Copper zinc tin sulfide is a quaternary semiconducting compound which has received increasing interest since the late 2000s for applications in thin film solar cells. The class of related materials includes other I2-II-IV-VI4 such as copper zinc tin selenide and the sulfur-selenium alloy CZTSSe. CZTS offers favorable optical and electronic properties similar to CIGS making it well suited for use as a thin-film solar cell absorber layer, but unlike CIGS, CZTS is composed of only abundant and non-toxic elements. Concerns with the price and availability of indium in CIGS and tellurium in CdTe, as well as toxicity of cadmium have been a large motivator to search for alternative thin film solar cell materials. Recent material improvements for CZTS have increased the efficiency to 12.6% in laboratory cells, but more work is needed for their commercialization. CZTS is a I2-II-IV-VI4 quaternary compound. From the chalcopyrite CIGS structure, one can obtain CZTS by substituting the trivalent In/Ga with a bivalent Zn and IV-valent Sn which forms in the kesterite structure.
Some literature reports have identified CZTS in the related stannite structure, but conditions under which a stannite structure may occur are not yet clear. First-principle calculations show that the crystal energy is only 2.86 meV/atom higher for the stannite than kesterite structure suggesting that both forms can coexist. Structural determination is hindered by disorder of the Cu-Zn cations, which are the most common defect as predicted by theoretical calculations and confirmed by neutron scattering; the near random ordering of Cu and Zn may lead to misidentification of the structure. Theoretical calculations predict the disorder of the Cu-Zn cations to lead to potential fluctuations in the CZTS and could therefore the cause for the large open circuit voltage deficit, the main bottle neck of state-of-the-art CZTS devices; the disorder can be reduced by temperature treatments. However, other temperature treatments alone do not seem to be able to yield ordered CZTS. Other strategies need to be developed to reduce this defect, such as tuning of the CZTS composition.
Carrier concentrations and absorption coefficient of CZTS are similar to CIGS. Other properties such as carrier lifetime are low for CZTS; this low carrier lifetime may be due to high density of active defects or recombination at grain boundaries. Many secondary phases are possible in quaternary compounds like CZTS and their presence can affect the solar cell performance. Secondary phases can provide shunting current paths through the solar cell or act as recombination centers, both degrading solar cell performance. From the literature it appears that all secondary phases have a detrimental effect on CZTS performance, many of them are both hard to detect and present. Common phases include ZnS, SnS, CuS, Cu2SnS3. Identification of these phases is challenging by traditional methods like X-ray diffraction due to the peak overlap of ZnS and Cu2SnS3 with CZTS. Other methods like Raman scattering are being explored to help characterize CZTS. CZTS has been prepared by a variety of non-vacuum techniques.
They mirror what has been successful with CIGS, although the optimal fabrication conditions may differ. Methods can be broadly categorized as vacuum deposition vs. non-vacuum and single-step vs. sulfization/selenization reaction methods. Vacuum-based methods are dominant in the current CIGS industry, but in the past decade there has been increasing interest and progress in non-vacuum processes owing to their potential lower capital costs and flexibility to coat large areas. A particular challenge for fabrication of CZTS and related alloys is the volatility of certain elements which can evaporate under reaction conditions. Once CZTS is formed, element volatility is less of a problem but then CZTS will decompose into binary and ternary compounds in vacuum at temperatures above 500 °C; this volatility and difficulty of preparing a single-phase material has resulted in the success of many traditional vacuum methods. The best CZTS devices have been achieved through certain chemical methods which allow CZTS formation at low temperatures avoiding volatility problems.
A continuous flow process using ethylene glycol as a solvent has been developed at Oregon State University which may be suitable for industrial scale mass production. CIGS and CdTe are two of the most promising thin-film solar cells and have seen growing commercial success. Despite continued rapid cost reduction, concerns about material price and availability as well as toxicity have been raised. Although current material costs are a small portion of the total solar cell cost, continued rapid growth of thin-film solar cells could lead to increased material price and limited supply. For CIGS, indium has been subject to growing demand because of the rapid expansion of indium tin oxide used in flat screen displays and mobile devices; the demand coupled with limited supply helped prices climb to over $1000/kg before the global recession. While processing and capital equipment make up the majority of the costs for producing a CIGS solar cells, the price of the raw material is the lower bound for future costs and could be a limiting factor in decades ahead if demand continues to increase with limited supply.
