Neodymium is a chemical element with symbol Nd and atomic number 60. It is a soft silvery metal. Neodymium was discovered in 1885 by the Austrian chemist Carl Auer von Welsbach, it is present in significant quantities in the ore minerals bastnäsite. Neodymium is not found in metallic form or unmixed with other lanthanides, it is refined for general use. Although neodymium is classed as a rare earth, it is a common element, no rarer than cobalt, nickel, or copper, is distributed in the Earth's crust. Most of the world's commercial neodymium is mined in China. Neodymium compounds were first commercially used as glass dyes in 1927, they remain a popular additive in glasses; the color of neodymium compounds—due to the Nd3+ ion—is a reddish-purple but it changes with the type of lighting, due to the interaction of the sharp light absorption bands of neodymium with ambient light enriched with the sharp visible emission bands of mercury, trivalent europium or terbium. Some neodymium-doped glasses are used in lasers that emit infrared with wavelengths between 1047 and 1062 nanometers.
These have been used in extremely-high-power applications, such as experiments in inertial confinement fusion. Neodymium is used with various other substrate crystals, such as yttrium aluminium garnet in the Nd:YAG laser; this laser emits infrared at a wavelength of about 1064 nanometers. The Nd:YAG laser is one of the most used solid-state lasers. Another important use of neodymium is as a component in the alloys used to make high-strength neodymium magnets—powerful permanent magnets; these magnets are used in such products as microphones, professional loudspeakers, in-ear headphones, high performance hobby DC electric motors, computer hard disks, where low magnet mass or strong magnetic fields are required. Larger neodymium magnets are used in generators. Neodymium, a rare-earth metal, was present in the classical mischmetal at a concentration of about 18%. Metallic neodymium has a bright, silvery metallic luster, but as one of the more reactive lanthanide rare-earth metals, it oxidizes in ordinary air.
The oxide layer that forms peels off, exposing the metal to further oxidation. Thus, a centimeter-sized sample of neodymium oxidizes within a year. Neodymium exists in two allotropic forms, with a transformation from a double hexagonal to a body-centered cubic structure taking place at about 863 °C. Neodymium metal tarnishes in air and it burns at about 150 °C to form neodymium oxide: 4 Nd + 3 O2 → 2 Nd2O3Neodymium is a quite electropositive element, it reacts with cold water, but quite with hot water to form neodymium hydroxide: 2 Nd + 6 H2O → 2 Nd3 + 3 H2 Neodymium metal reacts vigorously with all the halogens: 2 Nd + 3 F2 → 2 NdF3 2 Nd + 3 Cl2 → 2 NdCl3 2 Nd + 3 Br2 → 2 NdBr3 2 Nd + 3 I2 → 2 NdI3 Neodymium dissolves in dilute sulfuric acid to form solutions that contain the lilac Nd ion; these exist as a 3+ complexes: 2 Nd + 3 H2SO4 → 2 Nd3+ + 3 SO2−4 + 3 H2 Neodymium compounds include halides: neodymium fluoride. Occurring neodymium is a mixture of five stable isotopes, 142Nd, 143Nd, 145Nd, 146Nd and 148Nd, with 142Nd being the most abundant, two radioisotopes, 144Nd and 150Nd.
In all, 31 radioisotopes of neodymium have been detected as of 2010, with the most stable radioisotopes being the occurring ones: 144Nd and 150Nd. All of the remaining radioactive isotopes have half-lives that are shorter than eleven days, the majority of these have half-lives that are shorter than 70 seconds. Neodymium has 13 known meta states, with the most stable one being 139mNd, 135mNd and 133m1Nd; the primary decay modes before the most abundant stable isotope, 142Nd, are electron capture and positron decay, the primary mode after is beta minus decay. The primary decay products before 142Nd are element Pr isotopes and the primary products after are element Pm isotopes. Neodymium was discovered by Baron Carl Auer von Welsbach, an Austrian chemist, in Vienna in 1885, he separated neodymium, as well as the element praseodymium, from a material known as didymium by means of fractional crystallization of the double ammonium nitrate tetrahydrates from nitric acid, while following the separation by spectroscopic analysis.
