Superconductors are materials with zero resistivity. They are well-known to the general public due to their practical applications and have been mentioned several times throughout the text. High-temperature superconductors are materials that behave as superconductors at temperatures above 77 K (196.2 °C; 321.1 °F), the boiling point of liquid nitrogen, one of the simplest cryogenic coolants. At temperatures far below ambient, all materials currently known to conduct at ordinary pressures become superconducting and thus require cooling.
Superconductivity is a set of physical properties observed in certain materials in which electrical resistance disappears and magnetic flux fields are expelled. A superconductor is any material that possesses these properties. Ceramic materials make up the vast majority of high-temperature superconductors. Metallic superconductors, on the other hand, typically operate at temperatures below 200°C and are thus referred to as low-temperature superconductors. Metallic superconductors are also known as ordinary superconductors because they were discovered and used before high-temperature superconductors.
Ceramic superconductors are now suitable for some practical applications, but they still have many manufacturing issues and there are very few successful practical applications. Lanthanum, yttrium, or another rare-earth element, or bismuth or thallium; barium or strontium (both alkaline-earth elements); copper; and oxygen are all present. Because most ceramics are brittle, making wires from them is a difficult task.
The fact that high-temperature ceramic superconductors can be cooled with liquid nitrogen is a significant advantage. Metallic superconductors, on the other hand, typically require more difficult coolants, most notably liquid helium. Unfortunately, none of the high-temperature superconductors can be cooled with dry ice alone, and none of them work at room temperature and pressure (they work well below the lowest temperature recorded on Earth). All high-temperature superconductors necessitate the use of a cooling system.
Copper oxides are the most common type of high-temperature superconductors (only some particular copper oxides). The iron-based compounds are the second class of high-temperature superconductors in the practical classification. Magnesium diboride is occasionally found in high-temperature superconductors: It is relatively easy to make, but it only superconducts below 230 °C, making it unsuitable for liquid nitrogen cooling (approximately 30 °C below nitrogen triple point temperature). It can, for example, be cooled with liquid helium, which operates at much lower temperatures.
Many ceramic superconductors behave physically as second-type superconductors. The first high-temperature superconductor was discovered in 1986 by IBM researchers Bednorz and Müller, who received the Nobel Prize in Physics in 1987 “for their significant breakthrough in the discovery of superconductivity in ceramic materials.”
Some super hydride compounds with extremely high pressures are classified as high-temperature superconductors. In fact, many articles on high-temperature superconductors can be found in this research on high-pressure gases, which is not applicable in practice. Carbonaceous sulfur hydride currently holds the Tc record, beating lanthanum decahydride’s previous record by nearly 30 °C. However, the superconductivity of these compounds has recently been called into question, owing to the sharpness – or lack of width – of the superconducting transition.