Indium exists in low concentration ore deposits and is therefore obtained as a byproduct of zinc mining. Growth projections based on many assumptions suggest that indium supply could limit CIGS production to the range of 17–106 GW/yr in 2050. Tellurium is scarcer than indium, although demand has been lower. Tellurium abundan
The alkali metals are a group in the periodic table consisting of the chemical elements lithium, potassium, rubidium and francium. This group lies in the s-block of the periodic table of elements as all alkali metals have their outermost electron in an s-orbital: this shared electron configuration results in their having similar characteristic properties. Indeed, the alkali metals provide the best example of group trends in properties in the periodic table, with elements exhibiting well-characterised homologous behaviour; the alkali metals are all shiny, soft reactive metals at standard temperature and pressure and lose their outermost electron to form cations with charge +1. They can all be cut with a knife due to their softness, exposing a shiny surface that tarnishes in air due to oxidation by atmospheric moisture and oxygen; because of their high reactivity, they must be stored under oil to prevent reaction with air, are found only in salts and never as the free elements. Caesium, the fifth alkali metal, is the most reactive of all the metals.
In the modern IUPAC nomenclature, the alkali metals comprise the group 1 elements, excluding hydrogen, nominally a group 1 element but not considered to be an alkali metal as it exhibits behaviour comparable to that of the alkali metals. All the alkali metals react with water, with the heavier alkali metals reacting more vigorously than the lighter ones. All of the discovered alkali metals occur in nature as their compounds: in order of abundance, sodium is the most abundant, followed by potassium, rubidium and francium, rare due to its high radioactivity. Experiments have been conducted to attempt the synthesis of ununennium, to be the next member of the group, but they have all met with failure. However, ununennium may not be an alkali metal due to relativistic effects, which are predicted to have a large influence on the chemical properties of superheavy elements. Most alkali metals have many different applications. One of the best-known applications of the pure elements is the use of rubidium and caesium in atomic clocks, of which caesium atomic clocks are the most accurate and precise representation of time.
A common application of the compounds of sodium is the sodium-vapour lamp, which emits light efficiently. Table salt, or sodium chloride, has been used since antiquity. Lithium finds use as an anode in lithium batteries. Sodium and potassium are essential elements, having major biological roles as electrolytes, although the other alkali metals are not essential, they have various effects on the body, both beneficial and harmful. Sodium compounds have been known since ancient times. While potash has been used since ancient times, it was not understood for most of its history to be a fundamentally different substance from sodium mineral salts. Georg Ernst Stahl obtained experimental evidence which led him to suggest the fundamental difference of sodium and potassium salts in 1702, Henri-Louis Duhamel du Monceau was able to prove this difference in 1736; the exact chemical composition of potassium and sodium compounds, the status as chemical element of potassium and sodium, was not known and thus Antoine Lavoisier did not include either alkali in his list of chemical elements in 1789.
Pure potassium was first isolated in 1807 in England by Sir Humphry Davy, who derived it from caustic potash by the use of electrolysis of the molten salt with the newly invented voltaic pile. Previous attempts at electrolysis of the aqueous salt were unsuccessful due to potassium's extreme reactivity. Potassium was the first metal, isolated by electrolysis; that same year, Davy reported extraction of sodium from the similar substance caustic soda by a similar technique, demonstrating the elements, thus the salts, to be different. Petalite was discovered in 1800 by the Brazilian chemist José Bonifácio de Andrada in a mine on the island of Utö, Sweden. However, it was not until 1817 that Johan August Arfwedson working in the laboratory of the chemist Jöns Jacob Berzelius, detected the presence of a new element while analysing petalite ore; this new element was noted by him to form compounds similar to those of sodium and potassium, though its carbonate and hydroxide were less soluble in water and more alkaline than the other alkali metals.
