Gadolinium

Gadolinium — Material Page

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Gadolinium (Gd, atomic number 64) is a heavy lanthanide with HCP structure, melting point of 1,312 °C, and two properties of exceptional practical importance: ¹⁵⁷Gd has the highest thermal neutron absorption cross-section of any stable nuclide (σ = 254,000 barn), and Gd metal is ferromagnetic at room temperature — the only lanthanide to be ferromagnetic above 0 °C (Curie temperature 20 °C / 293 K). The 4f⁷5d¹6s² configuration gives Gd a half-filled 4f shell (maximum spin S = 7/2, J = 7/2, g = 2), which is the origin of its large magnetic moment (~7.94 µB) and its position at the maximum in the magnetocaloric effect among the lanthanides. Gd is extracted from monazite and bastnäsite; natural Gd has seven isotopes, with ¹⁵⁷Gd (15.65%) and ¹⁵⁵Gd (14.80%) both carrying enormous neutron capture cross-sections.

Gd³⁺ chelates — particularly Gd-DTPA (gadopentetate dimeglumine, Magnevist) and its macrocyclic analogues Gd-DOTA and Gd-HP-DO3A — are the dominant MRI contrast agents globally, with over 30 million administrations per year. Gd³⁺'s seven unpaired 4f electrons give it the largest paramagnetic relaxation enhancement of any stable ion; chelation ensures in vivo stability and renal clearance. Concerns about nephrogenic systemic fibrosis (NSF) in renally impaired patients and gadolinium retention in brain tissue have driven a shift from linear to macrocyclic chelate formulations (Gd-DOTA, Gd-HP-DO3A), which are kinetically far more stable. Natural Gd nanoparticles are also studied for neutron capture therapy (NCT) given ¹⁵⁷Gd's extraordinary cross-section.

Gd metal near its Curie temperature (20 °C) exhibits the largest magnetocaloric effect of any pure element — an adiabatic temperature change of ~3–4 K per tesla — making it the benchmark material for near-room-temperature magnetic refrigeration research and the active component in early prototype magnetic refrigerators. Gd₃Ga₅O₁₂ (GGG) is the standard substrate for garnet thin-film deposition and a key host for Ce:GGG scintillators. Gd₂O₂S:Tb (gadolinium oxysulfide, "Gadox") is the phosphor in X-ray intensifying screens and flat-panel X-ray detectors. Gd is also used in UO₂-Gd₂O₃ nuclear fuel pellets as a burnable absorber (¹⁵⁷Gd burns up rapidly over the first reactor cycle, self-limiting reactivity).

General Properties

Property	Value	Notes
Atomic Number	64	4f⁷5d¹6s²; +3 is the only stable oxidation state. The half-filled 4f⁷ shell (maximum spin multiplicity) gives Gd its large magnetic moment and places its Curie temperature just above room temperature (T_C = 293 K / 20 °C) — unique among the lanthanides. Both ¹⁵⁵Gd (I = 3/2) and ¹⁵⁷Gd (I = 3/2) are NMR-active.
Atomic Mass	157.25 u	Seven naturally occurring isotopes; ¹⁵⁸Gd (24.84%) is most abundant, followed by ¹⁶⁰Gd (21.86%) and ¹⁵⁶Gd (20.47%). ¹⁵²Gd is Stable* (alpha decay, t½ = 1.08 × 10¹⁴ yr). ¹⁵⁷Gd carries σ = 254,000 barn — the highest thermal neutron cross-section of any stable nuclide.
Density (20 °C)	7.90 g/cm³	Moderate lanthanide density. Relevant to Gd₂O₂S:Tb X-ray phosphor layer design (density affects X-ray stopping power) and to GGG substrate mass calculations for garnet film deposition.
Melting Point	1,312 °C (1,585 K)	Moderate among lanthanides. Gd oxidizes readily above ~200 °C in air; vacuum arc or induction melting under Ar is required for processing bulk Gd metal.
Boiling Point	3,272 °C	High boiling point; relevant to Gd evaporation source preparation for MBE growth of Gd-doped magnetic films and for Gd-containing oxide sputtering target fabrication.
Thermal Conductivity	10.6 W/m·K	Low conductivity typical of lanthanides. Relevant to thermal management in Gd-based magnetocaloric regenerator beds, where thermal transport through the Gd bed limits regenerator efficiency at high cycling frequencies.
Electrical Resistivity	131 nΩ·m (20 °C)	High resistivity typical of lanthanides; increases anomalously near T_C = 293 K due to spin-disorder scattering at the ferromagnetic transition — a textbook example of magnetic contribution to resistivity in itinerant-electron ferromagnets.
Crystal Structure	HCP (α-Gd), a = 3.636 Å, c = 5.783 Å	HCP below 1,235 °C; transforms to BCC above. Gd is ferromagnetic below 20 °C and becomes strongly paramagnetic above — the transition is sharp at ambient pressure and shifts with applied magnetic field, enabling the magnetocaloric effect exploited in solid-state magnetic refrigeration near room temperature.

