# Germanium

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Germanium,  32Ge
Germanium
Pronunciation
Appearancegrayish-white
Standard atomic weight Ar, std(Ge)72.630(8) [1]
Germanium in the periodic table
 Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
Si

Ge

Sn
galliumgermaniumarsenic
32
Group
Period period 4
Block p-block
Element category   Metalloid
Electron configuration [ Ar ] 3d10 4s2 4p2
Electrons per shell
2, 8, 18, 4
Physical properties
Phase at  solid
Melting point 1211.40  K (938.25 °C,1720.85 °F)
Boiling point 3106 K(2833 °C,5131 °F)
Density (near r.t.)5.323 g/cm3
when liquid (at m.p.)5.60 g/cm3
Heat of fusion 36.94  kJ/mol
Heat of vaporization 334 kJ/mol
Molar heat capacity 23.222 J/(mol·K)
Vapor pressure
P (Pa)1101001 k10 k100 k
at T (K)164418142023228726333104
Atomic properties
Oxidation states −4 −3, −2, −1, 0, +1, +2, +3, +4 (an  amphoteric oxide)
Electronegativity Pauling scale: 2.01
Ionization energies
• 1st: 762 kJ/mol
• 2nd: 1537.5 kJ/mol
• 3rd: 3302.1 kJ/mol
Van der Waals radius 211 pm
Spectral lines of germanium
Other properties
Natural occurrence primordial
Crystal structure face-centered diamond-cubic
Speed of sound thin rod5400 m/s(at 20 °C)
Thermal expansion 6.0 µm/(m·K)
Thermal conductivity 60.2 W/(m·K)
Electrical resistivity 1 Ω·m(at 20 °C)
Band gap 0.67  eV (at 300 K)
Magnetic ordering diamagnetic [2]
Magnetic susceptibility 76.84·10−6 cm3/mol [3]
Young's modulus 103 GPa [4]
Shear modulus 41 GPa [4]
Bulk modulus 75 GPa [4]
Poisson ratio 0.26 [4]
Mohs hardness 6.0
CAS Number 7440-56-4
History
Namingafter Germany, homeland of the discoverer
Prediction Dmitri Mendeleev (1869)
Discovery Clemens Winkler (1886)
Main isotopes of germanium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
68Ge syn 270.95 d ε 68Ga
70Ge20.52% stable
71Gesyn11.3 dε 71Ga
72Ge27.45%stable
73Ge7.76%stable
74Ge36.7%stable
76Ge7.75%1.78×1021 y ββ 76Se
| references

Germanium is a chemical element with the symbol Ge and atomic number 32. It is a lustrous, hard-brittle, grayish-white metalloid in the carbon group, chemically similar to its group neighbours silicon and tin. Pure germanium is a semiconductor with an appearance similar to elemental silicon. Like silicon, germanium naturally reacts and forms complexes with oxygen in nature.

A chemical element is a species of atom having the same number of protons in their atomic nuclei. For example, the atomic number of oxygen is 8, so the element oxygen consists of all atoms which have 8 protons.

In chemistry, a symbol is an abbreviation for a chemical element. Symbols for chemical elements normally consist of one or two letters from the Latin alphabet and are written with the first letter capitalised.

The atomic number or proton number of a chemical element is the number of protons found in the nucleus of every atom of that element. The atomic number uniquely identifies a chemical element. It is identical to the charge number of the nucleus. In an uncharged atom, the atomic number is also equal to the number of electrons.

## Contents

Because it seldom appears in high concentration, germanium was discovered comparatively late in the history of chemistry. Germanium ranks near fiftieth in relative abundance of the elements in the Earth's crust. In 1869, Dmitri Mendeleev predicted its existence and some of its properties from its position on his periodic table, and called the element ekasilicon . Nearly two decades later, in 1886, Clemens Winkler found the new element along with silver and sulfur, in a rare mineral called argyrodite. Although the new element somewhat resembled arsenic and antimony in appearance, the combining ratios in compounds agreed with Mendeleev's predictions for a relative of silicon. Winkler named the element after his country, Germany. Today, germanium is mined primarily from sphalerite (the primary ore of zinc), though germanium is also recovered commercially from silver, lead, and copper ores.

The history of chemistry represents a time span from ancient history to the present. By 1000 BC, civilizations used technologies that would eventually form the basis of the various branches of chemistry. Examples include extracting metals from ores, making pottery and glazes, fermenting beer and wine, extracting chemicals from plants for medicine and perfume, rendering fat into soap, making glass, and making alloys like bronze.

The abundance of elements in Earth's crust is shown in tabulated form with the estimated crustal abundance for each chemical element shown as parts per million (ppm) by mass. Note that the noble gases are not included, as they form no part of the solid crust. Also not included are certain elements with extremely low crustal concentrations: technetium, promethium (61), and all elements with atomic numbers greater than 83 except thorium (90) and uranium (92).

