Lanthanum Hexaboride (LaB6)
also called lanthanum boride, and LaB6 is an inorganic chemical, a boride of lanthanum. It is a refractory ceramic material with a dark purple appearance that has a melting point of 2210°C, and is insoluble in water and hydrochloric acid. When bombarded with ions, its physical appearance is altered, and it has a green color in place of its usual dark purple color.
The unique properties of lanthanum hexaboride crystals provide stable electron-emitting media with work functions near 2.70 eV.The low work function yields higher currents at lower cathode temperatures than tungsten, which means greater brightness, or current at the beam focus, and longer life. Typically, LaB6 cathodes exhibit 10 times the brightness and 50 times the service life of tungsten cathodes. In electron microscope applications, these characteristics translate to more beam current in a smaller spot at the sample, improved resolution, and less frequent cathode replacement.
Key Features Include
- Very Low Work Function: ~2.6–2.7 eV (much lower than tungsten’s 4.5+ eV) for efficient electron emission at lower temperatures.
- High Brightness: 5–10× brighter than tungsten cathodes, delivering sharper, lower-noise images.
- Long Lifetime: Extremely low evaporation rate; typical service life 500–2000+ hours at 1550–1650°C in 10⁻⁶–10⁻⁷ Torr vacuum (5–10× longer than tungsten).
- High Thermal & Chemical Stability: Melting point ~2210–2483°C; excellent resistance to thermal shock, oxidation, and ion bombardment.
- High Hardness: Mohs ~9.5; mechanically robust for demanding electron gun applications.
- Good Poisoning Resistance: More tolerant to oxide contamination than impregnated cathodes
Lanthanum Hexaboride Applications：
Thermionic emission (cathode)
Plasma source for plasma-enhanced coating(PECVD)
Vacuum electron beam welding machine
Electron beam surface reforming device
Electron beam lithography device Transmission electron microscope
Scanning electron microscope Surface analysis device Radiotherapy devices
Scanning electron microscope Surface analysis device Radiotherapy devices
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Lanthanum Hexaboride Properties:
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Properties
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Unit
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Lanthanum Hexaboride
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Purity
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%
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>99.5
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Density
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g/cm3
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>4.30
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Structure
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/
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Monocrystalline
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Vickers hardness
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HV
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1065
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Shore hardness
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HS
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HS
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Thermal conductivity
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W/mK
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15
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Electrical Conductivity
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S/m
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1.83*10^6
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Flexural strength
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MPa
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165
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FAQ
Q1: What is the main advantage of LaB₆ over tungsten cathodes?
A: Lower work function gives higher brightness (5–10×), better resolution, and much longer lifetime (typically 5–10× tungsten) at lower operating temperatures.
Q2: How long does a LaB₆ cathode typically last?
A: 500–2000+ hours at 1550–1650°C in high vacuum (10⁻⁶–10⁻⁷ Torr), depending on vacuum quality, temperature, and maintenance.
Q3: Is LaB₆ easy to contaminate, and how should it be handled?
A: It has good resistance to poisoning compared to impregnated cathodes, but requires high vacuum and clean handling. Avoid air/moisture exposure; pre-heat to activate and maintain vacuum during storage/use.