The name neodymium is derived from the Greek words neos and didymos, twin. Double nitrate crystallization was the means of commercial neodymium purification until the 1950s. Lindsay Chemical Division was the first to commercialize large-scale ion-exchange purification of neodymium. Starting in the 1950s, high purity
A diode is a two-terminal electronic component that conducts current in one direction. A diode vacuum tube or thermionic diode is a vacuum tube with two electrodes, a heated cathode and a plate, in which electrons can flow in only one direction, from cathode to plate. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material with a p–n junction connected to two electrical terminals. Semiconductor diodes were the first semiconductor electronic devices; the discovery of asymmetric electrical conduction across the contact between a crystalline mineral and a metal was made by German physicist Ferdinand Braun in 1874. Today, most diodes are made of silicon, but other materials such as gallium arsenide and germanium are used; the most common function of a diode is to allow an electric current to pass in one direction, while blocking it in the opposite direction. As such, the diode can be viewed as an electronic version of a check valve; this unidirectional behavior is called rectification, is used to convert alternating current to direct current.
Forms of rectifiers, diodes can be used for such tasks as extracting modulation from radio signals in radio receivers. However, diodes can have more complicated behavior than this simple on–off action, because of their nonlinear current-voltage characteristics. Semiconductor diodes begin conducting electricity only if a certain threshold voltage or cut-in voltage is present in the forward direction; the voltage drop across a forward-biased diode varies only a little with the current, is a function of temperature. Diodes' high resistance to current flowing in the reverse direction drops to a low resistance when the reverse voltage across the diode reaches a value called the breakdown voltage. A semiconductor diode's current–voltage characteristic can be tailored by selecting the semiconductor materials and the doping impurities introduced into the materials during manufacture; these techniques are used to create special-purpose diodes. For example, diodes are used to regulate voltage, to protect circuits from high voltage surges, to electronically tune radio and TV receivers, to generate radio-frequency oscillations, to produce light.
Tunnel, Gunn and IMPATT diodes exhibit negative resistance, useful in microwave and switching circuits. Diodes, both vacuum and semiconductor, can be used as shot-noise generators. Thermionic diodes and solid-state diodes were developed separately, at the same time, in the early 1900s, as radio receiver detectors; until the 1950s, vacuum diodes were used more in radios because the early point-contact semiconductor diodes were less stable. In addition, most receiving sets had vacuum tubes for amplification that could have the thermionic diodes included in the tube, vacuum-tube rectifiers and gas-filled rectifiers were capable of handling some high-voltage/high-current rectification tasks better than the semiconductor diodes that were available at that time. In 1873, Frederick Guthrie observed that a grounded, white hot metal ball brought in close proximity to an electroscope would discharge a positively charged electroscope, but not a negatively charged electroscope. In 1880, Thomas Edison observed unidirectional current between heated and unheated elements in a bulb called Edison effect, was granted a patent on application of the phenomenon for use in a dc voltmeter.
About 20 years John Ambrose Fleming realized that the Edison effect could be used as a radio detector. Fleming patented the first true thermionic diode, the Fleming valve, in Britain on November 16, 1904. Throughout the vacuum tube era, valve diodes were used in all electronics such as radios, sound systems and instrumentation, they lost market share beginning in the late 1940s due to selenium rectifier technology and to semiconductor diodes during the 1960s. Today they are still used in a few high power applications where their ability to withstand transient voltages and their robustness gives them an advantage over semiconductor devices, in musical instrument and audiophile applications. In 1874, German scientist Karl Ferdinand Braun discovered the "unilateral conduction" across a contact between a metal and a mineral. Indian scientist Jagadish Chandra Bose was the first to use a crystal for detecting radio waves in 1894; the crystal detector was developed into a practical device for wireless telegraphy by Greenleaf Whittier Pickard, who invented a silicon crystal detector in 1903 and received a patent for it on November 20, 1906.