Berzelius gave the unknown material the name "lithion/lithina", from the Greek word λιθoς, to reflect its discovery in a solid mineral, as opposed to potassium, discovered in plant ashes, sodium, known for its high abundance in animal blood. He named the metal inside the material "lithium". Lithium and potassium were part of the discovery of periodicity, as they are among a series of triads of elements in the same group that were noted by Johann Wolfgang Döbereiner in 1850 as having similar properties. Rubidium and caesium were the first elements to be discovered using the spectroscope, invented in 1859 by Robert Bunsen and Gustav Kirchhoff; the next year, they discovered caesiu
Photovoltaics is the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect, a phenomenon studied in physics and electrochemistry. A photovoltaic system employs solar panels, each comprising a number of solar cells, which generate electrical power. PV installations may be ground-mounted, rooftop mounted or wall mounted; the mount may use a solar tracker to follow the sun across the sky. Solar PV has specific advantages as an energy source: once installed, its operation generates no pollution and no greenhouse gas emissions, it shows simple scalability in respect of power needs and silicon has large availability in the Earth’s crust. PV systems have the major disadvantage that the power output works best with direct sunlight, so about 10-25% is lost if a tracking system is not used. Dust and other obstructions in the atmosphere diminish the power output. Another important issue is the concentration of the production in the hours corresponding to main insolation, which do not match the peaks in demand in human activity cycles.
Unless current societal patterns of consumption and electrical networks adjust to this scenario, electricity still needs to be stored for use or made up by other power sources hydrocarbons. Photovoltaic systems have long been used in specialized applications, stand-alone and grid-connected PV systems have been in use since the 1990s, they were first mass-produced in 2000, when German environmentalists and the Eurosolar organization got government funding for a ten thousand roof program. Advances in technology and increased manufacturing scale have in any case reduced the cost, increased the reliability, increased the efficiency of photovoltaic installations. Net metering and financial incentives, such as preferential feed-in tariffs for solar-generated electricity, have supported solar PV installations in many countries. More than 100 countries now use solar PV. After hydro and wind powers, PV is the third renewable energy source in terms of global capacity. At the end of 2016, worldwide installed PV capacity increased to more than 300 gigawatts, covering two percent of global electricity demand.
China, followed by Japan and the United States, is the fastest growing market, while Germany remains the world's largest producer, with solar PV providing seven percent of annual domestic electricity consumption. With current technology, photovoltaics recoups the energy needed to manufacture them in 1.5 years in Southern Europe and 2.5 years in Northern Europe. The term "photovoltaic" comes from the Greek φῶς meaning "light", from "volt", the unit of electro-motive force, the volt, which in turn comes from the last name of the Italian physicist Alessandro Volta, inventor of the battery; the term "photo-voltaic" has been in use in English since 1849. Photovoltaics are best known as a method for generating electric power by using solar cells to convert energy from the sun into a flow of electrons by the photovoltaic effect. Solar cells produce direct current electricity from sunlight which can be used to power equipment or to recharge a battery; the first practical application of photovoltaics was to power orbiting satellites and other spacecraft, but today the majority of photovoltaic modules are used for grid connected power generation.
In this case an inverter is required to convert the DC to AC. There is a smaller market for off-grid power for remote dwellings, recreational vehicles, electric cars, roadside emergency telephones, remote sensing, cathodic protection of pipelines. Photovoltaic power generation employs solar panels composed of a number of solar cells containing a photovoltaic material. Copper solar cables connect modules and sub-fields; because of the growing demand for renewable energy sources, the manufacturing of solar cells and photovoltaic arrays has advanced in recent years. Solar photovoltaic power generation has long been seen as a clean energy technology which draws upon the planet’s most plentiful and distributed renewable energy source – the sun. Cells require protection from the environment and are packaged in solar panels. Photovoltaic power capacity is measured as maximum power output under standardized test conditions in "Wp"; the actual power output at a particular point in time may be less than or greater than this standardized, or "rated", depending on geographical location, time of day, weather conditions, other factors.
Solar photovoltaic array capacity factors are under 25%, lower than many other industrial sources of electricity. For best performance, terrestrial PV systems aim to maximize the time. Solar trackers achieve this by moving PV panels to follow the sun; the increase can be by as much as 50 % in summer. Static mounted. Panels are set to latitude tilt, an angle equal to the latitude, but performance can be improved by adjusting the angle for summer or winter; as with other semiconductor devices, temperatures above room temperature reduce the performance of photovoltaics. A number of solar panels may be mounted vertically above each other in a tower, if the zenith distance of the Sun is greater than zero, the tower can be turned horizontally as a whole and each panels additionally around a horizontal axis. In such a tower the panels can follow the Sun exactly; such a device may be described as a ladder mounted on a turnable disk. Each step of that ladder is the middle axis of a rectangular solar panel.
