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Ytterbium
Ytterbium (Yb, atomic number 70) is unique among the lanthanides in having a fully filled 4f shell in the divalent metallic state (4f¹⁴, like Eu's half-filled 4f⁷): Yb metal has an FCC structure, a low melting point of 824 °C, anomalously high thermal conductivity (38.5 W/m·K), and low Young's modulus (24.8 GPa) — all reflecting the divalent (Yb²⁺) nature of metallic Yb, in contrast to the trivalent 4f¹³6s² electronic structure of Yb³⁺ in compounds. It has seven stable isotopes; ¹⁷⁴Yb is the most abundant (31.8%). ¹⁷¹Yb (I = 1/2) and ¹⁷³Yb (I = 5/2) are NMR-active. ¹⁷⁶Yb is the precursor for no-carrier-added ¹⁷⁷Lu production (¹⁷⁶Yb(n,γ)¹⁷⁷Yb → ¹⁷⁷Lu) for Lutathera and Pluvicto radiopharmaceuticals.
Yb:YAG and Yb-doped fibre lasers are the dominant high-power solid-state laser platform globally — the ²F₇/₂→²F₅/₂ transition at 1,030 nm has a simple two-level scheme with minimal thermal loading (quantum defect ~9% vs. ~24% for Nd:YAG at 808 nm pump), enabling kW-class diode-pumped thin-disk and fibre lasers used in automotive welding, EV battery tab laser welding, metal cutting, and precision materials processing. Yb:YAG thin-disk lasers (Trumpf TruDisk series) and Yb fibre lasers (IPG Photonics YLS series) account for the majority of the multi-billion-dollar industrial laser market above 1 kW. Mode-locked Yb:KGW, Yb:KYW, and Yb:CaF₂ lasers deliver <300 fs pulses at >100 W average power for ultrafast precision micromachining.
¹⁷¹Yb⁺ and ¹⁷⁴Yb⁺ trapped-ion optical lattice clocks hold world records for fractional frequency uncertainty (~10⁻¹⁸), surpassing Cs microwave standards by four orders of magnitude — enabling redefinition of the SI second, relativistic geodesy (chronometric levelling), and tests of fundamental physics including the variation of fundamental constants over time. Neutral ¹⁷⁴Yb atoms in optical lattice clocks (NIST, PTB, SYRTE) and ¹⁷¹Yb⁺ single-ion clocks (NPL, PTB) are the leading contenders for the next SI second definition. Yb is also the active ion in Yb³⁺-sensitised upconversion nanoparticles (co-doped with Er³⁺, Tm³⁺, or Ho³⁺) converting 980 nm to visible emission for bioimaging and solar cell spectral conversion.
General Properties
| Property | Value | Notes |
|---|---|---|
| Atomic Number | 70 | 4f¹⁴6s² in compounds (Yb³⁺: 4f¹³); metallic Yb is divalent (4f¹⁴, like Eu). +3 dominant in all Yb compounds. Yb²⁺ accessible under strongly reducing conditions (YbI₂). ¹⁷¹Yb (I = 1/2) and ¹⁷³Yb (I = 5/2) are NMR-active. |
| Atomic Mass | 173.045 u | Seven stable isotopes: ¹⁶⁸Yb (0.13%), ¹⁷⁰Yb (3.04%), ¹⁷¹Yb (14.28%, NMR-active I = 1/2), ¹⁷²Yb (21.83%), ¹⁷³Yb (16.13%, NMR-active I = 5/2), ¹⁷⁴Yb (31.83%, most abundant), ¹⁷⁶Yb (12.76%, ¹⁷⁷Lu precursor). No naturally radioactive isotopes. |
| Density (20 °C) | 6.90 g/cm³ | Anomalously low for a late lanthanide — a direct consequence of divalent metallic bonding (Yb²⁺ in metal vs. Yb³⁺ in compounds). Closely resembles Eu (5.24 g/cm³) in this respect. |
| Melting Point | 824 °C (1,097 K) | Second-lowest melting point of any lanthanide after Eu (822 °C), both anomalously low due to divalent metallic bonding. Yb can be melted and processed under Ar; less reactive than light lanthanides. |
| Boiling Point | 1,196 °C | Unusually low boiling point; Yb is volatile and evaporates readily from melts. Relevant to Yb:YAG crystal growth stoichiometry control and to Yb thin-film evaporation source design. |
