Germanium Ge

Discovery

In 1871 Mendeleev described a missing element below silicon, "eka-silicon", forecasting an atomic weight near 72, a density around 5.5 and a grey, high-melting solid.

In 1886 Clemens Winkler, at the mining academy in Freiberg, Saxony, analysed a newly found mineral called argyrodite. His results kept adding up to a few percent short of 100, and he suspected an unknown ingredient. After painstaking separations he isolated it. Its atomic weight turned out to be about 72.6 and its density about 5.32, a striking match to the prediction.

Germanium became a star of electronics in the mid-twentieth century. In 1947 John Bardeen and Walter Brattain at Bell Labs built the point-contact transistor on a germanium crystal. Silicon later took over because it is easier to process and forms a stable oxide layer, but germanium remained the material that launched the semiconductor age.

Origin of the name

Winkler named the element after Germania, the Latin name for Germany, and the symbol Ge comes from the same word.

Main uses

• Optical fibre: germanium dioxide added to the fibre core raises its refractive index so light stays trapped in the core over long distances.
• Infrared optics: germanium is opaque to visible light but transparent to much of the infrared, so it is used for thermal-imaging lenses and windows.
• Silicon–germanium (SiGe) chips improve the speed of high-frequency and communication circuits.
• Radiation detectors: high-purity germanium crystals measure gamma-ray energies with exceptional precision.
• Catalysis: germanium dioxide is used as a polymerisation catalyst for PET plastic.

Isotopes

Natural germanium has five isotopes. Germanium-70, -72, -73 and -74 are stable, and germanium-76 is technically radioactive but decays by double beta decay with a half-life far longer than the age of the universe. Germanium-74 is the most abundant. The radioactive isotope germanium-68, with a half-life of about 271 days, serves as the parent in generators that supply hospitals with gallium-68 for PET scans. Detectors enriched in germanium-76 are used to search for neutrinoless double beta decay, a hypothetical process that would reveal the nature of neutrinos.

In everyday life

Germanium is mostly recovered as a by-product of zinc refining and from certain coal fly ashes. It is present in submarine fibre-optic cables, night-vision cameras in cars and radio chips in phones.

Bracelets and supplements marketed as "germanium" health products have no proven benefit. Long-term intake of inorganic germanium compounds has been linked to kidney damage, so it should not be taken as a supplement. The metal itself is not considered hazardous to handle.