Mechanical Properties

Property	Value	Notes
Tensile Strength	~200 MPa (approximate)	Approximate value for annealed Gd; Gd is not used structurally. Relevant to foil and rod processing for magnetocaloric regenerator fabrication.
Young's Modulus	55 GPa	Low-moderate modulus typical of lanthanides. Used in stress modeling of GGG substrates under garnet film deposition and in magnetocaloric Gd plate/foil regenerator design.
Hardness	~60–70 HB (annealed)	Moderate hardness for an annealed lanthanide. Gd can be machined under Ar atmosphere and rolled into foil for magnetocaloric regenerator plates and sputtering targets.
Elongation at Break	~20%	Good ductility in high-purity form; Gd can be rolled into foil and machined for magnetocaloric regenerator plates and sputtering targets.
Poisson's Ratio	0.26	Typical for an HCP lanthanide. Used in thermal stress modeling of GGG single-crystal substrates and Gd-containing ceramic fuel pellets.

Chemical Properties

Property	Value / Behavior	Notes
Oxidation States	+3 only (Gd³⁺: GdCl₃, Gd₂O₃, Gd(NO₃)₃)	Gd³⁺ (4f⁷, ⁸S₇/₂) has the largest number of unpaired electrons of any stable tripositive ion — seven — giving it the strongest paramagnetic relaxation enhancement exploited in Gd-based MRI contrast agents. Gd³⁺ chelates (Gd-DOTA, Gd-DTPA) must be stable enough to prevent release of free Gd³⁺, which is highly toxic at clinical doses; macrocyclic chelates are preferred for their kinetic stability.
Corrosion Resistance	Poor; oxidizes readily in air forming Gd₂O₃; reacts with water and acids	Gd tarnishes within hours in moist air and must be stored under inert atmosphere or mineral oil. Fine powder is flammable. Gd dissolves readily in dilute HCl and HNO₃.
Surface Oxide	Gd₂O₃ (cubic C-type, white) forms in air	Gd₂O₃ is used as MRI contrast agent precursor, as a high-κ gate dielectric candidate (κ ~ 12–14), and as the Gd source in Gd-doped CeO₂ (CGO/GDC) SOFC electrolytes where Gd³⁺ substitutes for Ce⁴⁺ creating oxygen vacancies for ionic conduction.

Identifier	Value
Symbol	Gd
Atomic Number	64
CAS Number	7440-54-2
UN Number	UN3089 (powder)
EINECS Number	231-162-2

Isotope	Type	Notes
¹⁵²Gd	Stable*	0.20% natural abundance; I = 0; Stable* — alpha decay to ¹⁴⁸Sm measured, t½ = 1.08 × 10¹⁴ yr. The least abundant Gd isotope; used as an enriched IDMS spike for Gd quantification in geological and phosphor scrap samples.
¹⁵⁴Gd	Stable	2.18% natural abundance; I = 0. Used as a reference isotope in Sm-Nd and Gd isotope ratio measurements. Relatively low thermal neutron cross-section (σ ≈ 85 barn).
¹⁵⁵Gd	Stable	14.80% natural abundance; I = 3/2, NMR-active. Thermal neutron σ ≈ 61,000 barn — the second highest of any stable nuclide. ¹⁵⁵Gd NMR is used to characterize Gd³⁺ coordination in MRI contrast agent development and in solid-state Gd₂O₃ ceramics. Contributes significantly to natural Gd's bulk neutron absorption.
¹⁵⁶Gd	Stable	20.47% natural abundance; I = 0. Major component of natural Gd; used as a normalization isotope in Gd isotope ratio work. Moderate thermal neutron cross-section (σ ≈ 1.5 barn).
¹⁵⁷Gd	Stable	15.65% natural abundance; I = 3/2, NMR-active. Thermal neutron absorption cross-section σ = 254,000 barn — the highest of any stable nuclide, ~270× that of ¹⁰B (764 barn) and ~100× that of ¹⁶⁴Dy (2,650 barn). ¹⁵⁷Gd(n,γ)¹⁵⁸Gd is the dominant reaction in UO₂-Gd₂O₃ burnable absorber fuel; ¹⁵⁷Gd burns up very rapidly at beginning-of-life, transitioning to ¹⁵⁸Gd (σ ≈ 2.2 barn) — a nearly transparent product — giving an unusually sharp reactivity transition used to limit peak power in PWR and BWR fuel designs. Also the active isotope in Gd neutron capture therapy (Gd-NCT) research for brain tumors, and the basis of Gd-containing neutron shielding composites.
¹⁵⁸Gd	Stable	24.84% natural abundance — most abundant Gd isotope; I = 0. Product of ¹⁵⁷Gd neutron capture; nearly transparent to neutrons (σ ≈ 2.2 barn). Used as the primary normalization isotope in Gd isotope ratio measurements for nuclear forensics and environmental monitoring near reactor sites.
¹⁶⁰Gd	Stable	21.86% natural abundance; I = 0. Used as a reference isotope in ¹⁶⁰Gd/¹⁵⁸Gd ratio measurements for reactor burnup monitoring. ¹⁶⁰Gd(n,γ)¹⁶¹Gd (σ = 0.77 barn) produces ¹⁶¹Gd (t½ = 3.66 min), used in research reactor activation experiments.

