VO(2)(B) nanorods: solvothermal preparation, electrical properties, and conversion to rutile VO(2) and V(2)O(3)

The solvothermal reduction of V(2)O(5) by formaldehyde or isopropanol yields nanorods of the metastable, monoclinic VO(2)(B) phase. The structural transitior in VO(2)(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 pat erned contacts. A sudden, 10(5) increase in the electrical resistivity upon cooling below 290 K is seen in measurements on VO(2)(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 VO(2) upon cooling below 340 K. The metastable VO(2)(B) nanorods are converted to rutile VO(2) by heating in argon, and to corundum V(2)O(3) by reducing in 5%H(2):95%N(2). In both transformations, the structural integrity of the nanorods is compromised, with large dense, rutile VO(2) crystallites and less well-defined nanorods of V(2)O(3) being formed.