An element whose existence was postulated by Mendeleev, germanium was discovered by the German chemist Winkler in the mineral argyrodite (Ag8GeS6) in 1886. The metal took its name for the country of Germany. Today, germanium is primarily obtained from the smelting of zinc ores and is recovered from certain types of coal ash in Russia and China.
Germanium is a lustrous, grayish-white, hard and brittle semi-metallic element that oxidizes slowly in air. Along with silicon, gallium, bismuth, antimony, and water, it is one of the few substances that expands as it solidifies (i.e. freezes) from its molten state. Zone refining techniques have led to the production of crystalline germanium that has an impurity of only one part in 1010, making it amongst the purest materials ever obtained.
In 2005, Germanium with uranium and rhodium was the first metallic material discovered to become a superconductor in the presence of an extremely strong electromagnetic field.
APPLICATIONS OF GERMANIUM
Optics: Germanium oxide (GeO2 or Germania) has a high index of refraction and a low optical dispersion, making it especially useful for wide-angle camera lenses, microscopy, and for the core part of optical fibres. It has also displaced titania as the dopant for silica fibres thereby eliminating the need for subsequent heat treatment which made the fibres brittle.
Germanium is also used in infrared optical glasses that can be readily cut and polished into specialty lenses in cameras for passive thermal imaging, for hot-spot detection in night vision systems, and for fire fighting applications. It is also used in infrared spectroscopes and other optical equipment which require extremely sensitive infrared detectors.
Germanium antimony tellurides (GeSbTe) are used in the production of rewritable DVDs.
Electronics: Silicon germanide (SiGe) is an important semiconductor material used in high speed integrated circuits, and is beginning to replace gallium arsenide (GaAs) in wireless communications devices. SiGe chips can be made with low-cost, well-established production techniques of the silicon chip industry.
When doped with small amounts of arsenic, gallium, indium, antimony or phosphorus, germanium is used to make transistors for other electronic devices. Other uses in electronics include phosphors in fluorescent lamps, and germanium-based solid-state light-emitting diodes (LEDs).
Solar Cell: Because germanium and gallium arsenide have very similar lattice constants, germanium substrates can be used to make gallium arsenide solar cells. While silicon has superior electrical properties, it requires much higher purities than germanium or gallium arsenides.
Germanium-on-insulator substrates are seen as a potential replacement for silicon on miniaturized chips. Germanium is the substrate of the wafers for high-efficiency photovoltaic cells for space applications.
PET bottle: Germanium dioxide is used in catalysts for polymerisation in the production of polyethylene terephthalate (PET), the highly brilliant polyester produced used for PET bottles (marketed in Japan).
Medical: Some germanium compounds seem to be effective in killing some types of bacteria and are currently being studied for use in chemotherapy.
Other Uses: Germanium and germanium oxide, being transparent to infrared radiation, are used in infrared optical instruments and infrared detectors. Germanium has seen increasing use in precious metal alloys. In sterling silver alloys, it is found to reduce firescale, increase tarnish resistance and increase the alloy's response to precipitation hardening. A tarnish-proof sterling silver alloy, trademarked Argentium, requires 1.2% germanium.
High purity germanium single crystal detectors can precisely identify radiation sources—for example in airport security. Crystals of high purity germanium are used in detectors for gamma spectroscopy.