Terbium(III,IV) Oxide
Properties
| State | Solid |
| Color | Dark brown to black |
| Solubility | Insoluble in water; soluble in acids with reduction to Tb(III) |
| Melting Point | Decomposes above 1000 °C |
About Terbium(III,IV) Oxide
Terbium(III,IV) oxide is a dark-brown-to-black mixed-valence oxide (Tb4O7, 747.69 g/mol) and the form in which essentially all commercial terbium gets shipped. The formula is best read as 2 TbO2·Tb2O3 — two Tb(IV) centers and two Tb(III) centers per formula unit, in a fluorite-derived structure with ordered oxygen vacancies. The +4 oxidation state shows up here for the same reason it does in cerium: Tb(IV) reaches the half-filled 4f⁷ subshell, which provides just enough thermodynamic stabilization to make the higher oxide accessible in air. Calcine any Tb-containing salt (the carbonate, oxalate, nitrate) at 800–1000°C in air and you converge on Tb4O7 as the equilibrium product; reduce it under H2 at 1300°C and you get back Tb2O3. Two applications drive the entire Tb market: (1) green phosphor activator in trichromatic fluorescent lamps and white LEDs, where Tb³⁺ emits a narrow 545-nm line via the 5D4 → 7F5 transition; and (2) the heavy-rare-earth additive that lets sintered NdFeB permanent magnets keep their coercivity up to 200°C, the temperature an EV traction motor sees on a hot day. China controls roughly 95% of global heavy-rare-earth supply, which has made Tb4O7 a strategic-material headache for every Western EV program.
Where you'll encounter it
If you've ever stood under a high-CRI fluorescent tube in a museum or a dentist's office and noticed the light feels close to daylight, the green channel of that emission is Tb³⁺ doped into a yttrium-aluminate or magnesium-aluminate phosphor — Tb4O7 is the bulk source. The other place Tb4O7 shows up at industrial scale is at companies like Hitachi Metals and Shin-Etsu, who buy it by the metric ton, reduce it to Tb metal via molten-salt electrolysis (or convert to TbF3 for direct grain-boundary diffusion), then process it into sintered NdFeB magnet stacks for Tesla, BYD, and Toyota traction motors. Small amounts also feed into Terfenol-D production for sonar transducers and precision actuators — that's the magnetostrictive alloy the US Navy developed at the Naval Ordnance Laboratory in the 1970s, with strain coefficients an order of magnitude better than nickel.
Common Uses
- Bulk commercial form of terbium metal (the way Tb is shipped, stored, and traded)
- Green phosphor activator source for trichromatic fluorescent lamps and high-CRI white LEDs
- Heavy-rare-earth additive for high-coercivity NdFeB EV traction-motor magnets
- Feedstock for Terfenol-D magnetostrictive alloy (Tb0.3Dy0.7Fe1.9) for sonar transducers
- Precursor for Tb-doped YAG laser crystals and silicate scintillator single crystals
- Starting material for Tb metal production via molten-fluoride electrolysis
- Source of Tb for Faraday rotator glasses and other magneto-optic isolator components
Safety Information
GHS: Eye Irritation Category 2A (H319). Low acute oral toxicity (rat oral LD50 in the multi-g/kg range, typical of Ln oxides). The real chronic concern is dust inhalation: bulk handlers report mild pulmonary fibrosis on long-term exposure to lanthanide oxide dusts. No specific OSHA PEL; default to PNOC at 5 mg/m3 respirable, 15 mg/m3 total. The dark color makes it easy to spot contamination on glassware and hood surfaces — useful, because the fine dust travels easily and is reduced to soluble Tb(III) by sweat or aqueous workups. Standard dust mask, nitrile gloves, and goggles for weighing; HEPA-filtered local exhaust for any milling or sieving operation.
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.