Other experimenters tried a variety of other minerals as detectors. Semiconductor principles were unknown to the developers of these early rectifiers. During the 1930s understanding of physics advanced and in the mid 1930s researchers at Bell Telephone Laboratories recognized the potential of the crystal detector for application in microwave technology. Researchers at Bell Labs, Western Electric, MIT, Purdue and in the UK intensively developed point-contact diodes during World War II for application in ra
An optical fiber is a flexible, transparent fiber made by drawing glass or plastic to a diameter thicker than that of a human hair. Optical fibers are used most as a means to transmit light between the two ends of the fiber and find wide usage in fiber-optic communications, where they permit transmission over longer distances and at higher bandwidths than electrical cables. Fibers are used instead of metal wires. Fibers are used for illumination and imaging, are wrapped in bundles so they may be used to carry light into, or images out of confined spaces, as in the case of a fiberscope. Specially designed fibers are used for a variety of other applications, some of them being fiber optic sensors and fiber lasers. Optical fibers include a core surrounded by a transparent cladding material with a lower index of refraction. Light is kept in the core by the phenomenon of total internal reflection which causes the fiber to act as a waveguide. Fibers that support many propagation paths or transverse modes are called multi-mode fibers, while those that support a single mode are called single-mode fibers.
Multi-mode fibers have a wider core diameter and are used for short-distance communication links and for applications where high power must be transmitted. Single-mode fibers are used for most communication links longer than 1,000 meters. Being able to join optical fibers with low loss is important in fiber optic communication; this is more complex than joining electrical wire or cable and involves careful cleaving of the fibers, precise alignment of the fiber cores, the coupling of these aligned cores. For applications that demand a permanent connection a fusion splice is common. In this technique, an electric arc is used to melt the ends of the fibers together. Another common technique is a mechanical splice, where the ends of the fibers are held in contact by mechanical force. Temporary or semi-permanent connections are made by means of specialized optical fiber connectors; the field of applied science and engineering concerned with the design and application of optical fibers is known as fiber optics.
The term was coined by Indian physicist Narinder Singh Kapany, acknowledged as the father of fiber optics. Guiding of light by refraction, the principle that makes fiber optics possible, was first demonstrated by Daniel Colladon and Jacques Babinet in Paris in the early 1840s. John Tyndall included a demonstration of it in his public lectures in London, 12 years later. Tyndall wrote about the property of total internal reflection in an introductory book about the nature of light in 1870:When the light passes from air into water, the refracted ray is bent towards the perpendicular... When the ray passes from water to air it is bent from the perpendicular... If the angle which the ray in water encloses with the perpendicular to the surface be greater than 48 degrees, the ray will not quit the water at all: it will be reflected at the surface.... The angle which marks the limit where total reflection begins is called the limiting angle of the medium. For water this angle is 48°27′, for flint glass it is 38°41′, while for diamond it is 23°42′.
In the late 19th and early 20th centuries, light was guided through bent glass rods to illuminate body cavities. Practical applications such as close internal illumination during dentistry appeared early in the twentieth century. Image transmission through tubes was demonstrated independently by the radio experimenter Clarence Hansell and the television pioneer John Logie Baird in the 1920s. In the 1930s, Heinrich Lamm showed that one could transmit images through a bundle of unclad optical fibers and used it for internal medical examinations, but his work was forgotten. In 1953, Dutch scientist Bram van Heel first demonstrated image transmission through bundles of optical fibers with a transparent cladding; that same year, Harold Hopkins and Narinder Singh Kapany at Imperial College in London succeeded in making image-transmitting bundles with over 10,000 fibers, subsequently achieved image transmission through a 75 cm long bundle which combined several thousand fibers. Their article titled "A flexible fibrescope, using static scanning" was published in the journal Nature in 1954.
