Fig. 1: Space charge-induced dopant segregation.
a Distribution of dopants and electrostatic potential (donor-doping case) in ionic oxides based on the space charge theory (Supplementary Fig. 1 for acceptor-doping case). Strong segregation of dopants in the space charge layers is induced to compensate the excess charges on the crystal surfaces and bulk GBs (Supplementary Fig. 2). See Supplementary Note 1 for more details on the space charge theory. b Schematic illustration of the dopant segregation in different types of ionic oxide crystals: (I) Crystal with numerous GBs: dopants tend to segregate at the surface and GBs. (II) Disordered nanocrystals: a small number of dopants tend to segregate on the surface due to the lack of driving force even at high temperatures. (III) Ordered nanocrystals with highly aligned interfaces: a large number of dopants segregate on the outer surface because of interface sintering (GB elimination), creating numerous interfacial VO and narrowing the space charge layer to drive the charge migration.