| Thermal Conductivity | 38.5 W/m·K | Highest thermal conductivity of any lanthanide by a large margin — a direct consequence of divalent metallic bonding (Yb²⁺ metal resembles alkaline-earth metals in conductivity). Critical to Yb:YAG thin-disk laser thermal management; the high host conductivity limits thermal lensing at kW-class power levels. |
| Electrical Resistivity | 37.9 nΩ·m (20 °C) | Lowest resistivity of any lanthanide — again reflecting divalent metallic bonding. Becomes superconducting under high pressure (~89 GPa, T_c ~7 K). |
| Crystal Structure | β-Yb: FCC, a = 5.485 Å (RT) | FCC at RT (unique among lanthanides at RT apart from Ce's γ phase); transforms to BCC above ~795 °C. The FCC structure is consistent with divalent metallic bonding (cf. Ca, Sr). |
Mechanical Properties
| Property | Value | Notes |
|---|---|---|
| Tensile Strength | 138 MPa | Low tensile strength — Yb is the second-softest lanthanide after Eu. Can be readily rolled and drawn under inert atmosphere; Yb foil is used as sputtering target and alloy precursor. |
| Young's Modulus | 24.8 GPa | Lowest Young's modulus of any lanthanide — a direct consequence of divalent metallic bonding. The Yb:YAG host crystal (69 GPa) is much stiffer than the metal; thermal stress calculations use crystal elastic constants, not metal values. |
| Hardness | ~20–25 HB (annealed) | Very soft — comparable to Pb. Second-softest lanthanide after Eu. Can be deformed by hand pressure on bulk samples; all processing under Ar or inert conditions. |
| Elongation at Break | ~30% | Excellent ductility consistent with FCC structure and divalent bonding. Yb foil and wire (99.9%+) are fabricated for sputtering targets and Yb-doped fibre preform doping research. |
| Poisson's Ratio | 0.21 | Relatively low; consistent with soft, compliant FCC divalent metal structure. |
Chemical Properties
| Property | Value / Behavior | Notes |
|---|---|---|
| Oxidation States | +3 dominant in all compounds (YbCl₃, Yb₂O₃, Yb(OTf)₃); +2 in solids (YbI₂, YbO, YbS) and under reducing conditions | YbI₂ is a mild single-electron reductant (weaker than SmI₂), used in organic synthesis for selective reductions and C–C couplings. Yb(OTf)₃ is a Lewis acid catalyst for aqueous reactions. Metallic Yb itself is the divalent Yb⁰ form of the element. |
| Corrosion Resistance | Moderate in dry air; more stable than light lanthanides; reacts slowly with water; dissolves in dilute acids | Yb is more chemically stable than La, Ce, or Nd in air. Bulk Yb can be handled briefly under ambient conditions; fine powder and wire should be stored under Ar. |
| Surface Oxide | Yb₂O₃ (cubic C-type) forms in air | Yb₂O₃ (mp ~2,355 °C) is the precursor for Yb:YAG crystal growth (8–12 at% Yb substitution on Y sites), Yb-doped silica fibre preforms (MCVD/OVD doping with Yb₂O₃ aerosol), and ¹⁷⁶Yb-enriched targets for ¹⁷⁷Lu production. |
| Identifier | Value |
|---|---|
| Symbol | Yb |
| Atomic Number | 70 |
| CAS Number | 7440-64-4 |
| UN Number | UN3089 (powder) |
| EINECS Number | 231-173-2 |
| Isotope | Type | Notes |
|---|---|---|
| ¹⁶⁸Yb | Stable | 0.13%; I = 0. Lowest natural abundance of any stable Yb isotope. Used as enriched IDMS spike for high-precision Yb concentration determinations. |
| ¹⁷⁰Yb | Stable | 3.04%; I = 0. Low abundance; used as IDMS reference isotope in REE geochemical analysis. |
