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Lanthanum

Lanthanum — Material Page
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Lanthanum (La, atomic number 57) is the first and most reactive of the lanthanides — a soft, ductile, silvery-white metal with a melting point of 920 °C, the largest atomic radius in the series, and a 5d¹6s² configuration with an empty 4f shell, which gives it purely trivalent chemistry without the 4f electron complexity of the heavier lanthanides. La has two natural isotopes: ¹³⁹La (99.91%, stable, I = 7/2, NMR-active) and ¹³⁸La (0.09%, radioactive, t½ = 1.02 × 10¹¹ yr). It oxidizes rapidly in moist air, reacts vigorously with water releasing H₂, and must be stored under mineral oil or inert atmosphere. La is extracted primarily from bastnäsite and monazite ores, with global production dominated by China; it is one of the most abundant rare-earth elements (~39 ppm crustal abundance) and often accumulates as a co-product of Ce extraction.

La is the largest-volume rare-earth metal used in catalysis: La-stabilized zeolite Y (La-USY, typically 3–5 wt% La₂O₃) is the active component of fluid catalytic cracking (FCC) catalysts used in virtually every petroleum refinery worldwide, where La³⁺ exchanges into the zeolite framework improve hydrothermal stability at the ~700 °C regenerator temperatures, maintaining cracking activity over multiple cycles. Global FCC catalyst demand consumes several thousand tonnes of La₂O₃ per year — the single largest application of any lanthanide by volume after Ce in TWCs. La is also critical for NiMH battery negative electrodes: LaNi₅ and mischmetal-Ni₅ alloys absorb and desorb hydrogen reversibly (~1.4 wt% H₂), and are the active material in all NiMH batteries used in hybrid electric vehicles (Toyota Prius and equivalents) — each HEV battery pack contains ~10–15 kg of La-containing AB₅ alloy.

La₂O₃ additions (up to 40–50 mol%) to optical glass dramatically increase the refractive index (n_d up to ~1.95) while maintaining low dispersion (Abbe number ~40–45), enabling compact, high-aperture camera, microscope, and telescope objective designs that would require physically impractical lens geometries with conventional silicate glass. La-based lanthanum crown (LaK) and lanthanum flint (LaF) glasses are standard in high-quality photographic objectives, microscope objectives, and broadcast camera lenses. La is also used as a dopant in BaTiO₃ and SrTiO₃ dielectric ceramics for multilayer ceramic capacitors (MLCCs), as a co-catalyst in automotive TWCs (La-stabilized Al₂O₃ support prevents γ→α-Al₂O₃ sintering at high temperatures), and as La₂NiO₄ cathode material in SOFCs.

General Properties

PropertyValueNotes
Atomic Number57 5d¹6s²; empty 4f shell distinguishes La from the heavier lanthanides. +3 is the only stable oxidation state. ¹³⁹La (I = 7/2) is NMR-active — ¹³⁹La NMR is used to characterize La³⁺ coordination in zeolite frameworks (La-USY catalyst), optical glass, and La-containing SOFC cathode materials.
Atomic Mass138.905 uTwo natural isotopes: ¹³⁸La (0.088%, radioactive, t½ = 1.02 × 10¹¹ yr, β⁻ + EC) and ¹³⁹La (99.912%, stable). ¹³⁸La/¹³⁸Ba and ¹³⁸La/¹³⁸Ce ratios are used in La-Ba geochronometry for ancient igneous rocks and in studies of s-process nucleosynthesis in stellar environments.
Density (20 °C)6.145 g/cm³Lowest density among the heavier light lanthanides, consistent with La's large atomic radius (lanthanide contraction has not yet begun). Relevant to LaNi₅ alloy density calculations for NiMH battery electrode engineering.
Melting Point920 °C (1,193 K)Relatively low melting point for a lanthanide — La is among the most easily melted of the rare-earth metals. Requires Ar-atmosphere or vacuum processing; reacts rapidly with crucible oxides at elevated temperatures, necessitating cold-crucible or water-cooled copper skull melting for high-purity La.
Boiling Point3,464 °CHigh boiling point relative to melting point. La evaporation sources are used in MBE and thermal evaporation of La-doped oxide films (La:HfO₂ high-κ gate dielectrics, La-doped BaTiO₃ for ferroelectric memory research).
Thermal Conductivity13.4 W/m·KLow conductivity typical of light lanthanides. Relevant to La-stabilized Al₂O₃ washcoat thermal modeling in TWC converters and to LaNi₅ hydride bed heat management in hydrogen storage systems.
Electrical Resistivity61 nΩ·m (20 °C)Moderate resistivity. La becomes superconducting below ~6 K (α-La, T_c ≈ 4.9 K; β-La, T_c ≈ 5.9–6.0 K) — among the highest T_c values for a pure elemental superconductor and the highest among the lanthanides.
Crystal Structureα-La: double HCP (dHCP), a = 3.770 Å, c = 12.159 Å (RT)La has three allotropes: α-La (dHCP, stable at RT), β-La (FCC, above 310 °C), γ-La (BCC, above 865 °C). The double HCP structure (ABAC stacking) is unusual among metals and reflects La's position at the onset of the lanthanide series before 4f orbital involvement in bonding.