The first practical fiber optic semi-flexible gastroscope was patented by Basil Hirschowitz, C. Wilbur Peters, Lawrence E. Curtiss, researchers at the University of Michigan, in 1956. In the process of developing the gastroscope, Curtiss produced the first glass-clad fibers. A variety of other image transmission applications soon followed. Kapany coined the term fiber optics, wrote a 1960 article in Scientific American that introduced the topic to a wide audience, wrote the first book about the new field; the first working fiber-optical data transmission system was demonstrated by German physicist Manfred Börner at Telefunken Research Labs in Ulm in 1965, followed by the first patent application for this technology in 1966. NASA used fiber optics in the television cameras. At the time, the use in the cameras was classified confidential, employees handling the cameras had to be supervised by someone with an appropriate security clearance. Charles K. Kao and George A. Hockham of the British company Standard Telephones and Cables were the first, in 1965, to promote the idea that the attenuation in optical fibers could be reduced below 20 decibels per kilometer, making fibers a practical communication medium.
They proposed th
Europium is a chemical element with symbol Eu and atomic number 63. It is named after the continent of Europe, it is a moderately hard, silvery metal which oxidizes in air and water. Being a typical member of the lanthanide series, europium assumes the oxidation state +3, but the oxidation state +2 is common. All europium compounds with oxidation state +2 are reducing. Europium has no significant biological role and is non-toxic compared to other heavy metals. Most applications of europium exploit the phosphorescence of europium compounds. Europium is one of the least abundant elements in the universe. Europium is a ductile metal with a hardness similar to that of lead, it crystallizes in a body-centered cubic lattice. Some properties of europium are influenced by its half-filled electron shell. Europium has the lowest density of all lanthanides. Europium becomes a superconductor when it is compressed to above 80 GPa; this is because europium is divalent in the metallic state, is converted into the trivalent state by the applied pressure.
In the divalent state, the strong local magnetic moment suppresses the superconductivity, induced by eliminating this local moment. Europium is the most reactive rare-earth element, it oxidizes in air, so that bulk oxidation of a centimeter-sized sample occurs within several days. Its reactivity with water is comparable to that of calcium, the reaction is 2 Eu + 6 H2O → 2 Eu3 + 3 H2Because of the high reactivity, samples of solid europium have the shiny appearance of the fresh metal when coated with a protective layer of mineral oil. Europium ignites in air at 150 to 180 °C to form europium oxide: 4 Eu + 3 O2 → 2 Eu2O3Europium dissolves in dilute sulfuric acid to form pale pink solutions of the hydrated Eu, which exist as a nonahydrate: 2 Eu + 3 H2SO4 + 18 H2O → 2 3+ + 3 SO2−4 + 3 H2 Although trivalent, europium forms divalent compounds; this behavior is unusual to most lanthanides, which exclusively form compounds with an oxidation state of +3. The +2 state has an electron configuration 4f7.
In terms of size and coordination number and barium are similar. For example, the sulfates of both barium and europium are highly insoluble in water. Divalent europium is a mild reducing agent, oxidizing in air to form Eu compounds. In anaerobic, geothermal conditions, the divalent form is sufficiently stable that it tends to be incorporated into minerals of calcium and the other alkaline earths; this ion-exchange process is the basis of the "negative europium anomaly", the low europium content in many lanthanide minerals such as monazite, relative to the chondritic abundance. Bastnäsite tends to show less of a negative europium anomaly than does monazite, hence is the major source of europium today; the development of easy methods to separate divalent europium from the other lanthanides made europium accessible when present in low concentration, as it is. Occurring europium is composed of 2 isotopes, 151Eu and 153Eu, with 153Eu being the most abundant. While 153Eu is stable, 151Eu was found to be unstable to alpha decay with half-life of 5+11−3×1018 years, giving about 1 alpha decay per two minutes in every kilogram of natural europium.
