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I have really some trouble to find information about where to find rare earth elements in electronics. When I look at my electronic board, I open several datasheets, I am not able to find any rare earth elements. There is no information. Where are they?

The 17 rare-earth elements are cerium (Ce), dysprosium (Dy), erbium (Er), europium (Eu), gadolinium (Gd), holmium (Ho), lanthanum (La), lutetium (Lu), neodymium (Nd), praseodymium (Pr), promethium (Pm), samarium (Sm), scandium (Sc), terbium (Tb), thulium (Tm), ytterbium (Yb), and yttrium (Y).

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    \$\begingroup\$ I found that some mad scientists have made a protein based rare earth detector to detect rare earth hiding in the smart phone: livemint.com/technology/tech-news/…. I need to google more. \$\endgroup\$ – tlfong01 Aug 21 at 10:08
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    \$\begingroup\$ I found another article talking about rare earth. It seems that they are everywhere, but not detected by we stupid human eyes, and stupid me cannot even spell the name of any one of the eight rare earth guys. (But I have no problem spelling the acronym REE.:) (1) jjsmanufacturing.com/blog/… \$\endgroup\$ – tlfong01 Aug 21 at 10:14
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    \$\begingroup\$ You won't see this in a datasheet and most companies probably wouldn't tell you if asked \$\endgroup\$ – Voltage Spike Aug 22 at 0:20
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    \$\begingroup\$ Also note that some materials might be used in the manufacturing process, but aren't part of the finished product. \$\endgroup\$ – bta Aug 22 at 3:38
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The "rare earth elements" are in several places in common electronics.

Strong magnets commonly use rare earth elements.

Ceramic capacitors also use rare earth elements. Pretty much any piece of modern electronic equipment will contain ceramic capacitors.

Semiconductors (transistors, diodes, and the integrated circuits built from them) all use various amounts of rare earth elements. Pure silicon is a semiconductor by itself, but it doesn't do much of interest. It has to have specific amounts of "impurities" (properly called dopants) to get it to do the cool things it does. Those dopants are purposefully (and carefully) introduced in specific amounts in specific places to make silicon semiconductor devices work.

You'll rarely (if at all) see the rare earth elements listed in a datasheet. The datasheets tell you how a part works and how to use it, not what it is made of.

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    \$\begingroup\$ The first things like semiconductors were of various minerals. Quartz was used (and still is used) to make oscillators, but not because of any semiconductor properties. Quartz flexes when you apply voltage to it. If you cut it and polish it just right, it always flexes at the same speed. The mechanical vibration gets back into the electrical circuit as an electrical oscillation. \$\endgroup\$ – JRE Aug 21 at 11:43
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    \$\begingroup\$ You won't be building a smartphone without rare earth elements. Nearly every part you need has at least a trace of them - and all of them will depend on rare earth elements to some extent. Even for copper, there'll be rare earth elements in the machines used to mine it, refine it, transport it, and make wire of it. \$\endgroup\$ – JRE Aug 21 at 11:46
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    \$\begingroup\$ Wait! What semiconductor devices are intentionally doped with rare earth elements? Can you either add some supporting information for that or remove it? \$\endgroup\$ – uhoh Aug 22 at 0:40
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    \$\begingroup\$ I second @uhoh, the answer seems to imply that rare earth elements are used as dopants, but for what I know this is not true. \$\endgroup\$ – Vladimir Cravero Aug 23 at 9:09
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    \$\begingroup\$ I'm going to agree with @uhoh. Dopants for silicon need to fit the crystal. Silicon's highest electron orbit is a 3p orbit (14 electrons). Cerium has a 6s orbit. (58 electrons). That won't fit. Besides, typical dopants are Group III and V materials (P- and n-type), to add a single hole or valence electron. \$\endgroup\$ – MSalters Aug 23 at 12:47
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Some examples of where some less-common (not necessarily true rare-earth metals) they are used in electronics manufacturing: For ICs:

Arsenic, Boron, Antimony and phosphorus are used as dopants in silicon-based processes. Platinum and tungsten have been used for contacts, tantalum in barrier layers. Usually high-k dielectrics are used for gate dielectrics, often using something like hafnium or zirconium.

Lots of phones will use RF amplifiers and LNAs based on more exotic III-V technologies, such as GaAs (Gallium Arsenide), InP (Indium-Phosphide), etc, all of which use some less-common elements too.

