Germanium dioxide, also called germanium(IV) oxide, germania, and salt of germanium, is an

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemis ...

with the chemical formula Ge O₂. It is the main commercial source of germanium. It also forms as a passivation layer on pure germanium in contact with atmospheric oxygen.

Structure

The two predominant polymorphs of GeO₂ are hexagonal and tetragonal. Hexagonal GeO₂ has the same structure as β-quartz, with germanium having

coordination number In chemistry, crystallography, and materials science, the coordination number, also called ligancy, of a central atom in a molecule or crystal is the number of atoms, molecules or ions bonded to it. The ion/molecule/atom surrounding the central io ...

4. Tetragonal GeO₂ (the mineral argutite) has the

rutile Rutile is an oxide mineral composed of titanium dioxide (TiO2), the most common natural form of TiO2. Rarer polymorphs of TiO2 are known, including anatase, akaogiite, and brookite. Rutile has one of the highest refractive indices at visib ...

-like structure seen in

stishovite Stishovite is an extremely hard, dense tetragonal form ( polymorph) of silicon dioxide. It is very rare on the Earth's surface; however, it may be a predominant form of silicon dioxide in the Earth, especially in the lower mantle. Stishovite ...

. In this motif, germanium has the coordination number 6. An amorphous (glassy) form of GeO₂ is similar to

fused silica Fused quartz, fused silica or quartz glass is a glass consisting of almost pure silica (silicon dioxide, SiO2) in amorphous (non- crystalline) form. This differs from all other commercial glasses in which other ingredients are added which ch ...

. Germanium dioxide can be prepared in both

crystalline A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...

and

amorphous In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid, glassy solid) is a solid that lacks the long-range order that is characteristic of a crystal. Etymology The term comes from the Greek language, Gr ...

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

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

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.

Reactions

Heating germanium dioxide with powdered

germanium Germanium is a chemical element with the symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid in the carbon group that is chemically similar to its group neighbors ...

at 1000 °C forms germanium monoxide (GeO). The hexagonal (''d'' = 4.29 g/cm³) form of germanium dioxide is more soluble than the rutile (''d'' = 6.27 g/cm³) form and dissolves to form acid, H₄GeO₄, or Ge(OH)₄.Egon Wiberg, Arnold Frederick Holleman, (2001) ''Inorganic Chemistry'', Elsevier . GeO₂ is only slightly soluble in acid but dissolves more readily in alkali to give

germanate In chemistry, germanate is a compound containing an oxyanion of germanium. In the naming of inorganic compounds it is a suffix that indicates a polyatomic anion with a central germanium atom, for example potassium hexafluorogermanate, K2GeF6.Egon ...

s. The germanic acid forms stable complexes with di- and polyfunctional

carboxylic acids In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic ...

, poly-alcohols, and

o-diphenols In organic chemistry, dihydroxybenzenes (benzenediols) are organic compounds in which two hydroxyl groups () are substituted onto a benzene ring (). These aromatic compounds are classed as phenols. There are three structural isomers: 1,2-dihydro ...

. In contact with

hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the dige ...

, it releases the volatile and corrosive

germanium tetrachloride Germanium tetrachloride is a colourless, fuming liquid with a peculiar, acidic odour. It is used as an intermediate in the production of purified germanium metal. In recent years, GeCl4 usage has increased substantially due to its use as a reagent ...

Uses

The

refractive index In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, ...

(1.7) and

optical dispersion In optics, and by analogy other branches of physics dealing with wave propagation, dispersion is the phenomenon in which the phase velocity of a wave depends on its frequency; sometimes the term chromatic dispersion is used for specificity to o ...

properties of germanium dioxide make it useful as an optical material for

wide-angle lens In photography and cinematography, a wide-angle lens refers to a lens whose focal length is substantially smaller than the focal length of a normal lens for a given film plane. This type of lens allows more of the scene to be included in the ...

es, in

optical microscope The optical microscope, also referred to as a light microscope, is a type of microscope that commonly uses visible light and a system of lenses to generate magnified images of small objects. Optical microscopes are the oldest design of micro ...

objective lenses, and for the core of fiber-optic lines. See

Optical fiber An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass ( silica) or plastic to a diameter slightly thicker than that of a human hair Hair is a protein filament that grows ...

for specifics on the manufacturing process. Both germanium and its glass oxide, GeO₂, are transparent to the

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...

(IR) spectrum. The glass can be manufactured into IR windows and lenses, used for night-vision technology in the military, luxury vehicles, and thermographic cameras. GeO₂ is preferred over other IR transparent glasses because it is mechanically strong and therefore preferred for rugged military usage. A mixture of silicon dioxide and germanium dioxide ("silica-germania") is used as an optical material for

optical fiber An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass ( silica) or plastic to a diameter slightly thicker than that of a human hair Hair is a protein filament that grows ...

s and

optical waveguide An optical waveguide is a physical structure that guides electromagnetic waves in the optical spectrum. Common types of optical waveguides include optical fiber waveguides, transparent dielectric waveguides made of plastic and glass, liquid light ...

s. 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 Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

in production of

polyethylene terephthalate Polyethylene terephthalate (or poly(ethylene terephthalate), PET, PETE, or the obsolete PETP or PET-P), is the most common thermoplastic polymer resin of the polyester family and is used in fibres for clothing, containers for liquids and food ...

resin, and for production of other germanium compounds. It is used as a feedstock for production of some

phosphor A phosphor is a substance that exhibits the phenomenon of luminescence; it emits light when exposed to some type of radiant energy. The term is used both for fluorescent or phosphorescent substances which glow on exposure to ultraviolet or v ...

s and

semiconductor material A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. ...

s. Germanium dioxide is used in algaculture as an inhibitor of unwanted

diatom A diatom ( Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising se ...

growth in algal cultures, since 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 their complete elimination, with little effect on non-diatom algal species. For this application, the concentration of germanium dioxide typically used 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 it is

nephrotoxic Nephrotoxicity is toxicity in the kidneys. It is a poisonous effect of some substances, both toxic chemicals and medications, on kidney function. There are various forms, and some drugs may affect kidney function in more than one way. Nephrotoxins ...

in higher doses. Germanium dioxide is used as a germanium supplement in some questionable

dietary supplement A dietary supplement is a manufactured product intended to supplement one's diet by taking a pill, capsule, tablet, powder, or liquid. A supplement can provide nutrients either extracted from food sources or that are synthetic in order ...

s and "miracle cures". High doses of these resulted in several cases of germanium poisonings.

References

{{Oxides Germanium(IV) compounds Oxides Optical materials Ceramic materials Glass compositions Transparent materials