Tungsten(IV) oxide, chemical formula WO₂, is a significant compound of tungsten. It appears as a bronze-colored, crystalline solid, distinct from the yellow WO₃. This material exhibits metallic conductivity, setting it apart from many other oxides. Its electrical resistivity is relatively low, typically in the range of 10⁻³ to 10⁻⁴ ohm-cm.
(tungsten iv oxide)
Structurally, WO₂ adopts a distorted rutile (TiO₂) crystal lattice. This distortion arises from the formation of tungsten-tungsten bonds, creating chains within the structure. These direct metal-metal interactions are crucial for its characteristic electrical conductivity and metallic luster. It is often classified as a bronze-phase material.
WO₂ is typically prepared by carefully reducing tungsten trioxide (WO₃) under controlled conditions. Common reducing agents include tungsten metal powder or hydrogen gas, often at elevated temperatures (e.g., 900-1000°C). Precise control of temperature and atmosphere is essential to achieve pure WO₂ and avoid further reduction or oxidation.
Its applications leverage its unique electrical properties. WO₂ is investigated for use in resistive gas sensors, particularly for detecting reducing gases like hydrogen sulfide or ammonia, where changes in its resistivity upon gas exposure provide the sensing signal. Its plasmonic properties in the infrared range make it a candidate material for applications like tunable metamaterials and thermophotovoltaics. It also finds some use as a catalyst or catalyst support.
(tungsten iv oxide)
Handling WO₂ requires caution. It is sensitive to air oxidation, especially at elevated temperatures, and can revert to WO₃. Consequently, it must often be stored and handled under inert atmospheres. Synthesis can be challenging, requiring precise conditions to prevent over-reduction to sub-oxides or tungsten metal. Despite these challenges, its distinct metallic character within the oxide family drives ongoing research interest.
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