Vanadium (IV) oxide structure and Metal to Semiconductor Transition
In recent years vanadium (IV) oxide (VO2) has been considered as a suitable material for thermochromic window
coatings; this is due to change with the temperature of its optical and electrical properties. The change is caused by a
phase transition, specifically a Metal-to-Semiconductor Transition (MST). At room temperature, vanadium (IV) oxide
most stable phase is a monoclinic (M) structure, which behaves as a semiconductor. At higher temperatures, however,
the rutile (R) structure, with semimetal properties, is more stable. The MST transition takes place at 68 oC and it is
reversible [13].
The monoclinic structure has very low reflectance and high resistivity, due to its wide band gap semiconductor
nature; the rutile structure, on the other hand, shows much higher reflectance, particularly in the infrared and electrical
conductivity. In the visible region, however, almost no change can be observed. Indeed both forms of vanadium (IV)
oxide absorb in the visible,