This value is in reasonable agreement with theoretical predictions. Besides the natural radioisotope 151Eu, 35 artificial radioisotopes have been characterized, the most stable being 150Eu with a half-life of 36.9 years, 152Eu with a half-life of 13.516 years, 154Eu with a half-life of 8.593 years. All the remaining radioactive isotopes have half-lives shorter than 4.7612 years, the majority of these have half-lives shorter than 12.2 seconds. This element has 8 meta states, with the most stable being 150mEu, 152m1Eu and 152m2Eu; the primary decay mode for isotopes lighter than 153Eu is electron capture, the primary mode for heavier isotopes is beta minus decay. The primary decay products before 153Eu are isotopes of samarium and the primary products after are isotopes of gadolinium. Europium is produced by nuclear fission, but the fission product yields of europium isotopes are low near the top of the mass range for fission products. Like other lanthanides, many isotopes isotopes with odd mass numbers and neutron-poor isotopes like 152Eu, have high cross sections for neutron capture high enough to be neutron poisons.
151Eu is the beta decay product of samarium-151, but since this has a long decay half-life and short mean time to neutron absorption, most 151Sm instead ends up as 152Sm. 152Eu and 154Eu cannot be beta decay products because 152Sm and 154Sm are non-radioactive, but 154Eu is the only long-lived "shielded" nuclide, other than 134Cs, to have a fission yield of more than 2.5 parts per million fissions. A larger amount of 154Eu is produced by neutron activation of a significant portion of the non-radioactive 153Eu. 155Eu has a fission yield of 330 parts per million for thermal neutrons. Overall, europium is overshadowed by caesium-137 and strontium-90 as a radiation hazard, by samarium and others as a neutron poison. Europium is not found in nature as a free element. Many minerals contain eur
Holmium is a chemical element with symbol Ho and atomic number 67. Part of the lanthanide series, holmium is a rare-earth element. Holmium was discovered by Swedish chemist Per Theodor Cleve, its oxide was first isolated from rare-earth ores in 1878. The element's name comes from the Latin name for the city of Stockholm. Elemental holmium is a soft and malleable silvery-white metal, it is too reactive to be found uncombined in nature, but when isolated, is stable in dry air at room temperature. However, it reacts with water and corrodes and burns in air when heated. Holmium is found in the minerals monazite and gadolinite and is commercially extracted from monazite using ion-exchange techniques, its compounds in nature and in nearly all of its laboratory chemistry are trivalently oxidized, containing Ho ions. Trivalent holmium ions have fluorescent properties similar to many other rare-earth ions, thus are used in the same way as some other rare earths in certain laser and glass-colorant applications.
Holmium has the highest magnetic permeability of any element and therefore is used for the polepieces of the strongest static magnets. Because holmium absorbs neutrons, it is used as a burnable poison in nuclear reactors. Holmium is a soft and malleable element, corrosion-resistant and stable in dry air at standard temperature and pressure. In moist air and at higher temperatures, however, it oxidizes, forming a yellowish oxide. In pure form, holmium possesses a metallic, bright silvery luster. Holmium oxide has some dramatic color changes depending on the lighting conditions. In daylight, it has a tannish yellow color. Under trichromatic light, it is fiery orange-red indistinguishable from the appearance of erbium oxide under the same lighting conditions; the perceived color change is related to the sharp absorption bands of holmium interacting with a subset of the sharp emission bands of the trivalent ions of europium and terbium, acting as phosphors. Holmium has the highest magnetic moment of any occurring element and possesses other unusual magnetic properties.
When combined with yttrium, it forms magnetic compounds. Holmium is paramagnetic at ambient conditions, but is ferromagnetic at temperatures below 19 K. Holmium metal tarnishes in air and burns to form holmium oxide: 4 Ho + 3 O2 → 2 Ho2O3Holmium is quite electropositive and is trivalent, it reacts with cold water and quite with hot water to form holmium hydroxide: 2 Ho + 6 H2O → 2 Ho3 + 3 H2 Holmium metal reacts with all the halogens: 2 Ho + 3 F2 → 2 HoF3 2 Ho + 3 Cl2 → 2 HoCl3 2 Ho + 3 Br2 → 2 HoBr3 2 Ho + 3 I2 → 2 HoI3 Holmium dissolves in dilute sulfuric acid to form solutions containing the yellow Ho ions, which exist as a 3+ complexes: 2 Ho + 3 H2SO4 → 2 Ho3+ + 3 SO2−4 + 3 H2 Holmium's most common oxidation state is +3. Holmium in solution is in the form of Ho3+ surrounded by nine molecules of water. Holmium dissolves in acids. Natural holmium contains one stable isotope, holmium-165; some synthetic radioactive isotopes are known. All other radioisotopes have ground-state half-lives not greater than 1.117 days, most have half-lives under 3 hours.
