The nature of the charge ordering in Fe2BO4 was carefully examined by in situ TEM observations from 360 down to 20K. An incommensurate structural modulation with the wave vector q = (1/2,0,ε) became plainly visible in association with the charge ordering transition at TCO≈340K. Careful structural analysis suggested that this incommensurate structure originates from a well-defined Fe2+/Fe3+ ionic order along the FeO6 octahedral ribbons (in the a-axis direction) and from a discommensurate antiphase stripe order along the c-axis direction. The average periodicity of antiphase stripes changed notably with lowering temperature and, via certain intermediate states, toward a superstructure phase with modulation wave vector of q=(1/2,0,0) at ∼150K in association with a magnetic phase transition.

Charge-Ordering Transition and Incommensurate Antiphase Structure of Fe2BO4 as Seen Via Transmission Electron Microscopy. Y.J.Song, H.X.Yang, H.F.Tian, C.Ma, Y.B.Qin, L.J.Zeng, H.L.Shi, J.B.Lu, J.Q.Li: Physical Review B, 2010, 81[2], 020101