The nature of the metallic state in V2O3and related oxides

The Hall constant (R) and thermopower have been measured in single-crystal V2O3 at temperatures up to 800°K. R in the ‘metallic’ phase is n-type, independent of temperature and corresponds to 0·6 carriers per vanadium atom. The conductivity of V2O3 and VO2 crystals has been measured down to 7°K. Below ∼40°K there is evidence of impurity conduction with activation energies of order 0·001 ev. We infer that the ‘metallic’ state is not due to a high density Fermi gas moving in a narrow band. Recent models are examined, which propose mixed conduction with or without polaron formation, and a comparison is made with VO2 and Fe3O4