Dmitri Ivanovich Mendeleev was a Russian chemist and inventor. He formulated the Periodic Law, created a farsighted version of the periodic table of elements, and used it to correct the properties of some already discovered elements and also to predict the properties of eight elements yet to be discovered.

Elemental germanium is used as a semiconductor in transistors and various other electronic devices. Historically, the first decade of semiconductor electronics was based entirely on germanium. Presently, the major end uses are fibre-optic systems, infrared optics, solar cell applications, and light-emitting diodes (LEDs). Germanium compounds are also used for polymerization catalysts and have most recently found use in the production of nanowires. This element forms a large number of organogermanium compounds, such as tetraethylgermanium, useful in organometallic chemistry. Germanium is considered a technology-critical element.

A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It is composed of semiconductor material usually with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals controls the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.

Infrared vision is the capability of biological or artificial systems to detect infrared radiation. The terms thermal vision and thermal imaging, are also commonly used in this context since infrared emissions from a body are directly related to their temperature: hotter objects emit more energy in the infrared spectrum than colder ones.

A solar cell, or photovoltaic cell, is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon. It is a form of photoelectric cell, defined as a device whose electrical characteristics, such as current, voltage, or resistance, vary when exposed to light. Individual solar cell devices can be combined to form modules, otherwise known as solar panels. The common single junction silicon solar cell can produce a maximum open-circuit voltage of approximately 0.5 to 0.6 volts.

Germanium is not thought to be an essential element for any living organism. Some complex organic germanium compounds are being investigated as possible pharmaceuticals, though none have yet proven successful. Similar to silicon and aluminium, natural germanium compounds tend to be insoluble in water and thus have little oral toxicity. However, synthetic soluble germanium salts are nephrotoxic, and synthetic chemically reactive germanium compounds with halogens and hydrogen are irritants and toxins.

Organic chemistry is a subdiscipline of chemistry that studies the structure, properties and reactions of organic compounds, which contain carbon in covalent bonding. Study of structure determines their chemical composition and formula. Study of properties includes physical and chemical properties, and evaluation of chemical reactivity to understand their behavior. The study of organic reactions includes the chemical synthesis of natural products, drugs, and polymers, and study of individual organic molecules in the laboratory and via theoretical study.

Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a substructure of the organism, such as a cell (cytotoxicity) or an organ such as the liver (hepatotoxicity). By extension, the word may be metaphorically used to describe toxic effects on larger and more complex groups, such as the family unit or society at large. Sometimes the word is more or less synonymous with poisoning in everyday usage.

The halogens are a group in the periodic table consisting of five chemically related elements: Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I), and Astatine (At). The artificially created element 117 may also be a halogen. In the modern IUPAC nomenclature, this group is known as group 17.

## History

In his report on The Periodic Law of the Chemical Elements in 1869, the Russian chemist Dmitri Mendeleev predicted the existence of several unknown chemical elements, including one that would fill a gap in the carbon family, located between silicon and tin. [5] Because of its position in his periodic table, Mendeleev called it ekasilicon (Es), and he estimated its atomic weight to be 70 (later 72).

Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard and brittle crystalline solid with a blue-grey metallic lustre; and it is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic table: carbon is above it; and germanium, tin, and lead are below it. It is relatively unreactive. Because of its high chemical affinity for oxygen, it was not until 1823 that Jöns Jakob Berzelius was first able to prepare it and characterize it in pure form. Its melting and boiling points of 1414 °C and 3265 °C respectively are the second-highest among all the metalloids and nonmetals, being only surpassed by boron. Silicon is the eighth most common element in the universe by mass, but very rarely occurs as the pure element in the Earth's crust. It is most widely distributed in dusts, sands, planetoids, and planets as various forms of silicon dioxide (silica) or silicates. More than 90% of the Earth's crust is composed of silicate minerals, making silicon the second most abundant element in the Earth's crust after oxygen.

Tin is a chemical element with the symbol Sn (from Latin: stannum) and atomic number 50. Tin is a silvery metal that characteristicly has a faint yellow hue. Tin, like indium, is soft enough to be cut without much force. When a bar of tin is bent the so-called "tin cry" can be heard as a result of sliding tin crystals reforming; this trait is shared by indium, cadmium and frozen mercury. Pure tin after solidifying keeps a mirror-like appearance similar to most metals. However, in most tin alloys (such as pewter) the metal solidifies with a dull gray color. Tin is a post-transition metal in group 14 of the periodic table of elements. It is obtained chiefly from the mineral cassiterite, which contains stannic oxide, SnO2. Tin shows a chemical similarity to both of its neighbors in group 14, germanium and lead, and has two main oxidation states, +2 and the slightly more stable +4. Tin is the 49th most abundant element on Earth and has, with 10 stable isotopes, the largest number of stable isotopes in the periodic table, thanks to its magic number of protons. It has two main allotropes: at room temperature, the stable allotrope is β-tin, a silvery-white, malleable metal, but at low temperatures, it transforms into the less dense grey α-tin, which has the diamond cubic structure. Metallic tin does not easily oxidize in air.

