Cerium hexaboride ( Ce B₆, also called cerium boride, CeBix, CEBIX, and (incorrectly) CeB) is an inorganic chemical, a

boride A boride is a compound between boron and a less electronegative element, for example silicon boride (SiB3 and SiB6). The borides are a very large group of compounds that are generally high melting and are covalent more than ionic in nature. Some b ...

cerium Cerium is a chemical element; it has Chemical symbol, symbol Ce and atomic number 58. It is a hardness, soft, ductile, and silvery-white metal that tarnishes when exposed to air. Cerium is the second element in the lanthanide series, and while it ...

. It is a

refractory In materials science, a refractory (or refractory material) is a material that is resistant to decomposition by heat or chemical attack and that retains its strength and rigidity at high temperatures. They are inorganic, non-metallic compound ...

ceramic A ceramic is any of the various hard, brittle, heat-resistant, and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcela ...

material. It has a low

work function In solid-state physics, the work function (sometimes spelled workfunction) is the minimum thermodynamic work (i.e., energy) needed to remove an electron from a solid to a point in the vacuum immediately outside the solid surface. Here "immediately" ...

, one of the highest

electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

emissivities known, and is stable in

vacuum A vacuum (: vacuums or vacua) is space devoid of matter. The word is derived from the Latin adjective (neuter ) meaning "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressur ...

. The principal use of cerium hexaboride is a coating of

hot cathode In vacuum tubes and gas-filled tubes, a hot cathode or thermionic cathode is a cathode electrode which is heated to make it emit electrons due to thermionic emission. This is in contrast to a cold cathode, which does not have a heating element ...

s. It usually operates at temperature of 1450 °C.

Applications

Lanthanum hexaboride Lanthanum hexaboride ( La B6, also called lanthanum boride and LaB) is an inorganic chemical, a boride of lanthanum. It is a refractory ceramic material that has a melting point of 2210 °C, and is insoluble in water and hydrochloric acid. ...

(LaB₆) and cerium hexaboride (CeB₆) are used as coating of some high-current

s. Hexaborides show low

, around 2.5 eV. They are also somewhat resistant to cathode poisoning. Cerium boride cathodes show lower evaporation rate at 1700 K than lanthanum boride, but it becomes equal at 1850 K and higher above that. Cerium boride cathodes have one and half the lifetime of lanthanum boride, due to its higher resistance to carbon contamination. Boride cathodes are about ten times as "bright" than the

tungsten Tungsten (also called wolfram) is a chemical element; it has symbol W and atomic number 74. It is a metal found naturally on Earth almost exclusively in compounds with other elements. It was identified as a distinct element in 1781 and first ...

ones and have 10–15 times longer lifetime. In some laboratory tests, CeB₆ has proven to be more resistant to the negative impact of carbon contamination than LaB₆. They are used e.g. in

electron microscope An electron microscope is a microscope that uses a beam of electrons as a source of illumination. It uses electron optics that are analogous to the glass lenses of an optical light microscope to control the electron beam, for instance focusing it ...

microwave tube Microwave is a form of electromagnetic radiation with wavelengths shorter than other radio waves but longer than infrared waves. Its wavelength ranges from about one meter to one millimeter, corresponding to frequencies between 300 MHz and ...

electron lithography Electron-beam lithography (often abbreviated as e-beam lithography or EBL) is the practice of scanning a focused beam of electrons to draw custom shapes on a surface covered with an electron-sensitive film called a resist (exposing). The electron ...

electron beam welding Electron-beam welding (EBW) is a fusion welding process in which a charged-particle beam, beam of high-velocity electrons is applied to two materials to be joined. The workpieces melt and flow together as the kinetic energy of the electrons is ...

X-Ray tube An X-ray tube is a vacuum tube that converts electrical input power into X-rays. The availability of this controllable source of X-rays created the field of radiography, the imaging of partly opaque objects with penetrating radiation. In contras ...

s, and

free electron laser A free-electron laser (FEL) is a fourth generation light source producing extremely brilliant and short pulses of radiation. An FEL functions much as a laser but employs relativistic electrons as a gain medium instead of using stimulated emission ...

s. Cerium Hexaboride is also investigated for use in

radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or a material medium. This includes: * ''electromagnetic radiation'' consisting of photons, such as radio waves, microwaves, infr ...

detection devices due to its efficiency in detecting photon radiation. Research indicates that a three-layer sensor configuration, incorporating CeB₆, can outperform single-layer designs in terms of energy resolution and counting rate. Cerium hexaboride, like lanthanum hexaboride, slowly evaporates during cathode operation. In conditions where CeB₆ cathodes are operated below 1850 K, CeB₆ should maintain its optimum shape longer and therefore last longer. While the process is about 30% slower than with lanthanum boride, the cerium boride deposits are reported to be more difficult to remove. Ce heavy fermion compounds have attracted much attention since they show a variety of unusual and interesting macroscopic properties. In particular, interest has been focused on the 4f narrow-band occupancy, and the role of hybridization with the conduction band states which strongly affects the physical properties.

References

{{Borides Cerium compounds Borides Refractory materials Ceramic materials