|Jmol-3D images||Image 1|
|Molar mass||104.6388 g/mol|
|Appearance||white powder or colourless crystals|
1115 °C, 1388 K, 2039 °F
|Solubility in water||4.47 g/L (25 °C)
10.7 g/L (100 °C)
|Solubility||insoluble in HF, HCl
soluble in other acid and alkali
|Refractive index (nD)||1.650|
|EU Index||Not listed|
|LD50||3700 m/kg (rat, oral)|
|Other anions||Germanium disulfide
|Other cations||Carbon dioxide
|Related compounds||Germanium monoxide|
| (what is: / ?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Germanium dioxide, also called germanium oxide and germania, is an inorganic compound, an oxide of germanium. Its chemical formula is GeO2. Other names include germanic acid, G-15, and ACC10380. It forms as a passivation layer on pure germanium in contact with atmospheric oxygen.
The forms of germanium dioxide to an extent parallel those of silicon dioxide. Hexagonal GeO2 has the same structure as β-quartz (germanium having coordination number 4); tetragonal GeO2 (the mineral argutite) has the rutile-like structure of stishovite (germanium having coordination number 6); and amorphous (glassy) GeO2 is similar to fused silica.
Germanium dioxide can be prepared in both crystalline and amorphous forms. At ambient pressure the amorphous structure is formed by a network of GeO4 tetrahedra. At elevated pressure up to approximately 9 GPa the germanium average coordination number steadily increases from 4 to around 5 with a corresponding increase in the Ge-O bond distance. At higher pressures, up to approximately 15 GPa, the germanium coordination number increases to 6 and the dense network structure is composed of GeO6 octahedra. When the pressure is subsequently reduced, the structure reverts to the tetrahedral form. At high pressure, the rutile form converts to an orthorhombic CaCl2 form.
The rutile form of germanium dioxide is more soluble than the hexagonal form and dissolves to form germanic acid, H4GeO4 or Ge(OH)4. GeO2 is only slightly soluble in acid but dissolves more readily in alkali to give germanates.
The refractive index (1.7) of germanium dioxide and optical dispersion properties makes it useful as an optical material for wide-angle lenses and in optical microscope objective lenses. It is transparent in infrared.
A mixture of silicon dioxide and germanium dioxide ("silica-germania") is used as an optical material for optical fibers and optical waveguides. Controlling the ratio of the elements allows precise control of refractive index. Silica-germania glasses have lower viscosity and higher refractive index than pure silica. Germania replaced titania as the silica dopant for silica fiber, eliminating the need for subsequent heat treatment, which made the fibers brittle.
Germanium dioxide is also used as a catalyst in production of polyethylene terephthalate resin, and for production of other germanium compounds. It is used as a feedstock for production of some phosphors and semiconductor materials. In the manufacture of integrated circuits and transistors, germanium dioxide is a rather poor dielectric and is chemically unstable, which is one of the disadvantages of germanium in comparison with silicon.
Furthermore germanium dioxide is used in algaculture as an inhibitor of unwanted diatom growth in algal cultures since a contamination with the comparatively fast-growing diatoms often inhibits the growth of or outcompetes the original algae strains. GeO2 is readily taken up by diatoms and leads to silicon being substituted by germanium in biochemical processes within the diatoms, causing a significant reduction of the diatoms' growth rate or even a complete elimination of the contaminating algae practically without affecting non-diatom algal species. For this application the typically used concentration of germanium dioxide in the culture medium is between 1 and 10 mg/l, depending on the stage of the contamination and the species.
Toxicity and medical 
Germanium dioxide has low toxicity, but in higher doses it is nephrotoxic. Germanium dioxide is used as a germanium supplement in some questionable dietary supplements and "miracle cures". High doses of these resulted in several cases of germanium poisonings.
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