Fig. 19: Illustration of the hybrid improper ferroelectricity in artificial perovskite superlattices.

a Oxygen octahedral rotation around [001] direction. b Oxygen octahedral tilt around [110] direction. c Antipolar displacement (X5+ mode) on A-site atoms. d Residual polarization arises from the non-canceled antipolar A-site displacements in 1LaGaO3/1YGaO3 superlattice. Reprinted from ref. 200, Copyright (2012), with permission from Elsevier.