Mechanical Properties

PropertyValueNotes
Tensile Strength~210 MPaModerate tensile strength for a soft lanthanide. La is not used structurally; mechanical properties are relevant to LaNi₅ electrode pellet fabrication and to La foil rolling for sputtering targets.
Young's Modulus36 GPaVery low modulus — among the most compliant metallic elements. Relevant to stress modeling of La-containing optical glass elements and to LaNi₅ particle fracture during hydrogen absorption/desorption cycling in NiMH battery electrodes.
Hardness~35–40 HB (annealed)Soft and ductile — La can be cut with a knife and is readily rolled and drawn under inert atmosphere. Good ductility makes La foil and rod straightforward to fabricate from high-purity ingot.
Elongation at Break~25%Good ductility in high-purity annealed form. La foil (99.9%+) is used as sputtering targets for La-doped oxide film deposition and as a precursor for LaNi₅ alloy preparation.
Poisson's Ratio0.28Typical for a soft, compliant metal. Used in elastic modeling of La-stabilized zirconia and alumina ceramic components in TWC and SOFC applications.

Chemical Properties

PropertyValue / BehaviorNotes
Oxidation States+3 only (La³⁺: LaCl₃, La₂O₃, La(NO₃)₃·6H₂O)La³⁺ is the largest tripositive lanthanide ion (ionic radius 1.032 Å in 6-coordination), which drives its preference for high coordination numbers (8–12) and its use as a framework stabilizer in zeolites and as a dopant in large-site perovskites (La-doped BaTiO₃, LaCoO₃ SOFC cathode).
Corrosion ResistancePoor; oxidizes rapidly in moist air; reacts vigorously with water releasing H₂; dissolves in dilute acidsLa is one of the most reactive lanthanides — more reactive than Ca in some conditions. Bulk La must be stored under mineral oil or sealed Ar; even brief air exposure causes significant surface tarnishing. La powder is flammable and must be handled with care.
Surface OxideLa₂O₃ (hexagonal A-type structure) forms rapidly in air; converts to La(OH)₃ in moist conditionsLa₂O₃ is hygroscopic and continues to react with atmospheric moisture and CO₂ (forming La(OH)₃ and La₂(CO₃)₃), which can cause bulk La samples to disintegrate over time. La₂O₃ is calcined at >800 °C before use in catalyst and optical glass formulations to remove absorbed moisture and carbonate.
IdentifierValue
SymbolLa
Atomic Number57
CAS Number7439-91-0
UN NumberUN3089 (powder)
EINECS Number231-099-0
IsotopeTypeNotes
¹³⁸La Radioactive 0.088% natural abundance; I = 5; t½ = 1.02 × 10¹¹ yr; decays by β⁻ (to ¹³⁸Ce, 66.4%) and electron capture (to ¹³⁸Ba, 33.6%). Long-lived enough to be effectively stable in all practical contexts but measurably radioactive — relevant in high-precision nuclear physics experiments with La-based scintillators (LaBr₃:Ce detectors show intrinsic radioactive background from ¹³⁸La). The ¹³⁸La/¹³⁸Ba ratio provides a rare chronometer for very ancient rocks (>10⁹ yr), complementary to the Lu-Hf and Sm-Nd systems. LaBr₃:Ce scintillators combine the excellent energy resolution (~2.6% at 662 keV) with ¹³⁸La's intrinsic radiation background, which must be modeled in low-background γ-spectroscopy applications.
¹³⁹La Stable 99.912% natural abundance; I = 7/2, NMR-active. ¹³⁹La NMR (I = 7/2; moderate quadrupole moment; chemical shift range ~1,500 ppm) is widely used to characterize La³⁺ coordination in zeolite catalysts (La-USY framework stability), solid electrolytes (La-doped ceria, LLZO Li-ion conductors), and La-based optical glass formulations. Dominates La isotopic composition; used as the monitoring isotope in ICP-MS REE analysis. Thermal neutron σ = 8.93 barn — low enough that La is not a significant neutron poison in reactor environments.

