A domain wall in ferroïc compounds is not necessarily a passive region that accommodates the different ferroic-order orientations of the domains that border it. Working on TbMnO3, Farokhipoor et al. recently highlighted that it can also be a reactive area that generates and stabilizes new two-dimensional crystallographic phases never observed in bulk materials and not achievable by conventional means. In a News & Views advertising that work, Ph. Ghosez and J.-M. Triscone clarify that their findings is related to a trilinear coupling of lattice modes and should be a generic feature of certain ferroelastic domain walls in Pnma perovskites. 

Ph. Ghosez and J.-M. Triscone, Nature 515, 348-350 (2014).

Farokhipoor, S. et al. Nature 515, 379-383 (2014).