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![[Figure 7]](iu5044fig7mag.jpg)
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Figure 7
(a) Schematic of the diffraction mode selected at 25 K and room temperature and the final mode set, plotted alongside the modes obtained from DFT. The 40 DFT modes with an absolute value greater than 0.13 Å are marked in red, and whenever the same mode is included in any of the diffraction mode sets, it is also marked in red there. Black marks indicate modes that were not selected as one of the 40 DFT modes but are included in the diffraction mode sets. The fractions indicate how many of the selected diffraction modes are also among the 40 DFT modes, i.e. number of red modes over number of total modes (red + black). The mode amplitudes are indicated for the DFT modes and the final mode set at room temperature. (b) Ama2 unit cell with blue arrows indicating the distortion direction of the antiferroelectric mode 44. NbO6 octahedra in grey with Nb at the centre in green (oxygen omitted for clarity), Na in yellow (mostly on the square A1 site) and Ba in red (mostly on the pentagonal A2 site). The illustration was made using VESTA (Momma & Izumi, 2011  ). |
![[Figure 7]](iu5044fig7.jpg)
 | JOURNAL OF APPLIED CRYSTALLOGRAPHY |
ISSN: 1600-5767
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