Iridium(IV) oxide

Iridium(IV) oxide, IrO₂, is the only well-characterised oxide of iridium. It is a blue-black solid, used with other rare oxides to coat anodes.

Iridium(IV) oxide

Names
Other names Iridium dioxide
Identifiers
CAS Number	12030-49-8 Y
3D model (JSmol)	Interactive image
ChemSpider	10605808 Y
ECHA InfoCard	100.031.572
PubChem CID	82821
UNII	CL6CQW9MWS Y
CompTox Dashboard (EPA)	DTXSID1051222
InChI InChI=1S/Ir.2O/q+4;2*-2 Y Key: NSTASKGZCMXIET-UHFFFAOYSA-N Y InChI=1/Ir.2O/q+4;2*-2 Key: NSTASKGZCMXIET-UHFFFAOYAQ
SMILES [Ir+4].[O-2].[O-2]
Properties
Chemical formula	IrO2
Molar mass	224.22 g/mol
Appearance	blue-black solid
Density	11.66 g/cm3
Melting point	1,100 °C (2,010 °F; 1,370 K) decomposes
Solubility in water	insoluble
Magnetic susceptibility (χ)	+224.0·10−6 cm3/mol
Structure
Crystal structure	Rutile (tetragonal)
Coordination geometry	Octahedral (Ir); Trigonal (O)
Hazards
Flash point	Non-flammable
Related compounds
Other anions	iridium(IV) fluoride, iridium disulfide
Other cations	rhodium dioxide, osmium dioxide, platinum dioxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Synthesis

As described by its discoverers, it can be formed by treating the green form of iridium trichloride with oxygen at high temperatures:

2 IrCl₃ + 2 O₂ → 2 IrO₂ + 3 Cl₂

A hydrated form is also known.^[1]

Structure

The compound adopts the TiO₂ rutile structure, featuring six coordinate iridium and three coordinate oxygen.^[2] It forms a tetragonal lattice with lattice parameters of 4.5Å and 3.15Å.^[3]

Mechanical properties

Oxide materials are typically hard and brittle.^[4] Indeed, iridium oxide does not easily deform under stress,^[5] instead cracking easily.^[6] Measured deflections of a thin, cantilevered iridium oxide film indicate a Young’s modulus of 300 ± 15 GPa,^[5] substantially lower than the Young's modulus of metallic iridium (517 GPa).^[7]

Applications

Iridium dioxide can be used to make coated electrodes^[8] for industrial electrolysis or as microelectrodes for electrophysiology.^[9] In electrolytic applications, IrO₂ films evolve O₂ efficiently.^[10]

Electrode manufacture typically requires high-temperature annealing.^[11]

Fracture and delamination are well-known problems when fabricating devices that incorporate iridium oxide film. One cause of delamination is lattice mismatch between iridium oxide and the substrate. Sputtering iridium oxide on a liquid crystal polymer has been proposed to avoid mismatch,^[12] but sputtered films spontaneously delaminate during cyclic voltammetry if the maximum potential bias exceeds 0.9 V.^[13]