In mid-1885, at a mine near Freiberg, Saxony, a new mineral was discovered and named argyrodite because of its high silver content. [note 1] The chemist Clemens Winkler analyzed this new mineral, which proved to be a combination of silver, sulfur, and a new element. Winkler was able to isolate the new element in 1886 and found it similar to antimony. He initially considered the new element to be eka-antimony, but was soon convinced that it was instead eka-silicon. [7] [8] Before Winkler published his results on the new element, he decided that he would name his element neptunium, since the recent discovery of planet Neptune in 1846 had similarly been preceded by mathematical predictions of its existence. [note 2] However, the name "neptunium" had already been given to another proposed chemical element (though not the element that today bears the name neptunium, which was discovered in 1940). [note 3] So instead, Winkler named the new element germanium (from the Latin word, Germania, for Germany) in honor of his homeland. [8] Argyrodite proved empirically to be Ag8GeS6. Because this new element showed some similarities with the elements arsenic and antimony, its proper place in the periodic table was under consideration, but its similarities with Dmitri Mendeleev's predicted element "ekasilicon" confirmed that place on the periodic table. [8] [15] With further material from 500 kg of ore from the mines in Saxony, Winkler confirmed the chemical properties of the new element in 1887. [7] [8] [16] He also determined an atomic weight of 72.32 by analyzing pure germanium tetrachloride (GeCl
4
), while Lecoq de Boisbaudran deduced 72.3 by a comparison of the lines in the spark spectrum of the element. [17]

A mineral is, broadly speaking, a solid chemical compound that occurs naturally in pure form. Minerals are most commonly associated with rocks due to the presence of minerals within rocks. These rocks may consist of one type of mineral, or may be an aggregate of two or more different types of minerals, spacially segregated into distinct phases. Compounds that occur only in living beings are usually excluded, but some minerals are often biogenic and/or are organic compounds in the sense of chemistry. Moreover, living beings often synthesize inorganic minerals that also occur in rocks.

Argyrodite is an uncommon silver germanium sulfide mineral with formula Ag8GeS6. The color is iron-black with a purplish tinge, and the luster metallic.

Silver is a chemical element with the symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal. The metal is found in the Earth's crust in the pure, free elemental form, as an alloy with gold and other metals, and in minerals such as argentite and chlorargyrite. Most silver is produced as a byproduct of copper, gold, lead, and zinc refining.

Winkler was able to prepare several new compounds of germanium, including fluorides, chlorides, sulfides, dioxide, and tetraethylgermane (Ge(C2H5)4), the first organogermane. [7] The physical data from those compounds—which corresponded well with Mendeleev's predictions—made the discovery an important confirmation of Mendeleev's idea of element periodicity. Here is a comparison between the prediction and Winkler's data: [7]

PropertyEkasilicon
Mendeleev
prediction (1871)
Germanium
Winkler
discovery (1887)
atomic mass72.6472.59
density (g/cm3)5.55.35
melting point (°C)high947
colorgraygray
oxide type refractory dioxiderefractory dioxide
oxide density (g/cm3)4.74.7
oxide activityfeebly basicfeebly basic
chloride boiling point (°C)under 10086 (GeCl4)
chloride density (g/cm3)1.91.9

Until the late 1930s, germanium was thought to be a poorly conducting metal. [18] Germanium did not become economically significant until after 1945 when its properties as an electronic semiconductor were recognized. During World War II, small amounts of germanium were used in some special electronic devices, mostly diodes. [19] [20] The first major use was the point-contact Schottky diodes for radar pulse detection during the War. [18] The first silicon-germanium alloys were obtained in 1955. [21] Before 1945, only a few hundred kilograms of germanium were produced in smelters each year, but by the end of the 1950s, the annual worldwide production had reached 40 metric tons (44 short ton s). [22]

The development of the germanium transistor in 1948 [23] opened the door to countless applications of solid state electronics. [24] From 1950 through the early 1970s, this area provided an increasing market for germanium, but then high-purity silicon began replacing germanium in transistors, diodes, and rectifiers. [25] For example, the company that became Fairchild Semiconductor was founded in 1957 with the express purpose of producing silicon transistors. Silicon has superior electrical properties, but it requires much greater purity that could not be commercially achieved in the early years of semiconductor electronics. [26]