On PCB-level, you have components such as tantalum capacitors which (you guessed it) contain tantalum. Ceramic capacitors might use things like barium, magnesium, and paladium. Lanthanum is sometimes used in barrier layers here. I also seem to recal strontium being used here somewhere, but I don't remember where exactly.

PCBs themselves might use paladium as barrier layer for gold plating in some applications.

A chemist friend told me once that no other industry uses so much (dangerous) chemical elements and compounds than the semiconductor industry.

(this is not an exhaustive list, but just what I could remember off the top of my head)

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    \$\begingroup\$ Thank you for your answer ! For those who you would like to see what are the rare earth element, here they are : " The 17 rare-earth elements are cerium (Ce), dysprosium (Dy), erbium (Er), europium (Eu), gadolinium (Gd), holmium (Ho), lanthanum (La), lutetium (Lu), neodymium (Nd), praseodymium (Pr), promethium (Pm), samarium (Sm), scandium (Sc), terbium (Tb), thulium (Tm), ytterbium (Yb), and yttrium (Y)." from wikipedia \$\endgroup\$ – Jess Aug 21 at 11:55
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    \$\begingroup\$ The normal silicon dopants aren't classed as "rare earth". The ones people complain about are tantalum in the capacitors (which can be substituted at the cost of space) and cobalt in the batteries. I don't think any of that list get used in phones at all, except neodymium in magnets. \$\endgroup\$ – pjc50 Aug 21 at 12:03
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    \$\begingroup\$ Pick those 17 elements out of the classic Tom Lehrer song. \$\endgroup\$ – Spehro Pefhany Aug 21 at 12:07
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    \$\begingroup\$ Tantale is not a "rare earth" apparently, nevertheless it could be more rare than "rare earth" :D \$\endgroup\$ – Jess Aug 21 at 12:14
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    \$\begingroup\$ I literally state in my reply 'not necessarily true rare-earth metals'. \$\endgroup\$ – Joren Vaes Aug 21 at 12:17
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Googling 'rare earth elements in electronics' gave me two articles(see references) which lists the specific usage of these elements in various applications:

  • Cerium - the most abundant of the rare earth elements, used in magnets, electrodes and carbon-arc lighting, as a catalyst in
    catalytic converters and for precision glass polishing
  • Neodymium - a soft silvery metal used to create strong permanent magnets for computer disks, microphones and headphones and in the production of powerful infrared lasers
  • Dysprosium - one of the most highly magnetic elements used in the manufacture of electronics, computer disks, lasers, commercial lighting and energy-efficient vehicles
  • Terbium - a soft, silvery metal used as an additive in rare earth magnets, in some electronic devices and in sonar systems
  • Holmium - another rare earth element with powerful magnetic properties, used in the microwave equipment and nuclear control rods
  • Lanthanum - a highly reactive rare earth element used in the manufacture of telescope lenses and infrared absorbent glass
  • Scandium - used in the manufacture of popular consumer products such as televisions and energy-saving lamps
  • Yttrium - a silvery metal found in superconductors, lasers, and surgical supplies.

References

  1. https://www.jjsmanufacturing.com/blog/rare-earth-elements-electronics-manufacturing
  2. https://www.bbc.com/news/world-17357863
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In addition to magnets mentioned in several answers, rare earth's have certain atomic transitions in near IR and visible light that make them very useful in a variety of applications!

erbium doped fiber amplifiers are used in long runs of single mode fiber optic communications. The simpler passive optical amplifiers boost the signal several times until various dispersion mechanisms and intermodulation distortions degrade the pulses so much that they need to be electronically regenerated by less frequently distributed and more complex devices.

Erbium is used around the most common 1.55 micron wavelength. For other wavelengths, other rare earth elements are used which provide gain. According to the linked article

Thulium doped fiber amplifiers have been used in the S-band (1450–1490 nm) and Praseodymium doped amplifiers in the 1300 nm region.

File:Doped_fibre_amplifier.svg Source

The original green laser pointers were amazing little optical benches! They were diode-pumped solid state lasers having an AlGaAs diode laser circa 800 nm pumping a rare-earth (usually neodymium) doped crystal lasing at 1064 nm, which was then frequency doubled by a non-linear crystal to become visible green light. Now many are made from simpler III-V semiconductor lasers with a band gap in green light.