Scientific & Research Applications

Use Case	Form Typically Used	Description
MRI Contrast Agent Research	Gd³⁺ chelate complexes: Gd-DOTA, Gd-DTPA, Gd-HP-DO3A (synthesized from GdCl₃ or Gd₂O₃)	Gd³⁺'s seven unpaired 4f electrons give the largest T₁ relaxivity of any stable ion (~3–5 mM⁻¹s⁻¹ for small chelates; up to ~50 mM⁻¹s⁻¹ for macromolecular Gd conjugates). Research focuses on macrocyclic chelates (higher kinetic stability, lower Gd retention), targeted Gd-labeled nanoparticles, and high-relaxivity Gd-protein conjugates for molecular MRI. Over 30 million clinical doses administered annually worldwide.
Magnetocaloric Effect Research	Gd metal foil, plates, or spheres (99.9%+); Gd₅Si₂Ge₂ powder	Gd metal at T_C = 293 K (20 °C) has an adiabatic temperature change of ~3–4 K/T — the largest of any pure element near room temperature. It is the benchmark material for active magnetic regenerator (AMR) prototypes in near-room-temperature magnetic refrigeration, with potential COP advantages over vapor-compression systems. Gd₅Si₂Ge₂ exhibits a giant magnetocaloric effect (~14 K/T) at a first-order transition near 276 K.
Neutron Capture Therapy (Gd-NCT)	¹⁵⁷Gd-enriched compounds (Gd-DTPA or Gd-porphyrin nanoparticles) for tumor delivery	¹⁵⁷Gd(n,γ)¹⁵⁸Gd releases ~8 MeV of internal conversion electrons, Auger electrons, and γ-rays with a mean free path of ~2–10 µm — suitable for killing individual tumor cells if sufficient Gd can be delivered. Research is active in brain tumor models; combined MRI-contrast / NCT-therapeutic Gd agents (theranostics) are a key aim.
Scintillator & Phosphor Research	Gd₂O₂S:Tb powder; Ce:GGG single crystals; Gd₃Ga₅O₁₂ substrates	Gd₂O₂S:Tb (Gadox) converts X-rays to green light (~545 nm) with ~15% efficiency and is the standard phosphor in medical X-ray flat-panel detectors and intensifying screens. Ce:GGG (Ce-doped Gd₃Ga₅O₁₂) is a fast scintillator for particle physics. GGG single-crystal substrates are the standard for LPE-grown yttrium iron garnet (YIG) and other magnetic garnet films in microwave and magnonic device research.
Solid Oxide Fuel Cell Electrolyte Research	Gd-doped CeO₂ (GDC / CGO, Gd₀.₁Ce₀.₉O₁.₉₅) powders and pellets	Gadolinium-doped ceria (GDC) has ~10× higher oxide ion conductivity than YSZ at 500–700 °C, enabling intermediate-temperature SOFC operation. GDC is used as a buffer layer in high-performance SOFC stacks and as the sole electrolyte in IT-SOFC designs; Gd³⁺ substitution creates oxygen vacancies that carry the ionic current.

