Ytterbium

Ytterbium was first separated in 1878 by the Swiss chemist Jean Charles Galissard de Marignac, from the ore that had already given up several rare earths. Its name is the last and fullest of the four drawn from Ytterby, the Swedish village whose quarry proved so extraordinarily rich. Ytterbium is a soft, silvery rare-earth metal, used in certain high-precision atomic clocks and as a dopant in lasers and in stainless steel. Ytterbium features in some of the most accurate optical atomic clocks yet built, as an amplifying dopant in fibre lasers, in certain stainless steels and as a gauge of pressure in geology, and it is one of the more tractable rare earths to prepare.

Ytterbium optical lattice clocks, developed at institutions including NIST and JILA in the United States, rank among the most precise timekeeping devices ever built, stable enough that two such clocks would not be expected to drift apart by even a second over a span longer than the current age of the universe, a level of precision now being explored for a possible future redefinition of the SI second itself, potentially displacing caesium from the role it has held since 1967. Marignac drew ytterbium from the same erbium residues that had already yielded several other lanthanides, a testament to how many separate elements a single Ytterby mineral sample could still be made to give up decades after the quarry's ores were first studied.

Ytterbium completes the remarkable quartet, yttrium, terbium, erbium and ytterbium, whose names are all made from the syllables of a single Swedish place. That one small quarry should have named four elements, and supplied the ores for several more, is unmatched anywhere in the periodic table, and it stands as a monument to the Scandinavian chemists who did so much of the painstaking work of separating the lanthanides. Ytterbium has no mythological or alchemical association, being a nineteenth-century discovery; its identity is purely geographical, the final and most complete echo of Ytterby. Its later value in atomic clocks lends the humble village name an unexpected role at the frontier of precision timekeeping.

Thin foils of ytterbium change their electrical resistance in a precise, repeatable way when subjected to a sudden shock wave, a property that has made ytterbium gauges a standard tool for measuring the fleeting pressures generated in explosives testing and other high-speed impact research, translating a violent, microsecond event into a readable electrical signal. The element's comparative ease of preparation, unusual among the lanthanides, also made it one of the more affordable rare earths for such specialised instrumentation.