Indium(III) Oxide
Properties
| State | Solid |
| Color | Pale yellow to greenish-yellow |
| Solubility | Insoluble in water; slowly soluble in hot HCl and H2SO4 |
| Melting Point | 1910 °C |
| Boiling Point | Approximately 2000 °C (sublimes with decomposition) |
About Indium(III) Oxide
Indium(III) oxide is the crystallographically odd member of the trivalent oxide family — it crystallizes in the cubic bixbyite structure (space group Ia-3) with In(III) sitting in two distinct octahedral sites in a 3×3×3 fluorite-derived supercell with a quarter of the oxygen sites systematically vacant. That vacancy ordering, shared with the rare-earth sesquioxides, gives In2O3 a 3.75 eV bandgap (transparent through the visible) but enough native carrier density from oxygen vacancies to be modestly conductive on its own. The reason every chemistry teacher should care about In2O3, though, is what you make from it: indium tin oxide (ITO), the transparent conductive coating on essentially every LCD, OLED, smartphone touchscreen, solar-cell front contact, and heated automotive windshield in production. ITO targets are made by hot-pressing 90:10 In2O3:SnO2 powders at ~1400 °C, then sputtering them onto glass or PET to give 100–200 nm films that are ~90% transparent across the visible and have sheet resistances of 10–30 Ω/sq — a combination no rival material has fully matched. The ITO market consumes the vast majority of mined indium and is roughly $5 B/yr globally. In2O3 also gets used as a CO2 hydrogenation catalyst (the Topsøe and Lurgi methanol routes), as a Li-ion anode candidate, and as a high-refractive-index layer in dielectric optical coatings.
Where you'll encounter it
If you're reading this on a phone screen, a laptop display, or a touchscreen of any kind, an In2O3-derived ITO film a few hundred nanometers thick is sitting on top of every pixel as the transparent electrode that lets the backlight through while still letting current drive the liquid crystal or OLED stack. In a sputter-deposition lab patterning thin-film solar cells, an ITO target hot-pressed from 90:10 In2O3:SnO2 powders gets argon-ion-bombarded to grow 100–200 nm films at 90% transmission and 10–30 Ω/sq sheet resistance — the combination no rival material has matched. In a CO2-hydrogenation reactor at the bench scale, Pd-promoted In2O3 catalysts run methanol synthesis from CO2 + H2 at 50 bar and 280 °C with selectivity that has outperformed traditional Cu/ZnO/Al2O3 in several recent comparisons.
Common Uses
- Feedstock for sintered ITO sputter targets (In2O3:SnO2 90:10) used in display manufacturing
- Transparent conductive electrode in LCDs, OLEDs, smartphone touchscreens
- Front transparent contact in CIGS and CdTe thin-film photovoltaics
- Heterogeneous catalyst for CO2 + H2 → methanol on Pd-promoted In2O3 supports
- Gas-sensor active layer for ozone, NO2, and ethanol detection
- High-index dielectric layer in multilayer optical interference coatings
Safety Information
GHS: STOT-RE Cat 1 (respiratory tract). OSHA PEL 0.1 mg/m³ as In. Inhalation of ITO dust during target sanding, polishing, or recycling causes pulmonary alveolar proteinosis ('indium lung') with progressive interstitial fibrosis — a serious occupational disease first documented in Japanese ITO production workers in 2003 with several fatalities. NIOSH and the Japanese Ministry of Health both issued tightened exposure controls after the early case reports. Any dry-powder handling or machining of ITO ceramics requires HEPA-filtered local exhaust and respiratory PPE; lab-scale handling of bulk crystalline In2O3 is far less hazardous because the dust loading is low.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.