Influence of Ta doping on the phase transition characteristics of VO2 polycrystalline thin films

V2O5 and Ta2O5 mixed powders were pressed as sputtering target. Ta-doped vanadium oxide thin films were deposited on SiO, substrates by modified Ion Beam Enhanced Deposition (IBED) method, The VO2 film with a preferential orientation (002) was formed after post-annealing in nitrogen or argon atmosphere. The measurement results of resistance dependence on temperature indicated that the vanadium dioxide films showed a typical characteristic of phase transition. The phase transition temperature of the IBED VO2 film doped with 3 atm.% Ta decreased from 68 degrees C to about 48 degrees C. The reasons why the Ta-doping decrease the phase transition temperature were as followed: the atom radius of Ta larger than that of V atom, which introduce strain in the grain; the replacement of When V4+ replaced by Ta5+ the ionic bond could elongate and introduce superfluous electrons in the d valence shell, then make the gap of d energy band to decrease.