“…Since initial reports of domain wall conduction in WO 3 [29] and BiFeO 3 (BFO) [30,31], the phenomenon has been observed in a range of materials systems such as uniaxial ferroelectrics [28,32,33,34,35] (LiNbO 3 ; Pb(Zr/Ti)O 3 ; LiTaO 3 ; BaTiO 3 , KTiOPO 4 ), multiferroics and improper ferroelectrics [36,37,38,39] ( R MnO 3 , R : Er, Y, Dy, Lu; (Ca,Sr) 3 Ti 2 O 7 ; Cu 3 B 7 O 13 Cl), and magnetic systems [40,41]. Domain walls in ferroelectrics or multiferroics are characterized by the angle between polarization vectors in neighboring domains and their charge state.…”