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Gadolinium(III) Oxide

Gd2O3 oxide
Molar Mass
362.497 g/mol
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Properties

StateSolid
ColorWhite
SolubilityInsoluble in water; slowly soluble in dilute mineral acids
Melting Point2420 °C
Boiling Point3900 °C

About Gadolinium(III) Oxide

Gadolinium(III) oxide (Gd2O3, 362.497 g/mol) is a white refractory oxide that adopts the cubic C-type bixbyite structure at room temperature, transitioning to monoclinic B-type above 1200 °C and ultimately hexagonal A-type before melting at 2420 °C. Two things make Gd chemistry distinctive among the lanthanides, and both of them flow from the 4f^7 half-filled-shell configuration of Gd(III). First, the half-filled f shell has zero orbital angular momentum (L = 0, S = 7/2, total J = 7/2), which means there are no allowed f-f transitions in the visible — Gd2O3 is colorless, unlike the famously colored neighbors Pr2O3 (green), Nd2O3 (blue-purple), Sm2O3 (cream), Eu2O3 (pink), Tb2O3 (brown). Second, those seven unpaired f electrons give Gd(III) a spin-only magnetic moment of 7.94 µB, the largest of any stable trivalent ion in the periodic table. That magnetic moment is the entire reason Gd dominates the MRI-contrast market: chelated Gd(III) shortens T1 relaxation of nearby water protons, brightening tumors, vessels, and sites of blood-brain-barrier disruption on T1-weighted images. Gd2O3 is also one of the strongest thermal-neutron absorbers known — natural Gd has a 49,000-barn cross-section, second only to B-10 — and the isotopes Gd-155 and Gd-157 push the per-isotope numbers above 60,000 and 254,000 barns respectively. That makes Gd2O3 the burnable neutron poison of choice in pressurized-water reactor fuel assemblies.

Where you'll encounter it

If you have ever loaded a CHN-O analyzer, the Sn or Ag combustion boats sometimes have a thin Gd2O3 coating to absorb stray oxygen. In a research reactor, Gd2O3 mixed at 6-9% into UO2 fuel pellets is what flattens the power profile during the first burn cycle — the gadolinium absorbs neutrons aggressively at startup and gradually 'burns out' as Gd-155 and Gd-157 transmute, which is exactly the slow rolloff the reactor designer wants. In a contrast-agent formulation suite, Gd2O3 dissolves in HCl to give the GdCl3 stock that feeds chelation reactions producing Magnevist or Dotarem at multi-tonne scale. In a magnetocaloric-refrigeration prototype targeting sub-Kelvin temperatures, a 1 kg Gd2O3-derived gadolinium gallium garnet (GGG) salt pill is the cold sink that adiabatic demagnetization steps the temperature down through 100 mK in dilution-fridge experiments.

Common Uses

  • Burnable neutron poison at 6-9% in PWR UO2 fuel pellets to flatten startup power profile
  • Precursor for synthesis of Gd-DTPA, Gd-DOTA, and other MRI contrast chelates
  • Magnetocaloric refrigerant near room temperature for sub-Kelvin physics experiments
  • Phosphor host matrix for Gd2O2S:Tb x-ray intensifier screens in radiography
  • Sintering aid in YSZ thermal-barrier coatings for jet engine turbine blades
  • High-k dielectric layer in research-grade MOS capacitor structures
  • Neutron-shield ceramic in cold-neutron beamline collimators
  • Glass-additive Faraday-rotator constituent in fiber-optic isolators

Safety Information

GHS: Eye irritation (Cat 2A, H319). Low acute toxicity in bulk solid form — oral LD50 in rats >5 g/kg. The clinical concern is downstream: Gd3+ released in vivo from poorly stable linear-chelate MRI contrast agents (Omniscan, OptiMARK) deposits in skin, brain, bone, and connective tissue, causing Nephrogenic Systemic Fibrosis in renal-impaired patients (eGFR <30 mL/min) — basis for the FDA black-box warning on linear agents. Macrocyclic chelates (Dotarem, Gadavist, ProHance) have far lower release rates and minimal NSF risk. Powder-handling: respirable dust under the 15 mg/m3 OSHA total-dust nuisance limit; use HEPA-filtered local exhaust. Reactor-grade Gd2O3 is alpha-radioactive at trace levels from rare isotope decay chains; handle per institutional radioisotope protocol.

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.

Constituent Elements

Gd — Gadolinium O — Oxygen

Frequently Asked Questions

What is the molar mass of gadolinium(III) oxide?
Gd2O3 has a molar mass of 362.497 g/mol. The breakdown: 2 × Gd (2 × 157.25 = 314.50) + 3 × O (3 × 15.999 = 47.997). Density is 7.41 g/cm³, which puts it among the densest of the lanthanide sesquioxides — useful when you are calculating thickness for a neutron-absorber slab and need to know how much shielding you get per millimeter.
How does Gd enhance MRI contrast?
Gd(III) carries seven unpaired 4f electrons (the half-filled-shell maximum) and an unusually long electron-spin relaxation time around 10^-9 s — that combination makes it an exceptionally efficient T1 relaxation agent. When chelated Gd(III) (Gd-DTPA, Gd-DOTA) sits in tissue, it dramatically shortens the T1 relaxation of nearby water protons through dipole-dipole coupling, brightening those regions on T1-weighted images. Sites with leaky vasculature — tumors, infarcts, blood-brain-barrier breaches — accumulate Gd faster than surrounding tissue and light up. Worldwide, about 30 million MRI doses of Gd contrast agents are administered annually.
Why is Gd such a strong neutron absorber?
Two of the seven natural Gd isotopes carry enormous thermal-neutron capture cross-sections: Gd-157 at 254,000 barns and Gd-155 at 61,000 barns, with natural abundances of 15.6% and 14.8% respectively. The cross-section comes from a near-resonance match between the incoming thermal neutron energy and a nuclear excited state in the compound nucleus — Gd-158 in the case of Gd-157(n,γ). The natural-isotope-mix average is about 49,000 barns, second only to boron-10 (3,840 barns is the natural abundance-weighted figure for boron, but enriched B-10 reaches ~3,800 barns by itself). That is exactly the property exploited in PWR burnable-poison fuel: Gd2O3 mixed into UO2 absorbs excess startup reactivity, then transmutes away over the first 12-18 months of burn.