Meanwhile, the demand for germanium for fiber optic communication networks, infrared night vision systems, and polymerization catalysts increased dramatically. [22] These end uses represented 85% of worldwide germanium consumption in 2000. [25] The US government even designated germanium as a strategic and critical material, calling for a 146  ton (132  tonne) supply in the national defense stockpile in 1987. [22]

Germanium differs from silicon in that the supply is limited by the availability of exploitable sources, while the supply of silicon is limited only by production capacity since silicon comes from ordinary sand and quartz. While silicon could be bought in 1998 for less than $10 per kg, [22] the price of germanium was almost$800 per kg. [22]

## Characteristics

Under standard conditions, germanium is a brittle, silvery-white, semi-metallic element. [27] This form constitutes an allotrope known as α-germanium, which has a metallic luster and a diamond cubic crystal structure, the same as diamond. [25] While in crystal form, germanium has a displacement threshold energy of ${\displaystyle 19.7_{-0.5}^{+0.6}~{\text{eV}}}$ [28] . At pressures above 120 kbar, germanium becomes the allotrope β-germanium with the same structure as β-tin. [29] 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. [29]

Germanium is a semiconductor. Zone refining techniques have led to the production of crystalline germanium for semiconductors that has an impurity of only one part in 1010, [30] making it one of the purest materials ever obtained. [31] The first 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. [32]

Pure germanium suffers from the forming of whiskers by spontaneous screw dislocations. If a whisker grows long enough to touch another part of the assembly or a metallic packaging, it can effectively shunt out a p-n junction. This is one of the primary reasons for the failure of old germanium diodes and transistors.

### Chemistry

Elemental germanium starts to oxidize slowly in air at around 250 °C, forming GeO2 . [33] Germanium is insoluble in dilute acids and alkalis but dissolves slowly in hot concentrated sulfuric and nitric acids and reacts violently with molten alkalis to produce germanates ([GeO
3
]2−
). Germanium occurs mostly in the oxidation state +4 although many +2 compounds are known. [34] Other oxidation states are rare: +3 is found in compounds such as Ge2Cl6, and +3 and +1 are found on the surface of oxides, [35] or negative oxidation states in germanides, such as −4 in Mg
2
Ge
. Germanium cluster anions (Zintl ions) such as Ge42−, Ge94−, Ge92−, [(Ge9)2]6− have been prepared by the extraction from alloys containing alkali metals and germanium in liquid ammonia in the presence of ethylenediamine or a cryptand. [34] [36] The oxidation states of the element in these ions are not integers—similar to the ozonides O3.

Two oxides of germanium are known: germanium dioxide (GeO
2
, germania) and germanium monoxide, (GeO). [29] The dioxide, GeO2 can be obtained by roasting germanium disulfide (GeS
2
), and is a white powder that is only slightly soluble in water but reacts with alkalis to form germanates. [29] The monoxide, germanous oxide, can be obtained by the high temperature reaction of GeO2 with Ge metal. [29] The dioxide (and the related oxides and germanates) exhibits the unusual property of having a high refractive index for visible light, but transparency to infrared light. [37] [38] Bismuth germanate, Bi4Ge3O12, (BGO) is used as a scintillator. [39]

Binary compounds with other chalcogens are also known, such as the disulfide (GeS
2
), diselenide (GeSe
2
), and the monosulfide (GeS), selenide (GeSe), and telluride (GeTe). [34] GeS2 forms as a white precipitate when hydrogen sulfide is passed through strongly acid solutions containing Ge(IV). [34] The disulfide is appreciably soluble in water and in solutions of caustic alkalis or alkaline sulfides. Nevertheless, it is not soluble in acidic water, which allowed Winkler to discover the element. [40] By heating the disulfide in a current of hydrogen, the monosulfide (GeS) is formed, which sublimes in thin plates of a dark color and metallic luster, and is soluble in solutions of the caustic alkalis. [29] Upon melting with alkaline carbonates and sulfur, germanium compounds form salts known as thiogermanates. [41]

Four tetrahalides are known. Under normal conditions GeI4 is a solid, GeF4 a gas and the others volatile liquids. For example, germanium tetrachloride, GeCl4, is obtained as a colorless fuming liquid boiling at 83.1 °C by heating the metal with chlorine. [29] All the tetrahalides are readily hydrolyzed to hydrated germanium dioxide. [29] GeCl4 is used in the production of organogermanium compounds. [34] All four dihalides are known and in contrast to the tetrahalides are polymeric solids. [34] Additionally Ge2Cl6 and some higher compounds of formula GenCl2n+2 are known. [29] The unusual compound Ge6Cl16 has been prepared that contains the Ge5Cl12 unit with a neopentane structure. [42]

