Hafnium(IV) oxide

Hafnium(IV) oxide
IUPAC name Hafnium(IV) oxide
Other names Hafnium dioxide Hafnia
Identifiers
CAS number	12055-23-1 Y
PubChem	292779
ChemSpider	258363 Y
Jmol-3D images	Image 1
SMILES O=[Hf]=O
InChI InChI=1S/Hf.2O Y Key: CJNBYAVZURUTKZ-UHFFFAOYSA-N Y InChI=1/Hf.2O/rHfO2/c2-1-3 Key: CJNBYAVZURUTKZ-MSHMTBKAAI
Properties
Molecular formula	HfO2
Molar mass	210.49 g/mol
Appearance	off-white powder
Density	9.68 g/cm3, solid
Melting point	2758 °C
Boiling point	5400 °C
Solubility in water	insoluble
Hazards
EU Index	Not listed
Flash point	Non-flammable
Related compounds
Other cations	Titanium(IV) oxide Zirconium(IV) oxide
Related compounds	Hafnium nitride
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Hafnium(IV) oxide is the inorganic compound with the formula HfO₂. Also known as hafnia, this colourless solid is one of the most common and stable compounds of hafnium. It is an electrical insulator with a band gap of approximately 6 eV. Hafnium dioxide is an intermediate in some processes that give hafnium metal.

Hafnium(IV) oxide is quite inert. It reacts with strong acids such as concentrated sulfuric acid and with strong bases. It dissolves slowly in hydrofluoric acid to give fluorohafnate anions. At elevated temperatures, it reacts with chlorine in the presence of graphite or carbon tetrachloride to give hafnium tetrachloride.

Applications

Hafnia is used in optical coatings, and as a high-k dielectric in DRAM capacitors. Hafnium-based oxides are currently leading candidates to replace silicon oxide as a gate insulator in field effect transistors. The advantage for transistors is its high dielectric constant: The dielectric constant of HfO₂ is 25, whereas the dielectric constant of SiO₂ is only 3.9.

Because of its very high melting point, hafnia is also used as a refractory material in the insulation of such devices as thermocouples, where it can operate at temperatures up to 2500 °C.