Vanadium(IV) oxide
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| Names | |
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IUPAC name
Vanadium(IV) oxide
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| Other names
Vanadium dioxide
Divanadium tetroxide |
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| Identifiers | |
| ECHA InfoCard | 100.031.661 |
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PubChem CID
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| Properties | |
| 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 |
| +270.0·10−6 cm3/mol | |
| Structure | |
| Distorted rutile (<70 °C, monoclinic) Rutile (>70 °C, tetragonal) |
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| Hazards | |
| R-phrases (outdated) | 36/37/38 |
| S-phrases (outdated) | 26-36/37/39 |
| NFPA 704 | |
| Flash point | Non-flammable |
| Related compounds | |
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Other anions
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Vanadium disulfide Vanadium diselenide Vanadium ditelluride |
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Other cations
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Niobium(IV) oxide Tantalum(IV) oxide |
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Vanadium(II) oxide Vanadium(III) oxide Vanadium(V) oxide |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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 (what is   ?) |
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| 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 Tc=340 K, VO
2 has a monoclinic (space group P21/c) crystal structure. Above Tc, 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.
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