Germane (GeH4) is a compound similar in structure to methane. Polygermanes—compounds that are similar to alkanes—with formula GenH2n+2 containing up to five germanium atoms are known. [34] The germanes are less volatile and less reactive than their corresponding silicon analogues. [34] GeH4 reacts with alkali metals in liquid ammonia to form white crystalline MGeH3 which contain the GeH3 anion. [34] The germanium hydrohalides with one, two and three halogen atoms are colorless reactive liquids. [34]

The first organogermanium compound was synthesized by Winkler in 1887; the reaction of germanium tetrachloride with diethylzinc yielded tetraethylgermane (Ge(C
2
H
5
)
4
). [7] Organogermanes of the type R4Ge (where R is an alkyl) such as tetramethylgermane (Ge(CH
3
)
4
) and tetraethylgermane are accessed through the cheapest available germanium precursor germanium tetrachloride and alkyl nucleophiles. Organic germanium hydrides such as isobutylgermane ((CH
3
)
2
CHCH
2
GeH
3
) were found to be less hazardous and may be used as a liquid substitute for toxic germane gas in semiconductor applications. Many germanium reactive intermediates are known: germyl free radicals, germylenes (similar to carbenes), and germynes (similar to carbynes). [43] [44] The organogermanium compound 2-carboxyethylgermasesquioxane was first reported in the 1970s, and for a while was used as a dietary supplement and thought to possibly have anti-tumor qualities. [45]

Using a ligand called Eind (1,1,3,3,5,5,7,7-octaethyl-s-hydrindacen-4-yl) germanium is able to form a double bond with oxygen (germanone). [46]

### Isotopes

Germanium occurs in 5 natural isotopes: 70
Ge
, 72
Ge
, 73
Ge
, 74
Ge
, and 76
Ge
. Of these, 76
Ge
is very slightly radioactive, decaying by double beta decay with a half-life of 1.78×1021 years. 74
Ge
is the most common isotope, having a natural abundance of approximately 36%. 76
Ge
is the least common with a natural abundance of approximately 7%. [47] When bombarded with alpha particles, the isotope 72
Ge
will generate stable , releasing high energy electrons in the process. [48] Because of this, it is used in combination with radon for nuclear batteries. [48]

At least 27 radioisotopes have also been synthesized, ranging in atomic mass from 58 to 89. The most stable of these is 68
Ge
, decaying by electron capture with a half-life of 270.95 days. The least stable is 60
Ge
, with a half-life of 30  ms . While most of germanium's radioisotopes decay by beta decay, 61
Ge
and 64
Ge
decay by
β+
delayed proton emission. [47] 84
Ge
through 87
Ge
isotopes also exhibit minor
β
delayed neutron emission decay paths. [47]

### Occurrence

Germanium is created by stellar nucleosynthesis, mostly by the s-process in asymptotic giant branch stars. The s-process is a slow neutron capture of lighter elements inside pulsating red giant stars. [49] Germanium has been detected in some of the most distant stars [50] and in the atmosphere of Jupiter. [51]

Germanium's abundance in the Earth's crust is approximately 1.6  ppm. [52] Only a few minerals like argyrodite, briartite, germanite, and renierite contain appreciable amounts of germanium. [25] [53] Only few of them (especially germanite) are, very rarely, found in mineable amounts. [54] [55] [56] Some zinc-copper-lead ore bodies contain enough germanium to justify extraction from the final ore concentrate. [52] An unusual natural enrichment process causes a high content of germanium in some coal seams, discovered by Victor Moritz Goldschmidt during a broad survey for germanium deposits. [57] [58] The highest concentration ever found was in Hartley coal ash with as much as 1.6% germanium. [57] [58] The coal deposits near Xilinhaote, Inner Mongolia, contain an estimated 1600  tonnes of germanium. [52]

## Production

About 118  tonnes of germanium was produced in 2011 worldwide, mostly in China (80 t), Russia (5 t) and United States (3 t). [25] Germanium is recovered as a by-product from sphalerite zinc ores where it is concentrated in amounts as great as 0.3%, [59] especially from low-temperature sediment-hosted, massive ZnPbCu(–Ba) deposits and carbonate-hosted Zn–Pb deposits. [60] A recent study found that at least 10,000 t of extractable germanium is contained in known zinc reserves, particularly those hosted by Mississippi-Valley type deposits, while at least 112,000 t will be found in coal reserves. [61] [62] In 2007 35% of the demand was met by recycled germanium. [52]

YearCost
(\$/kg) [63]
19991,400
20001,250
2001890
2002620
2003380
2004600
2005660
2006880
20071,240
20081,490
2009950
2010940
20111,625
20121,680
20131,875
20141,900
20151,760
2016950

