Octahedral rotation-induced ferroelectricity in cation ordered   perovskites
  Increasing demands for electric field-tunable electric, magnetic, and orbital (EMO) materials has renewed interests in ferroelectricity and its coupling to EMO properties in complex perovskite oxides. The historic design strategy to achieve a spontaneous polarization involves the incorporation of second-order Jahn-Teller (SOJT) active cations. The challenge, however, is that this mechanism is limited to specific chemistries and the polar distortions that arise are largely decoupled from EMO properties, limiting their use as field-tunable multifunctional technology materials. Here we report the crystal-chemistry criteria which circumvents those restrictions and enables the rational design of new materials displaying octahedral rotation-induced ferroelectricity - an innovative route to realize electric polarization without the need for SOJT cations - from non-polar building blocks. The strategy exploits the centric octahedral rotation patterns, which strongly couple to EMO properties, and cation ordering commonly observed in non-polar $AB$O$_3$ perovskites. By uniting switchable electric polarizations to the connectivity of the transition-metal oxygen octahedra, electric-field control over materials properties is possible. 
James M. Rondinelli and Craig J. Fennie
cond-mat.mtrl-sci