Germanium dioxide, also called germanium(IV) oxide, germania, and salt of germanium, is an
inorganic compound
An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bondsthat is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''.
Inorgan ...
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 GeO
2 are hexagonal and tetragonal. Hexagonal GeO
2 has the same structure as α-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 ion ...
4. Tetragonal GeO
2 (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 vis ...
-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 w ...
. In this motif, germanium has the coordination number 6. An amorphous (glassy) form of GeO
2 is similar to
fused silica.
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, macrosc ...
and
amorphous
In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid) is a solid that lacks the long-range order that is a characteristic of a crystal. The terms "glass" and "glassy solid" are sometimes used synonymousl ...
forms. At ambient pressure the amorphous structure is formed by a network of GeO
4 tetrahedra. At elevated pressure up to approximately 9
GPa the germanium average
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 ion ...
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
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 ion ...
increases to 6, and the dense network structure is composed of GeO
6 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; it has Symbol (chemistry), symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid or a nonmetal in the carbon group that is chemically ...
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 germanates. 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 Substituent, R-group. The general formula of a carboxylic acid is often written as or , sometimes as with R referring to an organyl ...
, poly-alcohols, and o-diphenols.
In contact with hydrochloric acid
Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...
, 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 the ratio of the apparent speed of light in the air or vacuum to the speed in the medium. The refractive index determines how much the path of light is bent, or refrac ...
(1.7) and optical dispersion
Dispersion is the phenomenon in which the phase velocity of a wave depends on its frequency. Sometimes the term chromatic dispersion is used to refer to optics specifically, as opposed to wave propagation in general. A medium having this common ...
properties of germanium dioxide make it useful as an optical material for wide-angle lens
In photography and cinematography, a wide-angle lens is a Photographic lens, lens covering a large angle of view. Conversely, its focal length is substantially smaller than that of a normal lens for a given film plane. This type of lens allows mo ...
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 micros ...
objective lenses
A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), ...
, and for the core of fiber-optic lines. See Optical fiber
An optical fiber, or optical fibre, is a flexible glass or plastic fiber that can transmit light from one end to the other. Such fibers find wide usage in fiber-optic communications, where they permit transmission over longer distances and at ...
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 that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...
(IR) spectrum. The glass can be manufactured into IR windows and lenses, used for night-vision technology in the military, luxury vehicles, and thermographic camera
Infrared thermography (IRT), thermal video or thermal imaging, is a process where a Thermographic camera, thermal camera captures and creates an image of an object by using infrared radiation emitted from the object in a process, which are exa ...
s. 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, is a flexible glass or plastic fiber that can transmit light from one end to the other. Such fibers find wide usage in fiber-optic communications, where they permit transmission over longer distances and at ...
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 ligh ...
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 used as a colorant in borosilicate glass, used in lampworking. When combined with copper oxide, it provides a more stable red. It gives the glass a very reactive/changeable color, “a wonderful rainbow effect” when combined with silver oxide, that can shift light amber to a somewhat reddish and even deep purple appearance. The color can vary based on flame chemistry of the flame used to melt the glass (whether it has more oxygen or whether it has more fuel) And also it can change colors depending on the temperature of the kiln used to anneal the glass.
Germanium dioxide is also used as a catalyst
Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...
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 synthetic fibre, fibres for clothing, packaging, conta ...
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 ...
s and semiconductor material
A semiconductor is a material with electrical conductivity between that of a Electrical conductor, conductor and an Insulator (electricity), insulator. Its conductivity can be modified by adding impurities ("doping (semiconductor), doping") to ...
s.
Germanium dioxide is used in algaculture as an inhibitor of unwanted diatom
A diatom (Neo-Latin ''diatoma'') is any member of a large group comprising several Genus, genera of algae, specifically microalgae, found in the oceans, waterways and soils of the world. Living diatoms make up a significant portion of Earth's B ...
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 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 a person's diet by taking a pill (pharmacy), pill, capsule (pharmacy), capsule, tablet (pharmacy), tablet, powder, or liquid. A supplement can provide nutrients eithe ...
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