However, the metastable 166m1Ho has a half-life of around 1200 years because of its high spin. This fact, combined with a high excitation energy resulting in a rich spectrum of decay gamma rays produced when the metastable state de-excites, makes this isotope useful in nuclear physics experiments as a means for calibrating energy responses and intrinsic efficiencies of gamma ray spectrometers. Holmium was discovered by Jacques-Louis Soret and Marc Delafontaine in 1878 who noticed the aberrant spectrographic absorption bands of the then-unknown element; the following year, Per Teodor Cleve independently discovered the element while he was working on erbia earth. Using the method developed by Carl Gustaf Mosander, Cleve first removed all of the known contaminants from erbia; the result of that effort was one brown and one green. He named the green one thulia. Holmia was found to be the holmium oxide, thulia was thulium oxide. In Henry Moseley's classic paper on atomic numbers, holmium was assigned an atomic number of 66.
Evidently, the holmium preparation he had been given to investigate had been grossly impure, dominated by neighboring dysprosium. He would have seen x-ray emission lines for both elements, but assumed that the dominant ones belonged to holmium, instead of the dysprosium impurity. Like all other rare earths, holmium is not found as a free element, it does occur combined with other elements in gadolinite and other rare-earth minerals. No holmium-dominant mineral has yet been found; the main mining areas are China, United States, India, Sri Lanka, Australia with reserves of holmium estimated as 400,000 tonnes. Holmium makes up 1.4 parts per million of the Earth's crust by mass. This makes it the 56th most abundant element in the Earth's crust. Holmium makes up 1 part per million of the soils, 400 parts per quadrillion of seawater, none of Earth's atmosphere. Holmium is rare for a lanthanide, it makes up 500 parts per trillion of the universe by mass. It is commercially extracted by ion exch
The Fermi level chemical potential for electrons of a body is the thermodynamic work required to add one electron to the body. It is a thermodynamic quantity denoted by µ or EF for brevity; the Fermi level does not include the work required to remove the electron from wherever it came from. A precise understanding of the Fermi level—how it relates to electronic band structure in determining electronic properties, how it relates to the voltage and flow of charge in an electronic circuit—is essential to an understanding of solid-state physics. In band structure theory, used in solid state physics to analyze the energy levels in a solid, the Fermi level can be considered to be a hypothetical energy level of an electron, such that at thermodynamic equilibrium this energy level would have a 50% probability of being occupied at any given time; the position of the Fermi level with the relation to the band energy levels is a crucial factor in determining electrical properties. The Fermi level does not correspond to an actual energy level, nor does it require the existence of a band structure.
Nonetheless, the Fermi level is a defined thermodynamic quantity, differences in Fermi level can be measured with a voltmeter. Sometimes it is said that electric currents are driven by differences in electrostatic potential, but this is not true; as a counterexample, multi-material devices such as p–n junctions contain internal electrostatic potential differences at equilibrium, yet without any accompanying net current. The electrostatic potential is not the only factor influencing the flow of charge in a material—Pauli repulsion, carrier concentration gradients, electromagnetic induction, thermal effects play an important role. In fact, the quantity called voltage as measured in an electronic circuit has a simple relationship to the chemical potential for electrons; when the leads of a voltmeter are attached to two points in a circuit, the displayed voltage is a measure of the total work transferred when a unit charge is allowed to move from one point to the other. If a simple wire is connected between two points of differing voltage, current will flow from positive to negative voltage, converting the available work into heat.