While it is produced mainly from sphalerite, it is also found in silver, lead, and copper ores. Another source of germanium is fly ash of power plants fueled from coal deposits that contain germanium. Russia and China used this as a source for germanium. [64] Russia's deposits are located in the far east of Sakhalin Island, and northeast of Vladivostok. The deposits in China are located mainly in the lignite mines near Lincang, Yunnan; coal is also mined near Xilinhaote, Inner Mongolia. [52]

The ore concentrates are mostly sulfidic; they are converted to the oxides by heating under air in a process known as roasting:

GeS2 + 3 O2 → GeO2 + 2 SO2

Some of the germanium is left in the dust produced, while the rest is converted to germanates, which are then leached (together with zinc) from the cinder by sulfuric acid. After neutralization, only the zinc stays in solution while germanium and other metals precipitate. After removing some of the zinc in the precipitate by the Waelz process, the residing Waelz oxide is leached a second time. The dioxide is obtained as precipitate and converted with chlorine gas or hydrochloric acid to germanium tetrachloride, which has a low boiling point and can be isolated by distillation: [64]

GeO2 + 4 HCl → GeCl4 + 2 H2O
GeO2 + 2 Cl2 → GeCl4 + O2

Germanium tetrachloride is either hydrolyzed to the oxide (GeO2) or purified by fractional distillation and then hydrolyzed. [64] The highly pure GeO2 is now suitable for the production of germanium glass. It is reduced to the element by reacting it with hydrogen, producing germanium suitable for infrared optics and semiconductor production:

GeO2 + 2 H2 → Ge + 2 H2O

The germanium for steel production and other industrial processes is normally reduced using carbon: [65]

GeO2 + C → Ge + CO2

## Applications

The major end uses for germanium in 2007, worldwide, were estimated to be: 35% for fiber-optics, 30% infrared optics, 15% polymerization catalysts, and 15% electronics and solar electric applications. [25] The remaining 5% went into such uses as phosphors, metallurgy, and chemotherapy. [25]

### Optics

The notable properties of germania (GeO2) are its high index of refraction and its low optical dispersion. These make it especially useful for wide-angle camera lenses, microscopy, and the core part of optical fibers. [66] [67] It has replaced titania as the dopant for silica fiber, eliminating the subsequent heat treatment that made the fibers brittle. [68] At the end of 2002, the fiber optics industry consumed 60% of the annual germanium use in the United States, but this is less than 10% of worldwide consumption. [67] GeSbTe is a phase change material used for its optic properties, such as that used in rewritable DVDs. [69]

Because germanium is transparent in the infrared wavelengths, it is an important infrared optical material that can be readily cut and polished into lenses and windows. It is especially used as the front optic in thermal imaging cameras working in the 8 to 14  micron range for passive thermal imaging and for hot-spot detection in military, mobile night vision, and fire fighting applications. [65] It is used in infrared spectroscopes and other optical equipment that require extremely sensitive infrared detectors. [67] It has a very high refractive index (4.0) and must be coated with anti-reflection agents. Particularly, a very hard special antireflection coating of diamond-like carbon (DLC), refractive index 2.0, is a good match and produces a diamond-hard surface that can withstand much environmental abuse. [70] [71]

### Electronics

Silicon-germanium alloys are rapidly becoming an important semiconductor material for high-speed integrated circuits. Circuits utilizing the properties of Si-SiGe junctions can be much faster than those using silicon alone. [72] Silicon-germanium is beginning to replace gallium arsenide (GaAs) in wireless communications devices. [25] The SiGe chips, with high-speed properties, can be made with low-cost, well-established production techniques of the silicon chip industry. [25]

Solar panels are a major use of germanium. Germanium is the substrate of the wafers for high-efficiency multijunction photovoltaic cells for space applications. High-brightness LEDs, used for automobile headlights and to backlight LCD screens, are an important application. [25]

Because germanium and gallium arsenide have very similar lattice constants, germanium substrates can be used to make gallium arsenide solar cells. [73] The Mars Exploration Rovers and several satellites use triple junction gallium arsenide on germanium cells. [74]

Germanium-on-insulator (GeOI) substrates are seen as a potential replacement for silicon on miniaturized chips. [25] CMOS circuit based on GeOI substrates has been reported recently. [75] Other uses in electronics include phosphors in fluorescent lamps [30] and solid-state light-emitting diodes (LEDs). [25] Germanium transistors are still used in some effects pedals by musicians who wish to reproduce the distinctive tonal character of the "fuzz"-tone from the early rock and roll era, most notably the Dallas Arbiter Fuzz Face. [76]

### Other uses

Germanium dioxide is also used in catalysts for polymerization in the production of polyethylene terephthalate (PET). [77] The high brilliance of this polyester is especially favored for PET bottles marketed in Japan. [77] In the United States, germanium is not used for polymerization catalysts. [25]

