Growth Of Nanotubes In Sol-gel-derived V_2o_5 Powders And Films Prepared Under Acidic Conditions

摘要

The structural evolution with temperature of some V_2O_5 gels and thin films is presented, and the role of the hydrolysis conditions is investigated. Several techniques, i.e., x-ray diffraction, differential thermal analysis, infrared, and temperature-dependent Raman spectroscopy, have been used to follow the thermal behavior of the samples. When the bulk xerogels begin to change from a nanocrystalline phase to the orthorhombic α-V_2O_5, in the temperature range 280 to 300 ℃, a growth of vanadium oxide nanotubes also occurs, while at higher temperatures the crystallization into the a phase prevails. A slightly different evolution is observed for heat treated thin films, which show a structure containing polyvanadate chains near room temperature. They also present a growth of nanotubes for intermediate temperatures and a complete crystallization into the a phase when the temperature is further increased.