Local structure of ReO${}_3$ at ambient pressure from neutron total-scattering study

A hypothesis that the local rotations of ReO${}_6$ octahedra persist in the crystallographically untilted ambient phase of ReO${}_3$ is examined by the high-resolution neutron time-of-flight total scattering based atomic pair distribution function analysis. Three candidate models were tested, $Pm$$\overline{3}$$m$, $P4/mbm$, and $Im$$\overline{3}$, for the local structure of ReO${}_3$ at ambient pressure and 12 K, and both quantitative and qualitative assessments of the data were performed. No evidence for large local octahedral rotations was found, suggesting that the local and the average structures are the same ($Pm$$\overline{3}$$m$) as normally assumed.

Figure 1

Structural motif of ReO${}_3$ (space group $Pm$$\overline{3}$$m$): Re is shown as large spheres, while small spheres represent O.

Figure 2

Neutron experimental data of ReO${}_3$ at 12 K and at ambient pressure: (a) reduced total scattering structure function, $F\left(Q\right)$, and (b) corresponding atomic PDF, $G\left(r\right)$. Inset shows Rietveld refinement using $Pm$$\overline{3}$$m$ model (solid line) of the normalized intensity (symbols) with the difference curve offset for clarity.

Figure 3

Refinement of various models (solid black lines) to the 12 K neutron PDF data (open symbols): (a) $Pm$$\overline{3}$$m$ model, (b) $P4/mbm$ model, and (c) $Im$$\overline{3}$ model. The difference curves are offset for clarity.

Figure 4

Visual comparison of ReO${}_3$ PDFs: (a) neutron PDF data, and various calculated PDFs of competing models: (b) ambient pressure $Pm$$\overline{3}$$m$, (c) 5.2 kbar $P4/mbm$ (average rotation angle $3^{\circ }$), (d) 5.2 kbar $Im$$\overline{3}$ (average rotation angle $3^{\circ }$), and (e) 7.3 kbar $Im$$\overline{3}$ (average rotation angle $6.6^{\circ }$). In panels (c)–(e) gray-line PDF profile is that of $Pm$$\overline{3}$$m$ shown in panel (b), and is given for comparison. See text for details.