Scientific & Research Applications

Use CaseForm Typically UsedDescription
LaBr₃:Ce Scintillator ResearchLaBr₃:Ce single crystals (0.5–5 mol% Ce, grown from LaBr₃ + CeBr₃ melt); La metal as precursorLaBr₃:Ce offers ~2.6% energy resolution at 662 keV — the best of any inorganic scintillator at room temperature — combined with high light yield (~63,000 photons/MeV) and fast decay time (~16 ns). Used in portable γ-ray isotope identification systems, nuclear safeguards verification, and medical imaging research. The intrinsic ¹³⁸La background limits use in ultra-low-background experiments but is modeled and subtracted in standard applications.
NiMH Battery & Hydrogen Storage ResearchLaNi₅ alloy (La:Ni = 1:5 by atom); mischmetal-Ni₅ (La-rich mischmetal replacing pure La)LaNi₅ reversibly absorbs ~1.4 wt% H₂ at mild pressure and temperature, with fast kinetics and hundreds of absorption/desorption cycles without significant degradation. Research addresses substitution of La with mischmetal and partial Ni substitution with Al, Mn, Co, or Ti to tune plateau pressure, capacity, and cycle life for HEV and stationary applications.
¹³⁹La NMR SpectroscopyLa³⁺ solution standards (LaCl₃, La(NO₃)₃); La-doped solid powders¹³⁹La solution NMR characterizes La³⁺ complexation equilibria with ligands relevant to MRI contrast agent design, REE separation solvent extraction chemistry, and La speciation in geochemical fluids. Solid-state ¹³⁹La NMR (MAS and static) characterizes La site symmetry in zeolite catalysts, perovskite oxides, and La-based optical glass, providing structural information complementary to XRD.
High-κ Gate Dielectric Research (La:HfO₂)La₂O₃ ALD precursors (La(iPrCp)₃, La(thd)₃); La₂O₃ sputtering targetsLa doping of HfO₂ (1–5 at% La) shifts the threshold voltage of CMOS transistors toward flat-band, reduces interface trap density, and suppresses crystallization of the HfO₂ film — enabling equivalent oxide thickness (EOT) <1 nm in sub-5 nm technology nodes. La₂O₃ capping layers on HfO₂ gate dielectrics are used in Intel, TSMC, and Samsung finFET and gate-all-around transistor processes.
Optical Glass ResearchLa₂O₃ glass batches (20–50 mol% La₂O₃ in borosilicate or phosphate base glass)La₂O₃ is the primary refractive index-raising component in lanthanum crown (LaK) and lanthanum dense flint (LaSF) optical glass types, achieving n_d up to ~1.95 with Abbe numbers of 40–45. These glasses enable compact, high-numerical-aperture objectives for microscopy, photography, and cinema camera lenses. Research focuses on heavy-metal-free La-glass formulations replacing traditional Pb- and As-containing optical glasses under RoHS constraints.