Industrial & Commercial Applications

Sector	Form / Grade Used	Description
Nuclear Reactor Burnable Absorber	UO₂-Gd₂O₃ mixed oxide fuel pellets (1–10 wt% Gd₂O₃); natural Gd or ¹⁵⁷Gd-enriched	¹⁵⁷Gd burns up extremely rapidly at beginning-of-life in LWR fuel (σ = 254,000 barn), then converts to nearly transparent ¹⁵⁸Gd (σ ≈ 2.2 barn), giving a sharp reactivity transition that suppresses excess reactivity at fresh fuel loading and enables higher initial enrichment with longer cycle life. Used in virtually all modern PWR and BWR fuel assemblies.
MRI Contrast Agents (Clinical)	Gd-DOTA (Dotarem), Gd-HP-DO3A (ProHance), Gd-DTPA (Magnevist); 99.9%+ Gd₂O₃ precursor	Clinical Gd-chelate contrast agents are administered intravenously at ~0.1 mmol/kg for T₁-weighted MRI enhancement. Macrocyclic agents (Gd-DOTA, Gd-HP-DO3A) are now preferred over linear chelates in most markets due to superior kinetic stability and lower retention risk. Global market ~$1.5B/year.
X-ray Detection Phosphors	Gd₂O₂S:Tb (Gadox) powder screens; Gd₂O₂S:Pr,Ce ceramic scintillator plates	Gadox (Gd₂O₂S:Tb) is the dominant phosphor in medical X-ray flat-panel detectors (FPDs) and computed radiography (CR) plates — high X-ray absorption (Gd K-edge at 50.2 keV), ~15% light conversion efficiency, and emission at 545 nm matched to CCD/CMOS sensors. Present in virtually all modern digital X-ray imaging systems in hospitals worldwide.
Gadolinium Iron Garnet & YIG Films	GGG (Gd₃Ga₅O₁₂) single-crystal substrates; Gd-substituted YIG target material	GGG is the near-ideal substrate for LPE and PLD growth of YIG (Y₃Fe₅O₁₂) and Gd-substituted garnet films for magnonic waveguides, spin-wave devices, and microwave circulators. The lattice constant match between GGG and YIG (mismatch <0.1%) minimizes film strain and enables ultra-low-damping YIG films with Gilbert damping α < 10⁻⁴.

Purity	Main Uses	Notes
99% (2N)	Industrial-grade applications such as neutron shielding and magnetic materials.	Suitable for bulk applications where ultra-high purity is not critical.
99.9% (3N)	Scientific research, MRI contrast agent synthesis, and advanced magnetic materials.	High-purity form preferred for applications requiring low impurities and strong magnetic properties.

Synonym / Alternative Name	Context
Gd	Chemical symbol; named after Johan Gadolin (1760–1852), the Finnish chemist who first identified the rare-earth element yttria. Used in MRI contrast agent specifications (Gd-DOTA, Gd-DTPA), nuclear reactor fuel assembly drawings (UO₂-Gd₂O₃ pellet notation), and REE ICP-MS databases.
Gd metal	Commercial designation for elemental Gd ingot, foil, rod, or powder. Used in magnetocaloric regenerator fabrication datasheets, sputtering target specifications, and MBE source material procurement for Gd-doped magnetic film growth.
Gd element	Scientific designation distinguishing elemental Gd from Gd compounds. Used in condensed matter physics literature on Gd ferromagnetism, magnetocaloric effect measurements, and Hall effect studies in rare-earth metals.
Gadolinium metal	Full commercial designation used in REACH/RoHS documentation, ASTM REE metal standards, and procurement specifications for Gd additions to magnetocaloric alloy and garnet substrate production.
Gadolinium element	Used in academic databases (WebElements, NIST), geochemistry texts, and nuclear engineering references specifying Gd neutron cross-section data for reactor physics calculations.
Gadolinium rare earth metal	Trade and regulatory designation in EU Critical Raw Materials Act and US DOE Critical Minerals lists; used in supply chain and policy documents for Gd-dependent medical imaging and nuclear industries.
Gadolinium rare earth element	Geochemical designation used in REE deposit assessments, chondrite-normalized REE pattern databases, and IUPAC nomenclature for Gd-bearing minerals (gadolinite).
Element 64	Periodic table designation used in XRF/ICP-MS software, nuclear data libraries (ENDF/B-VIII ¹⁵⁷Gd cross-section at 254,000 barn), and reactor physics codes (MCNP, ORIGEN) tracking Gd burnup in fuel assemblies.

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