fig2
Figure 2. Improper ferroelectric structure with geometric distortion. (A) Hexagonal YMnO3 structure with centrosymmetric non-polar (left), down-polar (middle), and up-polar (right). Distortion of MnO5 triangular bipyramids is indicated with arrows. (B) Ruddlesden-Popper Sr3Zr2O7 layered structures showing polar and anti-polar characteristics. ZrO6 octahedral rotations determine the polarity of the structure. Reproduced with permission[52]. Copyright 2018, WILEY-VCH Verlag Gmbh & Co. KGaA, Weinheim.
