Small-polaron conduction and short-range order in Fe3O4

A microscopic theory of the electrical small-polaron (SP) conductivity of Fe 3 O 4 is presented taking into account the polaronic short-range order (SRO) due to intersite SP-SP interaction. The theory is based on a SP correlation model in the narrow-band limit. The concept of SRO and its role in explaining the equilibrium and transport properties are accentuated. The calculation of the SP conductivity above and below T v indicates that the conductivity of Fe 3 O 4 results from the superposition of SP band and SP hopping conduction. Concerning the DC conductivity below room temperature, the SP band conduction is the dominant mechanism. The observed maximum in the optical conductivity near 0.2 eV is explained as an SP hopping effect.