf{\hat{z}}$ | (2c) | La I |
| $\mathbf{B_{5}}$ | = | $\frac{1}{4} \, \mathbf{a}_{1}+\frac{1}{4} \, \mathbf{a}_{2}+z_{3} \, \mathbf{a}_{3}$ | = | $\frac{1}{4}a \,\mathbf{\hat{x}}+\frac{1}{4}a \,\mathbf{\hat{y}}+c z_{3} \,\mathbf{\hat{z}}$ | (2c) | Se II |
| $\mathbf{B_{6}}$ | = | $\frac{3}{4} \, \mathbf{a}_{1}+\frac{3}{4} \, \mathbf{a}_{2}- z_{3} \, \mathbf{a}_{3}$ | = | $\frac{3}{4}a \,\mathbf{\hat{x}}+\frac{3}{4}a \,\mathbf{\hat{y}}- c z_{3} \,\mathbf{\hat{z}}$ | (2c) | Se II |
References
- C. Graf and T. Doert, LaSe$_{1.85}$, CeSe$_{1.83}$, NdSe$_{1.83}$ and SmSe$_{1.84}$ - Four new polychalcogenides of the rare earth metals with incommensurate site occupancy and displacive modulation 224, 568–579 (2009), doi:10.1524/zkri.2009.1197.
Found in
- Inorganic Crystal Structure Database}. Entry 420787 (LaSe$_{1.85$).
First cited in
- N. Anderson, M. J. Mehl, H. Eckert, S. Divilov, X. Campilongo, S. Curtarolo, The AFLOW Library of Crystallographic Prototypes: Part 5. Submitted to Computational Materials Science (2026).
Geometry files
Prototype Generator
aflow --proto=AB2_tP6_129_c_ac --params=$a,c/a,z_{2},z_{3}$