(color online) (a) Atomic resolution image of domains and domain walls in BFO crystal recorded parallel to the direction. A stripe-domain wall outlined by yellow area consists of two segments, DW1 between domain D1 and domains D2, and DW2 between domain D1 and domain D3. Another domain wall DW3 (blue area) separates domain D2 from D3. Vertical arrows denote the direction of the component of the type polarization vector. Magnified image of the atom arrangement in (b) domains D1 and D3, (c) domain D2, and (d) domain wall area DW3.^[30]