Vanadium dioxide

Vanadium(IV) oxide

Names
IUPAC name Vanadium(IV) oxide
Other names Vanadium dioxide Divanadium tetroxide
Identifiers
CAS Number	12036-21-4 Y
ECHA InfoCard	100.031.661
PubChem CID	82849
Properties
Chemical formula	VO2
Molar mass	82.94 g/mol
Appearance	Deep Blue Powder
Density	4.571 g/cm3 (monoclinic) 4.653 g/cm3 (tetragonal)
Melting point	1,967 °C
Magnetic susceptibility (χ)	+270.0·10−6 cm3/mol
Structure
Crystal structure	Distorted rutile (<70 °C, monoclinic) Rutile (>70 °C, tetragonal)
Hazards
R-phrases (outdated)	36/37/38
S-phrases (outdated)	26-36/37/39
NFPA 704	0 2 0
Flash point	Non-flammable
Related compounds
Other anions	Vanadium disulfide Vanadium diselenide Vanadium ditelluride
Other cations	Niobium(IV) oxide Tantalum(IV) oxide
Related vanadium oxides	Vanadium(II) oxide Vanadium(III) oxide Vanadium(V) oxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y  (what is YN ?)
Infobox references

Vanadium(IV) dioxide is an inorganic compound with the formula VO₂. It is a dark blue solid. Vanadium(IV) dioxide is amphoteric, dissolving in non-oxidising acids to give the blue vanadyl ion, [VO]²⁺ and in alkali to give the brown [V₄O₉]²⁻ ion, or at high pH [VO₄]⁴⁻. VO₂ has a phase transition very close to room temperature(~66 °C). Electrical resistivity, opacity, etc, can change up several orders. Due to these properties, it has been widely used in surface coating, sensors, and imaging. Potential applications include use in memory devices.

At temperatures below T_c=340 K, VO
2 has a monoclinic (space group P2₁/c) crystal structure. Above T_c, the structure is tetragonal, like rutile TiO
2. In the monoclinic phase, the V⁴⁺ ions form pairs along the c axis, leading to alternate short and long V-V distances of 2.65 Å and 3.12 Å. In comparison, in the rutile phase the V⁴⁺ ions are separated by a fixed distance of 2.96 Å. As a result, the number of V⁴⁺ ions in the crystallographic unit cell doubles from the rutile to the monoclinic phase.

The equilibrium morphology of rutile VO
2 particles is acicular, laterally confined by (110) surfaces, which are the most stable termination planes. The surface tends to be oxidized with respect to the stoichiometric composition, with the oxygen adsorbed on the (110) surface forming vanadyl species. The presence of V⁵⁺ ions at the surface of VO
2 films has been observed by x-ray photoelectron spectroscopy (XPS) measurements.