The Fermi level of a body expresses the work required to add an electron to it, or the work obtained by removing an electron. Therefore, VA − VB, the observed difference in voltage between two points, A and B, in an electronic circuit is related to the corresponding chemical potential difference, µA − µB, in Fermi level by the formula V A − V B = μ A − μ B − e where −e is the electron charge. From the above discussion it can be seen that electrons will move from a body of high µ to low µ if a simple path is provided; this flow of electrons will cause the lower µ to increase and cause the higher µ to decrease. Μ will settle down to the same value in both bodies. This leads to an important fact regarding the equilibrium state of an electronic circuit: An electronic circuit in thermodynamic equilibrium will have a constant Fermi level throughout its connected parts; this means that the voltage between any two points will be zero, at equilibrium. Note that thermodynamic equilibrium here requires that the circuit be internally connected and not contain any batteries or other power sources, nor any variations in temperature.
In the band theory of solids, electrons are considered to occupy a series of bands composed of single-particle energy eigenstates each labelled by ϵ. Although this single particle picture is an approximation, it simplifies the understanding of electronic behaviour and it provides correct results when applied correctly; the Fermi–Dirac distribution, f, gives the probability that a state having energy ϵ is occupied by an electron: f = 1 e / k T + 1 Here, T is the absolute temperature and k is Boltzmann's constant. If there is a state at the Fermi level this state will have a 50% chance of being occupied; the distribution is plotted in the left figure. The closer f is to 1, the higher chance this state is occupied; the closer f is to 0, the higher chance this state is empty. The location of µ within a material's band structure is important in determining the electrical behaviour of the material. In an insulator, µ lies within a large band gap, far away from any states that are able to carry current.
In a metal, semimetal or degenerate semiconductor, µ lies within a delocalized band. A large number of states nearby µ are thermally active and carry current. In an intrinsic or doped semiconductor, µ is close enough to a band edge that there are a dilute number of thermally excited carriers residing near that band edge. In semiconductors and semimetals the position of µ rel
Germanium is a chemical element with symbol Ge and atomic number 32. It is a lustrous, 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 reacts and forms complexes with oxygen in nature; because it 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, called the element ekasilicon. Nearly two decades 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 Germany. Today, germanium is mined from sphalerite, though germanium is recovered commercially from silver and copper ores. Elemental germanium is used as a semiconductor in various other electronic devices; the first decade of semiconductor electronics was based on germanium. Presently, the major end uses are fibre-optic systems, infrared optics, solar cell applications, light-emitting diodes. Germanium compounds are used for polymerization catalysts and have most 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. 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, synthetic chemically reactive germanium compounds with halogens and hydrogen are irritants and toxins. 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; because of its position in his periodic table, Mendeleev called it ekasilicon, he estimated its atomic weight to be 70. In mid-1885, at a mine near Freiberg, Saxony, a new mineral was discovered and named argyrodite because of its high silver content; the chemist Clemens Winkler analyzed this new mineral, which proved to be a combination of silver, a new element. Winkler found it similar to antimony, he considered the new element to be eka-antimony, but was soon convinced that it was instead eka-silicon. 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 been preceded by mathematical predictions of its existence.
However, the name "neptunium" had been given to another proposed chemical element. So instead, Winkler named the new element germanium in honor of his homeland. 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. With further material from 500 kg of ore from the mines in Saxony, Winkler confirmed the chemical properties of the new element in 1887, he determined an atomic weight of 72.32 by analyzing pure germanium tetrachloride, while Lecoq de Boisbaudran deduced 72.3 by a comparison of the lines in the spark spectrum of the element. Winkler was able to prepare several new compounds of germanium, including fluorides, sulfides and tetraethylgermane, the first organogermane; 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: Until the late 1930s, germanium was thought to be a poorly conducting metal. 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 diodes; the first major use was the point-contact Schottky diodes for radar pulse detection during the War. The first silicon-germanium alloys were obtained in 1955. 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; the development of the germanium transistor in 1948 opened the door to countless applications of solid state electronics. From 1950 through the early 1970s, this area provided an increasing market for germanium, but high-purity silicon began replacing germanium in transistors and rectifiers.
For example, the company that became Fairchild Semiconductor was founded in 1957 with the express purpose of producing silicon transist