In 1986, at the IBM research lab near Zurich, in Switzerland, Bednorz and Müller were looking for superconductivity in a new class of ceramics: the copper oxides, or cuprates.īednorz encountered a particular copper oxide whose resistance dropped to zero at a temperature around −238 ☌ (35.1 K). īy the late 1970s, superconductivity was observed in several metallic compounds (in particular Nb-based, such as NbTi, Nb 3Sn, and Nb 3Ge) at temperatures that were much higher than those for elemental metals and which could even exceed 20 K (−253.2 ☌). Ever since, researchers have attempted to observe superconductivity at increasing temperatures with the goal of finding a room-temperature superconductor. Superconductivity was discovered by Kamerlingh Onnes in 1911, in a metal solid. Magnesium diboride and other low-temperature or high-pressure metallic BCS superconductors are displayed for reference as green circles. Cuprates are displayed as blue diamonds, and iron-based superconductors as yellow squares. On the right one can see the liquid nitrogen temperature, which usually divides superconductors at high from superconductors at low temperatures. The superconductivity in these compounds, however, has recently come under question. The current T c record holder is carbonaceous sulfur hydride, beating the previous record held by lanthanum decahydride by nearly 30 °K. In fact, many articles on high-temperature superconductors can be found on this research on high pressure gases, which are not suitable for practical applications. Some extremely-high pressure superhydride compounds are usually categorized as high-temperature superconductors. Magnesium diboride is sometimes included in high-temperature superconductors: It is relatively simple to manufacture, but it superconducts only below 43°K, which makes it unsuitable for liquid nitrogen cooling (approximately 30 °K below nitrogen triple point temperature). The second class of high-temperature superconductors in the practical classification is the iron-based compounds. The main class of high-temperature superconductors is copper oxides combined with other metals, especially the Rare-earth barium copper oxides (REBCOs) such as Yttrium barium copper oxide (YBCO). However, overcoming these drawbacks is the subject of considerable research, and progress is ongoing. For example, most ceramics are brittle which makes the fabrication of wires from them very problematic. Ceramic superconductors are suitable for some practical uses but they still have many manufacturing issues. The majority of high-temperature superconductors are ceramic materials, as opposed to the previously known metallic materials. This is important when constructing superconducting magnets, a primary application of high- T c materials. A second advantage of high- T c materials is they retain their superconductivity in higher magnetic fields than previous materials. The major advantage of high-temperature superconductors is that they can be cooled by using liquid nitrogen, as opposed to the previously known superconductors which require expensive and hard-to-handle coolants, primarily liquid helium. Most high- T c materials are type-II superconductors. The first high-temperature superconductor was discovered in 1986, by IBM researchers Bednorz and Müller, who were awarded the Nobel Prize in Physics in 1987 "for their important break-through in the discovery of superconductivity in ceramic materials". In absolute terms, these "high temperatures" are still far below ambient, and therefore require cooling. The adjective "high temperature" is only in respect to previously known superconductors, which function at even colder temperatures close to absolute zero. High-temperature superconductors (abbreviated high- T c or HTS) are defined as materials that behave as superconductors at temperatures above 77 K (−196.2 ☌ −321.1 ☏), the boiling point of liquid nitrogen. Thanks to its higher operating temperature, cuprates are now becoming competitors for more ordinary niobium-based superconductors, as well as magnesium diboride superconductors. BSCCO is a cuprate superconductor based on bismuth and strontium. Notably, it does not contain rare-earths. A sample of Bismuth strontium calcium copper oxide (BSCCO) which currently is one of the most practical high-temperature superconductors.
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