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High-temperature superconductors are defined as materials with critical temperature above 77 K, the boiling point of liquid nitrogen. They are only "high-temperature" relative to previously known superconductors, which function at even colder temperatures, close to absolute zero. The "high temperatures" are still far below ambient, and therefore require cooling. The first break through of high-temperature superconductor was discovered in 1986 by IBM researchers Georg Bednorz and K. Alex Müller. Although the critical temperature is around 35.1 K, this new type of superconductor was readily modified by Ching-Wu Chu to make the first high-temperature superconductor with critical temperature 93 K. Bednorz and Müller were awarded the Nobel Prize in Physics in 1987 "for their important break-through in the discovery of superconductivity in ceramic materials". Most high-Tc materials are type-II superconductors.
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A room-temperature superconductor is a hypothetical material capable of displaying superconductivity at temperatures above 0 °C, which are commonly encountered in everyday settings. As of 2023, the material with the highest accepted superconducting temperature was highly pressurized lanthanum decahydride, whose transition temperature is approximately 250 K (−23 °C) at 200 GPa.
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Superconductivity is the phenomenon of certain materials exhibiting zero electrical resistance and the expulsion of magnetic fields below a characteristic temperature. The history of superconductivity began with Dutch physicist Heike Kamerlingh Onnes's discovery of superconductivity in mercury in 1911. Since then, many other superconducting materials have been discovered and the theory of superconductivity has been developed. These subjects remain active areas of study in the field of condensed matter physics.
Lanthanum carbide (LaC2) is a chemical compound. It is being studied in relation to the manufacture of certain types of superconductors and nanotubes.
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Residual-resistivity ratio is usually defined as the ratio of the resistivity of a material at room temperature and at 0 K. Of course, 0 K can never be reached in practice so some estimation is usually made. Since the RRR can vary quite strongly for a single material depending on the amount of impurities and other crystallographic defects, it serves as a rough index of the purity and overall quality of a sample. Since resistivity usually increases as defect prevalence increases, a large RRR is associated with a pure sample. RRR is also important for characterizing certain unusual low temperature states such as the Kondo effect and superconductivity. Note that since it is a unitless ratio there is no difference between a residual resistivity and residual-resistance ratio.
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Lanthanum decahydride is a polyhydride or superhydride compound of lanthanum and hydrogen (LaH10) that has shown evidence of being a high-temperature superconductor. It was the first metal superhydride to be theoretically predicted, synthesized, and experimentally confirmed to superconduct at near room-temperatures. It has a superconducting transition temperature TC around 250 K (−23 °C; −10 °F) at a pressure of 150 gigapascals (22×106 psi), and its synthesis required pressures above approximately 160 gigapascals (23×106 psi).
References
- ↑ Snare, Joanne (1977), Superconducting Transition Temperatures and Residual Resistivities of Highly Disordered Lanthanum-Gold Films, University of North Carolina at Chapel Hill, Bibcode:1977PhDT........77S
- ↑ IEEE Fellows directory, IEEE, retrieved 2021-06-08
- ↑ "IEEE Fellows 1996 | IEEE Communications Society".
- ↑ Front matter, IEEE Circuits & Devices, Vol. 11, 1995