The most common DPSSL in use is the 532 nm wavelength green laser pointer. A powerful (>200 mW) 808 nm wavelength infrared GaAlAs laser diode pumps a neodymium-doped yttrium aluminium garnet (Nd:YAG) or a neodymium-doped yttrium orthovanadate (Nd:YVO4) crystal which produces 1064 nm wavelength light from the main spectral transition of neodymium ion. This light is then frequency doubled using a nonlinear optical process in a KTP crystal, producing 532 nm light. Green DPSSLs are usually around 20% efficient, although some lasers can reach up to 35% efficiency. In other words, a green DPSSL using a 2.5 W pump diode would be expected to output around 500-900 mW of 532 nm light.

Rare earths are also found in some phosphors because of their visible light transitions, think old televisions or monitors or oscilloscopes!

Phosphors are often transition-metal compounds or rare-earth compounds of various types. In inorganic phosphors, these inhomogeneities in the crystal structure are created usually by addition of a trace amount of dopants, impurities called activators. (In rare cases dislocations or other crystal defects can play the role of the impurity.) The wavelength emitted by the emission center is dependent on the atom itself and on the surrounding crystal structure.


See:

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This might be because rare earth elements are not used that much in electronics. While they may be important as dopants, the needed quantities are rather small.
(BTW, rare earth elements are not rare. They are "everywhere". However, the concentrations of these materials tend to be extremely small, so that extraction is rarely worthwhile.)

Rare-earths metals (in particular: neodymium, samarium, praseodymium, dysprosium, terbium, gadolinium, yttrium) are important to build powerful electric magnets for machines with limited mass. You'll find them in the generators of wind turbines, the motors of electric cars and many speakers.

They may also alter the optical properties and are used in the fabrication of specialty glasses, liquid crystal displays and lasers. Some of them are used for radar.

They're also used as catalysts in refineries, in contrast media for MRT analyses, as a polish material, in alloys for airplane engines, in batteries,...

If you can read German (maybe using DeepL or GoogleTranslate): Rare Earth Elements (REE) - Vorkommen, Herstellung, Verwendung

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Main ones: magnets, capacitors, things that spit out white light

Assuming by "rare earths" we are referring to the lanthanide series of elements on the periodic table (with a nod to yttrium as it's sometimes lumped in with them), then indeed, the primary place you'd run into them in an electronic device is in a powerful magnet. While this is is less of a concern for small electronics that can get by alright with only a couple of small permanent magnets, such as in the vibrate motor and speaker/transducer in a smartphone, larger motorized devices such as electric vehicles and appliances using inverter drives may use fairly large rare-earth magnets in DC or inverter-driven motors.

A more common, although smaller-quantity, application is the use of lanthanide dopants in ceramic capacitors, as documented here. This appears to be peculiar to Class II (X5R/X7R) dielectrics, though.

Other common places that might have them are white LEDs, used for space-lighting and backlighting, and their oddly closely related fluorescent tube cousins, both the cold-cathode flavors used for backlighting LCDs and the hot-cathode versions used for outright lighting applications. They don't play a role in semiconductor devices otherwise, though.

Old and odd: CRTs, optics, some microwave bits, and the occasional superconductor

Other places you might find them are in CRT phosphors in old devices that still have those, as well as in a variety of optical applications such as lasers (Nd:YAG and so on) and nonlinear crystals of various flavors (think optical amplifiers or frequency doublers).

With a nod to the occasional yttrium-bearing superconductor in a MRI machine somewhere, we move onto the final application that most folks will ever hear of, and that's older microwave gear that used YIG (yttrium-iron-garnet) devices. These were used for some microwave functions (such as filters) before cost-effective semiconductors and board techniques were available at those frequencies, but better PCB substrates, PCB-based distributed element techniques, and semiconductor devices have rendered them largely obsolete.

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  • \$\begingroup\$ Very nice, comprehensive answer! For the capacitors, are those " lanthanide dopants" only, or is the dielectric ceramic actually all lanthanide oxide? \$\endgroup\$ – uhoh Aug 22 at 12:44
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    \$\begingroup\$ @uhoh -- it's dopants only -- the base material is barium titanate, at least for Class II (X5R/X7R) caps. (C0G uses a different base, and I haven't found any info that points at rare earths being present in them) \$\endgroup\$ – ThreePhaseEel Aug 22 at 13:49
  • \$\begingroup\$ okay got it, thanks! \$\endgroup\$ – uhoh Aug 22 at 13:53
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Yttrium is used in making the super conductor YBCO. It’s not used in common electronics but it has many uses and it’s really cool.

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