Industrial & Commercial Applications

SectorForm / Grade UsedDescription
Petroleum FCC CatalystsLa₂O₃ (3–8 wt%) exchanged into zeolite Y (La-USY) during catalyst preparation; 93–99% La₂O₃ precursorLa³⁺ exchange into zeolite Y framework stabilizes the structure against hydrothermal dealumination at FCC regenerator temperatures (~700 °C), maintaining Brønsted acid site density and cracking selectivity over multiple cycles. Global FCC catalyst consumption represents the largest single REE application by mass for any lanthanide other than Ce, consuming several thousand tonnes of La₂O₃ per year across refineries worldwide.
NiMH Battery Electrodes (HEV)LaNi₅ or La-rich mischmetal-Ni₅ alloy (ingot, powder, or electrode paste; 99%+ La content)La-containing AB₅ alloys are the active negative electrode material in all NiMH batteries — the dominant battery chemistry for hybrid electric vehicles (Toyota Prius, Honda Insight, and equivalents). Each HEV NiMH pack contains ~10–15 kg of La-containing alloy. Though being displaced by Li-ion in BEVs, NiMH/HEV production continues at substantial volume globally.
Optical Glass ManufacturingLa₂O₃ powder (99–99.99%), melted with B₂O₃, SiO₂, and ZnO at 1,200–1,400 °CLa-based optical glasses (Schott LaK, LaSF series; OHARA LAK/LASF series) are standard components in high-quality photographic, microscope, and broadcast camera objectives. The high refractive index and low dispersion combination available only with La₂O₃ cannot be matched by conventional silicate or borosilicate glass at equivalent Abbe number.
TWC Alumina StabilizationLa₂O₃ (2–5 wt%) co-precipitated with Al₂O₃ or surface-deposited on γ-Al₂O₃ washcoat supportLa addition to γ-Al₂O₃ washcoat support in automotive TWCs suppresses the γ→α-Al₂O₃ phase transformation above 1,000 °C, preserving high surface area (>100 m²/g) for Pt/Pd/Rh dispersion over vehicle lifetime. Without La stabilization, γ-Al₂O₃ sinters to low-surface-area α-Al₂O₃ at engine-off temperatures, dramatically reducing catalyst activity.
PurityApplicationsNotes
93% (1N3)Suitable for alloy production and general-purpose catalyst formulations.Cost-effective grade for bulk industrial use where high purity is not essential.
99% (2N)Used in battery materials, steel refining, and glass enhancement.Commercially pure grade for semi-technical and chemical processes.
99.9% (3N)Preferred in optical materials, phosphor compounds, and hydrogen storage alloys.High-purity grade for research and precision-engineered materials.
Synonym / Alternative NameContext
LaChemical symbol; from Greek lanthanein (to lie hidden), named by Carl Gustaf Mosander in 1839. Used in FCC catalyst specifications (La-USY zeolite loading), NiMH battery electrode alloy datasheets (LaNi₅ stoichiometry), and ICP-MS REE databases (¹³⁹La as primary analytical isotope).
La metalCommercial designation for elemental La in ingot, rod, foil, or powder form. Used in sputtering target datasheets, LaNi₅ alloy synthesis procurement specifications, and optical glass batch composition documents.
La elementScientific designation distinguishing elemental La from La compounds. Used in condensed matter physics literature on La superconductivity (T_c ~6 K), crystal structure allotropy (dHCP/FCC/BCC), and surface science studies of La oxidation and hydroxide formation.
Lanthanum metalFull commercial designation used in REACH/RoHS documentation, ASTM REE metal standards, and procurement specifications for La additions to optical glass batches, FCC catalyst precursor preparation, and La-Al₂O₃ TWC washcoat stabilizer production.
Lanthanum elementUsed in academic databases (WebElements, NIST), educational resources, and geochemistry texts specifying La crustal abundance, La/Ce/Pr fractionation in REE patterns, and La anomaly behavior in igneous and marine geochemical systems.
Lanthanum rare earth metalTrade designation classifying La among the light rare-earth elements (LREEs) on critical materials lists. La is classified as moderately critical — abundant and widely sourced, but still subject to supply concentration risk given China's dominant role in REE separation and refining.
Lanthanum rare earth elementGeochemical and mineralogical designation used in REE deposit assessments (bastnäsite, monazite, ion-adsorption clay deposits), IUPAC nomenclature for La-bearing minerals (lanthanum fluocarbonate in bastnäsite), and chondrite-normalized La/Yb ratios used to quantify LREE enrichment in igneous and sedimentary rocks.
Element 57Periodic table designation used in XRF/ICP-MS software, nuclear data libraries (ENDF/B-VIII for ¹³⁸La decay data), and reactor physics codes tracking La as a fission product in spent nuclear fuel inventory calculations.
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