In case the zenith distance of the Sun reaches zero, the "ladder" may be rotated
Thin-film solar cell
A thin-film solar cell is a second generation solar cell, made by depositing one or more thin layers, or thin film of photovoltaic material on a substrate, such as glass, plastic or metal. Thin-film solar cells are commercially used in several technologies, including cadmium telluride, copper indium gallium diselenide, amorphous thin-film silicon. Film thickness varies from a few nanometers to tens of micrometers, much thinner than thin-film's rival technology, the conventional, first-generation crystalline silicon solar cell, that uses wafers of up to 200 µm thick; this allows thin film cells to be flexible, lower in weight. It is used in building integrated photovoltaics and as semi-transparent, photovoltaic glazing material that can be laminated onto windows. Other commercial applications use rigid thin film solar panels in some of the world's largest photovoltaic power stations. Thin-film technology has always been less efficient than conventional c-Si technology. However, it has improved over the years.
The lab cell efficiency for CdTe and CIGS is now beyond 21 percent, outperforming multicrystalline silicon, the dominant material used in most solar PV systems. Accelerated life testing of thin film modules under laboratory conditions measured a somewhat faster degradation compared to conventional PV, while a lifetime of 20 years or more is expected. Despite these enhancements, market-share of thin-film never reached more than 20 percent in the last two decades and has been declining in recent years to about 9 percent of worldwide photovoltaic installations in 2013. Other thin-film technologies that are still in an early stage of ongoing research or with limited commercial availability are classified as emerging or third generation photovoltaic cells and include organic, dye-sensitized, as well as quantum dot, copper zinc tin sulfide, nanocrystal and perovskite solar cells. Thin film cells are well-known since the late 1970s, when solar calculators powered by a small strip of amorphous silicon appeared on the market.
It is now available in large modules used in sophisticated building-integrated installations and vehicle charging systems. Although thin-film technology was expected to make significant advances in the market and to surpass the dominating conventional crystalline silicon technology in the long-term, market-share has been declining for several years now. While in 2010, when there was a shortage of conventional PV modules, thin-film accounted for 15 percent of the overall market, it declined to 8 percent in 2014, is expected to stabilize at 7 percent from 2015 onward, with amorphous silicon expected to lose half of its market-share by the end of the decade. Thin-film technologies reduce the amount of active material in a cell. Most sandwich active material between two panes of glass. Since silicon solar panels only use one pane of glass, thin film panels are twice as heavy as crystalline silicon panels, although they have a smaller ecological impact; the majority of film panels have 2-3 percentage points lower conversion efficiencies than crystalline silicon.
Cadmium telluride, copper indium gallium selenide and amorphous silicon are three thin-film technologies used for outdoor applications. Cadmium telluride is the predominant thin film technology. With about 5 percent of worldwide PV production, it accounts for more than half of the thin film market; the cell's lab efficiency has increased in recent years and is on a par with CIGS thin film and close to the efficiency of multi-crystalline silicon as of 2013. CdTe has the lowest Energy payback time of all mass-produced PV technologies, can be as short as eight months in favorable locations. A prominent manufacturer is the US-company First Solar based in Tempe, that produces CdTe-panels with an efficiency of about 14 percent at a reported cost of $0.59 per watt. Although the toxicity of cadmium may not be that much of an issue and environmental concerns resolved with the recycling of CdTe modules at the end of their life time, there are still uncertainties and the public opinion is skeptical towards this technology.
The usage of rare materials may become a limiting factor to the industrial scalability of CdTe thin film technology. The rarity of tellurium—of which telluride is the anionic form—is comparable to that of platinum in the earth's crust and contributes to the module's cost. A copper indium gallium selenide solar cell or CIGS cell uses an absorber made of copper, gallium, while gallium-free variants of the semiconductor material are abbreviated CIS, it is one of three mainstream thin-film technologies, the other two being cadmium telluride and amorphous silicon, with a lab-efficiency above 20 percent and a share of 2 percent in the overall PV market in 2013. A prominent manufacturer of cylindrical CIGS-panels was the now-bankrupt company Solyndra in Fremont, California. Traditional methods of fabrication involve vacuum processes including sputtering. In 2008, IBM and Tokyo Ohka Kogyo Co. Ltd. announced they had developed a new, non-vacuum, solution-based manufacturing process for CIGS cells and are aiming for efficiencies of 15% and beyond.
