Coccinite (Red HgI$_{2}$, $C13$) Structure: AB2_tP6_137_a_d-001
| Prototype | HgI$_{2}$ |
| AFLOW prototype label | AB2_tP6_137_a_d-001 |
| Strukturbericht designation | $C13$ |
| Mineral name | coccinite |
| ICSD | 241175 |
| Pearson symbol | tP6 |
| Space group number | 137 |
| Space group symbol | $P4_2/nmc$ |
| AFLOW prototype command |
aflow --proto=AB2_tP6_137_a_d-001
--params=$a, \allowbreak c/a, \allowbreak z_{2}$ |
- HgI$_{2}$ can be found in a variety of forms (Gumiński, 1997):
- The ground state, coccinite (this structure), also known as red or $\alpha$–HgI$_{2}$ and given the Strukturbericht designation $C13$. It is stable up to 135$^\circ$C.
- At higher temperatures this transforms into yellow or $\beta$–HgI$_{2}$ in the HgBr$_{2}$ ($C24$) structure. This is stable up to the melting point at 258$^\circ$C.
- (Schwarzenbach, 1969) studied the metastable orange HgI$_{2}$ body-centered tetragonal ($I4_{1}/amd$ #141) phase. This structure was refined by (Hostettler, 2002).
- (Hostettler, 2002) also found a second orange HgI$_{2}$ phase in a simple tetragonal ($P4_{2}/nmc$ #137) cell.
- The last two structures differ by stacking order. (Hostettler, 2002) used them to produce an averaged orange HgI$_{2}$ structure, space group $P\overline{4}m2$ #115.
- We use the data for coccinite taken by (Schwarzenbach, 2007) at 293 K.
- The CIF and POSCAR files contain the data at room temperature, 293 K. ZrO$_{2}$ (A2B_tP6_137_d_a) and HgI$_{2}$ (AB2_tP6_137_a_d) have similar AFLOW prototype labels (i.e., same symmetry and set of Wyckoff positions with different stoichiometry labels due to alphabetic ordering of atomic species). They are generated by the same symmetry operations with different sets of parameters (
--params) specified in their corresponding CIF files
\[ \begin{array}{ccc}
\mathbf{a_{1}}&=&a \,\mathbf{\hat{x}}\\\mathbf{a_{2}}&=&a \,\mathbf{\hat{y}}\\\mathbf{a_{3}}&=&c \,\mathbf{\hat{z}}
\end{array}\]
Basis vectors
| Lattice coordinates | Cartesian coordinates | Wyckoff position | Atom type | |||
|---|---|---|---|---|---|---|
| $\mathbf{B_{1}}$ | = | $\frac{3}{4} \, \mathbf{a}_{1}+\frac{1}{4} \, \mathbf{a}_{2}+\frac{3}{4} \, \mathbf{a}_{3}$ | = | $\frac{3}{4}a \,\mathbf{\hat{x}}+\frac{1}{4}a \,\mathbf{\hat{y}}+\frac{3}{4}c \,\mathbf{\hat{z}}$ | (2a) | Hg I |
| $\mathbf{B_{2}}$ | = | $\frac{1}{4} \, \mathbf{a}_{1}+\frac{3}{4} \, \mathbf{a}_{2}+\frac{1}{4} \, \mathbf{a}_{3}$ | = | $\frac{1}{4}a \,\mathbf{\hat{x}}+\frac{3}{4}a \,\mathbf{\hat{y}}+\frac{1}{4}c \,\mathbf{\hat{z}}$ | (2a) | Hg I |
| $\mathbf{B_{3}}$ | = | $\frac{1}{4} \, \mathbf{a}_{1}+\frac{1}{4} \, \mathbf{a}_{2}+z_{2} \, \mathbf{a}_{3}$ | = | $\frac{1}{4}a \,\mathbf{\hat{x}}+\frac{1}{4}a \,\mathbf{\hat{y}}+c z_{2} \,\mathbf{\hat{z}}$ | (4d) | I I |
| $\mathbf{B_{4}}$ | = | $\frac{1}{4} \, \mathbf{a}_{1}+\frac{1}{4} \, \mathbf{a}_{2}+\left(z_{2} + \frac{1}{2}\right) \, \mathbf{a}_{3}$ | = | $\frac{1}{4}a \,\mathbf{\hat{x}}+\frac{1}{4}a \,\mathbf{\hat{y}}+c \left(z_{2} + \frac{1}{2}\right) \,\mathbf{\hat{z}}$ | (4d) | I I |
| $\mathbf{B_{5}}$ | = | $\frac{3}{4} \, \mathbf{a}_{1}+\frac{3}{4} \, \mathbf{a}_{2}- z_{2} \, \mathbf{a}_{3}$ | = | $\frac{3}{4}a \,\mathbf{\hat{x}}+\frac{3}{4}a \,\mathbf{\hat{y}}- c z_{2} \,\mathbf{\hat{z}}$ | (4d) | I I |
| $\mathbf{B_{6}}$ | = | $\frac{3}{4} \, \mathbf{a}_{1}+\frac{3}{4} \, \mathbf{a}_{2}- \left(z_{2} - \frac{1}{2}\right) \, \mathbf{a}_{3}$ | = | $\frac{3}{4}a \,\mathbf{\hat{x}}+\frac{3}{4}a \,\mathbf{\hat{y}}- c \left(z_{2} - \frac{1}{2}\right) \,\mathbf{\hat{z}}$ | (4d) | I I |
References
- D. Schwarzenbach, H. Birkedal, M. Hostettler, and P. Fischer, Neutron diffraction investigation of the temperature dependence of crystal structure and thermal motions of red HgI$_{2}$, Acta Crystallogr. Sect. B 63, 826–835 (2007), doi:10.1107/S0108768107043327.
- M. Hostettler, H. Birkedal, and D. Schwarzenbach, The structure of orange HgI$_{2}$. I. Polytypic layer structure, Acta Crystallogr. Sect. B 58, 903–913 (2002), doi:10.1107/S010876810201618X.
- D. Schwarzenbach, The crystal structure and one-dimensional disorder of the orange modification of HgI$_{2}$, Z. Kristallogr. 128, 97–114 (1969), doi:10.1524/zkri.1969.128.1-2.97.
Found in
- R. T. Downs and M. Hall-Wallace, The American Mineralogist Crystal Structure Database, Am. Mineral. 88, 247–250 (2003).
Prototype Generator
aflow --proto=AB2_tP6_137_a_d --params=$a,c/a,z_{2}$