Due to the similarity between silica (SiO2) and germanium dioxide (GeO2), the silica stationary phase in some gas chromatography columns can be replaced by GeO2. [78]

In recent years germanium has seen increasing use in precious metal alloys. In sterling silver alloys, for instance, it reduces firescale, increases tarnish resistance, and improves precipitation hardening. A tarnish-proof silver alloy trademarked Argentium contains 1.2% germanium. [25]

Semiconductor detectors made of single crystal high-purity germanium can precisely identify radiation sources—for example in airport security. [79] Germanium is useful for monochromators for beamlines used in single crystal neutron scattering and synchrotron X-ray diffraction. The reflectivity has advantages over silicon in neutron and high energy X-ray applications. [80] Crystals of high purity germanium are used in detectors for gamma spectroscopy and the search for dark matter. [81] Germanium crystals are also used in X-ray spectrometers for the determination of phosphorus, chlorine and sulfur. [82]

Germanium is emerging as an important material for spintronics and spin-based quantum computing applications. In 2010, researchers demonstrated room temperature spin transport [83] and more recently donor electron spins in germanium has been shown to have very long coherence times. [84]

### Germanium and health

Germanium is not considered essential to the health of plants or animals. [85] Germanium in the environment has little or no health impact. This is primarily because it usually occurs only as a trace element in ores and carbonaceous materials, and the various industrial and electronic applications involve very small quantities that are not likely to be ingested. [25] For similar reasons, end-use germanium has little impact on the environment as a biohazard. Some reactive intermediate compounds of germanium are poisonous (see precautions, below). [86]

Germanium supplements, made from both organic and inorganic germanium, have been marketed as an alternative medicine capable of treating leukemia and lung cancer. [22] There is, however, no medical evidence of benefit; some evidence suggests that such supplements are actively harmful. [85]

Some germanium compounds have been administered by alternative medical practitioners as non-FDA-allowed injectable solutions. Soluble inorganic forms of germanium used at first, notably the citrate-lactate salt, resulted in some cases of renal dysfunction, hepatic steatosis, and peripheral neuropathy in individuals using them over a long term. Plasma and urine germanium concentrations in these individuals, several of whom died, were several orders of magnitude greater than endogenous levels. A more recent organic form, beta-carboxyethylgermanium sesquioxide (propagermanium), has not exhibited the same spectrum of toxic effects. [87]

U.S. Food and Drug Administration research has concluded that inorganic germanium, when used as a nutritional supplement, "presents potential human health hazard". [45]

Certain compounds of germanium have low toxicity to mammals, but have toxic effects against certain bacteria. [27]

## Precautions for chemically reactive germanium compounds

Some of germanium's artificially produced compounds are quite reactive and present an immediate hazard to human health on exposure. For example, germanium chloride and germane (GeH4) are a liquid and gas, respectively, that can be very irritating to the eyes, skin, lungs, and throat. [88]

## Notes

1. From Greek, argyrodite means silver-containing. [6]
2. Just as the existence of the new element had been predicted, the existence of the planet Neptune had been predicted in about 1843 by the two mathematicians John Couch Adams and Urbain Le Verrier, using the calculation methods of celestial mechanics. They did this in attempts to explain the fact that the planet Uranus, upon very close observation, appeared to be being pulled slightly out of position in the sky. [9] James Challis started searching for it in July 1846, and he sighted this planet on September 23, 1846. [10]
3. R. Hermann published claims in 1877 of his discovery of a new element beneath tantalum in the periodic table, which he named neptunium, after the Greek god of the oceans and seas. [11] [12] However this metal was later recognized to be an alloy of the elements niobium and tantalum. [13] The name "neptunium" was later given to the synthetic element one step past uranium in the Periodic Table, which was discovered by nuclear physics researchers in 1940. [14]

## Related Research Articles

Gallium is a chemical element with the symbol Ga and atomic number 31. Elemental gallium is a soft, silvery blue metal at standard temperature and pressure; however in its liquid state it becomes silvery white. If too much force is applied, the gallium may fracture conchoidally. It is in group 13 of the periodic table, and thus has similarities to the other metals of the group, aluminium, indium, and thallium. Gallium does not occur as a free element in nature, but as gallium(III) compounds in trace amounts in zinc ores and in bauxite. Elemental gallium is a liquid at temperatures greater than 29.76 °C (85.57 °F), above room temperature, but below the normal human body temperature of 37 °C (99 °F). Hence, the metal will melt in a person's hands.

