A brittle, silvery-gray, metallic chemical element, Ge, atomic number 32, atomic weight 72.59, melting point 937.4°C (1719°F), and boiling point 2830°C (5130°F), with properties between silicon and tin. Germanium is distributed widely in the Earth's crust in an abundance of 6.7 parts per million (ppm). Germanium is found as the sulfide or is associated with sulfide ores of other elements, particularly those of copper, zinc, lead, tin, and antimony. See also Periodic table.
Germanium has a metallic appearance but exhibits the physical and chemical properties of a metal only under special conditions since it is located in the periodic table where the transition from nonmetal to metal occurs. At room temperature there is little indication of plastic flow and consequently it behaves like a brittle material.
As it exists in compounds, germanium is either divalent or tetravalent. The divalent compounds (oxide, sulfide, and all four halides) are easily reduced or oxidized. The tetravalent compounds are more stable. Organogermanium compounds are many in number and, in this respect, germanium resembles silicon. Interest in organogermanium compounds has centered around their biological action. Germanium in its derivatives appears to have a lower mammalian toxicity than tin or lead compounds.
The properties of germanium are such that there are several important applications for this element, especially in the semiconductor industry. The first solid-state device, the transistor, was made of germanium. Single-crystal germanium is used as a substrate for vapor-phase growth of GaAs and GaAsP thin films in some light-emitting diodes. Germanium lenses and filters are used in instruments operating in the infrared region of the spectrum. Mercury-doped and copper-doped germanium are used as infrared detectors; synthetic garnets with magnetic properties may have applications for high-power microwave devices and magnetic bubble memories; and germanium additives increase usable ampere-hours in storage batteries.