| ¹⁷¹Yb | Stable | 14.28%; I = 1/2, NMR-active. ¹⁷¹Yb⁺ single-ion optical clock (~467 nm E3 transition, fractional uncertainty ~10⁻¹⁸) is one of the leading candidates for the next SI second definition. ¹⁷¹Yb NMR characterises Yb³⁺ coordination in laser glass and crystal precursors. |
| ¹⁷²Yb | Stable | 21.83%; I = 0. Used as reference isotope in Yb isotope ratio measurements and as IDMS spike. |
| ¹⁷³Yb | Stable | 16.13%; I = 5/2, NMR-active. ¹⁷³Yb NMR complements ¹⁷¹Yb NMR for characterising Yb³⁺ environments; the quadrupolar I = 5/2 provides linewidth information on site symmetry in Yb-doped crystals and glasses. |
| ¹⁷⁴Yb | Stable | 31.83%; I = 0. Most abundant Yb isotope; primary ICP-MS monitoring isotope. Used in neutral ¹⁷⁴Yb optical lattice clocks (world-leading fractional uncertainty at NIST, PTB). σ(thermal) = 65 barn. |
| ¹⁷⁶Yb | Stable | 12.76%; I = 0. Key precursor for ultra-high specific-activity ¹⁷⁷Lu production: ¹⁷⁶Yb(n,γ)¹⁷⁷Yb (t½ = 1.9 hr) → ¹⁷⁷Lu (β⁻, t½ = 6.647 days) via chemical separation of Lu from Yb matrix. Enriched ¹⁷⁶Yb targets (~99% ¹⁷⁶Yb) are irradiated in high-flux reactors; subsequent Yb/Lu separation gives no-carrier-added ¹⁷⁷Lu of much higher specific activity than direct ¹⁷⁶Lu(n,γ)¹⁷⁷Lu routes, critical for Lutathera and Pluvicto radiopharmaceutical manufacturing. |
Scientific & Research Applications
| Use Case | Form Typically Used | Description |
|---|---|---|
| Yb Optical Lattice & Ion Trap Clocks | Enriched ¹⁷¹Yb⁺ ions or ¹⁷⁴Yb atoms in MOT/lattice; ultrapure Yb metal for oven sources | ¹⁷⁴Yb optical lattice clocks (¹S₀→³P₀ clock transition at 578 nm) and ¹⁷¹Yb⁺ single-ion clocks (E3 octupole transition at 467 nm) achieve fractional frequency uncertainties of ~10⁻¹⁸ — enabling relativistic geodesy (mapping gravitational potential from clock comparisons), tests of Lorentz invariance, and searches for dark matter via temporal variation of fundamental constants. |
| Yb:YAG & Yb Fibre Laser Research | Yb:YAG crystals (8–12 at% Yb, Czochralski); Yb-doped double-clad silica fibre; Yb:CaF₂, Yb:KGW crystals | Yb laser research focuses on power scaling in thin-disk geometry (>100 kW peak, >10 kW CW), ultrashort pulse generation (<100 fs at >100 W average power in Yb:CaF₂ and Yb:KYW), and coherent beam combination of Yb fibre laser arrays. Yb:YAG is the benchmark thin-disk laser material due to its high thermal conductivity host (YAG: 10 W/m·K) and Yb²⁺-suppressed concentration quenching at high dopant levels. |
| Upconversion Nanoparticle Research (Yb³⁺ Sensitiser) | Yb³⁺/Er³⁺, Yb³⁺/Tm³⁺, Yb³⁺/Ho³⁺ co-doped NaYF₄ core/shell NPs; Yb₂O₃ (99.9%+) as precursor | Yb³⁺ (²F₇/₂→²F₅/₂, 980 nm) is the near-universal sensitiser in upconversion nanoparticles, absorbing 980 nm NIR and transferring energy to Er³⁺, Tm³⁺, or Ho³⁺ activators that emit green/red, blue/NIR, or green/NIR respectively. Applications include deep-tissue bioimaging, photodynamic therapy activation, solar spectral upconversion, and anti-counterfeiting inks. |
| ¹⁷⁶Yb Target Irradiation for ¹⁷⁷Lu | Enriched ¹⁷⁶Yb₂O₃ targets (≥98% ¹⁷⁶Yb); high-flux reactor irradiation | Irradiation of enriched ¹⁷⁶Yb targets produces ¹⁷⁷Yb (t½ = 1.9 hr) which decays to ¹⁷⁷Lu; chemical Yb/Lu separation then gives no-carrier-added ¹⁷⁷Lu at specific activities ~100× higher than the direct ¹⁷⁶Lu(n,γ) route. This high specific-activity ¹⁷⁷Lu is essential for Lutathera and Pluvicto manufacturing where high molar activity is required for effective tumour targeting. |