Hyperspectral imaging has been used to characterize these cells. Researchers from IRDEP in collaboration with Photon etc.¸ were able to determine the splitting of the quasi-Fermi level with photoluminescence mapping while the electroluminescence data were used to derive the external quantum efficiency. Through a light
Photovoltaic solar panels absorb sunlight as a source of energy to generate electricity. A photovoltaic module is a packaged, connected assembly of 6x10 photovoltaic solar cells. Photovoltaic modules constitute the photovoltaic array of a photovoltaic system that generates and supplies solar electricity in commercial and residential applications; the most common application of solar energy collection outside agriculture is solar water heating systems. Photovoltaic modules use light energy from the Sun to generate electricity through the photovoltaic effect; the majority of modules use wafer-based crystalline silicon cells or thin-film cells. The structural member of a module can either be the back layer. Cells must be protected from mechanical damage and moisture. Most modules are rigid, but semi-flexible ones based on thin-film cells are available; the cells must be connected electrically in one to another. A PV junction box is attached to the back of the solar panel and it is its output interface.
Externally, most of photovoltaic modules use MC4 connectors type to facilitate easy weatherproof connections to the rest of the system. USB power interface can be used. Module electrical connections are made in series to achieve a desired output voltage or in parallel to provide a desired current capability; the conducting wires that take the current off the modules may contain silver, copper or other non-magnetic conductive transition metals. Bypass diodes may be incorporated or used externally, in case of partial module shading, to maximize the output of module sections still illuminated; some special solar PV modules include concentrators in which light is focused by lenses or mirrors onto smaller cells. This enables the use of cells with a high cost per unit area in a cost-effective way. Solar panels use metal frames consisting of racking components, reflector shapes, troughs to better support the panel structure. In 1839, the ability of some materials to create an electrical charge from light exposure was first observed by Alexandre-Edmond Becquerel.
Though the premiere solar panels were too inefficient for simple electric devices they were used as an instrument to measure light. The observation by Becquerel was not replicated again until 1873, when Willoughby Smith discovered that the charge could be caused by light hitting selenium. After this discovery, William Grylls Adams and Richard Evans Day published "The action of light on selenium" in 1876, describing the experiment they used to replicate Smith's results. In 1881, Charles Fritts created the first commercial solar panel, reported by Fritts as "continuous, constant and of considerable force not only by exposure to sunlight but to dim, diffused daylight." However, these solar panels were inefficient compared to coal-fired power plants. In 1939, Russell Ohl created the solar cell design, used in many modern solar panels, he patented his design in 1941. In 1954, this design was first used by Bell Labs to create the first commercially viable silicon solar cell; each module is rated by its DC output power under standard test conditions, ranges from 100 to 365 Watts.
The efficiency of a module determines the area of a module given the same rated output – an 8% efficient 230 W module will have twice the area of a 16% efficient 230 W module. There are a few commercially available solar modules that exceed efficiency of 24% Depending on construction, photovoltaic modules can produce electricity from a range of frequencies of light, but cannot cover the entire solar range. Hence, much of the incident sunlight energy is wasted by solar modules, they can give far higher efficiencies if illuminated with monochromatic light. Therefore, another design concept is to split the light into six to eight different wavelength ranges that will produce a different color of light, direct the beams onto different cells tuned to those ranges; this has been projected to be capable of raising efficiency by 50%. A single solar module can produce only a limited amount of power. A photovoltaic system includes an array of photovoltaic modules, an inverter, a battery pack for storage, interconnection wiring, optionally a solar tracking mechanism.
Scientists from Spectrolab, a subsidiary of Boeing, have reported development of multi-junction solar cells with an efficiency of more than 40%, a new world record for solar photovoltaic cells. The Spectrolab scientists predict that concentrator solar cells could achieve efficiencies of more than 45% or 50% in the future, with theoretical efficiencies being about 58% in cells with more than three junctions; the best achieved sunlight conversion rate is around 21.5% in new commercial products lower than the efficiencies of their cells in isolation. The most efficient mass-produced solar modules have power density values of up to 175 W/m2. Research by Imperial College, London has shown that the efficiency of a solar panel can be improved by studying the light-receiving semiconductor surface with aluminum nanocylinders similar to the ridges on Lego blocks; the scattered light travels along a longer path in the semiconductor which means that more photons can be absorbed and converted into current.