A semiconductor material has an electrical conductivity value falling between that of a conductor, such as metallic copper, and an insulator, such as glass. Its resistance decreases as its temperature increases, which is the behaviour opposite to that of a metal. Its conducting properties may be altered in useful ways by the deliberate, controlled introduction of impurities ("doping") into the crystal structure. Where two differently-doped regions exist in the same crystal, a semiconductor junction is created. The behavior of charge carriers which include electrons, ions and electron holes at these junctions is the basis of diodes, transistors and all modern electronics. Some examples of semiconductors are silicon, germanium, gallium arsenide, and elements near the so-called "metalloid staircase" on the periodic table. After silicon, gallium arsenide is the second most common semiconductor and is used in laser diodes, solar cells, microwave-frequency integrated circuits and others. Silicon is a critical element for fabricating most electronic circuits.

The carbon group is a periodic table group consisting of carbon (C), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), and flerovium (Fl). It lies within the p-block.

Gallium arsenide (GaAs) is a compound of the elements gallium and arsenic. It is a III-V direct band gap semiconductor with a zinc blende crystal structure.

Gallium nitride (GaN) is a binary III/V direct bandgap semiconductor commonly used in light-emitting diodes since the 1990s. The compound is a very hard material that has a Wurtzite crystal structure. Its wide band gap of 3.4 eV affords it special properties for applications in optoelectronic, high-power and high-frequency devices. For example, GaN is the substrate which makes violet (405 nm) laser diodes possible, without use of nonlinear optical frequency-doubling.

SiGe, or silicon-germanium, is an alloy with any molar ratio of silicon and germanium, i.e. with a molecular formula of the form Si1−xGex. It is commonly used as a semiconductor material in integrated circuits (ICs) for heterojunction bipolar transistors or as a strain-inducing layer for CMOS transistors. IBM introduced the technology into mainstream manufacturing in 1989. This relatively new technology offers opportunities in mixed-signal circuit and analog circuit IC design and manufacture. SiGe is also used as a thermoelectric material for high temperature applications.

In semiconductor production, doping is the intentional introduction of impurities into an intrinsic semiconductor for the purpose of modulating its electrical, optical and structural properties. The doped material is referred to as an extrinsic semiconductor. A semiconductor doped to such high levels that it acts more like a conductor than a semiconductor is referred to as a degenerate semiconductor.

Clemens Alexander Winkler was a German chemist who discovered the element germanium in 1886, solidifying Dmitri Mendeleev's theory of periodicity.

The heterojunction bipolar transistor (HBT) is a type of bipolar junction transistor (BJT) which uses differing semiconductor materials for the emitter and base regions, creating a heterojunction. The HBT improves on the BJT in that it can handle signals of very high frequencies, up to several hundred GHz. It is commonly used in modern ultrafast circuits, mostly radio-frequency (RF) systems, and in applications requiring a high power efficiency, such as RF power amplifiers in cellular phones. The idea of employing a heterojunction is as old as the conventional BJT, dating back to a patent from 1951. Detailed theory of heterojunction bipolar transistor was developed by Herbert Kroemer in 1957.

Germane is the chemical compound with the formula GeH4, and the germanium analogue of methane. It is the simplest germanium hydride and one of the most useful compounds of germanium. Like the related compounds silane and methane, germane is tetrahedral. It burns in air to produce GeO2 and water. Germane is a group 14 hydride.

Germanium dioxide, also called germanium oxide, germania, and salt of germanium, is an inorganic compound with the chemical formula GeO2. It is the main commercial source of germanium. It also forms as a passivation layer on pure germanium in contact with atmospheric oxygen.

Organogermanium compounds are organometallic compounds containing a carbon to germanium or hydrogen to germanium chemical bond. Organogermanium chemistry is the corresponding chemical science. Germanium shares group 14 in the periodic table with silicon, tin and lead, and not surprisingly the chemistry of organogermanium is in between that of organosilicon compounds and organotin compounds.

Isobutylgermane (IBGe, Chemical formula: (CH3)2CHCH2GeH3, is an organogermanium compound. It is a colourless, volatile liquid that is used in MOVPE (Metalorganic Vapor Phase Epitaxy) as an alternative to germane. IBGe is used in the deposition of Ge films and Ge-containing thin semiconductor films such as SiGe in strained silicon application, and GeSbTe in NAND Flash applications.

Germanium disulfide or Germanium(IV) sulfide is the inorganic compound with the formula GeS2. It is a white high-melting crystalline solid. The compound is a 3-dimensional polymer, in contrast to silicon disulfide, which is a one-dimensional polymer. The Ge-S distance is 2.19 Å.

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.

Digermane is an inorganic compound with the chemical formula Ge2H6. One of the few hydrides of germanium, it is a colourless liquid. Its molecular geometry is similar to ethane.

Germanium(II) hydroxide, normally written as Ge(OH)2 is a poorly characterised compound sometimes called hydrous germanium(II) oxide or germanous hydroxide. It was first reported by Winkler in 1886.

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