Fig. 4: Charge and trimeron orders in magnetite.

a Trimeron distribution in the low-temperature magnetite Cc cell, with Fe²⁺/Fe³⁺ shown as blue/yellow spheres and trimeron ellipsoids in green. The selectively oxidised B42 site is labelled, and the unusual termination of its trimeron by another Fe²⁺ is marked by a square. b (100) surface of cubic magnetite showing trimerons in the surface layer. The B42 sites (blue and white ‘beachballs’) are expected to be oxidised in preference to other trimerons. Charge-ordered Fe²⁺/Fe³⁺ are shown as blue/yellow spheres, tetrahedral Fe/O sites are brown/red.