VO2(B) nanorods: solvothermal preparation, electrical properties, and conversion to rutile VO2 and V2O3

The solvothermal reduction of V2O5 by formaldehyde or isopropanol yields nanorods of the metastable, monoclinic VO2(B) phase. The structural transition in VO2(B), which occurs near room temperature, has been monitored using electrical resistivity measurements, performed both on pressed pellets of the nanorods as well as on nanorods dispersed on patterned contacts. A sudden, 105 increase in the electrical resistivity upon cooling below 290 K is seen in measurements on VO2(B) samples. Such a transition in the electrical resistivity has not previously been reported in this material. The transition is reminiscent of the metal-to-insulator transition observed in the case of pressed pellets of polycrystalline rutile VO2 upon cooling below 340 K. The metastable VO2(B) nanorods are converted to rutile VO2 by heating in argon, and to corundum V2O3 by reducing in 5%H-2 : 95%N-2. In both transformations, the structural integrity of the nanorods is compromised, with large, dense, rutile VO2 crystallites and less well-defined nanorods of V2O3 being formed.