Although these nanocylinders have been used the light scattering occurred in the near infrared region and visible light was absorbed strongly. Aluminum was found to have absorbed the ultraviolet part of the spectrum, while the visible and near infrared parts o
In mathematics and chemistry, a space group is the symmetry group of a configuration in space in three dimensions. In three dimensions, there are 230 if chiral copies are considered distinct. Space groups are studied in dimensions other than 3 where they are sometimes called Bieberbach groups, are discrete cocompact groups of isometries of an oriented Euclidean space. In crystallography, space groups are called the crystallographic or Fedorov groups, represent a description of the symmetry of the crystal. A definitive source regarding 3-dimensional space groups is the International Tables for Crystallography. Space groups in 2 dimensions are the 17 wallpaper groups which have been known for several centuries, though the proof that the list was complete was only given in 1891, after the much more difficult classification of space groups had been completed. In 1879 Leonhard Sohncke listed the 65 space groups. More he listed 66 groups, but Fedorov and Schönflies both noticed that two of them were the same.
The space groups in three dimensions were first enumerated by Fedorov, shortly afterwards were independently enumerated by Schönflies. The correct list of 230 space groups was found by 1892 during correspondence between Fedorov and Schönflies. Barlow enumerated the groups with a different method, but omitted four groups though he had the correct list of 230 groups from Fedorov and Schönflies. Burckhardt describes the history of the discovery of the space groups in detail; the space groups in three dimensions are made from combinations of the 32 crystallographic point groups with the 14 Bravais lattices, each of the latter belonging to one of 7 lattice systems. This results in a space group being some combination of the translational symmetry of a unit cell including lattice centering, the point group symmetry operations of reflection and improper rotation, the screw axis and glide plane symmetry operations; the combination of all these symmetry operations results in a total of 230 different space groups describing all possible crystal symmetries.
The elements of the space group fixing a point of space are the identity element, reflections and improper rotations. The translations form a normal abelian subgroup of rank 3, called the Bravais lattice. There are 14 possible types of Bravais lattice; the quotient of the space group by the Bravais lattice is a finite group, one of the 32 possible point groups. Translation is defined as the face moves from one point to another point. A glide plane is a reflection in a plane, followed by a translation parallel with that plane; this is noted depending on which axis the glide is along. There is the n glide, a glide along the half of a diagonal of a face, the d glide, a fourth of the way along either a face or space diagonal of the unit cell; the latter is called the diamond glide plane. In 17 space groups, due to the centering of the cell, the glides occur in two perpendicular directions i.e. the same glide plane can be called b or c, a or b, a or c. For example, group Abm2 could be called Acm2, group Ccca could be called Cccb.
In 1992, it was suggested to use symbol e for such planes. The symbols for five space groups have been modified: A screw axis is a rotation about an axis, followed by a translation along the direction of the axis; these are noted by a number, n, to describe the degree of rotation, where the number is how many operations must be applied to complete a full rotation. The degree of translation is added as a subscript showing how far along the axis the translation is, as a portion of the parallel lattice vector. So, 21 is a twofold rotation followed by a translation of 1/2 of the lattice vector; the general formula for the action of an element of a space group is y = M.x + D where M is its matrix, D is its vector, where the element transforms point x into point y. In general, D = D + D, where D is a unique function of M, zero for M being the identity; the matrices M form a point group, a basis of the space group. The lattice dimension can be less than the overall dimension, resulting in a "subperiodic" space group.
