Post-cotunnite phase of ${\text{TeO}}_2$ obtained from first-principles density-functional theory methods with random-structure searching

We have used first-principles density-functional theory methods with a random-structure-searching technique to determine the structure of the previously unidentified post-cotunnite phase of ${\text{TeO}}_2$. Our calculations indicate a transition from the cotunnite to post-cotunnite phase at 130 GPa. The predicted post-cotunnite structure has $P{2}_1/m$ space group symmetry and its calculated x-ray diffraction pattern is in reasonable agreement with the available experimental data. We find that the cotunnite phase reenters at about 260 GPa.

Figure 1

(Color online) Enthalpy per ${\text{TeO}}_2$ unit relative to that of the cotunnite structure as a function of pressure.

Figure 2

(Color online) (a) Cotunnite, (b) $P{2}_1/m$, (c) $Cmcm$, and (d) $P\overline{1}$ structures. The yellow (light) spheres are Te atoms and the red (dark) spheres are O atoms.

Figure 3

(Color online) Comparison of observed (red solid lines) and calculated (green dashed lines) x-ray diffraction data for the cotunnite structure (upper box) at 53 GPa and the $P{2}_1/m$ structure (lower box) at 130 GPa. The experimental diffraction data are from Ref. 8. The experimental and calculated data were obtained with an x-ray wavelength of $\lambda =0.4254\text{Å}$. The black arrows mark known impurity lines in the experimental data (Ref. 8) although other impurity lines may also be present.

Figure 4

(Color online) Volume per ${\text{TeO}}_2$ f.u. of the cotunnite and $P{2}_1/m$ structures.

Figure 5

(Color online) Band gaps of the cotunnite, $P{2}_1/m$, $Cmcm$, and $P\overline{1}$ structures as a function of pressure.