Superconductivity at room temperature

 

energy.gov

At normal temperatures, all materials have some amount of electrical resistance. This means they resist the flow of electricity. Because of resistance, some energy is lost as heat when electrons move through the electronic devices. But there are some exceptions called superconducting materials. Superconductivity is a phenomenon where a charge moves through a material without resistance. This allows electrical energy to be transferred between two points with perfect efficiency, losing nothing to heat. Superconductivity is one of nature’s most intriguing quantum phenomena. It was discovered more than 100 years ago in mercury cooled to the temperature of liquid helium (about -268.9°C, only a few degrees above absolute zero).Unlike an ordinary metallic conductor, whose resistance decreases gradually as its temperature is lowered even down to near absolute zero, a superconductor has a characteristic critical temperature below which the resistance drops abruptly to zero. An electric current through a loop of superconducting wire can persist indefinitely with no power source.

Wikipedia

The above video of the Meissner effect in a high-temperature superconductor (black pellet) with a NdFeB (neodymium magnet). Let us first understand the types of superconductors- High temperature superconductivity and Low temperature superconductivity. High-temperature superconductors are defined as materials that behave as superconductors at temperatures above 77 K (−196.2 °C). The majority of high-temperature superconductors are ceramic materials. A ceramic is  hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing a nonmetallic mineral, such as clay, at a high temperature. Common examples are earthenware, porcelain, and brick. LTS stands for "low temperature superconductor," which typically refers to Nb-based alloys and A15 superconductors that were already in use prior to the discovery of "high temperature" copper-oxide superconductors in 1986.

Pinterest

Meissner effect, the expulsion of a magnetic field from the interior of a material that is in the process of becoming a superconductor, that is, losing its resistance to the flow of electrical currents when cooled below a certain temperature, called the transition temperature, usually close to absolute zero. The Meissner effect, a property of all superconductors, was discovered by the German physicists W. Meissner and R. Ochsenfeld in 1933. As a superconductor in a magnetic field is cooled to the temperature at which it abruptly loses electrical resistance, all or part of the magnetic field within the material is expelled.Some superconductors, called type I (tin and mercury), can be made to exhibit a complete Meissner effect by eliminating various chemical impurities and physical imperfections and by choosing proper geometrical shape and size. Other superconductors, called type II (vanadium and niobium) exhibit only a partial Meissner effect at intermediate magnetic-field strengths no matter what their geometrical shape or size.

SciELO

One hundred years ago, on April 8, 1911,Heike Kamerlingh Onnes and his staff atthe Leiden cryogenic laboratory were the firstto observe superconductivity. In a frozen mercury wire, contained in sevenU-shaped capillaries in series, electrical resistance suddenly seemed to vanish at 4.16 kelvin. In 1913, lead was found to superconduct at 7 K, and in 1941 niobium nitride was found to superconduct at 16 K. Great efforts have been devoted to finding out how and why superconductivity works; the important step occurred in 1933, when Meissner and Ochsenfeld discovered that superconductors expelled applied magnetic fields, a phenomenon which has come to be known as the Meissner effect. In 1935, Fritz and Heinz London showed that the Meissner effect was a consequence of the minimization of the electromagnetic free energy carried by superconducting current.

Sciencenews

After decades, room temperature superconductivity is achieved. Above pic shows crushed between two diamonds, a compound of hydrogen, sulfur, and carbon superconducts at room temperature. Scientists have created a mystery material that seems to conduct electricity without any resistance at temperatures of up to about 15 °C. That’s a new record for superconductivity, a phenomenon usually associated with very cold temperatures. The superconductor has one serious limitation, however: it survives only under extremely high pressures, approaching those at the centre of Earth, meaning that it will not have any immediate practical applications. Still, physicists hope it could pave the way for the development of zero-resistance materials that can function at lower pressures.

Superconductors have a number of technological applications, from magnetic resonance imaging machines to mobile-phone towers, and researchers are beginning to experiment with them in high-performance generators for wind turbines. But their usefulness is still limited by the need for bulky cryogenics. Cryogenics is the production and behavior of materials at very low temperatures. Ultra-cold temperatures change the chemical properties of materials, which provide an interesting area of study for researchers. These studies have lead to advances in not only our understanding of different materials, but the creation of entirely new technologies and industries. Common superconductors work at atmospheric pressures, but only if they are kept very cold. Even the copper oxide-based ceramic materials work only below 133 kelvin (−140 °C). Superconductors that work at room temperature could have a big technological impact, for example in electronics that run faster without overheating.

Halperin, John Evans Professor of Physics at Northwesterns explains that now, a superconductor is just like there is no resistance to the charge. Therefore, no heat is generated when the current moves through the conductor. This is a good thing, because we don’t lose any energy in just heating the wire. 

Superconductors—special metals that can conduct electrical current with no loss of energy could one day have a great impact on the efficient transmission of power in the United States and around the world. They could also lead to great innovations in medical imaging, drug analysis, and even telecommunications. While limited amounts of superconductors are already being introduced into the grid, there is much work left to be done, especially in understanding how these compounds actually work and how they can be improved.