Industrial & Commercial Applications
| Sector | Form / Grade Used | Description |
|---|---|---|
| Yb:YAG & Yb Fibre Industrial Lasers | Yb:YAG thin-disk crystals (99.9%+ Yb₂O₃ precursor); Yb-doped double-clad silica fibre (MCVD/OVD) | Commercial Yb:YAG thin-disk lasers (Trumpf TruDisk: 2–16 kW CW, 1,030 nm) and Yb fibre lasers (IPG YLS: 0.1–100 kW) dominate industrial metal cutting, welding, and surface treatment. Low quantum defect (~9%) enables efficient thermal management at kW power levels. Used ubiquitously in automotive body welding, EV battery tab and cell welding, shipbuilding, and precision aerospace component fabrication. |
| Steel & Alloy Grain Refiner | Yb metal (99%+) as micro-addition to stainless steel and specialty alloy melts | Small Yb additions (0.01–0.1 wt%) to stainless steel and Ni superalloys refine grain size, improve high-temperature creep resistance, and enhance oxidation resistance by modifying oxide scale adhesion. Used in aerospace turbine blade and automotive exhaust component alloys. |
| Strain Gauge Alloys | Yb-based strain gauge alloys; Yb metal additions to sensor alloy melts | Yb-based alloys have low temperature coefficient of resistance and high gauge factor, making them suitable for high-precision strain gauges used in structural health monitoring, load cells, and pressure transducers in aerospace and civil engineering applications. |
| Purity | Applications | Notes |
|---|---|---|
| 99% (2N) | Alloying, chemical research, and electronics where ultra-high purity is not essential. | Standard grade for general-purpose scientific and industrial use. |
| 99.9% (3N) | Optical devices, spectroscopy, and quantum applications. | Preferred grade for advanced R&D and high-precision technology sectors. |
| Synonym / Alternative Name | Context |
|---|---|
| Yb | Chemical symbol; from Ytterby (Sweden), shared with Tb, Er, and Y. Used in Yb:YAG laser datasheets, Yb fibre laser specifications, optical clock publications (¹⁷¹Yb⁺, ¹⁷⁴Yb), and ICP-MS REE databases (¹⁷⁴Yb primary monitoring isotope). |
| Yb metal | Commercial form designation for ingot, rod, foil, or wire. Used in Yb:YAG crystal growth procurement, sputtering target specs, and ¹⁷⁶Yb-enriched target procurement for ¹⁷⁷Lu radiopharmaceutical production. |
| Yb element | Scientific designation used in condensed matter physics literature on Yb divalent metallic bonding, FCC crystal structure, and pressure-induced valence transition. |
| Ytterbium metal | Full commercial designation in REACH/RoHS documentation and ASTM REE metal standards. |
| Ytterbium element | Used in academic databases, optical clock physics publications, and nuclear medicine literature on ¹⁷⁶Yb target production for ¹⁷⁷Lu radiopharmaceuticals. |
| Ytterbium rare earth metal | Trade designation; Yb demand is growing driven by Yb:YAG/fibre laser adoption and ¹⁷⁶Yb target demand for ¹⁷⁷Lu radiopharmaceutical manufacturing. |
| Ytterbium rare earth element | Geochemical designation in REE deposit assessments and chondrite-normalised REE pattern databases. Yb/Lu ratios are used in mantle geochemistry to distinguish garnet- from spinel-peridotite source lithologies. |
| Element 70 | Periodic table designation used in XRF/ICP-MS software, nuclear data libraries (¹⁷⁶Yb neutron activation cross-section for ¹⁷⁷Lu production), and reactor physics codes. |