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Figure 8
Crystal structure of the P42mc phase at 300°C showing (a) the view down the a-axis highlighting in-phase tilting in this direction, and off-centring of Nb atoms along the polar c-axis and (b) the out-of-phase tilt along the c-axis.

IUCrJ
Volume 4| Part 3| May 2017| Pages 215-222
ISSN: 2052-2525
https://doi.org/10.1107/S2052252517002226