quality:corruption
Characteristics

Under standard conditions, germanium is a brittle, silvery-white, semiconductor. This form constitutes an allotrope known as α-germanium, which has a metallic luster and a diamond cubic crystal structure, the same structure as silicon and diamond. In this form, germanium has a threshold displacement energy of 19.7 − 0.5 + 0.6 eV {\displaystyle 19.7_{-0.5}^{+0.6}~{\text{eV}}}. At pressures above 120 kbar, germanium becomes the metallic allotrope β-germanium with the same structure as β- tin. Like silicon, gallium, bismuth, antimony, and water, germanium is one of the few substances that expands as it solidifies (i.e. freezes) from the molten state.

Germanium is a semiconductor having an indirect bandgap, as is crystalline silicon. Zone refining techniques have led to the production of crystalline germanium for semiconductors that has an impurity of only one part in 10, making it one of the purest materials ever obtained. The first semi-metallic material discovered (in 2005) to become a superconductor in the presence of an extremely strong electromagnetic field was an alloy of germanium, 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, as, depending on what they eventually touch, they may lead to an electrical short.