For:: One-dimensional line groups: Two-dimensional line groups: frieze groups: Wallpaper groups: Three-dimensional line groups. Some of these methods can assign several different names to the same space group, so altogether there are many thousands of different names. Number; the International Union of Crystallography publishes tables of all space group types, assigns each a unique number from 1 to 230. The numbering is arbitrary, except that groups with the same crystal system or point group are given consecutive numbers. International symbol or Hermann–Mauguin notation; the Hermann–Mauguin notation describes the lattice and some generators for the group. It has a shortened form called the international short symbol, the one most used in crystallography
Copper is a chemical element with symbol Cu and atomic number 29. It is a soft and ductile metal with high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orange color. Copper is used as a conductor of heat and electricity, as a building material, as a constituent of various metal alloys, such as sterling silver used in jewelry, cupronickel used to make marine hardware and coins, constantan used in strain gauges and thermocouples for temperature measurement. Copper is one of the few metals; this led to early human use in several regions, from c. 8000 BC. Thousands of years it was the first metal to be smelted from sulfide ores, c. 5000 BC, the first metal to be cast into a shape in a mold, c. 4000 BC and the first metal to be purposefully alloyed with another metal, tin, to create bronze, c. 3500 BC. In the Roman era, copper was principally mined on Cyprus, the origin of the name of the metal, from aes сyprium corrupted to сuprum, from which the words derived and copper, first used around 1530.
The encountered compounds are copper salts, which impart blue or green colors to such minerals as azurite and turquoise, have been used and as pigments. Copper used in buildings for roofing, oxidizes to form a green verdigris. Copper is sometimes used in decorative art, both in its elemental metal form and in compounds as pigments. Copper compounds are used as bacteriostatic agents and wood preservatives. Copper is essential to all living organisms as a trace dietary mineral because it is a key constituent of the respiratory enzyme complex cytochrome c oxidase. In molluscs and crustaceans, copper is a constituent of the blood pigment hemocyanin, replaced by the iron-complexed hemoglobin in fish and other vertebrates. In humans, copper is found in the liver and bone; the adult body contains between 2.1 mg of copper per kilogram of body weight. Copper and gold are in group 11 of the periodic table; the filled d-shells in these elements contribute little to interatomic interactions, which are dominated by the s-electrons through metallic bonds.
Unlike metals with incomplete d-shells, metallic bonds in copper are lacking a covalent character and are weak. This observation explains the low high ductility of single crystals of copper. At the macroscopic scale, introduction of extended defects to the crystal lattice, such as grain boundaries, hinders flow of the material under applied stress, thereby increasing its hardness. For this reason, copper is supplied in a fine-grained polycrystalline form, which has greater strength than monocrystalline forms; the softness of copper explains its high electrical conductivity and high thermal conductivity, second highest among pure metals at room temperature. This is because the resistivity to electron transport in metals at room temperature originates from scattering of electrons on thermal vibrations of the lattice, which are weak in a soft metal; the maximum permissible current density of copper in open air is 3.1×106 A/m2 of cross-sectional area, above which it begins to heat excessively. Copper is one of a few metallic elements with a natural color other than silver.
Pure copper acquires a reddish tarnish when exposed to air. The characteristic color of copper results from the electronic transitions between the filled 3d and half-empty 4s atomic shells – the energy difference between these shells corresponds to orange light; as with other metals, if copper is put in contact with another metal, galvanic corrosion will occur. Copper does not react with water, but it does react with atmospheric oxygen to form a layer of brown-black copper oxide which, unlike the rust that forms on iron in moist air, protects the underlying metal from further corrosion. A green layer of verdigris can be seen on old copper structures, such as the roofing of many older buildings and the Statue of Liberty. Copper tarnishes when exposed to some sulfur compounds, with which it reacts to form various copper sulfides. There are 29 isotopes of copper. 63Cu and 65Cu are stable, with 63Cu comprising 69% of occurring copper. The other isotopes are radioactive, with the most stable being 67Cu with a half-life of 61.83 hours.
Seven metastable isotopes have been characterized. Isotopes with a mass number above 64 decay by β−, whereas those with a mass number below 64 decay by β+. 64Cu, which has a half-life of 12.7 hours, decays both ways.62Cu and 64Cu have significant applications. 62Cu is used in 62Cu-PTSM as a radioactive tracer for positron emission tomography. Copper is produced in massive stars and is present in the Earth's crust in a proportion of about 50 parts per million. In nature, copper occurs in a variety of minerals, including native copper, copper sulfides such as chalcopyrite, digenite and chalcocite, copper sulfosalts such as tetrahedite-tennantite, enargite, copper carbonates such as azurite and malachite, as copper or copper oxides such as cuprite and tenorite, respectively; the largest mass of elemental copper discovered weighed 420 tonnes and was found in 1857 on the Keweenaw Peninsula in Michigan, US. Native copper is a polycrystal