Germanium

Germanium is a chemical element with the symbol Ge and atomic number 32. It is a lustrous, hard, greyish-white metalloid in the carbon group, chemically similar to its group neighbours tin and silicon. Germanium has five naturally occurring isotopes ranging in atomic mass number from 70 to 76. It forms a large number of organometallic compounds, including tetraethylgermane and isobutylgermane.

Germanium is an important semiconductor material used in transistors and various other electronic devices. Its major end uses are fiber-optic systems and infrared optics, but it is also used for polymerisation catalysts, in electronics and in solar electric applications. Germanium is mined primarily, though it is also recovered from silver, lead, and copper ores.

Characteristics

Under standard conditions germanium is a brittle, silvery-white, semi-metallic element. This form constitutes an allotrope technically known as α-germanium, which has a metallic luster and a diamond cubic crystal structure, the same as diamond. At pressures above 120 kbar, a different allotrope known as β-germanium forms, which has the same structure as β-tin. 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.

Germanium is a semiconductor. Zone refining techniques have led to the production of crystalline germanium for semiconductors this has resulted in one of the purest materials ever obtained. The first metallic material discovered (in 2005) to become a superconductor in the presence of an extremely strong electromagnetic field was an alloy of germanium with uranium and rhodium.

Pure germanium is known to spontaneously extrude very long screw dislocations, referred to as germanium whiskers. The growth of these whiskers is one of the primary reasons for the failure of older diodes and transistors made from germanium; depending on what they eventually touch, they may lead to an electrical short.

Elemental germanium oxidizes slowly to GeO2 at 250 °C. Germanium is insoluble in dilute acids and alkalis but dissolves slowly in concentrated sulphuric acid and reacts violently with molten alkalis to produce germanates ([GeO3]2−). Germanium occurs mostly in the oxidation state +4 although many compounds are known with the oxidation state of +2 Other oxidation states are rare, such as +3 found in compounds such as Ge2Cl6, and +3 and +1 observed on the surface of oxides, or negative oxidation states in germanes, such as -4 in GeH4. Germanium cluster anions (Zintl ions) such as Ge42−, Ge94−, Ge92−, [(Ge9)2]6− have been prepared by the extraction from alloys containing alkali metals and germanium in liquid ammonia in the presence of ethylenediamine or a cryptand. The oxidation states of the element in these ions are not integers—similar to the ozonides O3−.

Two oxides of germanium are known: germanium dioxide (GeO2, germania) and germanium monoxide, (GeO). The dioxide, GeO2 can be obtained by roasting germanium sulphide (GeS2), and is a white powder that is only slightly soluble in water but reacts with alkalis to form germanates. The monoxide, germanous oxide, can be obtained by the high temperature reaction of GeO2 with Ge metal. The dioxide (and the related oxides and germanates) exhibits the unusual property of having a high refractive index for visible light, but transparency to infrared light. Bismuth germanate, Bi4Ge3O12, (BGO) is used as a scintillator.

Value

The base value of each unit of ranges between 1 and 15Ð per unit, with up to 7 units being found at any one time.

Presence on Mars: Common